CW Manual

Connell Wagner Pty Ltd ACN 005 139 873

Structural Design Guidelines February 2004

Structural Design Guidelines Connell Wagner Pty Ltd

Doc Ref: P:\9660\08\Design Guidelines\Table of Contents

Version No : 1.0 Issue Date : 29/10/97

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Controlled Copies Issue Register

Office Copy Number Current Version No

Melbourne (Master) 0 1.0

Melbourne (Office) 1 1.0

Melbourne (Spare) 2 1.0

Sydney 3 1.0

Brisbane 4 1.0

Adelaide 5 1.0

Perth 6 1.0

Mackay 7 1.0

Newcastle 8 1.0

Wellington 9 1.0

Auckland 10 1.0

Gold Coast 11 1.0

Darwin 12 1.0




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TABLE OF CONTENTS Section

Version

Action Author

1.0 INTRODUCTION 1.0 Perth (GR)

2.0 DESIGN PRINCIPLES AND PROCEDURES 1.0 Melb

(JB) 2.1 Design Philosophy

2.2 Project Procedures

2.2.1 Introduction 2.2.2 Briefing 2.2.3 Preliminary design 2.2.4 Final design 2.2.5 Budget and Time 2.2.6 Computers 2.2.7 Computations 2.2.8 Drawings

2.3 Specifications 2.4 Problem Areas 2.5 Meetings 2.6 Correspondence 2.7 Checking

3.0 DESIGN LOADS 1.0 Perth

(PR) 3.1 Introduction

3.2 Codes 3.3 References 3.4 Technical Notes 3.5 Properties of Materials 3.6 Construction Loads

4.0 STRUCTURAL ANALYSIS 1.0 Melb

(PL) 4.1 Introduction

4.2 Codes 4.3 References 4.4 Technical Notes 4.5 Input

4.5.1 Load Estimation 4.5.2 Load Summary 4.5.3 Design Criteria

4.6 Model Selection 4.7 Analysis




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Section

Version

Action Author

4.7.1 Analysis of Concrete Frames 4.7.2 Analysis of Steel Frames 4.7.3 Analysis of brickwork Panels 4.7.4 Computer Analysis 4.7.5 Formulae for Estimation of Beam Frame

Shear, Moment and Deflection

4.7.6 Formulae of Plates and Tanks 4.7.7 Analysis of Irregular shaped concrete

columns 4.7.8 Analysis of Structures for Fatigue 4.7.9 Section Property Analysis

4.8 Verification of Analysis 5.0 REINFORCED & PRESTRESSED CONCRETE 1.0 Syd

(MB) 5.1 Introduction

5.2 References 5.3 Technical Notes 5.4 Reinforced Concrete Floor Systems

5.4.1 General 5.4.2 Flexural Member Size Selection 5.4.3 Typical Reinforcement Quantities 5.4.4 Deflection Limitations 5.4.5 Flat Slabs and Flat Plates 5.4.6 Banded Slabs 5.4.7 Precast Floor Systems 5.4.8 Reinforced Concrete Beams

5.5 Prestressed Concrete Floor System 5.5.1 General

5.5.2 Design Check List 5.5.3 Analysis 5.5.4 Deflection Limitations 5.5.5 Prestressing Tendons and Details 5.5.6 Flat Slab Design 5.5.7 Banded Slab Design 5.5.8 Earthquake Detailing

5.6 Reinforced Concrete Column




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Section

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Action Author

5.6.1 Scope 5.6.2 Load Rundowns 5.6.3 Design Loads 5.6.4 Reinforcement 5.6.5 Concrete Strengths 5.6.6 Bending Moments 5.6.7 Slenderness Ratios 5.6.8 Fire Resistance and Cover 5.6.9 General Design Notes 5.6.10 Preliminary Design 5.6.11 Column ties 5.6.12 Column Starter Bars 5.6.13 Column Size Reductions 5.6.14 Top Terminations of Column

Reinforcement 5.6.15 Bundles Bars 5.6.16 Column Splices 5.6.17 Mechanical Tension Splices 5.6.18 Column Axial Shortening 5.6.19 High Strength Concrete 5.6.20 Bending Moments in Columns 5.6.21 Concrete Placing, Stripping and Curing

5.7 Reinforced Concrete Walls 5.7.1 Design Approach

5.7.2 Walls - Low to Medium Rise 5.7.3 Core Walls - High Rise (greater than 20

storeys) 5.7.4 Influence of Creep 5.7.5 Relaxation 5.7.6 Basement Retaining Walls

5.8 Foundations 5.8.1 Strip footings

5.8.2 Pad footings 5.8.3 Combined and Strapping Footings 5.8.4 Raft (or Mat) Footings 5.8.5 Pile Footings 5.8.6 Bored Piles 5.8.7 Driven Piles

5.9 Water Retaining Structures 5.9.1 Introduction

5.9.2 Design Philosophy 5.9.3 Design Analysis 5.9.4 Concrete Technology 5.9.5 Construction

5.10 Corbels, Dapped, Beams ends and Deep Beams

5.10.1 Corbels 5.10.2 Dapped Beams Ends 5.10.3 Deep Beams 5.10.4 Repairing Concrete




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Section

Version

Action Author

6.0 PRECAST CONCRETE 1.0 Adel (JW)

6.1 Introduction 6.2 Codes 6.3 References 6.4 Technical Notes 6.5 Design Principles

6.5.1 Non-Load Bearing Precast Cladding Panels

6.5.2 Design of Precast Concrete Panels 6.5.3 Finishes 6.5.4 Design Criteria for Fixings 6.5.5 Tolerances 6.5.6 Fixing Ferrules and Lifting Devices 6.5.7 Fixing and Design Aids 6.5.8 Prototypes 6.5.9 Notes to be Placed on the Precast

Drawings 6.5.10 Typical Panel Connections 6.5.11 Load Bearing Precast 6.5.12 Tilt-up Construction 6.5.13 Floor Panels 6.5.14 Detailing 6.5.15 Joints 6.5.16 Standard Details 6.5.17 Shop Drawings

7.0 STRUCTURAL STEELWORK 7.1 Introduction

7.2 Codes 7.3 References 7.4 Technical Notes 7.5 Purlins and Girts

7.5.1 Design 7.5.2 Use of Purlins and Girts

7.6 Beams 7.6.1 General

7.6.2 Connections 7.6.3 Effective Lengths, Moment Gradient 7.6.4 Members subject to Bending 7.6.5 Angles as Beams - Extract from

Reference (6) 7.6.6 Members Subject to Axial Compression 7.6.7 Members Subject to Combined Action 7.6.8 Penetrations 7.6.9 Allowable Deflections

7.7 Trusses




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Section

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7.7.1 General 7.7.2 Analysis 7.7.3 Member Sizing 7.7.4 Connection 7.7.5 Fabrication, Transport and Erection 7.7.6 Weld Testing

7.8 Portal Frames 7.8.1 General

7.8.2 Rafters 7.8.3 Bean Columns 7.8.4 Columns 7.8.5 End Wall Mullions 7.8.6 Flybraces 7.8.7 Connections 7.8.8 Bracing 7.8.9 Roof Bracing 7.8.10 Wall Bracing 7.8.11 Temperature Range 7.8.12 Footings

7.9 Other Structural Forms 7.9.1 Space Frames

7.9.2 Cable Structures 7.9.3 Masts and Lattice Towers 7.9.4 Cold Formed Steel 7.9.5 Painting of Steelwork 7.9.6 Erection of Steelwork

8.0 COMPOSITE DESIGN 1.0 Melb

(MS) 8.1 Introduction

8.2 Codes 8.3 References 8.4 Technical Notes 8.5 Steel Beams

8.5.1 Composite Program - “COMPBEAM” 8.5.2 Dynamics 8.5.3 Composite Beam Deflections

8.6 Slabs 8.6.1 Design Method 8.7 Columns 8.7.1 Design Methods

8.7.2 Concrete Filled Steel Tubes

9.0 MASONRY 1.0 Adel

(JW)




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Section

Version

Action Author

9.1 Introduction 9.2 Codes 9.3 References 9.4 Technical Notes 9.5 Responsibility

9.5.1 General 9.5.2 Design/Documentation 9.5.3 Inspections

9.6 Loadings 9.6.1 Wind Loads

9.6.2 Earthquake Loads 9.6.3 Vertical Loads 9.6.4 Load Combinations

9.7 Design Details 9.7.1 Design of Control Joints

9.7.2 Design of Wall Ties 9.7.3 Fire Rating

9.8 Materials 9.8.1 Masonry

9.8.2 Mortar 9.8.3 Grout 9.8.4 Masonry 9.8.5 Reinforcement 9.8.6 Accessories

10.0 TIMBER DESIGN 1.0 Perth

(DP) 10.1 Introduction

10.2 Codes 10.3 References 10.4 Technical Notes 10.5 Availability 10.6 Timber Sizes

10.6.1 Moisture Content 10.6.2 Strength Grading 10.6.3 Creep 10.6.4 Durability 10.6.5 Differing Strength Characteristics

Perpendicular or Parallel to Grain

10.7 Designing Timber Structures 10.7.1 Beams

10.7.2 Trusses 10.7.3 Fabricated Plywood Elements 10.7.4 Joints

11.0 GLASS AND CURTAIN WALL DESIGN 1.0 Bris

(MK)




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Section

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Action Author

11.1 Introduction 11.2 Codes 11.3 References 11.4 Technical Note 11.5 Glass Design Principles

11.5.1 General 11.5.2 Mechanical Properties 11.5.3 Annealed Glass 11.5.4 Toughened Glass 11.5.5 Heat Strengthened Glass 11.5.6 Laminated Glass 11.5.7 Available Glass Thicknesses 11.5.8 Considerations in Glass Selection 11.5.9 Design of Glass for Wind Loading 11.5.10 Gravity Loading 11.5.11 Design for Human Impact 11.5.12 All-Glass Assemblages 11.5.13 Jointing 11.5.14 Aquaria and Underwater Observation

Panels

11.6 Curtain Wall Design Principles 11.6.1 Introduction

11.6.2 Factors Requiring Consideration 11.6.3 Building Movements 11.6.4 Building and Curtain Wall Tolerances 11.6.5 material Properties 11.6.6 Silicone Sealants 11.6.7 Structural Silicone 11.6.8 Curtain Wall Component Design 11.6.9 Structural Sealant Design 11.6.10 Structural Silicone Testing 11.6.11 Waterproofness

11.7 Curtain Wall Prototype Testing 11.8 Curtain Wall Fabrication and Erection 11.9 Quality Control and Inspection 11.10 Future Inspection and Maintenance 11.11 Curtain Walls - Connell Wagner’s Role 11.12 Curtain Wall Problems

12.0 NATURAL STONE 1.0 Adel

(JW) 12.1 Introduction

12.2 Codes 12.3 References 12.4 Technical Notes 12.5 Design Principles




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Section

Version

Action Author

12.5.1 General 12.5.2 Natural Stone Facade Claddings 12.5.3 Stone Selection 12.5.4 Properties of Building Stone 12.5.5 Testing 12.5.6 Allowable Stresses 12.5.7 Methods of Supporting Stone 12.5.8 Considerations in Setting Up a Stone

Supply Contract

13.0 ALUMINIUM 1.0 Bris

(MK) 13.1 Introduction


13.5.1 Allowable Stresses 13.5.2 Fatigue 13.5.3 Thermal Movement 13.5.4 Connections 13.5.5 Dissimilar Materials 13.5.6 Chemical Corrosion Resistance

14.0 TENSILE MEMBRANE STRUCTURES 1.0 Melb

(MB) 14.1 Introduction

14.2 Codes 14.3 References 14.4 Technical Notes 14.5 Components

14.5.1 Membrane Material 14.5.2 Cables 14.5.3 Webbings 14.5.4 Fittings 14.5.5 Structural Steelwork 14.5.6 Foundations

14.6 Design Principles 14.6.1 Approximate Methods of Calculations

14.6.2 Formfinding 14.6.3 Design Loads 14.6.4 Analysis/Detailed Design/Patterning

15.0 GRC 1.0 Adel

(JW)




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Section

Version

Action Author

15.1 Introduction 15.2 Codes 15.3 References 15.4 Technical Notes 15.5 Design Principles

15.5.1 Materials 15.5.2 Glass Fibres 15.5.3 Quality Control 15.5.4 Production Methods 15.5.5 Methods of Transportation and On-Site

Handling 15.5.6 Mechanical and Physical Properties 15.5.7 Fixings 15.5.8 Surface Finishes 15.5.9 Waterproofness 15.5.10 Composite Panels

15.6 General Summary of Material 15.6.1 Typical Details for GRC 16.0 TEMPORARY WORKS DESIGN 1.0 Adel

(JW) 16.1 Introduction


16.5.1 Design Considerations 16.5.2 Underpinning 16.5.3 Shoring 16.5.4 Retaining Walls 16.5.5 Temporary Supports (for Walls) 16.5.6 Crane Bases and Ties 16.5.7 Site Gantries 16.5.8 Demolition

APPENDIX A

Technical Report TR96-1 - Earthquake Design to AS1170.4

1.0

Adel (JW)

APPENDIX B Technical Report TR96-4 - Cable Structures

1.0

Melb (RG)

APPENDIX C Technical Report TR96-5 - The Development of a Prefabricated Steel Framed Housing System

1.0

Adel (AL)

APPENDIX D Technical Report TR96-6 - Introduction to Structural Aspects of Fire Engineering Crown Casino Experience

1.0

Melb (SD)




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APPENDIX E Technical Report TR97-1 - Concrete Facade Repairs and Maintenance

1.0

Adel (DJ)

Version Register

Version No Section Changed By Issue Date

1.0 Initial Issue All 29 October 1997


Doc Ref: P:\9660\08\Design Guideline\Section1 to 4


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1. INTRODUCTION

The Design Guidelines Manual has been produced as a ‘firm guideline’ for the

common structural design processes by Connell Wagner’s structural engineers.

The manual is focused on the structural design issues which confront the engineer in

day to day work. It is a technical document giving guidelines for structural analysis

and design for the common building materials used in today’s building and

construction industry.

The document has been collated to reflect Connell Wagner’s combined knowledge,

experience and expertise in structure engineering.

The manual presents a rational and balanced approach to design and is intended to

generate uniformity in the more standard day to day design exercises. This uniformity

should be both evident within a particular office and also across the whole

organisation.

The manual shall be used on a regular basis by all structural engineers and as a first

point of reference for all work.

The expression "firm guidelines" in the first paragraph is used to emphasise that the

manual is to be used with sound judgement. The manual is not comprehensive of all

matters relevant to structural design. It is not intended to provide solutions for all

situations. The design engineer should always explore other sources of information

such as text books, Australian and international codes and standards. The design

engineer should discuss design issues and design problems with the project

structural discipline leader or other Connell Wagner management.

When using the manual, the design engineers must, at the outset ask the question; "Is

this a standard design?". If the design is special or unique, obtain advice from other

Connell Wagner staff with special expertise in the area or obtain additional information

and design guidance from other external sources.




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The manual is not intended to discourage innovation. Innovation in the correct

circumstances is encouraged by Connell Wagner but should be pursued with care

and only after discussion with the project discipline leader or management.

The following should be considered when using the Design Guidelines:

• The fundamental objective in design is to produce a structure which meets the

clients requirements, is structurally adequate, serviceable, functional, durable,

economic and if required, addresses aesthetics.

• The design process must meet the cost and time requirements of both the

client and those of Connell Wagner.

• Do not assume anything unless you have a valid basis for doing so. This must

appear at the beginning of the computations.

• Computations should recognise the level of accuracy to which loads and

material properties are known.

• Complex and rigorous analysis should not be used where simplified methods

will provide a satisfactory result. ( wl2 will often give a suitable answer).

8

• Minimum weight structures are not always the most economic solution. Be

aware of "real" construction costs. Generally, simple solutions using standard

details result in economic structures.

Recommendations for alterations/improvements to the Design Guidelines are

encouraged and should be referred to a Principal who in turn will refer this to the

Author of the manual. The Manual is a live working document which will be upgraded

on a regular basis.




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2. DESIGN PRINCIPLES AND PROCEDURES

2.1. Design Philosophy

The aim of the designer is to provide a functional and economic project on time and on

budget.

A functional project is one that is sufficient to meet the requirements of the brief and

comply with codes and regulations ie. it must have sufficient strength to carry the

applied loads and have adequate stiffness to limit deflections and vibrations. It must

also be durable against corrosion and deterioration and have adequate fire protection.

An economic project is one that has an optimisation of material and labour costs.

Minimum sizing does not always result in minimum cost. In designing we also need to

be aware of the importance of buildability and to document accordingly.

Spend the appropriate time on design of items. A refined design will be warranted for

a floor system repeated many times such as in a multi level building. Look at where

the cost is to the project and where design refinement will save the project money.

Use simplified or basic methods for analysing simple and one off members where the

cost of the member has little affect on the overall cost of the project.

When designing, avoid getting bogged down in numbers, computer output and paper.

Carry out simple checks of detailed work. Continually check your computations and

design assumptions to avoid duplication of errors. Five minutes spent checking your

own work on a regular basis can save hours of corrective work on design and drafting

later on.

Aim for a general uniformity of members or elements and details, and do not have a

multitude of sizes, types etc. It only confuses other designers, the drafters, and the

Builder/Contractor and will inevitably lead to mistakes, and possible future problems.

With our dependence on information from other Consultants and other Disciplines

within the office, it is important that we plan our time to ensure that deadlines are met.




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This means that we have to inform others as to deadlines for receipt of the necessary

information.

We must anticipate the requirements of other Consultants and other Disciplines and

not work away in isolation without due consideration being given to the influences of

their work.

Keep every Consultant and other Disciplines informed of the solution as it develops,

ensuring that they receive sufficient drawings and that their work does not clash with

the structure. It is not the intention that we co-ordinate the project unless we are

Prime Consultants but we must be aware of the restraints that other Consultants and

other Disciplines work may impose.

Never give a Client the impression that you are too busy. They must feel that this is

the most important job in the office.

Maintain a professional approach at all times but ensure that we provide the service

that our Client expects.

Be aware also of market opportunities in your work and communicate information,

intelligence and opportunities to those above you. The best marketing is by designing

each job well, on time and on budget.

Success means providing quality engineering and service and completing the job on

time and within budget. The budget must be worked out, and agreed with the Project

Principal. Regular reviews are necessary to ensure time and budget will not be

exceeded.

The philosophy of Connell Wagner is that every project must be a winner, especially

the hard ones even in the most difficult terms. Our aim is to provide world class

engineering at competitive prices.

2.2. Project Procedures

2.2.1. Introduction




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The Project Leader is the key person responsible for the day-to-day running of the

project within Connell Wagner. To achieve this, communication takes place between

all people involved in the project. Each person must properly brief the people

responsible to them. Conversely each individual must demand a proper briefing from

the person to whom they are responsible.

2.2.2. Briefing

Prior to commencing a job we must have an understanding of the job and obtain a

brief from the client.

The design must meet the requirements of the brief. If the brief does not adequately

describe the design requirements then we should confirm with the client the design

criteria we adopt before proceeding.

It is also important to understand what form of documentation is required and when it

is required to permit proper planning of the job.

• Is the project to be fully documented for tender?

• Is the project a fast track documentation?

• Is it a design and construct project?

• Will the tender documents be accompanied by the Quantity Surveyors Bill?

• Which form and when does the Quantity Surveyor require documents for

costing?

The Project Principal must properly brief the Project Leader. The briefing should

include the fee allowed, budget hours, key programme commitments and client briefs.

The Project Leaders should inturn brief the people responsible to them.

2.2.3. Preliminary Design

Typically a project will be divided into Preliminary Design and Final Design. These

stages are sometimes further broken down into concept design, preliminary design,

design development and final design.




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At the commencement of the project the design philosophy should be set out

by the Project Leader including design data sheet and loading sheets as appropriate.

This design philosophy must be approved by the Project principal before proceeding

with the design and documentation.

Preliminary Design

This stage of the project can include Conceptual design, Schematic design and

Design development. The amount of this work done varies widely according to the

size of the project.

Generally preliminary design includes reviewing the possible alternative systems and

deciding on the appropriate system for the project. This is then followed by developing

this structural framing system, in conjunction with the other Consultants and other

Disciplines, to identify all of the problems and conflicts and to confirm project budget

costs. These problems and conflicts are then solved by mutual agreement with the

other Consultants and other Disciplines.

At the completion of the preliminary design the solution should be virtually fixed. The

plans should be logical and sensible and allow a full assessment under the applied

conditions and loads. Preliminary plans and typical sections should have been drawn,

issued to the other Consultants and other Disciplines and accept by them.

These drawings should be relatively fixed with respect to the basic layout and profile

dimensions of the elements. They should be adequate to permit accurate cost

estimating. Having completed these steps, final designs can then commence.

Preliminary drawings must show:-

• Sizes of all major and basic elements.

• A grid reference system.

• A reference number system for elements.

• Design assumption for specialist areas are to be noted if information is not

available.

• Any other important design information such as assumed design loads.

• Important fundamental details around which the design is based.




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Remember that at this stage the other members of the design team are not interested

in detailing. They require controlling dimensions and conditions for the development of

their own documents and subsequent confirmation of our proposals.

During this preliminary design period there are various important aspects to consider,

as follows:-

• Connell Wagner encourages innovative ideas. The conceptual design period is

the time to initiate such innovation.

• Innovation will involve the senior people in the office but younger members can

contribute.

• We must put forward sensible innovative ideas to our Clients, even if they are

unlikely to be accepted.

• We must be aware of new construction methods being adopted by the building

industry and be prepared to pick up and vary these.

• Avoid preconceived ideas.

• Do not allow the Quantity Surveyor to unreasonably cost innovative proposals.

• Think laterally in your day to day work.

• Hold regular review meetings (both in-house and externally with design team)

to discuss solutions being considered.

Alternative schemes

• Alternative schemes should be carried out on all medium and large projects.

• Alternative schemes should always be costed and reported, and it is important

not to accept without question the Quantity Surveyor's estimate and this

means that the designer must become familiar with the cost of work in the

industry.

• Alternative schemes will give the Architect/Client and other members of the

design team an indication of our solutions and their constraints.

• Alternative schemes provide a means for introducing innovations and to show

that we are not locked into one form of construction or material.

• The extent and detail of documentation of alternative schemes must be

controlled to contain our costs.




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• Alternative schemes should be submitted to the Project Principal for review.

Obtain the opinion of other experienced people in the office, particularly those

who may have had experience with the type of project being considered.

2.2.4. Final design

Computations

Computations are an important part of producing the drawings, they being our final

product. Design data sheets should precede the actual computations in order to

summarise assumptions etc.

Design methods

It is assumed that all Engineers in the office are competent designers and are familiar

with the current regulations, codes and design methods. It is the Engineer's

responsibility to ensure that they are familiar with all relevant documents.

Drawings

Remember that the drawings are the end product of our work, not the computations.

These must be well presented, easily read, accurate, concise, consistent and must

properly convey the intention of the design.

2.2.5. Budget and Time

Every project has budget hours and costs within which our design hours and costs

must be contained. Every project has programme commitments which we have to

meet. Every effort must be made to ensure this is achieved on your project. The

Project Leader is the person for ensuring budget and time commitments are met but

all other designers and drafters must assist in meeting these commitments.




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Programme

The Project Leader is to obtain key programme dates from the Project Principal. If this

is not provided, we should constructively pursue it from the client as many cost

overruns are a result of floating client programmes.

A documentation programme should be prepared for all major projects.

The programme should also include all information we want and dates when required

from other Consultants and other Disciplines. It is vital this programme be established

right at the beginning of the documentation and monitored effectively. If others then

delay us, then we can avoid the costs and problems of this being our responsibility.

The programme should include persons to be allocated for design and drafting to meet

the commitments. Completion dates for Building Act Approval, tender, construction

packages, etc. must be shown as required.

The programme must be consistent with the project budget.

Progress against programme must be regularly monitored. If dates are not going to

be met, extra resources must be applied to the project and the Client must be notified

in advance. If key information has not been received which affects our ability to meet

our programme, notify the Client and discuss the solution with the Client. Do not just

fail to meet dates and make excuses afterwards. That is not acceptable to our clients

or Connell Wagner.

Budget

The Project Leader is responsible for managing resources to ensure the work is

completed within the budget allocated. Performance must be regularly monitored to

ensure the work will be completed within this budget.

Major Projects

Total hours will be allocated by the Project Principal based on the fees to be received.

The Project Leader is to review these and ensure that they are realistic hours and




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produce a final budget and break-up hours which should be approved by the Project

Principal before the project begins.

• A break down of the total hours available into the various sections of the job

should be initially undertaken. From this, detailed budget hours will be

prepared for design, drafting and graphical techniques for reviewing these.

The sheets will identify people who will be responsible for each of these

sections, and hence responsible for maintaining the work within the hours

allocated for these sections.

• Identify the drafting hours to be used with the Project Drafter for controlling the

work. Work with the Project Drafter to determine number of drawings for the

project and ensure this is feasible within the budget allocation.

• Make an allowance in the program for contingency, internal checking, co-

ordination and external certification.

• This can vary depending on the type of project and type of Client etc.

Obviously in the case of a difficult Client or difficult project the contingencies,

checking and co-ordination may be higher.

The budget and hours should be reviewed at regular intervals and records updated

fortnightly or weekly depending on the pace of the project.

Be prepared to reassess the budget and hours if the job is not meeting the allocated

hours and discuss with the Project Principal.

Small Projects

The Project Leader is to agree with the Project Principal the allocated hours for the

job. The Project Leader should ensure that the programme and budget are met or

preferably bettered.




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2.2.6. Computers

The use of computers in the office is encouraged. They should be used in an

intelligent and sensible way. Computer programmes should be used instead of

manual methods if their use can be shown to be beneficial to the client and to Connell

Wagner by saving time during the design process when compared to manual

methods. Engineers are to be familiar with all normal methods of design. Non

familiarity with a particular computer program is not an excuse for not using it.

Avoid over usage of computers by rationalising the design process.

Consider carefully the model being used and ensure it gives an accurate

representation of the system being analysed without excessive complexity or

unwarranted analysis. Ensure that you have the knowledge and ability to use complex

programs.

Include relevant information only in the final computation. Cull the computer output to

suit.

Do not blindly accept results from the computer. Always examine the answers and

carry out checking to satisfy yourself that the answers given are reasonable. If they

are not, determine why before proceeding. Remember the program has been written

by another person and may have "bugs" in it, and is only as good as the data inputted.

2.2.7. Computations

Computations are the quickest and often the only practical way, of making an

assessment of a project.

In particular they are an important record/reference for the design loads, design

assumptions, philosophies, methods, etc.

The computations are to be sufficiently legible to enable the designer to arrive at a

solution, and to enable any experienced engineer to later understand what the




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designer was doing. The computations must be indexed to permit quick reference to

required information.

General comments regarding computations are as follows:

i) Plan the overall production of computations - always include an index.

The importance of a mark no. in the computations which matches the mark no.

on the final drawing, is preferred. A key plan in the computations, which

somehow relates to an "area" of the final drawing can also be used.

In most projects, include a concise preamble which defines the task.

ii) Avoid excessive complexity.

iii) Deliberately design less elements - rationalise but ensure all elements are

designed and are noted in the computations.

iv) Strive to do computations once only, in final form, with editing only to finish them

off.

v) Adopt simpler, but conservative techniques if it suits the job eg, simpler methods

such as moment and shear coefficients provided they do not lead to excessive

conservatism.

vi) Distinguish trivial from significant.

vii) Avoid the tendency to waffle.

viii) Design repetitive elements carefully to achieve a viable economical solution.

Spend minimum time on "one-off" elements.

ix) Complicated or new elements must be proof checked before completion.

x) Heavily loaded elements must not be under-designed.

xi) Ensure that formulae are properly applied.

xii) Ensure the proper load factors and factors of safety for performance and

serviceability area used.




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xiii) Carefully check the applied loads. This is where errors occur. Ensure they ar

correct before design is commenced

xiv) Ensure during the design process that your computations are clearly and legibly

filed as others may need to access them in your absence.

2.2.8. Drawings

It is the responsibility of the Project Leader to ensure that the drawings correctly

represents the design - ie. CHECK THE DRAWINGS FOR WHICH YOU ARE

RESPONSIBLE.

Remember that the drawings are the most important product of the design phases.

Projects are constructed from the drawings, not from computations.

The objective is to produce clear and legible drawings to enable the Builder/Contractor

to construct a project that satisfies our Engineering requirements. In particular :

i) Engineering drawings of building type structures normally only show structural

information of the structure. It is generally not the responsibility of the

engineering drawings to describe the building cosmetics/profile.

ii) Deliberately reduce non-essential sections/detail.

iii) Show essential information only.

iv) Use standard details extensively where possible.

v) Defer final documentation until other members of the Design Team have

advanced their design and drawings.

vi) The Project team should meet at the start of the project to determine the

philosophy of documentation.

• Make drawings look simple and well set out (good impressions for

others).

• Do not duplicate similar details.

• Use schedules wherever possible.




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• Avoid calling up information twice.

vii) Preliminary Documentation

• Well done preliminary drawings allow for deferment of final drawings until

other disciplines have provided adequate input.

• CAD is an excellent medium for many schemes for quick output.

• Drafters are to avoid excessive drafting in preparing preliminary

drawings.

• Refer to examples for similar structure arrangements.

viii) Fast track jobs require progressive issues of documentation to suit construction

with a number of staged issues.

Only draw essential information ie, essential information at each stages.

ix) Checking all drawings is essential and is part of our Quality Assurance

procedures. This must include checking conformity with other Consultant and

other Discipline drawings as well as the discipline requirements.

x) When setting out and checking the drawings, always carry out a review as

though you are the Builder/Contractor trying to interpret the structure to ensure

that it can be built. Ask yourself the question "IS THERE ENOUGH

INFORMATION FOR A BUILDER/CONTRACTOR TO BUILD IT FROM THE

DRAWINGS"?

2.3. Specifications

Specifications must be given proper attention and detail during the final design. Do not

leave them until the last thing and do not rush them out.

Use Connell Wagner standard specifications, amended where required to suit the

project.

Check if the Principal Consultant wants our specification on disk, or e-mail and what

format etc.




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Write specific specification clauses for each project which do not contain irrelevant or

misleading information.

They must be written in clear and concise English. Avoid describing how the work is to be done. Do not over-specify. Specifications are legal documents and must be treated as such. Problem Areas The following areas have been identified as high risk areas in structural design. Careful attention must be given to these by all engineers: a) Errors in reading drawings by Contractor (poor documentation). b) Proper communication between site and the office. c) Design errors. d) Inadequate geotechnical information particularly levels of rock and water. e) Inadequate survey of existing services, levels, features etc. f) Secondary effects. g) Inadequate time spent on detailing. h) Underpinning of adjoining properties. i) Movement Joints. Need to be detailed carefully and closely supervised. j) Serviceability/deflections. Need to conform to brief and be wary of items affected by deflections, i.e. masonry partition walls, facade detailing. Need to advise facade engineers of expected building movements. k) Masonry walls. Need to coordinate jointing with the Architect. Masonry walls need proper design attention. Don't leave it to Architect. l) Balustrades. m) Advise the client/QS of potential cost over-run areas so that allowance can be made in the budget, i.e. grey areas in the design: doubts over founding material; possible additional work when refurbishing existing buildings. n) Get moneys allocated for specialist consultants, i.e. geotechnical, concrete technologists, specialist welding inspectors, wind tunnel testing.




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o) The extent of our work is not always clearly defined. Our normal engagement excludes the following: design certification geotechnical investigation corrosion protection of steelwork facade screeds and tanking Retaining walls

2.4. Meetings

Meetings are often our only direct contract with our Clients and are therefore a very

important activity. Remember that many critical decisions are made at meetings.

They are an opportunity for us to get our important points across to the design team.

Our performance at meetings is important because our contribution to the project, as

judged by the Client and others, is largely influenced by this performance.

The following points are to be taken into account:

• Punctuality is essential. If you are late for some unavoidable reason then have the

office phone and advise of your late arrival (only be late once).

• Be thoroughly prepared prior to the meeting.

• Notes should be taken to form a record and action list. These must be accurate and

not be capable of misinterpretation. They should be distributed and then filed. (Do

not write comments on the minutes as these can be used legally against us in any

court action).

• Make positive innovative contributions, even beyond our direct brief.

• Be aware of other team members' and other disciplines' role and their needs.

• Be conscious of time spent in meetings. Excuse yourself and leave early whenever

possible.

• Ensure all action items are carried out following the meeting, prior to the next

meeting.




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Carefully read minutes prepared well before the meeting and distributed by others to

ensure they are accurate especially if it is a multi-disciplinary project. Have items

corrected at the next meeting, if you are in disagreement (this is important).

• Confirm significant items back to the Client by letter.

2.5. Correspondence

Correspondence is vital part of our activities. The quality of our correspondence will

be seen by others to reflect the quality of our organisation. It is a vital part of forming a

permanent and accurate record of our interaction with other members of the team.

The following points are important:

• Ensure that the correspondence says what you actually intend to say. Be careful

with your English expression and punctuation.

• Keep in mind future legal implications.

• Letters or memoranda should be used to confirm significant advice given or

received.

• Direct correspondence to appropriate staff members of our design team (including

other Disciplines if appropriate).

• Respond to correspondence promptly, particularly internally to ensure prompt

circulation.

• Where appropriate, file memoranda should be distributed to all interested parties.

• If we expect the recipient of the letter/memo to take action as a result of the

letter/memo then SAY SO: Tell the recipient what action we expect to be taken eg.

"for issue to the Builder for construction" or "for your review and comment" or "we

await your approval" etc.




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• Agree with the Project Leader important Connell Wagner correspondence which

should be in a letter form as compared to less formal fax or e-mail correspondence.

2.6. Checking

All engineers are to examine their own computations on project completion to ensure

that they are correct and complete to the best of their ability. Where Engineers have

reservations about their expertise for a design task they must discuss this with the

Project Leader before carrying out the design. Engineers are also responsible for the

checking of drawings resulting from their computations to ensure the correct

interpretation of their design has been detailed. Engineers and Drafters MUST check

their own work thoroughly. The fact that an independent check is carried out in no way

reduces the responsibility of the engineer and draftpersons to get the job right in the

first place.

There is often too much time spent on computations and insufficient time on checking.

The Project Leader shall examine regularly sections of the computations completed by

Engineers working for them and the drawings resulting from their designs and assess

their adequacy.

In addition to this, all jobs prior to formal issue will have an independent check carried

out by an independent in-house checker.

It may be advisable that special sections of a project be checked prior to completion of

the total project as instructed by the Project Leader.

The detailed procedures for structural checking and/or verification shall be found in the

Quality Assurance Manuals.




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3. Design Loads

3.1. Introduction

This section briefly summarises the requirements for determining design loads.

Assumed loads should be;

• Nominated on the drawings;

• Clearly stated in the calculations at the beginning;

• Verified with the Discipline Leader.

Whilst virtually all design loads are prescribed by codes, the appropriate choice of

loads and combinations has arguably the most significant effect on both the safety and

cost effectiveness of structures.

The original determination of loads nominated in codes is generally based on historical

and empirical data. As such, loads should always be reviewed in relation to the

particular structure and location being designed. Loads nominated in codes are

minimum general requirements. Particular authorities and clients may have more

stringent requirements.

Do not ignore loads induced by actions other than gravity eg. Wind, thermal,

earthquake, shrinkage etc.

3.2. Codes

Australia and New Zealand are gradually moving towards common codes including

loading codes (albeit that the emphasis, particularly with regard to Earthquakes, may

be different). Load combinations are gradually being removed from materials codes

and transferred to the loading codes.

Codes of direct relevance are;

• Building Code of Australia

• AS 1170.1 “SAA Loading Code Part 1: Dead and live loads and load combinations”;

• AS 1170.2 “SAA Loading Code Part 2: Wind loads”;

• AS 1170.3 “SAA loading Code Part 3: Snow Loads”;

• AS 1170.4 “Minimum design loads on structures Part 4: Earthquake loads”;

• AUSTROADS BRIDGE Design Code - Section Two - Design Loads.




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Other relevant codes include;

• AS 3610 “Supp1-1995 Formwork for concrete”;

• AS 1418 “SAA Crane Code”;

• AS 1657 “SAA Code for Fixed Platforms, Walkways, Stairways and Ladders”;

• AS 3735 “Concrete structures for retaining liquids”;

• AS 3850.1&2 “Tilt-up concrete and precast concrete elements for use in buildings”.

• AS4324.1 "Mobile Equipment for continuous handling of bulk materials".

3.3. References

3.4. Technical Notes

3.5. Properties of Materials

Refer AS 1170.1, materials codes and attached data sheets.

3.6. Construction Loads

Refer AS 3610 for guidance. Construction loads should always be reviewed with the

Structural Discipline Leader.

Densities and Mass of Materials Note that the values given for bulk materials may vary significantly, and further data should be obtained if any doubt exists.

Mass per unit volume kg/m3 kN/m3

Concrete (normal aggregate) 2400 24

Concrete (lightweight aggregate) 1900 19

For each 1% reinforcement add 60 0.6

Cement 1500 14.7

Steel 7850 77

Timber

- Hardwood (refer AS 1720 for actual 800-1200

8-12

- Softwood species densities) 400-600 4-6

Water 1000 9.8

Asphalt 2160 21.2

Sand - dry 1600 15.7




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Silty - Loam saturated 1600 16

Clay 1800 18

Mudstone, Sandstones 2300 22.5

Limestone (dense) 2500 24.5

Limestone (Mt Gambier) 1300 12.5

Coal, loose, clean 900 8.8

Marble 2700 26.4

Granites, Basalts, Trachyte 2700 26

Aluminium 2700 26.7

Glass - Window (Soda Lime) 2600 26

Terrazzo 2750 27

Cork

- Normal 170 1.7

- Compressed 380 3.7

Lime Plaster 1880 18

Cement plaster 2260 22

Brick masonry 1950 19

Copper 8800 86.3

Brass 8520 83.5

Zinc 7150 70.0

Mass per unit volume kg/m3 kN/m3

Fibre Cement Sheet

- Uncompressed 1450 14.2

- Compressed 1760 17.2

- Fire resistant 920 9.1

Cast Iron 7200 70.7

Lead 11320 110.9

(Mass to Force : 1Kg = 9.81 N

eg 1000 kg/m3 = 9.81 kN/m3)

Mass per Unit Area kg/m2 kN/m2

Ceiling

Fibrous plaster

- 10 mm thick 9 0.09

- 13 mm thick 12 0.12

- 16 mm thick 16 0.16

Lime plaster - 13 mm thick 25 0.24




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Gypsum plaster - 13 mm thick 13 0.13

Portland Cement plaster 30 0.29

Suspended metal lath and gypsum plaster

- No FRL 15 0.15

- FRL 1 hour 25 0.25

- FRL 2 hour 50 0.50

Suspended 13 mm plaster board 17 0.17

Fyrcheck

- 2 layer 13 mm 24 0.24

- 2 layer 16 mm 26 0.26

Stramit board 18 0.18

Metal Pan Ceilings (approximate) 10 0.10

Plaster acoustic tiles 15 0.15-0.25

Mineral fibre acoustic tiles 6 0.06

Floors

Asphalt - 25 mm thick 54 0.53

Cinder - Concrete filling 25 mm thick 45 0.43

Clay tiling, 13 mm thick 27 0.27

Carpet 10 0.10

Vinyl tile - 3 mm 7.0 0.07

Terrazzo paving - 16 mm thick 44 0.43

Mass per unit area kg/m² kN/m²

Roofs

Acrylic resin corrugated sheet 6 0.06

Cellulose fibre and asbestos cement, super 6 corrugated including lap and fastenings

16 0.16

Fibre and asbestos cement slates 22 0.22

Aluminium, corrugated including lap and fastenings

- 1.26 mm 5 0.05

- 1.00 mm 4 0.04

- 0.79 mm 3 0.03

- 0.63 mm 2 0.02

Bituminous felf (5 ply) and gravel 44 0.43

Steel, corrugated including lap and fastenings

- 1.00 mm 12 0.12

- 0.8 mm 10 0.10

- 0.6 mm 8 0.08




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- 0.5 mm 5 0.05

Custom orb (0.42 mm) 5 0.04

Tiles

- Terracotta (French pattern) 58 0.57

- Concrete 54 0.53

- Decramastic 7 0.07

- Slate Tiles

4.7 mm thick 34 0.34

9.5 mm thick 68 0.67

Walls

Brick Masonry, sold - clay per 100 mm of thickness

195 1.9

Concrete hollow block masonry standard aggregate

- 100 145 1.42

- 150 175 1.73

- 200 225 2.20

Concrete hollow block masonry lightweight aggregate

- 100 120 1.18

- 150 125 1.25

- 200 175 1.70

Concrete block masonry per 100 mm thickness

- Standard aggregate 220 2.2

- Lightweight aggregate 180 1.8

Co-efficient of thermal expansion mm/mm/10-6°C

Material

Aluminium 23.1

Brass 18.8

Brick Masonry 6.1

Cast Iron 10.6

Concrete 9.9

Copper 16.8

Glass 7.2

Granite 8.0

Lead 28.6

Limestone 7.6

Marble 8.1

Nickel 12.6




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Plaster 16.6

Sandstone 9.7

Slate 8.0

Steel 11.7

Zinc 31.1




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4. STRUCTURAL ANALYSIS

4.1. Introduction

The simple procedure for structural analysis should include the following steps:

• Inputs

• Model selection

• Structural analysis

• Verification of analysis

4.2. Codes

AS 4100 Steel Structures Code Amd 1993

AS 3600 Concrete Structures Code 1994

BS 5400 Part 2 App.C - Beam Vibrations

AS 1170 Parts 1 to 4 Australian Standard Loading Code

4.3. References

Steel Designer's Handbook Gorenc Tinyou Syam 6th ed. 1996

Steel Designer's Manual. Constrado 5th ed. 1992

Formulas for Stress and Strains. Roark and Young 6th ed. 1989

Reinforced Concrete Design Handbook. Reynolds 10th ed. 1988


A95/4 Stability of buildings Feb 95 JW

A95/3 Structural Design Philosophy Jan 95 JW

M95/7 AS4100 1990 Section 11 Fatigue Feb 95 Bruce Wymond.

M95/5 Steel Mast Structure Fatigue Dynamic Analysis for along wind response Feb 95

JDB/BW

M91/M79/3 Warehouse design for wind March 1979 JHW

M91/M83/5 Plastic design of low rise steel portal frames Mar 83 WRG.

M91/M98/5 Hot dipped galvanised purlins Oct 78 JHW.

S96/1 Performance Brief for the design, detailing and documentation of post tensioned

floor structures by a post tensioning sub-contractor June 96 RWS

A95/7 Design of Columns using modified frame stiffness April 95 CS/NBT




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S94/1 Design of Pin Connections Aug 94 MB/JW

A95/2 Design of Masonry Jan 95 JW

M95/3 Hollow Core Plant design Feb 95 TL

4.5. Input

Inputs include items such as loads, geometry, support conditions, client requirements

(e.g. special deflection requirements), connection types, material properties, design

criteria (e.g. deflection limits) and codes which are to be followed.

Try to visualise or sketch out the structural details of the element you are to analyse

before starting any calculation or analysis. This process often points to other factors

which may influence your analysis, such as construction requirements, connection

types or other constraints.

4.5.1. Load Estimation

Your estimation of loads should be done carefully and be doubly checked as this is an

area where the most significant mistakes are made which have an impact on the final

design and costs. There is not always a need for your estimation to be exact but there

is always a need to know that you are correct.

You may be asked by the project design leader to estimate the design live loadings or

you may be given them. In any case, check that they are correct.

In estimating the load, contact will need to be made with the architect, client and the

services engineer. The architect is usually the first point of contact.

Questions to ask:

ie: What are the finishes?

Are the partitions to be masonry or non masonry?

Are there to be any high load areas such as storage or compactus?

Are there any plant areas ? What is the weight of the plant ?

Are there fire rating requirements which may dictate the type of

construction materials?

Refer also to Section 3 of Guidelines within this document.




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4.5.2. Load summary

The loading should be clearly indicated on Design Data sheets, approved by the

Project Design Leader and then given to all members of the structural design team.

These must appear at the front of the computations.

The live loads, wind and eqrthquake loads, plant loads and superimposed dead loads

should be shown on the drawings.

The client should be made aware of the design loadings used. A check should be

done to ensure that the loads are within the clients brief. This may only require

compliance to the Australian Standard Loading Code AS1170, Parts 1 to 4.

4.5.3. Design Criteria

The design criteria should be agreed with the Project Design Leader and should be

stated in your calculations. For larger projects this should take the form of a written

design philosophy setting out he structural form and loads.

Deflection Criteria

Deflection criteria are recommended in AS4100 and AS3600. A good summary of

some commonly accepted deflection criteria are provided in these Guidelines under

the appropriate material heading.

Vibration Criteria

• Deflection criteria for floor beams will normally give a suitable floor beam vibration

response. For long span floor beams or frames, limit the natural frequency of the

structure to greater than 8 Hz. Values less than this can be used if your model is

conservative, but this needs to be agreed with the project leader and client. Note

that floor systems that consist of beams supported by beams or beams

cantilevering from beam supports are more likely to have a lively vibration response

and should be designed carefully to avoid such occurrence.




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• For light weight composite floors refer Section 8 of these Guidelines.

4.6. Model Selection

Select an appropriate model making reasonable simplifications and assumptions. The

simple single span beam model is often the best solution. In considering the

complexity of the model consideration should be given to:

• the importance of the component in the overall design. A member that repeats

many times requires more accurate modelling than a one off element.

• the required accuracy of the results. There is no use in doing three slab analysis

when one is sufficient.

• constructability and cost of construction. For example consider carefully the

implications of adopting fixed end moment connections for steelwork.

4.7. Structural Analysis

Analysis methods depend on the complexity of the selected model. Analysis methods

that can be used include:

• Beam formulae

• Moment co-efficient

• Moment distribution

• Computer analysis

• Other design formula

Hand calculation of moments is now often replaced with a computer analysis which is

generally quicker. However, make yourself aware of design formulae which often give

sufficient information for design in less time than a computer analysis.

Note that a computer analysis results in a lot of output which needs time to be read,

printed and checked. The use of computer analysis must be agreed with the project

engineer so that your time can be well used.




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4.7.1. Analysis of Concrete Frames

Concrete frames and floor systems are typically analysed using SpaceGass or

ETABS in conjunction with RAPT. Building stability is typically analysed using

SpaceGass or ETABS (ie for Earthquake and Wind loadings). The design actions are

taken from this analysis to input in to RAPT for analysis and design of the floor

systems.

Care should be taken in using a "frame analysis" to design floor elements as the full

column moments may not be fully developed because of shrinkage cracking or

proposed construction methods. Increased floor deflections and midspan bending

moments may result. It may be appropriate to conservatively assume no moments

are developed into the columns for the floor. This assumption should be confirmed

with the project leader before analysis.

Refer AS3600 for guidelines on equivalent column stiffness; in particular, clause 7.7 of

AS 3600

4.7.2. Analysis of Steel Frames

Steel frames are typically analysed using SpaceGass for all load conditions. Steel

design may be done manually or within SpaceGass using the LIMSTEEL package or

design actions may be input into programmes such as MLPSTEEL. MLPSTEEL is a

steel design programme which can also be used to analyse single spans.

4.7.3. Analysis of Brickwork Panels

Refer tables in the Concrete Masonry Association of Australia Concrete Masonry

Buildings. A Practical Guide to Design, January 1992.

4.7.4. Computer Analysis

Our most frequently used analysis programs are Space Gass and RAPT. Other

structural analysis programs include ETABS, Strand and simple beam analysis

programs like Beam for Windows and MLPSTEEL.




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Most of our frame analysis is carried out on Space Gass. Space Gass has the

following special capabilities:

• non linear analysis - second order (p-delta) effects

• elastic buckling analysis - gives buckling load factors and effective lengths.

• dynamic analysis - gives mode shapes and their associated frequencies

• slaving modules

• response spectrum analysis - for refined earthquake analysis.

• cable elements - models catenary elements (zero bending stiffness)

• tension or compression only elements

• lime state.

ETABS is a similar analysis package which is set up specifically for multi-storey

buildings. ETABS is generally not as user-friendly as Space Gass but has the added

advantage of being able to model shear walls and also having a time-history analysis

for refined earthquake analysis.

Both Space Gass and ETABS are capable of carrying out non-linear analysis. Non-

linear analysis is generally adopted for steel and some concrete structures. Non-

linear analysis is critical for flexible frames with axial loads. It should be noted that for

a non-linear analysis to be valid any in-plane or out-of-plane restraints should be

properly modelled such that a realistic buckling load may be calculated.

RAPT is used to analyse and design floor systems. It is generally used to analyse

gravity loads only, however bending moment diagrams may be superimposed to allow

for lateral load cases. Note design actions from lateral loading must be calculated

elsewhere (ie. in a program like Space Gass or ETABS). For an accurate RAPT

deflection design, enter the actual reinforcement proposed. RAPT also has the facility

to limit steel stresses for liquid retaining concrete structure analysis.

Finite elements analysis is another, less common, type of analysis. Finite element

analysis is generally a higher tier analysis which is only adopted when the structure or

structural element cannot be adequately modelled by simple beam/column elements.

It is also sometimes used to calculate the internal actions and deflections of unusual

or non-uniform cross-sections. Before undertaking a FE analysis it is important input




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from those in the office obtained in such analysis techniques. Interpretation of results,

particularly for concrete structures, requires careful consideration.

The finite element package which is used in Connell Wagner is STRAND but

occasionally, when greater expertise or a more sophisticated analysis is required,

assistance may be sought outside Connell Wagner.

4.7.5. Formulae for Estimation of Beam and Portal Frame Shear, Moment and Deflection

Some common formulas are included in this manual. Refer Figures 4.1 to 4.5 in this

document. The references in Section 4.3 give a more comprehensive listing.

4.7.6. Formulae for Plates and Tanks

Refer References in Section 4.3.

4.7.7. Analysis of Irregular shaped concrete columns

RAPT and COLDES will give a design of irregular shapes columns however

slenderness effects must be manually estimated.

4.7.8. Analysis of Structures for Fatigue

Structures which we would more commonly require investigation of fatigue effects

include:

• Mast structures with fatigue induced by wind loading.

• Crane structures.

• Bridge structures.

4.7.9. Section Property Analysis

For core wall or irregular shaped section property analysis, THINSEC may be used.

4.8. Verification of Analysis

Analysis results should always be verified to the extent that the designer has an

appropriate level of confidence in the results. This verification would normally be done

by carrying out a more simplistic, independent analysis and comparing results.




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This verification process is the responsibility of the designer and should not be

confused with our QA design verification requirements.

Furthermore the model should be checked for its sensitivity to changes in input

variables. The variables which should be considered are those which the designer

has a degree of uncertainty about and may include the following:

• connection rigidity • support stiffness and/or settlements • loading variations including pattern loading • construction tolerances and/or techniques • material stiffness




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ESTIMATE OF THE DEFLECTION OF A SIMPLE PORTAL FRAME UNDER A SWAY LOADING

Figure 4.4




13 of 12

ESTIMATE OF THE DEFLECTION OF A COLUMN WITH A BEAM SUBFRAME

Figure 4.5


Doc Ref: P:\9660\08\Design Guideline\Section 5

Version No : 1.0 Issue Date : 29/10/97 1 of 51

5. REINFORCED AND PRESTRESSED CONCRETE

5.1. Introduction

The design of reinforced and prestressed concrete members in building structures

should be in accordance with the strength and servicability limit state requirements of

AS3600. The design is carried out using the design actions based on the loading

requirements of AS1170.1, AS1170.2, and AS1170.4 and those specific requirements

of the Client. The only exception to this rule is the design of water retaining structures

which is based on AS3735. The design principals for this code are stress limitation,

achievement of acceptable deflections, and minimisation of crack widths under

loadings.

5.2. References

• Warner Rangan and Hall ‘Reinforced Concrete’

• Warner and Faulker “Prestressed Concrete”

• TY Lin “Prestressed Concrete”

• RAPT Manual

• ‘Concrete Floor Systems’ and ‘Design Guide for Longspan Concrete Floors’

published by C&CA 1988 for guide to spans and framing

• CIRIA ‘Design of Deep Beams in Reinforced Concrete’

• Concrete Design Handbook published by the CIA

• ACI 318

• SAA ‘Guide to Concrete Repair’

5.3. Technical Notes Not completed.

5.4. Reinforced Concrete Floor Systems

5.4.1. General Reinforced concrete floor systems fall into many categories such as: • beam and slab

• flat slabs (slab with drop panels)

• flat plates (constant thickness slab)

• Banded slabs (slab with relatively wide but shallow beams having a width at least




twice their depth)

• A combination of any or all of the above

In recent times banded slabs have proven to be very popular because of superior

deflection control and relatively cheap construction costs.

5.4.2. Flexural Member Size Selection

The following criteria must be investigated and satisfied. As a general rule, as the

span increases for concrete members, the critical design parameter changes from

SHEAR to BENDING and then to DEFLECTION. Minimum material quantities in your

design do not necessarily lead to minimum total cost. This is due to high labour costs

in formwork and reinforcement placement. Furthermore, repetition on a job results in

reduction in the construction time and thus, total cost.

All members must meet the following criteria:

FIRE RESISTANCE - Fire Resistance requires minimum dimensions for members

and cover to reinforcement. Refer to the Building Code of Australia and to sections

5.5 and 5.6 AS 3600. Normally, it's the Architect’s responsibility to advise on project

specific fire-rating requirements.

DURABILITY - Durability requires minimum cover to reinforcement depending on

exposure conditions in accordance with section 4 of AS 3600.

SERVICEABILITY - Deflection Control Refer typical limitations in table 2.4.2 of AS

3600.

SHEAR -Cracking

One-way slabs Refer section 8.2 AS 3600

two-way slabs Refer section 9.2 of AS 3600

beams Refer section of 8.2 of AS3600.




BENDING - Typical reinforcement ratios are:

one-way slabs p = 0.003 - 0.0075

two way slabs p = 0.002 - 0.0060

beams p = 0.0075- 0.0180

footings p = 0.0020- 0.0025

AXIAL LOAD - Typical reinforcement ratios are:

walls p = 0.0015- 0.040

columns p = 0.005 - 0.0400

Generally a minor degree of crack control can be used as set out in clause 9.4.3.4 of

AS 3600. However, under certain circumstances, crack control will be more critical,

and special consideration should be given to reinforcement percentages and detailing.

These include:

1) those areas where concrete is to remain exposed

2) where brittle finishes are used on ceilings

3) water retaining structures.

The depth of a member is often selected to meet the deflection limitations. The

reinforcement content and width are then determined to meet bending and shear

requirements and constructability. The selection of a column dimension is influenced

by the axial load and moment. The influence of moment is greater at the top of a

structure and for exterior columns. Where shear is critical in the slab around a

column, it is preferable to provide a column head or increase the drop panel depth of a

flat slab. However, the simplicity of the flat plate type of formwork may overide this

criterion in some circumstances.

Also note that reinforcement is usually more expensive to carry load than concrete.

5.4.3. Typical Reinforcement Quantities

The following will assist Engineers in checking typical reinforcement quantities for their

projects.




M p x 7850 x C kg/m3 p average reinforcement ratio for gross cross-section,

allowing for top reinforcement. Note that reinforcement needs to be allowed for in two directions in slabs.

C allowance for splices, stirrups, ligatures and hooks

For Fy equal to 400 Mpa, the following allowances are appropriate:

Columns C 1.20 - 1.40

Beams C 1.10 - 1.30

Slabs C 1.05 - 1.10

Walls C 1.10 - 1.30

Range of Reinforcement Contents

These contents are indicative only and for each project they should be checked using

the above formula.

Member Type (kg/m3) Comment

Spread footings (on sand or clay)

(on rock)

40 - 60

150 - 300

Excluding column starter bars

Including column starter bars

Pile caps (single pile)

(multiple piles)

60 - 80

120 - 140

Strip footings 45 - 55

Rafts 30 - 50

Columns 150 - 250 Note that 1% = 150 kg/m³

Beams (RC overall depth) 150 - 230

One Way Slabs 70 - 90

Flat Slabs 90 - 110

Flat Plates 100 - 120

Band beam/slab (office)

(carpark)

110 - 135

90 - 115

Two Way Slabs 100 - 120




Waffle Slabs 100 - 120

Walls (minimum steel) 35 - 45

Walls (high-rise cores) 70 - 250

Walls (acting as column) Refer columns

Walls Retaining Earth 100 - 130

Cantilever Retaining Walls 100 -150

Slabs and banded slab (P/T) 30 (R/C) + 20 (P/T)

Where cost plans are prepared and tenders awarded on the basis of specified

reinforcement ratios, detailed analysis should be undertaken to confirm these rates

prior to issuing rates to the Q.S. These rates should be discussed and confirmed with

the Project Principal/Project Leader, and checked during final design. Also note that

these rates will need to be increased when earthquake detailing in accordance with

Appendix A of AS 3600 is required.

5.4.4. Deflection Limitations

Under serviceability loads, the deflection of reinforced concrete members must meet

two criteria:

• Total deflection less than span/250 and not to affect the appearance or

efficiency of the structure. A total deflection of span/250 will be aesthetically

unacceptable in many instances.

• Where concrete elements support masonry the incremental deflection should

not exceed span/500 unless closely spaced joints (at 6-8 m max) are provided.

Where the joints are not provided or the joint spacing is large, this limit should

be reduced to 1/1000.

The calculation of a deflection consists of two parts:

• an elastic or immediate deflection (short term)

• inelastic or creep deflection (long term)

AS 1170.1 sets out the various load combinations to be considered.




The calculated deflection is measured from a theoretical line diagram. The limit on

total deflection may not be adequate to prevent sagging of the member and ponding of

water. Accordingly, cambering of members may be required.

Longer span structures are particularly sensitive to long-term deflections and

vibrations.

An approximate guide is given below for span/overall depth ratio (L/D) for elements not

supporting brittle partitions or finishes. Note that these limits are appliable for live

loads in the range of 3 to 5kPa only.

One-Way Slabs L/D

Simply supported 25 - Continuous External span 28 Internal span 33

Cantilever 8 Note: For banded Slabs L is the clear dimension between the bands for internal

spans, or the centre of the edge support and face of band for end spans.

These span/depth ratios form the basis of concept and preliminary design and

RAPT should be used for final design.

Two-Way Slabs (with drop panels) L/D

Simply supported 30

Continuous External span 32 Internal span 36 without drops, multiply the above x 0.80

Beams L/D




Simply supported 14 Continuous External span 16

Internal span 20

Cantilever 6

Bands L/D

Simply supported 18

Continuous External span 20 Internal span 24

Cantilever 8

For brittle partitions and finishes, the above limits must be reduced by up to 25%.

RAPT should be used to accurately assess deflection. Be cautious about using

shallower sections without further investigation as serviceability is the most common

"failure" in structures.

Cantilever Deflection

Be wary of cantilevers as these are notorious for causing deflection problems.

Particular problems are return cantilevers (at corners), cantilevers which are heavily

loaded at the end by things such as planter boxes, and precast fascia elements,

cantilevers where the ends are fixed to deflection sensitive elements such as

brickworks or windows, and cantilevers where deflections are to be minimised and

preferably uniform for visual reasons.

It may be necessary to limit the total deflection for "longer" spans. In long span

structures, the FIP recommends that live load deflections not exceed 15mm.

Also note that when assessing deflections upper limits on the effective moment of

inertia should be used to account for 1) shrinkage cracking and 2) early age loading of

structure.

Experience suggests that for prestressed concrete members, Ieff = 0.7 Ig (max), and

for reinforced members, Ieff = 0.6 Ig (max).




5.4.5. Flat Slabs and Flat Plates

General

A flat plate, used in the context of a concrete slab, is a uniform thickness slab without

beams or drop panels. A flat slab is a uniform thickness slab without beams but with

drop panels around columns.

This form of construction has become less popular because of the limitation to spans

of about 8.5 m maximum due to their poor deflection performance. The design of flat

slabs (and flat plates) requires an understanding of their performance under 'normal

load' conditions such as office loads with light-weight partitions and abnormal load

conditions, such as masonry wall loads, heavy point loads, openings, set downs and

stair loads, etc.

Engineers must appreciate that, while deflection is just as important as strength in all

structural design, it is more so in the design of flat slabs and plates and special

attention must be given to the proportioning of the slab and drop panels before

proceeding with the final design. All preliminary drawings sent to the Architect must

show the immediate and long term deflections for the design proposed.

The design of flat slabs is covered in Section 7 of AS 3600. Engineers must fully

understand Section 7 of AS 3600 before proceeding with any design.

The computations for flat slabs should conform to the general procedures set out in

the following pages. If the Engineer has any sensible ideas for improvement in the

approach or set out, then discuss it with the Principal/Project Leader. Under no

circumstances are any changes to be implemented without the approval of the

Principal/Project Leader.

Based on past experience, consideration should be given to limiting reinforcement

stress under sustained loads to 170 MPa (or 300 MPa limit state) for column strip

reinforcement to assist in deflection control. This does not remove the necessity for

proper deflection calculations of critical spans, in particular, cantilevers and end

spans.

Flat slabs generally should be sensibly precambered (not overdone). Discuss with

Principal/Project Leader and remember to discuss with the Architect as it will affect




the finishes, etc.

Before you start your design, establish a grid reference system with the Architect so

that all bents (or frames) can be unambiguously identified.

Method of Design

Design of flat slabs can be carried out using either the Direct-Design Method (section

7.4 AS 3600) or the Equivalent Frame method as originally detailed in the Concrete

Code AS 1480 and modified in section 7.5 of AS 3600. Warner Rangan & Hall

‘Reinforced Concrete’ provides detailed discussion on this method, and Section 7 of

the "RAPT" manual also provides a very good overview of this method.

The Simplified Design Method may be used in appropriate situations provided the

designer is satisfied that the slab thickness is adequate for deflection control; that is,

by application of Section 9.3 of AS 3600.

The equivalent frame method involves the representation of the 3D slab system by a

series of 2D frames in two directions which are then analysed for the applied loads; ie

the full load in each direction.

The structure is considered to be made up of equivalent frames on column centre

lines taken longitudinally and transversely through the building.

The slab is divided into column and middle strips in accordance with AS 3600.

Analysis

Each equivalent frame shall be analysed in its entirety. Use judgement on similar

frames and discuss with the Project Leader as required.

5.4.6. Banded Slabs

General

A banded slab floor system consists of a series of parallel wide and shallow slab

bands on line with the columns with the floor slab spanning transversely between the




bands. The floor slab is designed as continuous haunched one-way slab, and the

bands are one-way shallow "beams" carrying all loads from the slab to the columns.

Slab bands are not treated as a beams, except for shear, subject to the provisions of

clause 8.2.5(c) AS 3600. AS a slab system, they are designed in accordance with

Section 7.5 of AS 3600. Concrete cover, fire ratings and reinforcement as required for

slabs in accordance with section 5, of AS 3600 are applicable to slab bands.

Particular attention must be given to the corners and the edges of the floor system

where two-way behaviour of slab may occur depending on the stiffness of edge

beams and columns.

The maximum span for reinforced concrete bands should not normally exceed 10.5m.

Above these spans bands should be prestressed. The slab band width should be

between band spacing/3 to band spacing/4 and where possible the width should be

based on the module of a standard sheet of formwork ply of 2.4m x 1.2m.

Vertical sides should be used to simplify formwork. Sloping sides are sometimes

used where bands are exposed to view or where the effective span of the slab needs

to be reduced. Typically for vertical sides, a slight slope is preferable to assist

formwork stripping.

Analysis of Vertical Loads

Analysis of banded slabs shall be carried out using the program "RAPT"

The floor slab is designed as a one-way slab continuous over the bands adopting a

knife edge support at the centre of the band (or column grid). The haunch effect

created by the slab band must be included in the analysis. A unit width of the slab is

considered in analysis using "RAPT". For structures with long end spans

consideration should be given to modelling the equivalent column stiffness. The

bands are designed to carry all the loads from the floor slab onto supporting columns

or walls.

Avoid pattern loading where possible - it is usually not required unless very heavy live

loads exists. (Refer Cl 7.6.4 of AS 3600.)




Flexural Reinforcement

Ultimate strength method shall be used in flexural design, earthquake design,

checking of shear resistance in slabs and design of shear reinforcement.

Generally only minimum reinforcement (1.0/fsy) is provided in slabs perpendicular to

the principal span of the slab, that is, in the secondary direction. This may result in

cracking parallel to the span of the slabs particularly at the column due to differential

shrinkage between the band beam and the slab. Check for restraint by walls at both

ends of a slab. Where the slab is exposed, an increase in the secondary

reinforcement should be considered.

Deflection

Deflection is as important in banded slabs as in flat slabs. Slab and slab bands must

be adequately proportioned and approved by the Principal/Project Leader before

sending designs to the Architect.

Precambers to slabs, based on deflection calculations shall be shown on the

drawings but use with care. Remember slabs are much more likely to deflect than

bands, as T beam action will occur in the bands between columns. "RAPT"

calculates deflections which have found to be generally reasonable but sometimes

conservative. Avoid excessive precambering, as cambers are very difficult to achieve

in 2-way systems, and it is suggested a maximum camber of approximately span/300.

Ensure the top surface is finished to a camber and not just the formwork. Also

consider the possibility that the camber will not come out.

Shear

Provisions for shear resistance of slabs shall be similar to those of flat slabs, and

shall comply with clause 8.2 of AS 3600. One-way shear in bands should also be

checked and two-way shear (punching shear) must be considered. Some shear

ligatures may be required for bands.

Reinforcement Detailing




Top and bottom slab reinforcement should be uniformly distributed across the full bent

width, except at columns where additional steel may be required for direct moment

transfer if columns included in the analysis. Remember, bottom reinforcement in the

end span MUST continue all the way to the extended edge support and at the first

support top reinforcement may need to be extended into the second span beyond the

1/4 point. It is a good idea to plot the moment profile for the end span and the first

internal span to check the correct curtailment of reinforcement for both the band and

slab. Bending moment diagrams and deflected shapes should always be plotted to

confirm modelling, and check adequacy of reinforcement curtailness.

It is good practice to provide top reinforcement a long column lines in the direction of

the span of the bands to control deflection induced cracking.

Ligatures, if required, should be open ligatures allowing for minimum cover

requirements to flexural steel. If earthquake design is necessary, then ligatures must

be closed.

Cold drawn wire and/or fabric ligatures should be considered, but plain wire ligatures

require much longer anchorage lengths. Do not use cold drawn wire for flexural

reinforcement in bands.

Distribution reinforcement to bands should be Y16 @ 1000 placed on top of the bottom

flexural reinforcement; ie second layer. Note that when shear reinforcement is

required, ties should sit under the main longitudinal reinforcement which reduces

effective depths.

Differential shrinkage between the large slab band and the slab may cause cracking

that will be aggravated in service if these cracks occur in the flexural tension zones. In

exposed slabs special attention must be paid to anchorage and lapping of distribution

steel, especially slab distribution steel parallel to the slab bands between column

centre-lines. The use of sloping sides to bands will reduce differential shrinkage

cracking.

The slab reinforcement must be the primary layers both top and bottom. This means

the top reinforcement to the bands will be in the secondary layer and bottom




reinforcement in the primary layer.

Where required, detail earthquake reinforcement in accordance with Appendix A of AS

3600 and AS 1170.4.

5.4.7. Precast Floor System

Scope

Precast floor systems are used on many projects because they can potentially offer:

1) Increased speed of construction where geometry is uniform.

2) Avoidance of propping leading to earlier installation of services.

3) Cost effectiveness compared with in-situ floor systems.

One potential drawback is lead times associated with procurement (shop drawing and

review, and should manufacture and construction).

There is a wide range of products including Humes prestressed hollow core planks,

ULTRA Floor and Transfloor. It is common to procure precast floor systems on a

Design and Construct basis.

Specific design information can be obtained from supplies catalogues.

5.4.8. Reinforced Concrete Beams

Scope

• This section covers the design of internal beams and external spandrel (edge)

beams in a reinforced concrete frame.

• Beam elements requiring special consideration must be discussed with the

responsible Project Principal or Project Leader will include:

i) Major transfer beams

ii) Core header beams - refer to "Core Wall" section




iii) Precast beams

General Design Parameters - To be Checked with the Project Principal/Project

Leader.

Analysis/Design Computer Programs

The analysis/design of beams can be carried out using RAPT but when spans are

repetitive, and pattern loading is not required, consider using moment coefficient from

section 7.2 AS 3600.

General Design Notes

i) For positive bending moments, design as a T- or L-beam provided the slab is cast

with the top of the beam.

ii) For deflection checks and frame analyses, analyse the beam as T- or L-beam to

realistically assess beam stiffness.

iii) Have the Project Leader confirm which beams are primary and which are

secondary (or tertiary).

(Note: Generally all reinforcement is primary except top reinforcement at beam-

to-beam connections.) Normally beam top steel is laid under top slab

reinforcement with stirrups in the sample plane as the slab top steel.

iv) Check with the Project Leader if there are any rebates or notches which reduce

effective beam dimensions, eg pocket for precast, corbels etc. Also, and

obviously, review the relevant architectural drawings.

v) For repetitive beam design, review reinforcement curtailment as this can

significantly reduce reinforcement costs, and where spans are uniform analyse

use the moment coefficients in section 7.2 of AS 3600 to save design time.

vi) Minimum reinforcement. Tensile reinforcement to comply with AS 3600. For

exposed beams, provide additional side face shrinkage reinforcement uniformly

distributed over beam depth to comply with AS 3600.




vii) Reinforcement detailing. Refer to Connell Wagner standard beam details and

schedules and the drafting manual. If the beam is part of a wind or earthquake

frame, special beam/column connection details are required to transfer wind and

earthquake forces. This usually requires continuous bottom reinforcement at the

column. Top reinforcement may be spread into the slab to reduce congestion.

Consider use of hard drawn wire ligatures for shear reinforcement.

viii) Torsion. In general, avoid designing beams for torsion. It is usually more

economic to resist the "out-of-balance" forces by the slabs in flexure than by the

beams in torsion. Discuss with the Project Leader as necessary.

a) Edge beam supporting banded slab

Refer to the "Banded Slab" section.

b) Edge beam supporting a flat slab is designed using the idealised frame method

(AS 3600). Redistribute at least 15% of the slab negative bending moment at

edge beam and increase the slab positive moment correspondingly. Max.

design torsion = Cracking torsional moment - see below.

ix) Ligature Detailing. Beams are usually detailed with closed ligatures. For

earthquake and torsion loads, ties must be closed.

Edge Beams Supporting Flat Slab

Torsion

Edge beams will be designed for:

a) 85% of the column strip moment

b) All loads directly on top of the beam, and

c) Torsional moments up to and including the cracking torsional moment.

Moments attributed to the beams greater than cracking torsional moment are to be

redistributed back into the adjacent span column strip.




Haunched Beams

Beams are sometimes haunched (deepened at ends where there is a fixity or

continuity) in order to achieve a reduced depth in the midspan regions. This may allow

ducts, etc, to pass under the beams without significantly increasing the floor to floor

height. However, the haunched section may require that the lights be positioned to

avoid beam locations, thereby reducing the flexibility of the tenancy layout.

Haunches may be either tapered or rectangular. Tapered haunches cause least

intrusion into the ceiling space but they are expensive to form because of varying depth

and every stirrup must be a different depth. However, they look better and are to be

preferred where beams are to be exposed. For the more normal case where beams

are hidden, rectangular haunches are preferable. Ends of beams can also be stiffened

by widening. This is not as efficient as a haunch but it is sometimes necessary. RAPT

can satisfactorily model haunches.

When designing a beam with a tapered haunch, account should be taken of the

upwards sloping compressive force at the bottom of the beam in the negative moment

region when considering shear reinforcement. Also, when the sloping and horizontal

bottom reinforcement meet, each must be provided with full anchorage. Do not bend

the bars and rely on local ties to resist the outwards component of the force tending to

straighten the bars.

Beam Penetrations

It is often difficult to accommodate horizontal penetrations through reinforced concrete

beams. However, when beams are fairly deep and narrow (rather than shallow and

wide) penetrations become a possibility.

Circular penetrations up to about one third of the overall depth can be easily

accommodated anywhere except within the depth of the beam from a support.

Rectangular penetrations of depth D/2 and width 1.5D can sometimes be

accommodated within the middle third of the span of a beam. The local area of the

beam is considered as a panel of a Vierendeel truss.

Because of the difficulty in getting sound concrete under the penetration formwork, it is




unwise to rely on this “bottom flange” to resist shear. Rather, drop the penetration as

far as cover to the bottom bars will allow, and design the resulting deeper top flange for

all of the shear using a strut and tie approach.

If the penetration must be kept as high as possible, then distribute the shear in

proportion to the areas of beam remaining and specify that the concrete be placed from

one end of the penetration only until the volume is completely filled as evidenced by

concrete flowing from the full depth at the other end. Strict supervision will be required

to ensure this happens.

Notched Beams

Ducts can be accommodated within the beam depth by notching a continuous beam

near midspan or a simply supported beam at the end. In the case of the latter, shear

becomes a major design consideration and may require a widening of the beam (a

thickening of the slab).

5.5. Prestressed Concrete Floor System

5.5.1. General

Prestressed concrete is to be designed in accordance with AS 3600.

• Typical flooring systems include flat slabs, flat plates, banded slabs and beams.

Generally prestressed concrete is used:

• for longer spans where reinforced concrete structure would deflect excessively; ie

9 m or more

• where dimensions of concrete must be minimised (depth)

• where control of deflection is essential

• where waterproofing is necessary although we should never infer that post-

tensioned structures will be waterproof




• where shear is a problem

• where costing analyses indicate that prestressing is beneficial.

Concrete can be either pre-tensioned or post-tensioned, and either partially or fully

prestressed.

Prestressing can include cables, bars, ground anchors etc. The most economical

solution is normally to have the same level of prestress in each span.

5.5.2. Design Check List

• Establish fire resistance ratings and covers.

• Ensure preliminary design has fully assessed all design parameters including

loads, degree of continuity. Check special heavily loaded areas, as these are not

as easy to handle as for RC design.

• Ensure adequate space is provided for anchorages, especially with two-way

systems and at columns and RC beams.

• Check shortening of floor and effect on walls and columns.

• Check end spans.

• Check position of holes for ducts, risers, as again, the position of these are not as

flexible as RC design.

• Carefully consider location of construction joints etc and distances between them.

For post-tensioned floors, we effectively set the construction sequence by the

location of the C.J.s. This need careful consideration and preferably input from

the builder.

• Avoid anchorages at edges of slabs and beams where this may involve

scaffolding for stressing.

• Avoid layouts requiring woven tenders.




• Can it be built?

5.5.3. Analysis

Linear elastic analysis is normally used. Analysis is generally carried out using the

"load balancing" methods.

Both the VSL and Austress design manuals provide detailed methods of design by

hand, and the previous section sets out a step-by-step method of design.

The computer program "RAPT" is to be normally used for detailed design of

prestressed members.

5.5.4. Deflection Limitations

An approximate guide is given below for span/overall depth ratios for elements not

supporting brittle partitions or finishes.

One-Way Slabs L/D

Simply Supported 30

Continuous External Span 32

Internal Span 40

Cantilever 10

Note: For banded Slabs L is the clear dimension between the bands for internal spans,

or the centre of the edge support and face of band for end spans. These

span/depth ratios form the basis of concept and preliminary design and RAPT

should be used for final design.




Two-Way Slabs (with drop panels) L/D

Simply Supported 32

Continuous - External Span 40

Internal Span 45

Beams L/D

Simply Supported 18


Internal Span 22

Cantilever 10

Banded Slab L/D

Simply Supported 24


Internal Span 28

Cantilever 12

• The most economical design system will occur if the end span is 80% of the

internal spans with the same effective depths, internal spans are equal, and

cantilevers are 30% of adjacent spans.

• The above ratios provide a quick preliminary size. This size must always be

checked before acceptance by the Designer.

• Sections being tensioned should be limited to 30-40 metres.

• The minimum slab thickness, where tendons are in the slab, is 150 mm to allow for

cables and dead and live end anchorages.




For brittle partitions on finishes the above limits must be reduced by up to 20%. The

exact span/depth ratio's must be calculated to meet the serviceability requirements of

AS 3600.

The most common problems with prestressed members is the use of excessive

stressing forces. Wherever possible, use partially prestressed design.

5.5.5. Prestressing Tendons and Details

The two usual strand sizes are 12.7 mm and 15.2 mm. The most common size is

12.7 mm. The strand used is usually low relaxation, stress relieved, super grade.

Only use one size strand on any project except in special circumstances.

The 12.7 mm strand has an area of 100 mm2 and a minimum strand breaking load of

184 KN. In slabs, the strands are usually grouped in galvanised flat ducts to create

tendons. The duct is fully pressure grouted after the strands have been fully

tensioned.

Ducts are:

70 mm wide x 19 mm for up to 5 strands

90 mm wide x 19 mm - 6 strands (not normally used)

For beams, round ducts from 60 mm to 140 mm in diameter are usually used.

However, 4 or 5 strand ducts are often used in beams in buildings. A friction factor of

0.2 is normally used for oval duct.

The duct should have a minimum cover of 25 mm with covers checked for durability

and fire rating as required.

Tendons are usually draped in a parabola in the case of a uniformly distributed load to

give uniform load balance.

Prestress losses must be calculated and include:

• immediate losses

• deferred losses




• frictional losses

• draw-in losses

• frame-resistance losses (ie losses due to restraint by the structure being

stressed).

Refer to written information from the various manufacturers such as VSL.

5.5.6. Flat Slab Design

Slabs shall be designed using load balancing. If the weight of the Concrete is

balanced, the long term deflections can be expected to be minimised. The designer

must check stresses at:

• transfer

• at full load

Tendons are usually draped in a parabolic shape to follow the same shape as the

bending moment diagram.

Tendons must end at the centroid of a cantilever or simply supported slab end;

otherwise, large secondary forces can occur.

The prestress level is generally in the range of 1.5-3.5 MPa working stress.

Losses in prestressing forces due to the following must be allowed:

• friction

• elastic shortening of concrete

• creep and shrinkage of concrete

Where draped tendons are greater than 20 m, they should be stressed from both

ends. The position of anchors and stressing ends need careful consideration to avoid

expensive scaffold for stressing access.

Details of connections to columns and RC walls needs careful consideration to avoid

cracking or restraint.




Slabs are normally stressed to 25% at 1-3 days to control slab shrinkage cracking with

final stressing at 7 days.

Design of slabs is normally carried out using the computer program "RAPT".

5.5.7. Banded Slab Design

The design of banded slabs is similar to slabs. They shall be designed using the

computer program "RAPT".

"RAPT" is a sophisticated program and should only be used by Designers who have a

reasonable "feel" for post-tensioned design and who have carried out some design by

hand.

5.5.8. Earthquake Detailing

Tendons should not be anchored or develop their strength in beam/columns/joints

where high moments develop under earthquake loads. In addition, ducts should be

corrugated. Refer to Appendix A of AS 3600 for specific requirements.

5.6. Reinforced Concrete Columns

5.6.1. Scope

This section covers the design of reinforced concrete columns in accordance with

AS 3600.

5.6.2. Load Rundowns

• Use a standard proforma sheet or a spreadsheet.

• The loads to be used must be obtained from the loading sheets in Section 3 of this

manual and are to be in accordance with AS 1170 Part 1, Dead and Live Loading

and Load Combinations.




• Typically apply live load reductions where possible in accordance with AS 1170

Part 1. Note that live load reductions to be applied are calculated on the cumulative

area of the floor or floors contributing load to the column above the level

considered. (Note: Live load reductions are not normally applied to individual

beams and slabs.)

• If loads for a particular area on a floor are not in the loading sheets, refer to the

Project Leader for direction.

• Where they have not been calculates, apply moment shear (elastic reaction)

factors to column loads in accordance with the following diagram. It is preferable to

calculate moment shears from actual bent runs. P is the total load on a column for

the simple contributing area indicated.

• Rundowns are calculated using a simple area basis proportioning the loads to each

vertical element by taking half the distance in each direction to the adjacent vertical

element. The areas should be marked up on the structural concrete profile plans

which are then scaled to determine the plan dimensions of each tributary area.

(Assumes equal spans between all columns).

• Also incorporate "fast track" load allowance where appropriate. Refer to the Project

Leader for these allowances.




5.6.3. Design Loads

List the loads for various elements supported by the column from each floor and roof

using the appropriate floor and roof areas. The unit loads for roof, floors, stairs and

walls (calculate the average load per metre length including where openings occur)

must be listed on first sheets of computations in the loading sections.

Include live load reduction where applicable, in accordance with AS 1170 Part 1.

Priior to completing the rundown of the loads for a column, check the Architect's and

other Consultants and Disciplines drawings to ensure that all loads have are included.

The following list covers the majority (but not all) of loads that can be expected in

column designs for multi-storey structures.

Roof (including finishes)

Floor (including finishes)

Partitions - light-weight, terrazzo, etc.

External walls - precast, curtain wall etc.

Internal masonry walls

Beams framing into column

Precast concrete wall units

Fascias and sunhoods

Lift machinery

Air Conditioning Equipment

Stairs

Heavy load area

Special equipment; ie water tank, generator etc.

Ceilings

Heavy architectural bulkheads.

Include in the column computations for moments due to:

a) The floor system (refer to the computations for the frames and loads).

b) Minimum Bending Moments as required by AS 3600.

c) Wind




d) Earthquake

e) Any other lateral loads.

In column design, it is important to correctly estimate the applied moments particularly

at the top of the building where column dimensions can be small and the bending

moments are high with low axial loads.

5.6.4. Reinforcement

Avoid high % of reinforcing steel as it is an uneconomical way of carrying axial loads,

which are most economically supported by maximising concrete strength or column

loads. Where tension controls, make sure the lap lengths are based on a tension

splice.

Check the curtailment of column bars at the top of columns and at changes in the size

of columns. Check that column and beam bars will fit at each intersection.

5.6.5. Concrete Strengths

The minimum concrete strength in any column should be 25 MPa. The maximum

strength currently allowed by AS 3600 is 50 Mpa. Considerable research is being

undertaken to investigate detailing requirements for higher strengths.

Connell Wagner has used strengths up to 80 Mpa on some projects. When using

higher strength concrete, refer to latest internal technical notes on this subject.

Economic studies have shown that the cheapest columns will almost always involve

the highest strength concrete and 1% reinforcement. On major projects always

determine what is the maximum strength available locally. On most projects, 60 Mpa

concrete can be used to keep column dimensions to a minimum, and achieve

economical results.




5.6.6. Bending Moments

Two cases of bending of columns will occur. These are:-

a) Uniaxial Bending Square (Rectangular and Circular)

b) Biaxial Bending (Rectangular) and Square

Note: The design moment in the columns is the moment at the top or bottom face of

the slab or beam and not the centre line of the slab. Use using second order

analysis in accordance with section 7 of AS 3600 to directly generate the

design actions, in both sway and braced frames. Also note that section 7

requires reduced stiffness for each structural elements. For prestressed

beam element use Ieff as calculated by RAFT.

5.6.7. Slenderness Ratios

Evaluate the slenderness ratio to determine if columns are short or slender, but when

using second order analysis only calculate d b based on actual member length.

5.6.8. Fire Resistance and Cover

Check covers for external columns or other special conditions, such as downpipes,

sewer and vent stacks included in columns, etc.

Check fire resistance of columns in accordance with sections 5.5 and 5.6 of AS 3600.

The actual fire ratings (resistance) for members is normally based on the Building

Code of Australia and should be provided by the Architect.

5.6.9. General Design Notes

• Group columns logically into a series of typical columns in order to minimise

computer time and analysis of every column.

• Use concrete strengths as follows: 60 Mpa, 50 MPa, 40 MPa, 32 MPa, 25 Mpa but

preference should be given to maximum strength to minimise reinforcement.




• Generally aim for about 1% maximum reinforcement content to achieve an

economical solutions. Absolute maximum 4% for few columns at the lower levels.

• Maintain column concrete strength the same on each floor level where possible.

This avoids the construction complications of placing different concrete grades.

• Prior to design ensure column sizes are agreed by Architect, especially where they

go through car parks and other architecturally sensitive areas.

• Check fire ratings of all columns, especially thinner "blade" columns, using section

5.6 of AS 3600.

• Minimum width of blade columns to be 300 mm if 2 hour fire resistance is required.

• Draw reinforcement intersection diagrams for critical beam/column and

beam/beam/column junctions. Optimise the position of the beam relative to the

column.

• Carefully check bar development/splice requirements are met:

I. at intersections between columns that change shape either side of a floor;

II. towards the tops of buildings where the axial stress is lower; and

III. in sway frames.

• Ensure "transmission of axial force" requirements of section 10.8 AS 3600 are met

for edge columns of floor structure or where columns sit on unconfined walls of

lower strength. Consider providing additional dowel bars rather than introducing

"blobs" of concrete of a higher strength.

• Ensure ties are detailed in accordance with clause 8.2.12 of AS 3600. Where bars

are cranked it is necessary to provide additional ties to resist the lateral bursting

forces. Ties must continue through the floor beam sections to maintain lateral

restraint to column bars.




• Ensure ties meet the requirements of Appendix A of AS 3600.

• Consider 2 storey lifts for cages where possible.

• Design columns using RAPT or Coldes. Recent “bench testing” of various design

methods by Brisbane office has proven that RAPT is the best design tool. RAPT

can also take account of internal voids, and handle unusual shapes.

5.6.10.Preliminary Design

A short column can be approximately sized using A = P*/(0.5 Fc'). The approximation

is derived on the basis the reinforcement percentage will be around 2 percent.

To control the column size it is most cost effective to use high strength concrete than

large percentages of reinforcement (50 or even 60 Mpa). As the load diminishes

reduce the reinforcement first, then the concrete strength and finally the column size.

The mass of reinforcement used for preliminary costing of the structure is shown

below. It can be seen that the relationship approximates to the easily remembered

following sequence.

1% longit reinf. 150 kg/m³

2% 250

3% 350

etc.

These rates must always be confirmed by analysis before issuing of Tender

documentation. These rates may increase when earthquake detailing is required.

5.6.11.Column Ties

Always arrange reinforcement so that there is a large space free of any obstruction to

the placing and compacting of concrete. If the ties become excessively congested,

consider bundling the longitudinal reinforcement.

5.6.12.Column Starter Bars




Starter bars out of footings should be embedded in the footing a distance equal to the

compression development length, 20db, if the footing is able to develop column fixity

and the column reinforcement goes into tension, the tension development length must

be used.

Only straight lengths of bars transfer compression via bond - the length of the bar

beyond a 90° bend has been shown by strain gauging to be unstressed, so there is

nothing to be gained by extending cogs beyond the length needed to support the

starters on the footing reinforcement. However there is no need to make all footings

over 20db thick as, besides transferring load by bond, the bars transfer load by bearing

around the underside of the bend.

5.6.13.Column Size Reductions

It is often appropriate to reduce the column size as the load diminishes. (However, as

changes to formwork cause cost increases, the need to reduce the size should be

seriously considered). Reinforcement at reductions may be cranked across at 1 in 6

where the reduction does not exceed 75mm. For greater reductions, separate starter

bars must be provided.

Remember that unequal steps in the faces of a column create loading eccentricity

which must be considered in design, either by treating the movement in the column or

by resolving the movement using propping forces in the floor.

5.6.14.Top Termination of Column Reinforcement

Because columns attract bending moments, column reinforcement should be

anchored into the slab or beam sufficiently to develop its full tensile strength, i.e. for its

full development length, Lsy. Always carefully draw out these details to prove that full

anchorage can be achieved.

5.6.15.Bundles Bars

For large, heavily reinforced columns, it is often advantageous to use bundled bars.

Usually compression will govern so that simple splice sleeves such as G-Locs can be

used. Bundling of bars reduces the number of ties required but Y12 ties should be

used.




It is often possible to use 2 storey high bars when bundled. This halves the number of

splices and facilitates the staggering of splices in bundles of 4 bars.

Note: Never use bundled bars unnecessarily as they can significantly slow up

construction. The perimeter beams and columns are usually the critical elements

during construction of multi-storey buildings. Usually speed of construction is

increased by prefabricating column reinforcement but this cannot be done when bars

are bundled; each bar has to be individually positioned.

5.6.16.Column Splices

The normal reinforcement splice is a lapped compression splice.

Bars usually cranked at their top as this will often leave the inwards bend well confined

by concrete and it may also facilitate the passage of the top reinforcement of

intersecting beams.

However, sometimes the crank ban be beneficially located at the bottom of the bars to

suit the meshing of beam and column steel.

Column design is governed by tension or compression in the reinforcement,

depending on where the design lies on the interaction diagram. Laps should be

proportioned accordingly.

5.6.17.Mechanical Tension Splices

Swaged Splices

CCL Alpha splices are sometimes used. These are crushed on to deformed bars

using a swaging jack. The splices come in two types (1) fully swaged and (2) swaged

and threaded. The latter is used when it is necessary to end the couples flush (e.g.

against the inner face of formwork) or when it is impossible to insert the jack because

of the proximity of other bars.

These splices are bulky (so leave enough space) and expensive (so consider

alternatives before specifying).




Screwed Couplers

Leonton manufacture screwed tension couples.

A comprehensive range of coupling devices, all utilising a tapered thread are available.

The range includes couplers to enable bars to be inserted between cast-in couplers

nuts to anchor bars in concrete or behind a steel plate, plugged anchors cast into

concrete for future bar extensions and of course, standard bar couplers (which are

less bulky than Alpha splices).

Epoxy Grouted Sleeves

Epoxy grouted sleeves are available from A H Reid Pty Ltd. These rely on mechanical

interlock via the epoxy grout between the deformed bar and deformations inside the

sleeve. They are often used by the precast industry in the USA as they will tolerate a

small amount of bar misalignment.

Epoxy grouted sleeves are at least as expensive as screwed CCL Alpha Splices.

5.6.18.Column Axial Shortening

All compression members shorten under axial load but concrete members exhibit

more shortening than steel members because of shrinkage and creep. This factor

must be including in the design of facades of multi-storey buildings and in the detailing

of lift guide rails in the services core. It is also a factor for serious investigation where

a highly stressed column is adjacent to a much lower stressed column or wall.

It is not desirable to locate internal columns only a corridor width away from concrete

core walls given the difference in shortening expected on these 2 elements.

Similarly, investigation is necessary when a change in the plan size of the floor of a tall

building results in adjacent columns carrying vastly different axial stresses. In such a

case, the axial stresses of the 2 columns may be able to be evened up by a transfer




beam. Alternatively, prestressing the lightly loaded column so it behaves as a heavily

loaded column may be appropriate.

5.6.19.High Strength Concrete

There may be occasions when it s necessary to use significantly stronger concrete in

isolated columns. When this occurs, it must be emphasised on the drawings over

and above the normal means of specifying the concrete strength.

High strength concrete requires that a number of additional requirements be

addressed as follows:-

1. Ability to Obtain the Strength

Not all localities produce aggregate able to achieve concrete strengths in excess of

about 60 MPa so check with the local concrete suppliers.

2. Continuity of Strength Through Floors

This will not be a problem where floors are of steel beams supporting a steel deck

and concrete slab. However, a full concrete floor where the concrete strength will

usually be 25 or 32 MPa, will require that the same high strength concrete be

placed in the column area during the floor pour. Such concrete should be colour

tinted to allow easy recognition. It should not be placed using the concrete pump

being used for the lower strength concrete. Specify detailing and strength

assessment requirements are set out in Section 10.8 of AS 3600. Alternatively

additional dowel bars can be added to achieve the necessary strength.

5.6.20.Bending Moments in Columns

Columns derive bending moments from lateral forces on the building and from

unbalanced bending moments in floor slabs or beams framing into the column.

Where such moments are difficult to accommodate, e.g. for small interior columns in

a low rise structure or for the external columns of a small building, the moments can

be minimised by taking full advantage of the allowable redistribution of moments in the

floor. Also, a critical review of the member stiffness (what will be cracked and what

will be uncracked) may result in a different set of moments.




Some columns, particularly corner columns, are always subjected to biaxial bending.

When the bending moments are significant about both axes it is necessary to design

the column for the biaxial effects.

In tall, flexible buildings, the sway creates additional moments due to the P-delta effect.

The second order moments may be up to 10% of the first order moments and should

not be overlooked.

5.6.21.Concrete Placing, Stripping and Curing

Concrete should be placed in a manner which avoids segregation. With widespread

use of pumping and with adequate clear space between column ties, segregation is

seldom a problem.

Concrete should always be placed in column forms and left to set before concrete is

poured for the floor. (A delay of an hour or two would suffice). The reason is that is

both column and floor are poured concurrently, a crack will often form through the

column just below the soffit of the floor due to settlement of the column concrete and

arching of the slab or beam concrete across the column.

Columns may be stripped as soon as the concrete is hard enough - usually after

about 24 hours. With 25 MPa concrete it is advisable to provide for additional curing

by wrapping the column with polythene but for stronger concrete this is unnecessary.

(High strength concrete is more dense and the small voids are rapidly sealed,

preventing the loss of water from the interior of the mass).




5.7. Reinforced Concrete Walls

5.7.1. Design approach

Refer Chapter 7 of the Reinforced Concrete Design Handbook.

5.7.2. Walls - Low to Medium Rise

Generally use Section 11 of AS 3600. This code is satisfactory for the majority of wall

designs in low rise buildings.

5.7.3. Core Walls - High Rise (greater than 20 Storeys)

Consisting of a number of interlinked walls of various lengths, thicknesses, stiffnesses

etc, and special provisions have been developed for these.

These provisions recognise the ability of core elements to plastically redistribute loads,

under ultimate conditions, enabling the total load capacity of core systems to be

obtained by the summation of individual core wall capacities.

There are some important restrictions:

I. Wall slenderness kL < 20

D

II. Two layers of reinforcement are required

III. Serviceability criteria

In solid walls subjected to vertical loads, stresses are forced to distribute evenly when

lateral restraints such as floors are present, irrespective of core wall layout.

Finite Element studies have shown this force distribution occurs at approximately 45°

or less (ie, rapidly enough to assume constant stress in tall buildings).




These findings consider Strain Compatibility, which implies uniform shortening and

thus reasonably constant element stress. This uniform stress will act at serviceability

conditions and will continue to do so until plastic redistribution (noted above) is

required at ultimate conditions.

5.7.4. Influence of Creep Relaxation

Large openings in walls and header beams significantly affect the stress distribution in

the core walls.

Depending on the stiffness of the header beam, load will be shared between adjacent

core elements.

However, over the life of the building the header beams will undergo creep relaxation

and will no longer transfer all of this stress.

5.7.5. Basement Retaining Walls

Loading

These walls are usually restrained against lateral movement by floor slabs, struts or

ground anchors etc. so that 'active' pressure conditions are not likely to be obtained.

The Soil Pressure diagram is not the normal triangular form but usually trapezoidal or

modified triangular shape.

The shape and design values for this diagram should be provided by the Geotechnical

Engineering Consultant. Generally maximum pressures are of the form

P max = AH + Bq

Where, A is a factor usually between 4 and 8

H is the height of the wall

B is a factor usually between 0.3 and 0.5

q is the surcharge pressure




Walls

Walls should be classified as either temporary or permanent.

Temporary Walls:

Temporary walls are those that are constructed to enable excavation to proceed prior

to the construction of a permanent wall immediately in front of them. The advantages

of using this type of wall are:

a) The wall can be placed outside the site boundary subject to approval of the

Council. (They will require later removal down to specified levels. Check with

the Council.)

b) Temporary ground anchors can be used - these anchors require no secondary

grouting and are cheaper than permanent ground anchors.

Note: Ungrouted stressed anchors should not be left in the ground, however

as they represent a hazard to future excavation.

c) Can take advantage of increased allowable steel and concrete stresses for the

temporary condition.

d) Can possibly take advantage of reduced pressure diagram for temporary

condition.

Temporary walls often take the form of double steel channel or I beam soldiers

vertically with infill insitu concrete panels or timber sleepers spanning horizontally.

The permanent wall in front of this is constructed either as reinforced or precast

concrete.

Permanent Walls:




Permanent walls are constructed to resist the permanently applied loads (including

water pressures) unless a proven system of drainage is provided. Walls normally

span vertically between the permanent structure at floor levels or sometimes where

spans are large or pressures high, permanent ground anchors will be required in lieu

of structure.

The main advantages of using a permanent wall in lieu of a temporary wall is that the

final wall can be completed in one operation. Typical walls of this nature are:

i) insitu bored pile soldiers with shotcrete infill arches (Connell Wagner Arch.)

ii) precast concrete soldiers with shotcrete in fill panels

iii) precast panel walls

All the above walls utilise temporary ground anchors or props in the temporary

(construction) condition.

All permanent walls must be wholly within the site boundaries. In the case of (i) and

(ii) above, considerable basement area can be lost to the wall structure and the

temporary props. For this reason these walls can be made load bearing and support

perimeter columns.

It is most economical to maximise the spacing between soldiers, the spacing being

dictated by the spanning ability of the soil behind (check with Geotechnical Engineer)

and the minimum requirements of the Council (some Councils require 2 m maximum

clear between soldiers).

Use closer spacing at adjoining buildings on the site boundary.

Analysis:

Assume pinned supports.

Ensure all load conditions (temporary and permanent) are analysed.




Be aware of car ramps adjacent to site boundaries as here no slab restraints are

present and walls must cantilever.

Detailing:

For detailing notes for permanent insitu concrete walls in front of temporary walls refer

cantilever wall section of these notes.

Arrange reinforcement in bored pile soldiers or precast soldiers to avoid the ground

anchors, which will be placed through a hole drilled or cast into the soldier.

Where bored piers are used as part of a retention system (ie, carrying bending

moments and shear forces) it is essential for the ligatures to be detailed as shear

reinforcement (as distinct from tie requirements in a column).

Development of shear reinforcement in narrow circular bored piers can be difficult and

it may be necessary for the ligatures to be welded or have laps.

Note: Welding is the least preferred and should be properly evaluated against lapping

of ligatures.

It is important that the ligature detail be clearly indicated on the drawings. Welding,

lapping and bending requirements must be specified.

For shotcrete or sprayed concrete arches between soldiers normally use 130 thick

with a fabric mesh central. This must be properly evaluated for each particular job. If

sprayed concrete between panels is not arched, thickness and reo must be calculated

and will be larger than for arched walls.

Show spoon drains at basement floor junctions with walls. In car parks where spoon

drains are below the level of the slab they must be connected to the sewerage system

as opposed to being connected to stormwater pipes if wholly above the slab.

Check with Hydraulics Engineer as this effects the detail used.




Provide vertical drains behind walls to minimise inflows of water into basements.

(These should not be relied upon to reduce water pressures to zero.) Where vertical

drains turn under the basement slab avoid carrying the pipe through the footing as this

must be cast-in, rather carry it above or below the footing.

Other issues needing Consideration:

If permanent ground anchors are required, it may be necessary to obtain easement

over the site. This will need to be discussed with the Project Manager and Client.

Always consider the need to carry out a dilapidation and level survey of adjoining

buildings before commencing basement excavations. Discuss this matter with your

Project Principal in the first instance. The purpose of their surveys is to protect our

client and ourselves against spurious claims from neighbouring parties. These

requirements should then be written into the specification and undertaken by the

builder.

5.8. Foundations

Foundations form the base of a building or bridge etc. They are generally permanently

hidden and not able to be inspected and maintained. A greater level of conservatism

needs to be applied to some aspects of their design, such as allowable stresses and

cover to reinforcement.

Before any footing design can commence, a detailed geotechnical investigation must

be obtained so that advice on appropriate bearing pressures and formulations types

can be obtained.

Footings transfer the loads from a structure to its foundation; that is, the natural soil or

rock on which it rests.

Footings are usually one of, or a combination of the following: strip footings, pad

footings, raft (or mat) footings and piled footings.




5.8.1. Strip footings

These are used to support line loads (such as walls). The principal effects needing to

be checked are bending of the footing projection beyond the wall (and shear if the

projection is relatively large, although this will seldom be a design issue), bending of

the footings across any discontinuities of the wall and of course the bearing pressure

on the soil. Strength design is based on strength limit state loadings while the bearing

pressure requirements are usually made on the basis of “working loads”.

Strip footings are widely used in domestic construction where their design is governed

by regulations (e.g. AS 2870, Residential Footings Code). Trench mesh is the

preferred reinforcement and ligatures exist only to keep the top layer of mesh in its

correct location.

In multi-storey building work, strip fittings may be used to transfer the load from walls

to rock foundations. In such cases footings must be deep enough to transfer the load

without the need to rely on flexural action, that is, the footing depth must be at least

equal to its projection beyond the wall.

In strong, horizontally bedded and jointed rock it could be argued that reinforcement is

not needed in footings. The rock is often stronger than the concrete footing which

serves merely to provide a means of easily anchoring wall reinforcement.

5.8.2. Pad Footings

These are used in support isolated members such as columns, bridge piers, etc.,

when the ground is adequate, that is, it is sufficiently strong and stable. Where the

ground is very weak or subject to significant settlement or movement due to variations

in moisture content, a different footing system such as piles should be used. The

depth of “shallow” pad footings, ie. Pads on other than hard rock, is dictated by the

following considerations:

• punching shear

• beam shear

• bending




• anchorage of column reinforcement

The design approach is no different from that applied to flat slab floors. For anchorage

requirements of column reinforcement see the column design section of this manual.

The depth of pad footings on rock should be sufficient to avoid the need to assume

bending action, that is, a depth of at least equal to the projection beyond the column

face. Reinforcement is then calculated using a struct-tie model. As with strip

footings, a case can be made for omitting reinforcement and similar comments apply.

However, because the quantity of tension steel for heavily loaded pads on strong rock

can be very significant when the design assumes the need for such steel, the cost of

proving the rock quality is not such a deterrent to justifying the omission of

reinforcement.

When the design bearing stress depends on defect-free rock, it is necessary to drill a

proving hole (or holes) below the founding level. The hole depth should be about 1.5

times the footing width. Usually a hand held percussion drill is used and the rock

tested for defects by “feeling” with a scraper. Care needs to be taken to ensure all

allowances for testing are included within cost plans.

Although columns may be of high strength concrete, there is no need to use the same

strength in the footing as the region under the column where the stress is highest is

well confined by the surrounding concrete. The column may be considered in a

manner similar to the manner prestressing anchor plates are considered. It is

advisable to provide a mat of small diameter reinforcement in the top of the footing

around the column to resist bursting tension forces.

For any reinforced concrete footing it is desirable to place a blinding layer of concrete

on the foundation material as soon as it has been inspected and accepted. This does

two things. First, it protects the foundation material from degradation or disturbance

and second, it provides a hard level surface on which to support the reinforcement,

thus assuring that the correct cover is achieved.

5.8.3. Combined and Strapping Footings




Sometimes two columns are too close together to economically provide separate pad

footings. In such cases it is acceptable to provide a single rectangular pad, designed

as a continuous beam.

Often, columns adjacent to a boundary must have eccentric footings and the bending

moment inducted would overstress the column and probably also create excessive

bearing pressure. In such instances it is usual to tie the footing with a stiff beam to an

adjacent footing within the building. Such footings are called “strapped footings”. In

order to ensure that all the load is transferred by bearing via the footings and not

through the beam as well, it is advisable to separate the beam soffit from the ground.

In soft ground it will be sufficient to loosen the soil under the beam but in rock it will

require the placing of softer material such as clay, polystyrene, etc. The beam resists

the tendency for the eccentrically loaded footings to rotate so it must be very stiff to be

effective. Bending moments and shears are calculated by the usual principles of

statics and reinforcement designed to suit.

5.8.4. Raft (or Mat) Footings

Raft footings are used in the following circumstances:

• When the foundation material is soft and liable to differential settlement.

• When numerous loading elements occur close together (as in a service core for tall

buildings).

Rafts range from a thin slab stiffened by a grid of shallow beams, as used in domestic

construction on reactive clay, to 3m or thicker slabs under tall buildings on stiff clay

foundations. The design of a raft slab is highly indeterminate, involving as it does the

interaction of a concrete slab, point and line loads above the slab and compressible

foundation soil. The usual design method utilises a finite element computer program

wherein the soil is modelled as either an elastic medium extending for a sufficient

distance below and around the raft or as a series of springs having an appropriate

stiffness - that is the stiffness of the soil combined with the area of soil lumped into the

isolated spring.




In order to provide a more even load distribution on the foundation, a raft may be

prestressed. Special attention must be paid to the soil-concrete interface in order the

minimise restraint to concrete shortening under the effects of the prestress. A

smooth, level surface and two layers of polythene should be provided as a minimum.

5.8.5. Pile Footings

Piles are used to transfer loads to more competent foundation materials at depth.

Pile types may be divided into driven piles and bored piles and further subdivided into

numerous varieties.

Large diameter bored piles are sometimes called piers or caissons.

When documenting piling, the designer must clearly communicate who is responsible

for the design and load capacity of the pile (ie desinger or installer). If the intention is

to make the installer responsible, then all loads including lateral loads must be clearly

shown on the drawings.

5.8.6. Bored Piles

Size will commonly vary between 300mm and 1500mm diameter although larger

sizes up to 2400mm may be available in some regions. The greatest depth is limited

by the length of the kelly bar on the drilling rig. A 40m depth is commonly available and

depths up to 64m may be obtained.

Liners and Bentonite

Where bored piles pass through unstable or water bearing ground, they may be lined

with a steel tube (which may be withdrawn as concrete is placed). Also, because

people need to descend to the bottom of bored piles (over about 750mm diameter), to

clean them out, test or inspect the base, liners are needed for safety reasons. In wet

ground the liners need to be sealed into relatively impervious material to control the

inflow of water. This can mean that a pile which could otherwise be belled above rock

to bear on the rock has to be belled completely in the rock. This aspect should be

covered on the tender documents.




In withdrawing a liner, care must be taken to ensure that the concrete surface is

sufficiently above the bottom of the liner to prevent the ingress of water, and that the

liner does not lift the concrete en mass.

Alternatively, the bored piers may be constructed under bentonite which stabilises the

hole prior to the placement of concrete.

Design

Piles are designed for axial load as short columns, as even the weakest ground is

usually sufficient to prevent buckling. Where bored piles must resist bending

moments, the design process is no different from that applying to columns.

Because it is not practicable to visually check the construction of a bored pile, it is

accepted practice to keep axial stress low - typically 0.25f’c. (This also has the

beneficial side effect of limiting axial shortening of long piles which, if significant, could

result in overstressing of the superstructure due to differential shortening effects).

It is commonly accepted practice to reinforce only the top portion of bored piles - that

portion likely to experience bending. This is acceptable only if the concrete can safely

take all the axial load.

When piles are subject to uplift forces it is necessary to provide reinforcement to

resist the whole of the tension and to ensure that the tension can be resisted. This

may be achieved by socketing into rock, mobilising a sufficient volume of soil or by

using prestressed ground anchors which, of course, also increase the compression

load on the pile and the foundation material.

Load Transfer to the Foundation

Load transfer occurs through end bearing, shaft adhesion or both. Analysis suggests

that for socket piles, very little load is shed by end bearing prior to the full mobilisation

of the shaft adhesion. That is, the adhesion (or shear) must “yield” to fully load the

base in bearing. Nevertheless, it is accepted practice to adopt an ultimate limit state

approach and utilise the full combined capacity of adhesion and end bearing.




When load requires the pile to be “belled” the documents should, whenever possible,

give the piling contractor the option of using as socket as, with a good drilling rig,

socketing could be more economical. The diameter of a bell should not exceed three

times the pile shaft diameter, as a general rule.

The design end bearing and adhesion allowable stresses must be obtained from a

geotechnical investigation. The value of shaft adhesion may be taken as 10% of the

end bearing stress for preliminary assessment of design options prior to receipt of the

geotechnical report, presuming of course that prior knowledge exists of the likely

ground conditions and allowable bearing pressures.

If the bored pile is constructed using a bentonite slurry rather than a steel liner to

ensure stability of the excavation, it is not normally possible to visually check the

founding material in situ or the cleanliness of the base. A more conservative approach

must then be taken to the bearing and adhesion values, particularly the latter, as a film

of bentonite over a smooth rock surface will adversely affect the load transfer.

Pile Caps

A pile cap is required if more than one pile is required to support a single column or if

the size of the loading element is larger than the pile. Otherwise, the top metre or so

of the pile shaft should be used to transfer the load from column to pile.

Reinforcement will be anchored in this region and the concrete used will be the same

strength as the column concrete.

Proving the Foundation

When reliance is placed on the defect-free or near defect-free rock in achieving high

bearing stresses, the quality of the rock must be verified by drilling a proving hole to a

depth of about 1.5 times the diameter of the pile base. This is usually done by a hand

held percussion drill which makes the drilling of a hole deeper than 2.4m, the

requirements should be discussed with the contractor and geotechnical engineer.

Having drilled the proving hole, a scraping tool is used to feel for soft seams and

fractured zones. An assessment is then made as to the acceptability of the

foundation at that level.




Load Testing

Because it is possible to visually check the base of large diameter bored piles and to

probe the rock beneath the base, it is not usual to load test such piles. However, there

are instances where tests are required. In such cases, the piles are jacked down

against a load of kentledge or against prestressed ground anchors located around the

test pile.

If it is not the foundation but rather the pile shaft which is to be tested, a preferred

method is to use ultrasonic integrity testing. There are various approaches to this.

One method uses cast in steel piles as conduits for an ultrasonic source and a

receiver. The pile can be tested continuously as they are each lowered at the same

rate down different water-filled conduits. Defects in the concrete show up as

reductions in the pulse velocity.

5.8.7. Driven Piles

The following gives an indication of the types of driven piles commonly available.

Timber

Steel - tubes

- rolled sections

Concrete - precast both reinforced and prestressed such as Franker piles

- grout injected.

Timber piles have capacities up to about 60t. The timber must be suitably treated or a

durable species. (These days it can be argued that the use of our prime quality,

durable timber for piles is not ecologically acceptable).

Timber piles, if not adequately treated or of an appropriate species, will rapidly decay

in zones where it is neither continuously dry nor always submerged in water.

However, timber which is always dry will last well and timber always submerged may

last virtually indefinitely.




Steel piles are often used for structures built over water, particularly if driven from a

floating platform when the movement of the platform could crack and possible break

concrete piles. Corrosion is prevented by protection coatings and by galvanic

protection. Usually tube piles are used.

One advantage of steel piles is that they are easily spliced by welding, allowing very

long lengths to be driven.

In assessing the capacity of a steel pile, it is normal to make a corrosion allowance by

assuming about 1.5mm of the steel on each surface will be lost. This is dependent on

the aggressiveness of the founding material.

Concrete piles are easily the most common form of driven pile. Capacities range from

about 8t for an 80mm square friction pile to over 200t for a 400mm square end bearing

pile. Piles are often prestressed.

Nowadays splicing of concrete piles is not the problem it used to be as most piles

utilise one of several proprietary bayonet splices capable of transferring both

compression and tension.

Concrete piles displace their own volume of soil. It is therefore not uncommon for

them to cause the ground to heave and even to lift adjacent piles which must be

monitored and redriven if they do rise.

Spacing of Driven Piles

The recommended spacing is about 2.75 to 3.5 pile widths.

While no code minimum spacings exist, the following are generally the accepted

minimums:

Friction piles 2.5 pile widths

(including enlarged base driven cast in situ piles)

End bearing piles 2.0 pile widths




With minimum spacing, there is a chance of a pile drifting into an adjacent pile,

causing an undetected fracture of the already driven pile.

5.9. Water Retaining Structures

5.9.1. Introduction

This section discusses the principal design issues relating to the design of water

retaining structures. Such structures include swimming pools, both on grade and

suspended, culverts and so on. The basic design requirements of these structures

are set out in AS 3735. This code is a “serviceability” limit state code. Rarely if ever

does the strength limit state control the design of these structures even though these

cases need to be checked.

5.9.2. Design Philosophy

The design philosophy of AS 3735 is to limit stresses in reinforcement so that cracks,

if they occur, fall within a range of 0.1mm to 0.17mm in width.

Loadings and loading combinations are specified in AS 3735, and these must be used

in preference to those set out in AS 1170.1. Basic stress limits for various loadings

are set out in AS 3735 but short term increases are permitted for example, where

maximum design loads occur under combinations such as dead and live loads.

When working in gound water, careful consideration should be given to the effect

small variations in water level will have on the design.

Maximum permitted stress levels are varied depending on the exposure conditions

(continuously submerged, intermittent wetting and drying). The latter case is the more

severe and requires increased cover requirements and the lowest stress levels.

The Australian Standard stress limits vary with bar size unlike most other similar

codes.




This approach was based on studies of other codes and observation of the behaviour

of water retaining structures. By working strictly in accordance with AS 3735 there is

no need to calculate crack widths as required by the equivalent British Standard.

5.9.3. Design Analysis

Analysis of any water retaining structure should proceed in the normal fashion - hard

calculation for simple static structures, or SPACEGASS for indeterminate structures.

Section sizes can be determined by limiting the flexural tensile stresses in concrete to

less than 2 Mpa which should be sufficient to ensure that the concrete does not crack.

Reinforcement is then proportioned using the simple formula:

Ast > M

0.85fsd

where fs is the steel reinforcement stress specified by AS 3735 and ‘d’ is the effective

depth. Note that in assessing ‘d’ AS 3735 specifies minimum cover requirements for

either the “wet” face or both faces when the wall has a certain minimum dimension.

Cover also varies with exposure condition. Preference should be given to selecting

small bar sizes (Y12, Y16) and relatively small spacings (say 200-300max) so that any

potential cracks are intercepted by reinforcement.

Where joints are possible, for example, a pool with floor slab say on ground, sensible

joints and panel sizes should be used (aspects ratios of 1 to 1.5 maximum, and

preferably smaller). Minimum percentages of reinforcement for slabs on grade vary

from 0.48% (Y12 bars) to 0.96% (Y24) depending on the assured degree of restraint

between the slab and subgrade.

Careful consideration needs to be given to detailing of reinforcement around pipes,

windows etc, particularly with regard to placement of trimmers inside main

reinforcement.

Any joint must be provided with two layers of water stop to prevent water leakage.

Preferably these water stops will include conventional external water stop with an

internal hydrophilic. The hydrophilic water stop works by expansion when wet

whereas the conventional waterstop expands and becomes taut when concrete




shrinks. The inserts provide an increased water path for any potential leak. Even

though two layers of waterstop are provided, the design should attempt to limit any

potential cracking through appropriate member thickness selection and careful

detailing of reinforcements.

5.9.4. Concrete Technology

Integral to the success and long term performance of water retaining structures is the

concrete specification. For any mix design we should specify the critical items

including:

• Cementatious content of at least 350/kg/m³. This figure includes cement and fly

ash or ground granulated blast furnace slag (ggbfs) or other appropriate material.

Recent experience is that mixes containing ggbfs have considerably higher

shrinkages compared with mixes containing fly ash, while ggbfs produces

structures which are significantly more impermeable.

• Specify a maximum drying shrinkage characteristics (say 550 microstrain) in

conjunction with a maximum water cement ratio (say 0.45).

• Specify high strength concretes to promote durability.

• Specify testing of mixes before acceptance.

• Avoid, if possible, the use of additives such as CALTITE because they are

expensive and offer little advantage when the structure is correctly designed and

detailed.

5.9.5. Construction

Protopye Testing

Prototype testing should, where possible, be carried out to test the efficiency of all

details, particularly for difficult geometry, for placement of reinforcement, and

waterstop, concrete placement and finishing.




Water Testing

Water testing is best described as “water tightness” against specified limits. AS3735

specifies that water loss is limited to the minimum of 10 min @ 0.2% of depth over a

period of 14 days. Interpretation of the results requires the input of a specialist such

as a hydrographer because of influence of rain and evaporation.

5.10. Corbels, Dapped, Beam ends and Deep Beams

These types of members do not satisfy the rules for flexural members and their span

to depth ratio makes them more or less rigid. The accepted method of analysis of

such members is by strut and tie methods or, where necessary, by finite element

computer analysis.

5.10.1.Corbels

Corbels are used to support beams or slabs at movement joints. Often corbels

supporting beams will be attached to columns, but they could be attached to other

beams. Corbels supporting slabs are usually in the form of a ledge projecting from the

side of a beam.

In all cases, complete separation of concrete each side of the joint is essential, as

concrete to concrete contact will result in unsightly spalling. Some form of bearing

pad must always be provided (see Hercules Engineering or Graynor catalogues).

Corbels must have a d/a ratio greater than 1.0. The loaded region must not extend

beyond the effective region of the tension reinforcement and the front corner of the

corbel should be chamfered to ensure deflection of the beam does not cause it to bear

on the weak corner and split it off.

There are three approaches to corbel design:

(a) Shear Friction:




As a first estimate of corbel depth limit the shear stress to 1.7 to 2.0 Mpa then

proceed using the design methodology in section 11 of AC1-318.

Consider limiting reinforcement stress to 240 Mpa under ultimate loads to

improve overall strength and stiffness, and low levels of stress under sustained

loads.

(b) Modified Beam Theory:

Modified beam theory is derived from the usual flexural approach (corbels are

not flexural members). The modifications have been derived from testing of

numerous corbels under laboratory conditions.

The following procedure may be followed:

1. Take all loads to be 1.33 times actual loads.

2. Ensure N*/fbd does not exceed.

3. Calculate As1 = N*a/1.4ffs;y

4. Calculate M* = N*a + H*(h - d)

5. Calculate F = bd2 and Ku = M*/F

6. Read p from the chart for Ku

7. Calculate As2 = pbd

8. Calculate As3= H*/ffsy (fsz = 230MPa)

9. If As2 > 2As1/3 then As = As2 + As3

10. If As2 < 2As1/3 then As = 2As1/3 + As3

11. Ensure 0.004 < As/bd 0.013

12. Ah= 0.5 (Ax - As3) distributed uniformly throughout the top two thirds of

d

Take f as 0.7 in all cases.

(c) Strut and Tie

The corbel is idealised as a simple truss comprising a concrete strut a steel tie

and concrete “nodes”.




The compression in the struts should not exceed 0.6f’c at the nodes.

The tensile reinforcement should be distributed over the depth of the node (the

steeper the strut the more concentrated the reinforcement). Horizontal steel

should be distributed over the depth of the corbel to resist the tensile forces

due to the spreading and convergence of the flow of force in the struts.

5.10.2.Dapped Beam Ends

A dap is the opposite to a haunch. That is, the beam depth is reduced at a support.

Dapped ends are used at corbel supports when the beam, because of space

requirements or for aesthetic reasons, cannot be seated totally above a support.

The approach to design is similar to that for corbels using either modified beam theory

or truss analogy; the beam end is merely a corbel with an upwards load. However,

inspection of the truss diagram will reveal that special treatment is required at the end

of the full depth beam section where the last concrete strut meets the bottom

reinforcement. Firstly, this reinforcement must be anchored as it is in significant

tension (approx V kN) right to its end and secondly, stirrups (suspension

reinforcement) must be concentrated at the end of the beam to transfer this final strut

force to the top of the beam.

Hence, the area of these stirrups must be V*/ffsy and the area of the bottom anchored

reinforcement must be similar (for 45° strut).

The stirrups should be concentrated as close to the end of the beam as practicable at

(say) 50mm centres. Y12 bars will usually be necessary.

Anchorage of the bottom reinforcement is best achieved by special bars lapped with

the main beam steel and anchored with a welded cross bar of the same diameter or

larger.

Reinforcement details must be clearly and fully detailed on the drawings. An isometric

drawing of the welded corbel reinforcement is useful for making our requirements

clear.




5.10.3.Deep Beams

Deep beams are usually defined as simply supported beams having a span to depth

ratio of less than 3:1 or continuous beams having a span to depth ratio less than 4:1.

While AS 3600 has some very basic guidelines - the design of such elements, design

should proceed using the guidelines contained in the CIRIA publication “The design of

deep beams in reinforced concrete”. Alternatively finite element analysis can be used

but the prime difficulty associated with this methodology is the interpretation of

“stresses” and how to proportion reinforcement based on these stresses.

The above publication provides guidance on the following:

1) Determination of effective depth;

2) On assessment of moments on continuous deep beam. The re-distribution of

moments is not permitted.

3) Reinforcement distribution in both simply supported and continuous beams.

4) Detailing of reinforcement at supports and indirect supports.

5) Assessment of shear capacity. Note that loads must be separated into shear

due to bottom loads (these cause direct-tensile stress in the beam and require

suspension reinforcement) and shear due to top loads.

6) Assessment of additional reinforcement requirements around simple

penetrations.

The following design sequence is recommended for these elements:

1) Establish significant dimensions. Note that in many cases the geometry of the

deep beam is dictated by geometric considerations within a building, and only

rarely by strength and serviceability considerations.

2) Determine applied forces separating out loads as noted in 5 above.




3) Check adequacy of the concrete section.

4) Determine reinforcement sizes and arrangement.

5.10.4.Repairing Concrete

This is a specialised area which requires experience.

This work requires the following general approach but each problem must be carefully

considered.

• General background to the problem and the project.

• Survey of the corroded or damaged concrete to establish the causes.

• Establishment of repair methods including trials on site.

• Carry out the work.

Basic guidance can be gained from the Standard Association of Australian publication

‘Guide to Concrete Repair and Protection’.




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6. PRECAST CONCRETE

6.1. Introduction

This section gives the broad principles that should be followed for design of precast

concrete elements. It is not intended to be a comprehensive precast manual, since

the subject is covered in detail in the references.

Precast concrete can take many forms, shapes, appearances and colours. Precast

includes cladding panels, load-bearing elements, beam and column shells, floor

panels, facing panels, nonstructural elements, tilt up panels, culverts, retaining walls,

core walls, planter boxes, lintels, paving, etc. Precast elements may be manufactured

either on site or in off-site casting yards, but in either case precast design must allow

for reuse of moulds to achieve an economical solution.

Precast concrete cladding panels are usually attached to the outside of the building to

provide an attractive aesthetic finish and to provide the primary protection against the

weather. The units do not normally carry vertical loads. Nevertheless, they are

structural elements in that they resist wind and earthquake loads once erected, have

to withstand handling and erection stresses, and must be fixed to the building so that

they can be simply erected and remain safely fixed for the life of the building. Design

of architectural precast concrete is not difficult, but it does require skill and experience

to achieve a good result.

Unfortunately in these days of tight competitive fees, there is a tendency to reduce

documentation and shed responsibility in the design area. Beware of specifying that

the precast subcontractor is to take full responsibility for the precast design, but then

wanting to change it without any cost to the project or change in responsibility when

the design does not meet your approval. Do not assume precast contractors have

detailed knowledge of the original architectural and overall structural design

requirements. The reality is that while precast contractors have considerable expertise

in their field, unless we carry out the precast design ourselves, they usually have to

engage another engineer to do the structural design for them.




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The precast industry has developed wide experience over the past 30 years or more

with proven methods and techniques, but many designers, engineers and architects

are not aware of the proper design requirements of precast and how it will work..

For example, designers are providing inadequate or sometimes, no lateral support to

panels. They are attempting to have panels with 20-40 mm deep grooves and rebates

span large distances without proper structural consideration. The water proofing

details of joints are often inadequate despite the fact that so much work has been

done in the past on joints by the CSIRO and others. While the architect is responsible

for water proofing the joints, we must discuss each type of joint with them and make

them aware of their responsibilities. Silicone sealant has been assumed to be a

'wonder' material, never needing replacement. Panel thicknesses of 100 mm or 125

mm are being used without due consideration of stepped joints for water proofing,

cover, dowel bars, overlapping bars, lifting hooks, ferrules, rebates etc.

The reality is that 150 mm is a minimum practical thickness for a load bearing precast

panel with a single layer of reinforcement in the middle. A minimum thickness of 170

mm to 180 mm for a precast panel is required when two layers of reinforcement are

used. When rebated joints are used for water proofing then the panel will need to be at

least 200 mm thick depending on the detail.

6.2. Codes

AS 3600 Concrete Structures Code

AS 3850.1 Tilt-up Concrete - Safety requirements

AS 3850.2 Tilt-up Concrete - Design, Casting and Erection

AS 1597 Precast Reinforced Box Culverts

BCA Clause C1.11

6.3. References

1 Precast Concrete Cladding (Non-Loadbearing) CP 297:1972 (UK)

2 Architectural Precast Concrete: Prestressed Concrete Institute, 1973 (USA)

3 Precast Concrete, Handling and Erection, A.C.I. Monograph No. 8, Joseph J.

Waddell, 1974 (USA)

4 PCI Design Handbook, Prestressed Concrete Institute, 1971 (USA)

5 Connection Details for Precast Prestressed Concrete, C & CA (AUST)




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6 Design and Detailing of Precast Concrete, CIA, 1983 (AUST)

7 Embedment Properties of Headed Studs, TRW Nelson Division.

(Available from Nelson Stud Welding Co.)

8 Tilt-up Technical Manual by the Cement and Concrete Association of, 2nd

Edition 1990 (AUST)

9 PCI Manual for Structural Design of Architectural Precast Concrete (USA)

10 Tilt-up Technical Manual - C and CA - 1980, 1990 (AUST)

11 Guidelines for the use of Structural Precast Concrete in Buildings, New

Zealand Concrete Society 1991 (Good for Earthquake Design). (NZ)

12 National Ready Mix Concrete Association, Data Sheets 1-6 for Tilt-Up. (AUST)

13 Design and Typical Details of Connections for Precast and Prestressed

Concrete, 2nd Edition 1988, PCI (USA)

14 Precast Concrete Facade Connection, CIA 1991 (AUST)

15PCI Manual on Design of Connections for Precast, Prestressed Concrete

PCI 1973.

* Excellent References


Tilt Up Concrete

• Technical Bulletin No 1 Coatings - Surface Treatment G. Pereira August 1993

• Technical Bulletin No 2 Finishes - Exposed Aggregate G. Pereira August 1993

• Technical Bulletin No 3 Double Storey Tilt-Up Offices G. Pereira August 1993

• Technical Bulletin No 4 Single Storey Commercial Development G. Pereira

August 1993

• Technical Bulletin No 5 Cost - Surface Finishes G. Pereira August 1993

• Technical Bulletin No 6 Retaining Walls - Cantilever G. Pereira August 1993

6.5. Design Principles

6.5.1. Non-Load Bearing Precast Cladding Panels

Non load-bearing panels have a number of advantages. These include:

• Building frame can proceed quickly.

• Wide range of colours and textures available.




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• Work is taken off site.

• Economies of scale.

• Buildings can be clad quickly.

• Achieve straight lines.

There are also disadvantages. These include:

• Structural elements not carrying vertical load.

• Expensive, especially with high quality finishes and cost of moulds.

• They are heavy.

• The frame to which they're attached has to be accurate.

• Long term corrosion.

• Need to consider relevant movement of adjacent materials.

The most important aspect of non-load bearing precast cladding panel fixings is that

the panel must be as free as possible from the structure so that the structure can

move, sway, shorten, settle, etc, without imposing loads onto the panels. To achieve

this, the panel is fixed to the structure to support the panels and restrain the panel

laterally against horizontal forces.

Two fixings (no more, no less), usually at the bottom of the panel should be used to fix

each unit to the structure to support the weight of the panel and to restrain the panel

laterally against horizontal forces. Movement is restricted in all three directions.

These fixings often take the form of corbels. Ensure they are properly designed.

The other two fixings usually at the top of the panel restrain the panel against

horizontal forces and prevent the panel from falling in or out.

The importance of proper horizontal joints between panels cannot be over

emphasised, since they prevent the panel from being axially loaded due to the building

shortening or differential deflections.

6.5.2. Design of Non-Load Bearing Precast Concrete Panels

The following procedure is recommended for design of the precast panels. (Note that

tilt-up panels can be either load bearing or non load bearing).




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• Select the panel thickness. This should preferably be 125 mm or more, and

the L/D ratio should generally be about 40, and no greater than 50. This

limitation helps to prevent warping of the panel. For thinner panels, less than

125 mm thick, consider using steel fibre reinforcement or galvanised

reinforcement. For panels up to 150 mm use one layer of reinforcement.

Above 170 mm use two layers of reinforcement.

• Select the concrete strength. It is recommended that f'c = 40 MPa at 28 days

with a maximum water cement ratio of 0.45 to give high permissible handling

stresses at an early age and better durability qualities. A minimum of 400 kg of

cement per cubic metre should be used. Specifying modulus of rupture may

be advisable (flexural tensile strength) besides the compressive strength in

special circumstances.

• Design the panels as uncracked, unreinforced concrete sections with a limiting

tension stress and with shrinkage control reinforcement to control cracking.

The purpose of this approach is to eliminate visible cracks that may be quite

unsightly, or unacceptable. Designing the member as a cracked section is

generally not recommended.

• The panels can be designed for controlled cracking, sometimes where fine

cracks may be acceptable. This would be done in the interests of achieving

economy, but the client must be fully aware of this. Refer to reference 12 for

design by this method.

• Permissible tension stress for uncracked panels. The Concrete Structures

Code, AS 3600 gives no guide for permissible tension stress in precast panels.

Reference 5 gives permissible tension stresses for prestressed members,

viz., 0.35√f'c, which is not really directly relevant here. Reference 8

recommends a permissible stress of 0.5 f'c that appears high. Reference 4

recommends 0.38√f'c. Reference 12 recommends 0.41√f'c. The following

values are recommended.




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a) The final in place condition for wind or earthquake loadings (usually not

critical). At this time f'c = 40 MPa.

ft = 0.33 √f'c MPa

ft f'c

1.87 32

2.09 40

b) Handling and erection condition. The method of handling and erection is

generally the responsibility of the Contractor. Nevertheless, we should

design the panel so that it can be easily handled without excessive

limitations and therefore expense. The following three approaches can

be used. Refer also to Reference 9 for graphs on lifting conditions, and

the Aries program for the design of lift-up panels.

• Method "A" Lift from one end

• Method "B" Lift at quarter point at one end

• Method "C" Lift at quarter points from both ends

Approach B is recommended, since A tends to be too severe on the

panel, and C tends to be too expensive or difficult in handling. The

recommended permissible tension stress during handling is -

ft = 0.38 √f'c MPa

(At this time f'c = 25 MPa to 30 MPa)

ft f'c

1.90 25

2.08 30

3.28 35




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• Deflections - Horizontal deflections under servicability loads should be

limited to span/150.

• Removal of the panel from the mould. This is usually not one of our

design criteria, and it is normally left to the precast manufacturer to

place the necessary number of lifting hooks. If we do get involved, it is

suggested that the panel be designed for a suction load of 1.0 kPa or 1.4

x panel self-weight, whichever is the greater for the initial lift. Assume the

concrete strength at this time is f'c = 15 - 25 MPa. The suction effect

may be eliminated entirely for flat panels by jacking the panel sideways or

inserting wedges to break the seal before removal or lifting forms.

• Reinforcement: The selection of bar or fabric reinforcement has a

number of criteria.

a) Design reinforcement: As well as designing the precast member

as an uncracked section with a limiting tensile stress, it should also

be checked as a cracked section with designed tension

reinforcement, so that if the panel does actually crack, it does not

structurally fail and collapse.

b) Place reinforcement to control shrinkage cracking. Heavier

reinforcement than that recommended in AS 3600 should be used

to limit the shrinkage and to control the shrinkage cracking. It is

suggested it should be a minimum of 0.003.

Always distribute this reinforcement evenly throughout the panel

and in each face of the panel. Avoid heavy concentrations of

reinforcement that may provide a shrinkage restraint thereby

causing cracking. Place at least 1 Y12 bar in panels up to 150

thick and 2 Y12 for thicker panels all around the perimeter of the

panel, lapped as necessary. All ferrules and fixings must be inside

this bar. Consider the use of a fabric with 100 bar-spacing if it is

available, and custom-made fabrics where large quantities of

reinforcement are involved.




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• Cover to reinforcement:

Minimum cover to outside face - 35 mm + 5, - 0 mm

Cover to inside face - 20 mm + 5, - 0 mm (check fire rating)

Careful attention should be given to fixing reinforcement to avoid exposed

bar chairs etc. Covers must not be less than specified in AS 3600, but

remember AS 3600 only sets minimum covers.

Also consider the effect of rebates and other surface detailing on cover.

Where panels or units are thin or small and cover maybe difficult to

achieve, consider the use of galvanised reinforcement.

• Allowance for impact in handling (after removal from the mould).

Design for an impact factor of 1.2 time the panel weight for normal

handling conditions. This may need to be increased to 1.4 where impact

effects maybe more severe.

Note that these are general rules which are applicable to architectural

precast concrete. Each project must be considered on its merits; eg, for

a developer owned and built shopping centre, minimum cost and ease of

construction rather than appearances may be the overriding

considerations and having some panels with hairline cracks may be

visually acceptable. One shopping centre project had 9000 mm x 7000

mm x 150 mm thick (L/D = 60) tilt up panels. The theoretical bending

stress was 3.8 MPa using strong backs, which is close to rupture stress.

However, very few panels cracked and none were structurally damaged.

This was very economical and therefore a successful project for the

developer.

• Sizes of a panel for handling.

Limiting the size of the panel is usual so that its weight does not exceed 5-

8 tonnes to suit site cranage. Also, limit the size of panels for transport.




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This generally should be 7 m x 3.5 m to avoid special permits. Larger

panels may be possible but consider carefully at the time of design. In the

case of tilt-up panels much, much larger loads can usually be handled with

appropriate planning. Typical loads will be in the 12-20 tonne range with 40

tonne or more loads not out of the question.

6.5.3. Finishes

Know of the type of finish the Architect requires at documentation. We must

understand how this is to be achieved and any special conditions resulting from it.

There is a wide range of finishes available such as off form (steel, concrete, ply etc.)

polished surfaces, exposed aggregate finishes, sand and water blast finishes, and

etched surfaces. ALL treated surfaces will reduce the cover from the cast face by up

to 5 - 10mm that must be added to the total cover, therefore the reason for 150

minimum thick panels. Consider carefully the use of acid washing and only permit if

no alternative available. Do not allow acid dipping under any circumstance.

The Architect may wish to use a veneer on the panels to achieve a type of finish.

These must be treated with EXTREME CAUTION and should not be included as part

of the structural panel or part of the concrete cover. Veneers should be avoided if

possible. Some points on veneers are:

i Is it a graded mix or a one-size mix? A one-size mix has a high permeability

and will not contribute to corrosion protection.

ii The veneer should be well vibrated to give a mix as dense as possible. This is

most easily done if the veneer is placed in the form first, i.e. panel cast face

down. Make this a mandatory specification item. This will be hard to achieve

with anything but a flat panel.

iii The veneer and parent concrete should be placed virtually as one pour, i.e. the

second element is placed and vibrated before the first has gone off. This will

give a homogeneous panel. Specify a maximum of one hour between pours.

iv If the veneer is considered as part of the cover and structure, it must be -

- a graded mix

- well vibrated




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- "homogeneous"

- well supervised

- tested for permeability

v Veneers should only be used for flat single plane panels. This allows the

veneer to be placed, properly moulded and vibrated before the backing

concrete is placed. All non flat panels, (corner panels etc.) should not be

veneered. The whole panel should be poured in the finished concrete.

vi The shrinkage characteristics of the veneer and the parent concrete and the

dimensions of the panel need to be examined to determine the possibility of

warping. Have shrinkage tests done with some prediction of warping if

possible.

A typical specification clause on this item would be:

"The mix design must not exceed a shrinkage at 90 days greater than 750 microstrain

with 95% confidence levels. The shrinkage sampling and testing shall be carried out

according to AS 1012, Part 13 "Method for the Determination of Drying Shrinkage of

Concrete". The shrinkage shall be measured at 2, 3, 4, 8, and 13 weeks and testing

shall be commenced immediately when the Contract is awarded so that data is

available to show that the mix is acceptable before production commences.

The difference in shrinkage at 90 days between the veneer and backing concrete

mixes shall not exceed 150 microstrain.

6.5.4. Design Criteria for Fixings

The design and detail of fixings are highly variable depending on the conditions and

restraints that prevail for each situation.

Some typical fixings are shown in our standard CAD details. There are a number of

basic principles that should be followed wherever possible. References 4,5 and 13

are useful for the design of fixings. Points to be noted are as follows:

• Check any special requirements before proceeding. Precast panels should be

designed such that the panel can be securely fixed in place on initial placement




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and the crane removed leaving the panel fixed in place subject to final

adjustment. Therefore Precasters prefer top hung panels as they have less

cranage time than panels bottom supported.

• Supporting the weight of the panel on bolts in shear, as permanent supports

shall not be used. The bolts cannot be relied on over a long time due to

corrosion and this method is too easily abused on the site to overcome poor fit.

• Support the weight of the panel directly on the concrete floor or by a corbel with

a dowel bar or anchor bolt wherever possible. Ensure corbels are properly

designed and not guessed. Concrete corbels will crack if they are loaded

outside the reinforced area, so provide a chamfer or rebate to these areas.

Also ensure the panel is designed for the corbel moment and the corbel

reinforcement is properly anchored into the panel.

• All fixings must be protected against corrosion by concrete encasing, hot dip

galvanising or another effective way. A very good quality hot dip galvanising is

required as the minimum protection. If hot dip galvanising is used with welding,

on the site cold galvanising will be necessary to repair damaged galvanising.

In corrosive atmospheres or external conditions, use stainless steel. Use one

grade, usually grade 316 for all fixings so as not to use dissimilar metals.

(Note Sydney City :Council may require stainless steel fixings in all

circumstances).

• Many precast fixings need to have a fire rating. Check with the Architect and

the BCA. Fire ratings can be achieved by concrete encasing, sprayed

fireproofing or painted intumescent paints. Ensure that the fireproofing does

not inhibit structure/panel relative movement, where applicable.

• An internal skin of block wall may provide a fire rating while giving a cavity wall

construction.

• Connection details, cast in details should be drawn accurately to large scales

(1:2 or 1:5) to ensure the elements can fit in.




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• Where angle brackets are used, a minimum of 150 x 150 angle is usually

necessary to get edge distances for fixings.

• Avoid cast in bolts in insitu concrete for connections because casting these

accurately in place is not always consistently possible. Use a cast in plate and

site welded stud or cast in ferrule or sleeve.

• Do not skimp on connections. Always provide a minimum of two bolts where

possible.

6.5.5. Tolerances

It is most important that the connections have adequate tolerances in all three

directions to enable erection on the site. These are provided by -

• Slotted holes in plates - allow 60 mm in each direction

• Packing plates

Packing plates must be galvanised and the same bearing area as the

reinforced part of the corbel unless grouted. High density nylon packers are

now common and can also be used.

• Oversize dowel holes in concrete

Dowel hole diameter 2 to 3 times the diameter of the dowel bar.

Note: Embrace a dowel hole with a reinforcing bar (eg hairpin or similar)

It may be necessary to "clamp up" these tolerance facilities, after erection and

alignment by grouting or welding.

Remember no precast panel is completely flat or square despite the best mould.

6.5.6. Fixing Ferrules and Lifting Devices

There is limited recommendation for safe loads on ferrules. Verbal recommendations

from precast manufacturers and ferrule manufacturers always indicate that the




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capacity of the ferrule exceeds the capacity of a commercial bolt in that ferrule, but

they never seem to be prepared to put this in writing.

Each lifting device shall be designed for a working load of not less that 1.65 times the

maximum static load at that point and an ultimate load not less than 4 times the

maximum static load. If commercial bolts are used, design by ultimate load will

automatically satisfy the working load requirement.

The following recommendations are made with respect to ferrule and lifting device

design.

• Multiply that static load by 4.0 and use this as the limit state design load

throughout.

• Where loads are constant consider using a factor of 6.0.

• Select a hexagon ferrule with an anchor bar, either cross bar or butt welded

stud similar to our standard details. Either nominate the brand name or put a

similar fully dimensioned ferrule detail on the drawing. Ensure cross bar is

anchored behind the fabric or panes walls.

• Use the ultimate commercial bolt capacity as the ultimate capacity of the

ferrule (thread included in stress plane). Modify this capacity if the ferrule is

close to the edge of the panel (ie, within 200 mm), by using the

recommendations given in section 6.5.7.

• For combined shear and tension, use the interaction formula given in section

6.5.7.

• For direct tension lifting ferrules, use a butt welded stud on the end of the

ferrule.

6.5.7. Fixing and Design Aids

Fixing loads have been presented in tabular form in this manual. An Excel

spreadsheet has been prepared by CW Adelaide for design. References 13 and 14

has been used for the design tables. Section 9.5.4.2 “Limit State Design of Portal

Frame Buildings” by Woolcock, Kitpornchai and Bradford also has useful information

of design of anchor bolts.

Ultimate capacity of ferrules




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Procedure

1 For bolts loaded in shear, determine capacity from Table A.

2 For bolts loaded in tension, determine capacity from Table B.

3 For bolts loaded in tension and shear, use the interaction formula given below.

For Concrete

[ (Pv/Pc) 2 + (Vu/Vc)

2 ] ≤ 1.0

for Bolts

[ (Pv/ Ps)2 + (Vu/ Vs)

2 ] ≤ 1.0




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TABLE A. Ultimate Bolt Shear Capacity (kN) (4.6 Bolts)

Bolt Size

Minimum

Bolt

Length

M12 M16 M20 M24

Min bolt length mm

mm mm 100 m 100mm 100mm 100mm

Distance to

free edge

50

75

100

125

150

175

200

225

250

275

300

400

500

5.7

10.5

15.2

15.2

15.2

5.7

10.5

15.2

19.8

24.6

28.3

28.3

28.3

5.7

10.5

15.2

19.8

24.6

29.3

34.0

38.7

5.7

10.5

15.2

19.8

24.6

29.3

34.0

38.7

Note

1 Line represents ultimate commercial bolt capacity, threads included in shear

plane, based on Fsy = 240 MPa.

2 For ferrules less that the "min. bolt length", multiply the given capacity by

(recommended length)½, (actual length)½. However, do not reduce length for

ferrules permanently loaded.

3 Multiply shear values by f'c/25 for values of f'c less than 25 Mpa. (Note you

should not use f'c less than 32 Mpa.

4 It is assumed that the ultimate shear strength is 0.75Fsy. Refers AS 4100.

TABLE B. Ultimate Bolt Pull-Out Capacity (kN) (4.6 bolts)




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Concrete capacity, full shear cone developed with bolt in direct tension using grade 4.6

bolts with the phi factor applied. For minimum depth of embedment the ultimate

capacity will be determined by the concrete but for reasonable embedment, the bolt

capacity will govern almost all the time. The table also assumes the ferrule is properly

anchored with an anchor bar or enlarged end into the concrete.

Bolt Size Max. Ultimate Bolt/Ferrule embedment length (mm)

Bolt Capacity 75 100 125 150 175 200 225

M12 12.1 39.4 67 103 146 197 256 322

M16 19.9 41.2 70 106 150 302 261 327

M20 35.3 43.0 72 109 154 206 265 333

M24 44.8 75 112 157 210 270 338

Note

1 Multiply table values by 0.85 for sand - lightweight concrete.

2 Multiply pull out capacity by f'c/32 for values of f'c less than 32 MPa.

3 Where the full concrete shear cone is not developed, e.g. close to the edge of

a concrete element, apply appropriate reduction factors.

4 Values shaded are given for use with the reduction factors, but the value used

should not in any case exceed the maximum ultimate bolt capacity.

6.5.8. Prototypes

Where there are many units of the one type, getting the first one correct with careful

inspection and proof of performance is important, e.g. lifting, handling, erection onto

fixings, etc., and careful study for cracks and if necessary, a testing programme.

Often prototypes are required to achieve the final finish for approval by the Architect or

where waterproofing, compaction or casting are of concern.

6.5.9. Notes to be Placed on the Precast Drawings

Refer to our standard notes for these.




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6.5.10.Typical Panel Connections

Refer to standard CAD details and past projects for these connections.

6.5.11.Load Bearing Precast

This type of construction is coming back into favour because of reduction of time on

the site and the fact the panel, the column etc. can often do two jobs - carry the

vertical load and provide a final finish or as formwork, etc. Tilt up is (usually) a form of

load bearing precast.

Members should be designed for lifting, minimum reinforcement. etc. and designed for

axial and lateral loads and frame moments to AS 3600.

Where member carry substantial axial load grouted dowels need to be used with fully

grouted end bearing to ensure full load transfer.

6.5.12.Tilt-up Construction

This form of construction is now very common, although it is not new. The tilt-up

panels originally were panels cast on the site and lifted into position, but often panels

can be made off site at a precast factory and delivered to the site.

Tilt up panels have a number of advantages. These include:

• Fast erections of walls, lift shafts, stair cases etc.

• Panels are usually load bearing.

• Variety of surface profiles and features available.

• Competitive with masonry.

• Suitable for sample type of panels.

It also has a number of disadvantages. These include:

• Space required on site for casting and cranage.

• Penetrations for services are difficult.

• Quality of panels cast on the site not as good as factory precast.




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• Complicated shapes are difficult to cast on the site.

• Generally butt joints can only be cast which can be difficult to waterproof.

• High quality off form or polished surfaces cannot be done. Often panels are

painted.

• Need for special fire rated ties to suit BCA Regulations.

For site cast panels grade 32 MPa should be used for panels lifted after 7 days and

grade 40 MPa for panels lifted after 3 days.

Design including cover etc. should be according to AS 3600.

The panel must be designed for:

• self weight

• lifting

• adhesion forces between the panel and the casting bed

• crane sling arrangement

• dynamic loading during lifting.

The "ARIES" computer program for panel design can be used.

Reinforcement should be according to the previous sections. A single layer of fabric

should ONLY be used in small panels of small thicknesses; eg 3m x 4m x 125 thick

or if thin panels are to be used with a single layer of fabric, then strong backs must be

used.

For larger panels; eg 6m x 3m x 150 thick, two layers of reinforcement can be used to

reduce cracking that may occur during lifting. If there is only one layer of

reinforcement then strong backs must be used for lifting.

Inserts for lifting must be properly anchored and the panels properly braced until

complete as part of the final structure.




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6.5.13.Floor Panels

There are a number of specialist precast floor panels available, including:

• Transfloor.

• Single and double tee units.

• Hollow core planks.

• Inverted U panels.

• Beam forms.

Refer to the manufacturer's information on standard design methods and details for

these elements. As floors act as diaphragms to transfer lateral loads to cores and

columns, it is essential these elements be properly tied together and to their

supporting structure so they can act as diaphragms.

6.5.14.Detailing

Designer should refer to previous major projects in their office and discuss typical

details with Senior Engineers and Drafters. Detailing is a very important part of the

design process and is often overlooked by designers. Buildability and ease of

construction are important matters. The following points should be noted:

• Drawings must realistically reflect all types of panels. Do not just draw a

typical panel. Draw all panels in sufficient detail to allow a shop drawing to be

prepared by others.

• Insist on the Architect fully detailing panels, dimensions and joints etc. Joints

are very important for water proofing and fire resistance. For high rise

buildings, use the open drained joint system, not butt joints if possible. Smoke

baffles may also be required. Discuss each joint with the architect so they are

aware of their responsibilities.

• Provide Y12 or Y16 trimmer bars around all edges including penetrations.

• Insist on the Architect detailing the fire proofing.




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• Reinforcement should be fabric of one sheet where possible.

• Provide reinforcement in both faces for panels greater than 150 thick.

• Do not skimp on fixings.

• Consider tolerances of the structure and expected movements both short term

and long term.

• Ensure sufficient panels and details are shown to allow the shop drawers to

detail panels fully.

• Check all rebates, drip grooves, joints etc. to ensure the reinforcement can be

fixed, including lifting hooks and ferrules.

6.5.15.Joints

Joints in precast can be a very important detail. Joints have a number of functions.

• Carry loads when load bearing

• Allow movement in non load-bearing panels

• Water proof precast

Often this area is ill-defined as it is part structural and part architectural and Architects

are often unaware of their responsibilities.

Once the structural requirements of the joint are determined, meet with the architect

and discuss each joint in detail, what is to be water proofed and how is it to be

achieved. Once a joint leaks it is very difficult to fix. Use stepped joints where

possible and appropriate flashings. A straight grouted joint has little resistance to

water. Wind can blow water upwards and through joints not properly sealed




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6.5.16.Standard Details

Connection must reflect the design requirements for the building as a whole; ie axial

shortening, sway.

The designer should also refer to previous projects with major precast and standard

details developed on CAD.

6.5.17.Shop Drawings

Refer to the Section in this Manual on shop drawings for specific comments.

Shop drawings are important documents that should be treated with respect and care.

Generally, the standard of the larger Subcontractors shop drawing is high. Checking

must ensure the full requirements of our design are shown on the shop drawings.

We do not normally check dimensions unless Prime Consultants have dimensioned

the panels on the drawings.




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7. STRUCTURAL STEELWORK

7.1. Introduction

The design of structural steelwork in building structures should be in accordance with

the limit state requirements of AS 4100 and AS 4600. The design is carried using

design actions based on the loading codes. Unless specifically requested, use only

steel sections manufactured by BHP.

7.2. Codes

AS 3990 Mechanical Equipment - Steelwork (old AS 1250)

AS 4100 Steel Structures

AS 4600 Cold-Formed Steel Structures

7.3. References

1. “Steel Designers Handbook” - Gorenc, Tinyou, Syam 6th Ed.

2. “Introductory Structural Design” - Structural Steel Design AS 4100" - R.D.

Nielsson (University of Queensland)

3. “Design Capacity Tables for Structural Steel - Vols. 1 and 2" AISC AS 4100

“Steel Structures” Code

4. “Limit State Design of Portal Frame Buildings” - Woolcock, Kitipornchai,

Bradford

5. “Fastener Handbook” - Ajax Fasteners

6. “Steel Structures Design Handbook” - Standards Australia SAA HB48-1993

7. “Design of Structural Connections” Hogan and Thomas (AISC)

8. Code of Practice for Safe Erection of Building Steelwork, Parts 1 & 2

“Design Guide - CHS Joints”, Packer Kurobane, et. al; CIDET

“Design Guide - RSH Joints”, Packer Kurobane, et. Al; CIDET

9. Design capacity tables for Duragal Steel Hallow Sections.

10. Duragal Design Capacity Tables for Structural Steel angles, channels and flats

11. BS8100 Part 1, 1986, Lattice Towers and Masts

12. “Wind Forces on Tubular Structures - Design Manual”, Tubemakers of Australia,

August 1987




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There are numerous Connell Wagner Technical Notes available - refer to library list.

7.5. Purlins and girts

7.5.1. Design

Note: Manufacturers load capacity tables are based on peak moments usually in the

end spans. Significant savings can be made in the purlin selections by using methods

(a) or (c).

(a) In accordance with AS 4600 ‘AS Cold Formed Steel Structures’ which has

specific sections governing purlin design.

(b) Comprehensive design tables by the major suppliers based on load tests and

calculations. The loads are calculated using permissible stress combinations

New . Check manufacturers data as future capacity tables may be in limit

state format. Note: the use of these tables is conservative for large multi span

or varying span buildings.

(c) i) Analyse design loads to obtain Reactions and Bending Moments for an

assumed spacing.

ii) Using the manufacturer’s tables for similar spans, effective lengths etc

ascertain midspan capacity and lapped moment capacity for various

purlins sizes, and bridging configurations.

iii) Select appropriate purlins.

iv) Iterate or modify for different spacings.

The permissible stress format design loading combinations are:

a) DL + LL or

b) 0.75 (DL + LL + WL in direction of DL and LL) or

c) Minimum possible DL - WL in direction opposite to DL

d) Max DL ± WL

Note: Allow for local wind pressure effects.




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7.5.2. Use of Purlins and Girts

Purlins and girts are major cost item, particularly in industrial buildings. The selection

of purlins and girts should not be underestimated.

a) Tolerances and Out of Straightness

Lysaght/BHP have a tolerance of span/500 for purlins and girts. A

specification of span/600 with a maximum of 20mm is preferred. This means

a 10m purlin can have up to 20mm out of straightness in either direction.

b) Bridging for Roofs

Bridging is necessary to provide both stability during erection of sheeting and

as a restraint to the compression flange for the design case of outward wind

load. Refer manufacturer’s details for bridging systems.

Where the roof is not symmetrical (e.g. skillion roof) and bridging is required,

it is necessary to provide flat strap bracing, rod bracing, or light angle bracing

to prevent the purlins from deflecting down the slope.

Bridging is required during erection to resist the tendency for the purlins to roll

over before the sheeting screws are installed. This situation is not adequately

allowed for in manufacturer’s design tables. It is a good policy to use one

central row of bridging even though this may not be required by design tables.

Bridging on curved roofs needs special care and thought. Standard bridging

systems do not cover this situation.

c) Bridging for Wall Girts

Struts or hangers are required to prevent the girts sagging between columns

during fixing of the wall cladding. Use struts except where cladding is fixed

prior to casting of the concrete floor, or where there are obstructions such as

off-set brick walls or openings. Alternatively hang the bridging from a

structural eaves member, or to using a light truss incorporating girt chords

and flat diagonal bracing or diagonal sag rods.




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d) Shallow Roofs and Deflections

Differential deflection of adjacent purlins can flatten a 1.5° to 2° roof pitch

causing water ponding and leakage through the side laps of the sheeting.

Also, if the roof is visible, it may be aesthetically unacceptable.

Roof pitches 3° to 7° are susceptible to water ingress at joints and will need

to be in one continuous sheet or comprise specifically detailed parts/laps.

Where possible, use a minimum 5° pitch. Never use less than the minimum

pitch recommended by the sheeting manufacturer.

e) Curving of Purlins and Girts

Cold formed purlins and girts cannot be curved.

f) Curved, Feature, Complicated and Bull-Nosed Roofs

Where specific architectural features such as bull-nosed sheeting or special

cladding details are required, it is important that tolerances are taken into

account. A secondary framing system with adjustable light gauge angles

fixed to the purlins or girts will often be required.

Bull-nosed sheeting is difficult to fix and has rolling tolerances from sheet to

sheet. It is preferable that the bull-nose sheeting has a bull-nose together

with a minimum straight length of sheeting over two purlins. This allows the

roofer to fix the sheeting and overcome any out of tolerance between

individual sheets by springing the sheet.

g) Hole Tolerance

Holes punched in purlins are generally 18 x 22 long slots to take M12 bolts.

(22mm holes and M16 bolts in Big Zeds). This can cause a number of

problems in connection with bracing and alignment.

With such large tolerances, the use of purlins as bracing and for the

transmission of forces needs to be considered carefully. Designers must be

aware of and detail for a slip of 5 to 10mm longitudinally in a purlin system.

h) Hips, Valleys and Sides




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Ends of sheets at hips and valleys and sides of sheets at walls, etc. must be

continuously supported. A 50 x 50 x 1.2 cold formed angle is often sufficient.

Be aware of possible need for valley gutters and the extended cleats required

for them. Forgetting these trimming angles is embarrassing and costly.

i) Purlin Cleats

Purlin cleats are subjected to axial loads and bending moments. The bending

moments result from the component of the weight of the roof sheeting in its

own plane, from the restraint provided by the sheeting to prevent lateral

buckling, and in the case of Z profiles, from lateral forces due to the inclination

of the principal axes to the plane of the roof.

Be aware that the size of these cleats is dependent on both the height and

the roof slope. Always check any “standard cleat” detail. Top flanges of

beams may require additional detail to maintain support for lateral torsional

buckling.

7.6. Beams

7.6.1. General

Design information for flexural members such as beams is comprehensively set out in

various well known references e.g. [1].

7.6.2. Connections

Refer to Section 9 of AS4100 for minimum design loads for connections. Connection

designs as set out in reference [7] are recommended for use. The tabling of

connection design loads on drawings to allow fabricators to prepare their own

connections is to be avoided. Limit state connection capacity tables are contained in a

Connell Wagner Design Aid. Do not skimp on connections. They are important

elements. Failure of these can be catostraphic.

7.6.3. Effective Lengths, Moment Gradient

Information on effective lengths is available in the Steel Code.




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7.6.4. Members Subject to Bending

Checking of members subject to bending:

(i) Determine the bending moment diagram, the type of supports and lateral

restraints.

(ii) For long span beams (> 25 times beam depth), first check the serviceability

limit of deflection, it will often be the control for long span beams.

(iii) For other beams, check the strength limit states:

a. Member Bending Capacity

• calculate the section capacity to provide a basic load capacity

irrespective of length

• calculate the member capacity which allows for member length

• check the adequacy of the restraining elements

b. Shear Capacity

c. Check the bearing condition at the support and if necessary provide

load bearing stiffeners.

Note: If a section is compact the effective section properties are the same as

the gross section properties. If the section is non-compact or slender, the

effective section properties are less than the gross section properties. Note

that the minimum radius of gyration ry is based on GROSS section geometry.

7.6.5. Angles as Beams - Extract from Reference (6)

For angles which are torsionally restrained at supports with the load applied at:

(i) the shear centre for angles with lateral restraints, or

(ii) the middle of the leg for angles without lateral restraints

The following approximation is applicable:




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(a) For an angle under continuous lateral restraint (see Figure 5.4a) subject to a

design moment M* about an axis n-n normal to the leg, it is recommended that

M* ≤ 0.9 fy Ze with Ze = 1.25 Z min

where Zmin is the minimum elastic section modulus about the relevant axis

normal to the leg.

(b) For an angle without lateral restraint (see Fig.5.4b) subject to the design

moment M* about an axis n-n normal to the leg, it is recommended that

M* ≤ 0.9 a fy Ze

where a is a reduction factor to be determined as follows:

• for equal angles a = 0.7

• for unequal angles with loading

parallel to short leg a = 0.8

parallel to long leg

- with leg up a = 0.6

- with leg down a = 0.5

Shear capacity may control the design of angles as beams for the following

situations:

(i) Equal angles of 150mm and 200mm legs with spans less than 4m

(ii) All other angles with spans less than 2m

7.6.6. Members Subject to Axial Compression

The procedure for checking a member subject to compression is as follows:

(i) Estimate the kf value for the section using the BHP Handbook or similar; for

fabricated sections use Section 6.2 of AS 4100.

(ii) Estimate the design section capacity i.e. the short column capacity Ns = 0.9 kf

Anfy.




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(iii) Select the member section constant ab, to allow for residual stresses and

section type.

(iv) Estimate the member effective length factor ke.

(v) Estimate the slenderness ratio (keL / r) for the relevant buckling axis.

(vi) Obtain the member slenderness reduction factor ac.

(vi) The axial load nominal design capacity is acNs.

Note that all columns in simple construction should be designed for a nominal load

eccentricity as per AS 4100 and therefore must be checked for combined axial

compression and bending.

7.6.7. Members Subject to Combined Action

The interaction equation for a section subject to an axial load, N*, a major axis bending

moment, M* x, and a minor axis moment M* y:

N* + M*x + M*y

___ ___ ____ <1.0

0.9N 0.9Mbx 0.9Mby

where

N = Nt or Nc = the nominal axial tension or compression capacity, respectively, of the

member (for a compression member it is the lesser of the capacities for either

principal axis).

Mbx = nominal capacity of the member in bending about the x-axis.

Mby = nominal capacity of the member in bending about the y-axis

Note: This is a simplified procedure which avoids the need for checking section and

member capacity separately. Considerably less conservative results can be obtained

by using the more complex checking procedure of AS4100.

Refer to Appendix B of [6] and [1] for more detail.




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7.6.8. Penetrations

(a) Recommended dapped end and penetration details are shown in figures 7.1

and 7.2 These are mostly applicable to composite floor construction, where

the reticulation of underfloor services, especially airconditioning ductwork, is a

prime consideration.

Figure 7.1 Penetration Details

Figure 7.2 Reduced Depth At Beam End

Alternatively, plateflange welded toweb




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7.6.9. Allowable Deflections The allowable deflections are to be approximately as shown in the table below.

Deflection Limits Purlins And Girts All Rafters Mullions Supporting Brittle Finish Walls Supporting Other Walls Eaves Deflection (Horizontal) Multi-Storey Building Industrial Building With Crane - requires careful specs. Refer reference1 “Crane Runway Girders" Industrial Building Floor Beams Supporting Brittle Walls No Provision For Movement Supporting Brittle Walls/Ceilings Some Provision For Movement Not Supporting Walls/Ceilings That Could Be Damaged By Movement Fascias Glazing Heads

Span Multiplier 1/300 1/150 1/150 But Max. 30mm 1/300 But Max. 50mm 1/150 1/150 But Max. 30mm 1/500 1/200 Knee Height Multiplier 1/500 1/300 1/150 1/300 1/100 Span Multiplier 1/1000 1/500 But Max. 20mm 1/300 But Max. 30mm 1/500 But Max. 20mm 1/500 But Max. 10mm

Load Type DL WI Wl DL WL WL WL WL WL LL WL WL WL Dl+LL Dl+LL LL DL DL

Remarks No Ceilings With Ceilings No Ceilings With Ceilings Metal Cladding Masonry Cladding Farm Building Deflection Due To WL As For Millions




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7.7. Trusses

7.7.1. General

Trusses have been used in Australia to efficiently span distances up to 120m.

Trusses are usually of the Warren, Pratt or Fink types. Trusses should be configured

such that panel points are evenly spaced, the top chord has adequate slope for roof

drainage and the diagonals meet the chord members between 35° and 55° to avoid

awkward connections. Large span trusses warrant the use of as large a purlin as

possible to achieve the maximum possible spacing (10 - 12m). Long lengths of

roofing material are not readily available, and overlapping may require special purlin

details.

7.7.2. Analysis

Bending moments in the truss members may arise from:

a) Frame moments

b) Joint eccentricities

c) Lateral loads between nodes

It is acceptable to ignore moments resulting from frame action, assume all members

are pin-jointed. However, moments due to joint eccentricities and applied loads

between nodes must be considered.

7.7.3. Member Sizing

Members must be sized to resist axial load and bending moments. Effective lengths

of members are dealt with in [1]. Out of plane (horizonal) buckling capacity of the

compression chord is improved by using a UB with web horizontal.

7.7.4. Connections

The detailing of connections has a significant effect upon the economics of trusses.

Smaller trusses may utilise gussetless connectors. Refer to Figures 7.3 and 7.6.

Heavier trusses require gussets to distribute web member loadings into the chords.




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Refer to Figures 7.3 and 7.4. It is necessary to carefully check force paths to ensure

loads can in fact find their way to the appropriate members.

The connections shown in Figures 7.3(d) and 7.4 do not work because the load from

the diagonal web members is delivered onto the flexible flange of the chord member.

Since stiffening of the chord member (using web stiffeners to support the flange) is

uneconomic, the truss member configurations of Figures 7.3(d) and 7.4 are to be

avoided. The effects of connection eccentricities must be rigorously examined to

ensure overstressing does not occur. Refer to Figure 7.6. An example of unusually

heavy truss connection is shown on Figures 7.3 and 7.7.

Figure 7.3 typical node connections for trusses

Composed of rolled sections

a) gusset less construction using T chords

b) gussets are required where diagonals carry large forces

c) T diagonals and chords, gusset less

d) & e) node detail or heavy truss work - 7.3 (d) is to be avoided.

f) bolted nodes




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Figure 7.4 UB And RHS Truss

Figure 7.5 Truss Connections With Tubular Sections




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Typical connections for roof trusses composed of tubular sections:

(a) connections using contoured tube ends

(b) & (d) reinforcing plate bent to tube curvature is often required at node

connections

(c) when negative eccentricity is used no reinforcing plate is required

(f) concentric reducer can be used where tubes are stepped down

(g) slotted-gusset connections are popular with fabricators who have no facilities

for contour cutting

(h) flattened end connections also avoid contour cutting

(i) slit tube connections

Figure 7.6 Gusset-Free Connections For Trusses

(a) centre of gravity lines intersect at the node

(b) eccentric connection can be a practical way of detailing but additional bending

stresses are induced as indicated in (c).

(c)




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Figure 7.7 Heavy Truss Connections

7.7.5. Fabrication, Transport and Erection

Large trusses may have to be fabricated in pieces to allow transport to site and field

splicing. Transportation limitations differ from state to state and should be checked

locally. Field splicing is usually by bolting but may, for very large trusses, be by

welding.

7.7.6. Weld Testing

For major jobs, a specialist welding inspector should be employed by the client or the

Company. It is necessary to specify the extent of non-destructive (and destructive)

testing in some detail (e.g. 100% of 50% of the welds etc.) and to show clearly on the

drawings which welds are to be tested. Non-destructive testing is usually the

ultrasonic method. Contractual arrangements as to who pays for testing vary but

should be clearly stated.

7.8. Portal Frames

7.8.1. General

Use frame programs for the design bending moments. Do not use coefficient as it is

inefficient. It is recommended that each loading for internal pressure, external

pressure etc. be analysed and combined with appropriate factors. This makes it

easier to reanalyse various conditions and makes checking simpler.




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The first trial run through the program must utilise assumed section sizes and these

should be refined for the final run, although the bending moment pattern is often not

highly sensitive to moderate variations in section size. Haunches should be input as a

number of short prismatic members ( 3 is usually adequate) of differing section

properties to model the haunch reasonably accurately, since bending moments vary

quickly in these areas. Fixed base portals should be avoided (refer to the section on

footings). However, depending on the footing type and base plate detail, a “partial-

fixity” may be generated at a base under serviceability loads.

7.8.2. Rafters

Rafter size is normally determined by bending moments, but occasionally by

deflections. The use of knee haunches means that the apex bending moment

governs the rafter size. Account should be taken of the beneficial effect of bending

moment shape factor (µm) which is automatically calculated in Limsteel. Refer 2.5.4.

Note that deletion of fly braces, by assuming the tension (top) flange provides bracing,

needs to be justified by rigorous analysis.

7.8.3. Beam Columns

Axial loads in columns are usually low except:

• where the column receives loads from a crane;

• where the column forms part of a wall bracing panel.

Specific guidance about effective lengths for columns supporting crane loads is

contained in [4]. Column bases, even where pinned bases are assumed for analysis

purposes, provide sufficient torsional restraint to have a significant effect upon

effective length of columns. Flybracing to columns is often overlooked, (especially

where the knee moment is the governing moment), and is often necessary. Crane

support beams, where they are supported off brackets on the columns provide

torsional restraint to the column if they are positively restrained against longitudinal

movement.




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Note that column moments usually decrease from a maximum at the top (use the

moment at the underside of the haunch) to zero at the bottom (pin base) and may

even reverse on the way down if lateral wind loads are acting. This has a significant

effect on the lateral torsional buckling capacity. Major and minor axis axial buckling

must also be considered since either can govern in combination with lateral torsional

buckling.

7.8.4. Columns

Central columns may be considered to be “sidesway prevented”.

Be aware of minimum design eccentricities and moments created by beam

connection details required under AS 4100.

7.8.5. End Wall Mullions

Two cases can occur:

• Future expansion is envisaged. All frames, including the end ones, are the

same moment resisting portals. End wall mullions are connected to the rafters

with vertically slotted holes of the appropriate length. No uplifts occur on the

columns which can be supported on slab thickenings.

• Future expansion is not envisaged. The end frame is a braced column/rafter

system. The end wall mullions receive uplift. This system may be no cheaper

than the case above. The end wall may be masonry, concrete or sheeted.

Check relative lateral deflections of portals and end frame, particularly if the end frame

is braced. Braced end frames with roof bracing back to the first portal will attract 1.5 -

2.0 times the “design” load which must be recognised in the design of the end wall

bracing.

7.8.6. Flybraces

Flybraces can take a variety of forms. Double angle, single angle and double strap

types have been used. The single angle type is normally the most economic. 38 x 38

x 3 L bracing is the smallest that should be used to accommodate a 12mm bolt. The




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lower purlin lap bolt hole can be used to connect the flybracing. Check the purlin for

this force in conjunction with its full design load to create worst scenario.

For beams and columns bigger than 410 UB provide a fly brace at the following

locations:

(a) Knee of portal frame.

(b) Ridge of portal frame.

(c) At regular intervals along the member to satisfy the assumed effective length.

7.8.7. Connections

(a) General

Opinion varies amongst designers and fabricators as to which knee joint detail

is the most economical in conjunction with the rafter splices. Where possible

confer with the known fabricator to determine the cheapest details.

Use Connell Wagner standard details in the absence of a known fabricator.

Connections should be designed, wherever possible, using AISC Standardised

Connections and Connell Wagner design aide. The terminology used in this

publication should always be used.

AISC standardised connections have been developed for the total industry

including designers, shop detailers and fabricators. Engineering design

drawings need only convey the essential strength characteristic of the

connections, e.g. size of component parts, number of bolts, etc. Bolts,

centres, coping sizes, etc. need not be shown, although of course, they must

be taken into account in the design.

Connections are critical components in the overall strength of structural

steelwork so a conservative approach is recommended. Full strength butt

welds are very expensive and their use should be minimised. Adopt partial

penetration butt welds instead wherever possible.

(b) Notes on Connections




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1. Wherever possible, use simple repetitive connections.

2. Dimension of all plants, bolts and spacings. Do not leave it to the shop

drawer to guess what you intended.

3. Web side plate connections are the simplest, allow easy erection for

small sections and provide a small length tolerance. If the supporting

member is not free to rotate (e.g. restrained by an adjacent beam on the

opposite side of the web) fixity moments develop which can overstress

the components.

4. Angle cleat connections are simple, provide some rotational freedom (i.e.

component parts are not overstressed by fixity moments), and can be

used each side of the same web. They are recommended for beam to

beam connections for heavy sections.

5. Angle seat and shear plate connections give excellent length tolerance

and are easy to erect. Top restraining cleats should be detailed to permit

end rotation of the supported beam. They are recommended for beam to

column connection for heavy sections.

6. Flexible end plate connections cannot be used on both sides of the same

web. Beams cannot be independently erected.

7. Flexible end plate connections cannot be used on both ends of the same

beam when the supporting members cannot be spread during erection.

This is the normal situation.

8. Flexible end plate connections do not provide any length tolerance.

Consideration should be given to the use of shim plates.

9. Flexible end plate connections provide some rotational freedom and give

good torsional restraint to the supporting member.




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10. Steelwork to insitu concrete connections requires large erection

tolerances.

Generally, use cast-in weld plates with suitable shear connections (flash

butt welded studs or reinforcement bar) and site welded shear plate or

angle cleat connections. Ensure that the connection provides end

rotational freedom. Always specify the erection tolerances and non-

destructive testing for site welds.

(c) Bolted Joints

1. Design on the basis of threads included in the shear plane.

Standard bolt is to be M20 - 8.8 N/S. The "N" signifies threads in the shear

plane.

2. Standard pitch 70mm

Standard edge distance 35mm

3. Commercial and high strength bolts used for structural work are available

in sizes M12, M16, M20, M24, M30 and M36. (M12 may not be available in

grade 8.8).

M12 - normally used for purlins and girts

M16 - minor steelwork, lightly loaded

M20, M24 - general structural connections, holding down bolts

M30, M36 - holding down bolts

4. Usage

• Use 8.8/TF bolts, only where a non-slip condition is required, e.g. a

cantilever moment connection or portal rafter connection using bolted

flange plates. TF bolts over M24 are very difficult if not impossible to

tensions.




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• Avoid the use of tensioned and untensioned high strength bolts, e.g.

8.8/S and 8.8/TF on the same project because it is hard to clearly

determine on site which bolts are to be tensioned and which bolts are

not to be tensioned.

• Pay careful attention to specification items regarding the non-painting

of plate interfaces with 8.8/TF bolts. (Note: inorganic zinc silicate

paint over a class 2½ preparation is acceptable on faying surfaces).

• 8.8/TF bolts are recommended to be used with Coronet load indicator

washers with no specified clearances. Normally, 0.40mm is used on

site, but lesser clearances may be required in particular locations, i.e.

when exposed to weather or moisture.

• Specify all bolts to be coated with some protection. Coating systems

available are galvanised, zinc plated, cadmium plated, chromium

plated and head/tin plated. The Ajax fasteners handbook provides

further guidance.

(d) Column Bases

Design

Refer to [4].

Design portal frame column bases usually as pin ended.

If lateral deflections are a problem provide fixity to the column base.

Compare deflections for pinned and fully fixed base and decide what

degree of fixity will be used for serviceability case only.

Design the footings for the selected column base moment and vertical and

horizontal reactions. Be aware that a small footing rotation may totally

relieve the portal base moment.




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Fixed column bases should not be considered where the foundation

bearing capacity is less than 400 kPa, as the footing must be prevented

from rotating and releasing the column moment. Be aware that soil creep

can occur, even in stiff clay.

Base Plates

Use a minimum thickness of 16mm for portal frames. For small columns

door frames and the like. 1.0 mm plates may suffice.

Bolt edge distance (minimum) is to be 1.6 x bolt diameter.

Base plate widths are to match standard plate widths where possible.

Holding Down Bolts

Use a minimum of 4 bolts for columns in portal frames or larger structures

so that they can free stand during erection. Use adjusting nut and washer

under the plate in certain circumstances. Allow adequate clearance under

the base plate for nut adjustment e.g. 50mm.

Design bolts for combined shear plus axial tension. Do not consider bolt

in bending.

For particularly large shear forces a shear key may be required.

(e) Welding

Welding is widely used in portal frame fabrication, and may be classified into

the categories of general purpose welding (GP) (not highly stressed) and

special or structural purpose welding (SP). SP welds require testing (usually

non-destructive) in accordance with the welding code. SP welds are normally

used and designers should ensure that appropriate notes are incorporated on

drawings and specifications.




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The welding code requires that the exact extent of non-destructive testing

(usually ultrasonic for fillet welds) be specified (e.g. 50% of length of 100% of

the welds, 100% of length of 50% of the welds etc.). This information must be

shown on the drawings. A specialist welding inspector should be employed by

the Company for major works.

It is highly recommended that all designers attend “handyman” welding

courses. This is the only effective way of gaining a real perspective on the

limitations and difficulties inherent in welding.

(f) Weld Testing

Welding shall comply with AS 1554.1, AS 1554.2 or AS 1554.5 as appropriate,

in accordance with AS 4100, clause 9.7.

Whilst methods of testing of welds are covered in AS 1554, the extent of

testing is left to the discretion of the engineer.

The weld category and type and extent of testing must be shown on the

drawings (AS 1554.1, Clauses 3.1.3, 7.4.1). Testing is dependent on the

category of weld required (GP or SP).

For guidance on the extent of testing required, refer to the following code

provisions:

AS 1554.1 - Clause 1.6 Weld Categories

- Section 6 Quality of Welds

- Section 7 Inspection

Appendix A Selection of Weld Category

Appendix F Suggested Extent of Non-Destruction Examination

AS 4100 - Clause 11.1.5 Designation of Weld Category (For Fatigue)

- Clause 13.8.2 (c) Requirement for Seismic Zone 1




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It is recommended that for major structural projects, the provision of AS 4100,

Clause 13.8.2 (c) is adhered to, irrespective of the Seismic Zone applicable.

All principle site welds should be non-destructively examined.

All butt welds must be tested.

Testing should be carried out by an independent approved NATA testing

authority. We are not welding experts and most experienced engineers would

not know a satisfactory weld by visual inspection.

If weld testing is required, it should be discussed (before tender) with the

testing authority to obtain their comments on the extent of testing, type of weld

testing, weldability of details, etc. This must then be specified with technical

details and the cost of testing allowed for, either as a PC sum or a cost to be

borne by the Contractor and/or steel fabricator.

The weld testing specification should include actual joint samples which should

be prepared and tested before fabrication commences. The welding inspector

should also visit the fabrication shop and inspect all welding on a regular basis

as part of their testing procedures.

7.8.8. Bracing

Frames are normally braced against longitudinal racking by roof and wall bracing. If

reinforced masonry or precast concrete (often tilt-up) walls are used, the portal frames

may be tied to these for longitudinal stability. Light wall bracing is still needed for

stability during erection and will usually be sized by the fabricator/erector. Extra loads

on the columns in the braced bay, and its supported footings, are induced by wall

bracing. Footing sizes normally increase in the braced bay. Column sizes should be

checked as extra column flybracing may be required.

Rods can be difficult to erect and require adjustment. Sag should be prevented by

hook bolts attached to purlins.

Use equal angles (or CHS for larger spans and forces).




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Design angles to buckle about X-X axis not V-V.

The effect of self weight moment on axial capacity is significant. Refer [4].

Check effect of sag on axial capacity if sag is greater than length divided by 200.

Connect as per Connell Wagner standard detail.

7.8.9. Roof Bracing

Roof bracing may be cross bracing (diagonal members usually rods or angles

designed for tension only), or a trussed system (diagonal members, usually tubes, to

take compression/tension). Except for small structures where purlins may provide

this strut action, provide property designed struts. Refer to Section 6.5.2 (g).

Bracing of internal bays requires running struts in the roof to the end walls unless the

purlins can take the axial load. (As a general rule, end bays should be braced to

facilitate erection). In portal systems this can provide problems of differential lateral

drift due to the end bays high stiffness.

Rod cross bracing should be avoided in all but small buildings since the preload to

minimise sag is impossible to monitor and can overstress the compression struts.

The bracing plane should be carefully chosen to avoid conflicts between the bracing

and purlins, flybracing etc. Mid-height of rafters is common.

Use purlins as struts in other bays to carry load into braced bay. Check the purlin

capacity for combined axial and bending loads if purlins are to carry end wall forces.

End wall rafters will distribute concentrated mullion load into 2 or 3 purlins by

transverse bending if required.

Use compression (not cross) bracing configuration as this may be the most cost

efficient in materials and ease of erection.

Eccentricity exists between the top of end wall columns and the level of the roof

bracing. If the eccentricity and/or loads are large, thought needs to be given at the




26 of 29

early design stages to how the load gets from the column connection to the roof

bracing. Roof bracing cleats are often large since this connection needs to

accommodate small eccentricities of the centre lines of the bracing numbers.

Connections which rely on web shear and bending to transfer bracing loads will not

work for significant loads. Particular care is required to transfer roof bracing loads into

the wall bracing without relying on web bending in the frame rafters. Economic end

connections for tubes are based on research carried out by Kitipornchai [4].

(Note that stressed skin bracing design is still not widely used and is not acceptable to

many local authorities and is difficult and expensive to detail. Normal roof sheeting

practice is not stressed skin bracing).

7.8.10.Wall Bracing

The connection of wall bracing to the web of the column using a vertical cleat plate will

usually overstress the column web in bending unless it is encased in concrete.

Alternately at the base, the bracing cleat can be welded to the baseplate and the

column web. The baseplate will prevent the column web bending.

Masonry/Concrete Walls

Reinforced concrete blockwork is often used to form the walls and may obviate the

need for wall bracing. Concrete walls will usually be precast, and may be either

factory precast or site tilt-up. Masonry walls parallel to portal frames attract

significantly higher lateral forces due to the relatively large stiffness. Take care with

connection details. These walls will usually require lateral restraint at the top from a

wind beam (channel or I beam with web horizontal). The walls must be positively fixed

to the wind beams, preferably with expanding anchors, to provide restraint to the walls,

and also to provide longitudinal restraint to the building.

Be aware that chemical anchors will fail in a fire situation. Ensure that there is

adequate connectivity to guarantee stability in a fire - refer to Precast Concrete section

- refer Building Code of Australia for requirements.

Expansion Joints




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Generally for “shed” type buildings consider use of an expansion joint if the building

length exceeds 100m.

For other types of building consider the effect of thermal movements on attached

architectural or rigid elements.

7.8.11.Temperature Range

When calculating thermal movements in purlins use:-

a) No insulation - temperature range 50°C.

b) insulated - seek advice on likely effect of insulation.

7.8.12.Footings

Fixed base portals should only be adopted where bored piers (or double piles of small

diameter with a pile cap) or similar deep foundations are adopted, since these can

more easily resist overturning loads than high level (pad) footings. Raft slabs are an

exception to this case, but are not often used in portal frame buildings. Heavy

concrete substructures, where required for other reasons, can be useful for fixing

portal bases.

Fixing portal bases will not reduce bending moments as significantly as they will

reduce deflections. Thus superstructure material savings may be outweighed by extra

footing costs, unless deflection is critical. Apart from difficulties with overturning loads

on footings, very thick base plates and (often) high strength holding down bolts are

required.

Uplift Loads

Care should be taken where the difference between wind uplift and dead load is small,

since small increases in wind load, or decreases in dead load, can produce significant

changes in calculated uplift.




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Pad Footings

The contribution of slab, wall and soil over the pad footing to hold down should be

included. The use of a 1m to 2m wide strip around the edge of the footing is common

depending on slab jointing pattern. If internal pressure contributes to the uplift, then the

internal pressure acting on the area of slab contributing to the hold down can be

utilised. This may be small but helpful. If uplift is important, top reinforcement in pad

footings is necessary.

Bored Piers

Section 5.8.6 sets out methods of designing bored piers for uplift and bending

moments. A pile cap is desirable to allow accurate location of the holding down bolts.

Casting HD bolts into bored piers is often not successful due to the difficulty in

controlling their final location.

Holding Down Bolts

Gorenc et al set out a detailed method of design for holding down bolts. Points to note

are:

• HD bolts must be embedded far enough to lap with reinforcement in the footing, if

the bolts are straight. If U bars, or bolts with anchor plates are used, then it is

sufficient to ensure that the footing reinforcement is anchored and the bolts are

sufficiently embedded such that a cone of concrete around the bolts cannot pull

out, since bond failure is no longer relevant.

• Sleeves around bolts are desirable to provide lateral adjustment.

• Avoid using high strength (Wade 8.8) steel for HD bolts, as they are often welded

into cages for accurate placement.

• Holding down bolts should always be galvanised as they cannot be replaced except

with great difficulty.

Horizontal Resistance




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For large spans, check the ability of footings to develop the horizontal resistance at

base of columns. If necessary, provide tie bar into floor slab or between opposite

footings under the slab.

7.9. Other Structural Forms

There are several specialised structural forms of which we should be aware.

Invariably these will require some degree of expert input and/or reference to

specialised literature and proprietary product information.

7.9.1. Space Frames

These tend to be 3 dimensional assemblies of struts and ties. In their simplest form

they may be a "flat plate" which gains economies by spanning in 2 directions. They

may extend to single or double layer shells, arches and domes.

Usually these structures are made by the use of proprietary systems, such as

Octalok, Mero and Harley.

7.9.2. Cable Structures

These structures have the ability to create very lightweight structural forms. They tend

to have large deflections than other structures and this must be considered in their

design. Structural response may be significantly non linear and special analysis

techniques may be required. In addition, the nature of the structure may lead to the

development of usual wind loads. The need for a wind tunnel study should be

considered.

Reference should be made to the Connell Wagner Technical Report "Cable

Structures", June 1996, a copy of which is contained in Appendix B.

7.9.3. Masts and Lattice Towers

Masts, flagpoles, lattice towers and chimneys require special consideration of their

dynamic response under wind loads. Excessive dynamic response can occur under




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very light winds. This can lead to fatigue problems. With such structures specialist

advice should be sought from a wind/dynamics expert.

Guidelines for the design of such structures are given in BS8100 Part 1, 1986, Lattice

Towers and Masts and "Wind Forces on Tubular Structures - Design Manual",

Tubemakers of Australia, August, 1987. Further guidance is also provided in AS1170 :

Wind Loads.

7.9.4. Cold Formed Steel

Cold-formed steel (<3mm thick) is used in a number of applications, most commonly

in roof and wall systems of industrial and commercial buildings, as structural

members for plane and space trusses, in domestic wall framing, and as steel decking

for composite construction. The use of thinner material in these sections, as well as

the residual stresses developed by the cold-forming processes, lead the sections to

behave differently than hot rolled members used in standard steel design. In

particular, the cold-formed sections are susceptible to local and distortional buckling,

twisting and web crippling. The cold-work involved in forming the sections may

produce a marked increase in the material strength, along with a reduction in material

ductility. The Cold-Formed Steel Structures Code, AS/NZS 4600/1996, takes into

account these factors and allows both the increase in material strength and the post

buckling capacity of the section to be utilised. A good aid in the design of cold-formed

structures is "Design of Cold-Formed Structures", 2nd Edition, by Gregory Hancock.

The current addition is based on AS1538-1988 but does include comment on the

procedures included in the updated code.

7.9.5. Painting of Steelwork Not Completed

7.9.6. Erection of Steelwork Not Completed


Doc Ref: P:\9660\08\Design Guideline\Section 8 to 11


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8. +COMPOSITE DESIGN

8.1. Introduction

Composite construction usually consists of the use of concrete and steel bonded

together to produce a combined section. Examples are steel beams bonded to the

slab over with shear connectors, slabs cast onto profiled steel sheeting which acts as

the formwork then becomes bottom reinforcement once the concrete has set, and

columns with either steel sections cast into the centre or steel tubes which are

concrete filled.

8.2. Codes

Steel Beams:AS2327.1 covers simply supported beams. The Standards Australia

committee intends to release AS2327.2 to cover continuous members in around 1999

(Mark Sheldon of CW Melbourne office is on this committee).

Slabs:Currently no Australian Standard exists for the design of composite slabs.

Detailing requirements occur in AS2327.1 regarding spacing of shear connections to

suit ribs etc. Similarly, AS1365 and AS1397 cover material requirements for the metal

decking. The three most commonly available proprietary decks conform to these

requirements. An Australia Standard AS2327.3 is proposed to be published in around

1999, and until its publication the use of proprietary design guides is recommended.

Columns:An Australian Standard AS2327.4 is proposed to be published, although the

timing of this is unknown.

8.3. References

Numerous reference papers have been published by BHP Research - look under Mark

Patrick,, Ken Watson and/or Daya Dayawansa in the library. A Handbook HB91-1997

has been published by Standards Australia as well as a computer program

"COMPBEAM" for the design of composite beams (refer section 8.5.1 below).

Connell Wagner published a design manual in 1992 titled, "Composite Concrete Filled

Steel Tubes".




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Connell Wagner and the University of Sydney prepared a report in 1986 titled "Victoria

Central Project - Composite Columns".


None.

8.5. Steel Beams

A new code AS 2327.1 was released by Standards Australia in November 1996. At

the time of preparing this technical manual, Connell Wagner staff will be making the

transition from AS 2321 Part 1-1980, and given the magnitude of the changes between

the new and old codes, extra detail has been included in this manual. The main

changes are:

• Converted to limit - state format consistent with AS 3600 and AS 4100.

• Adoption of concept of partial shear connection, potentially allowing less shear

studs.

• Applicable for more types of steel sections.

• Definition of staged construction loads to be designed for.

• Generally a nett increase in the design load carrying capacity of a composite beam,

with potential reduction in shear studs and transverse reinforcement.

The code provides a simplified design procedure which is similar to the old code and

generally gives a 5-10% saving in the steel beam weight, but with similar shear stud

and transverse reinforcement requirements. This is applicable for uniform loads only.

Savings in shear studs and transverse reinforcement can be made by using the more

detailed design procedure.

8.5.1. Composite Program - "COMPBEAM"

"Compbeam" is computer software developed by BHP Research for the design of

simply supported composite beams to AS2327.1 - 1996. It uses the general design

procedure and utilises “Partial Shear Connection” to minimise shear stud and

tranverse reinforcement requirements.




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This program requires the user to input the following variables:

• trial steel section (UB, UC, etc)

• profile steel sheeting type

• concrete details

• loads

Hardware and software requirements to run Compbeam are as follows:

• IBM compatible PC (with 3.5" drive)

• Microsoft Excel V4, V5 or V7.

• Printer which can be accessed by Windows Print Manager

This program supersedes CW program "COMPOSITE" which was written to AS2327-

1980.

8.5.2. Dynamics

The trend towards longer span lightweight floor systems (ie. composite floors) has led

to potential dynamic problems.

Composite beam floors tend to be:

• lighter

• lower frequency

• less effective natural damping

Some simple guidelines are outlined below:

Frequency

ACTIVITY f < 5Hz 5Hz < f < 10Hz

f > 10Hz

Normal activities (office, retail) Potential problem

Typically not a concern

Satisfactory

Repetitive activities (aerobics dancing)

Problem!! Potential problem

Typically not a concern

A simple method of determining the approximate frequency of a composite beam is

given by:




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18y0

(y0 = dead load deflection in "mm"). The frequency of the whole floor system can be

worked out by:

1

( f )= (

1f

)t

2 2el

∑

where ft = total frequency

and fel = individual element frequencies (slab, secondary beam,

primary beam etc)

8.5.3. Composite Beam Deflections

The simplified method should be used to determine deflections (section 7.0 -

AS2327.1). This is applicable when the stresses in the steel beam (bottom flange) do

not exceed 0.9fsy. Suggested limits for calculated deflections are outlined in Appendix

C AS2327.1, which are effectively identical to those in AS 3600.

If the beam soffit is not exposed, then unpropped construction deflections do not need

to be included. Conversely, if the soffit is exposed this deflection needs to be included,

otherwise the steel beam should be precambered.

8.6. Slabs

Bondek permanent lost formwork was introduced in the 1970's by Lysaghts. Condeck

became available in the mid 1980's. Conform is manufactured by Woodroofe and is

less widely distributed but with very similar properties and span tables to Condeck.

All Manufacturer's (BHP for Bondek, KH Stramit for Condeck & Woodroofe for

Conform) have produced technical design manuals for their product.

Generally the products can be interchanged subject to an appropriate design check,

however when supported by composite steel beams, take care that detailing for the

steel connectors and transverse reinforcement is not affected. Note that AS 2327.1

allows only 1 shear connector (or pair of studs) per deck tray. Based on the current




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profiles, this means for Bondek the minimum spacing is 200mm, whilst for Condeck

and Conform the minimum spacing is 300mm. Note also that for a 120mm slab, the

maximum spacing is 480mm, which in practical terms means 400mm for Bondek

slabs and 300mm for Condeck and Conform.

Care should be taken to ensure that deflection of the profiled steel sheeting under wet

concrete loads is visually acceptable. Deflections up to span/130 are permitted by AS

2327.1.

In plane shrinkage of a composite slab tends to be less than for a reinforced concrete

slab. When considering movement joints, a reduced shrinkage strain of 300

microstrain may be appropriate when estimating joint movements.

Particular care needs to be taken when using profiled steel sheeting for slabs

subjected to wheel or point loads. The reduced depth of slab above the sheeting rib

will substantially reduce the ability of the slab to distribute the load transversley across

the slab. The width of slab supporting the point load may only be the width between the

sheeting ribs.

8.6.1. Design Method

• Establish design loads, fire rating, concrete strength.

• Select slab size using the latest appropriate technical design manual and beam

spacings to suit building grid (generally spans should be around 2.5 - 3.0m for

unpropped construction). Typically a thickness of approximately 120mm is

adopted.

• Check minimum thickness of slabs for fire rating.

It is generally more economic to use the heavier sheeting with no propping than lighter

decking with propping.

Connell Wagner employees not familiar with the products should perform at least one

manual computation to assist with identifying the critical issues. Examples are given




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in the Bondek Manual. Similarly, designs which include irregular spans or loads

should be completed by hand. This will include:

• Check panels under construction load including wet concrete.

• Check the composite slab midspan bending capacities.

• Check the composite slab bond stress at the interface at the support.

• Analyse continuous slabs using elastic analysis to determine negative moments.

Provide main reinforcement in accordance with limit state design with secondary

reinforcement all in accordance with AS3600. (For unpropped construction the

weight of sheeting and concrete should be ignored in determining negative

moments for reinforcement design as this weight is supported by the sheeting

alone). Positive and negative reinforcement can be checked for the fire case in

accordance with AS3600 where self weight will be supported by the reinforcement.

However Bondek has a different approach to fire design (based on extensive

testing) which utilises plastic design, refer their design manual.

• Provide top reinforcement to simply supported slabs in accordance with AS3600.

It may be necessary to provide additional top reinforcement at mid-span due to

exposure or possible cracking, etc - refer to the Project Leader for direction.

Problems can be experienced with the use of fabric as top slab reinforcement over the

beams. During the initial fabric placing, it is often forced down over the shear studs

and under their heads and it cannot always be retrieved, unless the wire is bent or cut.

Shear studs should be specified as being fixed on a deck tray module, ie, 200, 300,

etc, and will thus always match the fabric.

Where we have a beam to beam connection and fabric is side lapped in thin slabs,

you can obtain up to 6 layers of fabric in one location and keyed joints in slabs are

often impossible.

It is possible to detail the top reinforcement over the secondary beam as stopped off

when it meets the top reinforcement of the main beam.

Care should also be taken to provide adequate bar chairs to ensure the top steel is not

pressed down over the studs.




7 of 9

8.7. Columns

A detailed study of various available design methods by Connell Wagner revealed that

the Eurocode - 4 is the only available document covering all aspects of composite

design of a symmetrical column section with codified limits. Our design methods are

based on Eurocode - 4 with additional Australian material and load factor

requirements. Australian requirements have been modelled after close consultation

with Associate Professor Russell Bridge of the School of Civil and Mining Engineering,

University of Sydney.

8.7.1. Composite Column - Design Method for Concrete Encased Steel Sections

Load Factors

Load factors to be used are 1.25 for dead load (G), 1.50 for live load (Q) and 1.5 for

wind load (Wu) to comply with AS3600.

Strength limit state load N* = 1.25G + 1.5Q

Squash Load and Ø Factor

Squash Load:

Nsq = 0.6 f'c Ac + As Fsy + 0.9 Ar Fry

Where c, s and r represent concrete, structural steel and reinforcement respectively.

Instead of partial safety factors proposed by Eurocode 4, a ∅ reduction factor of 0.85

was used to comply with AS3600 and

Npe = 0.85 (0.6 f'c Ac + As Fsy + 0.9 Ar Fry)

This is more conservative than Eurocode.

Slenderness and Minimum Eccentricity




8 of 9

Equivalent flexural stiffness of column.

(El)e = EcIc + EsIs + ErIr

Elastic critical load for the effective length, le

cr2

e2N = (EI ) / leπ

Relative slenderness:-

λ = (0.85 N / N )1/ 2sq cr

(Note: Flexural stiffness could be adjusted for the influence of long term loading based

on 8).

A further reduction coefficient "x" for slenderness based on buckling curve for the

particular steel column shape will account for the slenderness of the column.

Second order effects of bending moments are neglected when 8 < 0.2. In such a

condition, only local bending moments at the end of the columns are accounted for

using an appropriate interaction curve.

Interaction Curve for Bending and Axial Force

For the section which is symmetrical about both principal axes and using a

rectangular stress block for concrete, steel and reinforcement under plastic analysis,

a simple trilinear curve can be drawn to represent the interaction curve. The polygonal

trilinear curves could be drawn for both single axial and biaxial bendings based on the

Eurocode method with the ∅ factor of 0.85 introduced for both steel and concrete.

Limitations

a) The relative slenderness takes into account any steel imperfections and no

additional allowance is required.

b) Centres of areas of the steel section and the uncracked concrete section are

assumed to be coincident but this should be checked for large bending

moments.




9 of 9

c) The uncracked composite section is assumed to be symmetrical about both

principal axes.

d) Yield strength of steel to be less than 450MPa. For structural steel plates over

80mm, 330MPa is used as the steel yield strength, to comply with AS1250.

e) For rectangular hollow sections D/T < 52 (235/Fy)1/2.

f) Minimum cover to encased steel to be 40mm or one sixth of flange width.

g) To comply with the appropriate steel buckling curve, the load carried by the

steel in compression is to be between 20% and 90% of the overall

compressive strength.

h) When 8 <0.2 with any transverse loads and when 0.2 < 8 < 2.0 without any

transverse loads bending moments may be calculated ignoring second order

effects.

i) Minimum reinforcement (in addition to the steel section) to be 1% of the

concrete area.

Longitudinal Shear

Under the design ultimate loading, if the shear stress in the steel/concrete interface is

less than 0.6MPa for concrete encased columns and 0.4MPa for concrete filled tubes,

no shear connectors are required. Most of the load at all levels of the columns is

expected to be applied direct to the steel and these stress limitations are maintained to

establish the load paths for transfer of load between steel and concrete. When steel

beams frame into the steel columns, the total transfer stress must be checked for the

upper limit.

Elastic Shortening, Creep and Shrinkage

In-service behaviour of all elements is analysed to consider effects of these three

actions on the stresses. Using established modular ratios, shrinkage coefficients and

creep function and equating strains, the initial and final stresses of steel (including




10 of 9

long-term shedded load due to concrete creep) are calculated and checked for a

factor of safety more than one.

A maximum elastic deflection of 0.7mm/m length and final total shortening 1.0mm/m

length of column is possible under the considered load for a short column with the

steel core carrying 70% of the squash load.

Concrete

Nominal shear connectors are provided to retain the concrete adjacent to the flange.

These have been designed to withstand a tension load of 2.5% of the load in the

concrete adjacent to the flange.

8.7.2. Concrete Filled Steel Tube Colunns

Refer to the Design Manual published by Connell Wagner in 1992 for the design of such columns.




9. MASONRY

9.1. Introduction

This section gives the broad principles that should be followed for design of masonry

elements. It is not intended to be a comprehensive masonry manual, since the

subject is covered in detail in the references and selected texts.

Masonry is a very versatile material and can take many forms, shapes, appearances

and colour. It is one of the oldest man made building materials and has been around

for thousands of years. Masonry includes clay bricks and concrete blocks and bricks

but not stone which is covered elsewhere in this manual. Masonry can be cladding

elements, load-bearing elements, diaphragm walls, solid, veneer, and cavity walls,

piers and columns, facing panels, nonstructural elements, retaining walls etc

Masonry can be used to carry vertical loads as it has good compressive capacities. It

is often used in low rise buildings as load bearing walls. Unfortunately masonry is a

brittle material with low bending capacity unless it is reinforced. There is a common

perception that because masonry is a robust and solid looking material that it is

strong. This is a fallacy when loads causing bending are applied to masonry.

Generally masonry will span better horizontal than vertically. Masonry is often used as

walls on the outside of the building to provide an attractive aesthetic finish and to

provide the primary protection against weather. These masonry walls do not normally

serve any structural function. Nevertheless, they are structural elements in that they

resist wind and earthquake loads once built, and must be restrained safely.

Unfortunately in these days of tight competitive fees, fast track projects and

minimisation of documentation, responsibility in this design area is not understood by

most designers. Do not assume bricklayers have detailed knowledge of architectural

and structural design and can make the designs perform as required. Many designers,

engineers and architects are not recognising the proper design requirements of

masonry and how it should work.

Designers are often providing inadequate or sometimes, no lateral support to masonry

walls. They are attempting to have the wall panels span large distances without proper

structural consideration. Gable ends and parapets are particularly vulnerable

elements under lateral loads. The water proofing details of control joints are




sometimes not adequate. While the architect is responsible for water proofing the

joints, we must discuss each type of joint with them and make them aware of their

responsibilities. The role of silicone sealant has been assumed to be a 'wonder'

material, never needing replacement.

Masonry is an excellent material when it is documented correctly and built properly.

9.2. Codes

AS 1225 Clay Building Bricks

AS 1653 Calcium Silicate Building Bricks

AS 2699 Wall Ties for Masonry Construction

AS 2733 Concrete Masonry Units

AS 3700 SAA Masonry Code

AS 3700 Supp 1 - SAA Masonry Code - Commentary

9.3. References

1 Masonry Code of Practice - by PWD and ACEA (NSW) - 1984.

2 Monier Masonry Manual.

3 Australian Concrete Masonry CMA Volumes 1 - 2 1976.

4 A Practical Guide to Design CMA of Australia - 1992.

5 Australian Masonry Manual Baker, Lawrence and Page - 1991.

6 Structural/Masonry Designer Manual by Curtin Shaw, Beck and Bray - 1982.

7 Concrete Masonry Buildings- A Practical Guide to Design CMA - 1992.


A95/2 Design of Masonry

9.5. Responsibility

9.5.1. General

The responsibility for masonry design is a very vexed area especially for nonstructural

masonry elements such as internal walls, cladding wall, non-load bearing walls and

the like. If masonry is load bearing, then obviously we are responsible for the design

but for cladding and nonstructural brickwork what is our responsibility? If the wall is




subject to lateral loads such as wind, earthquake or other such loads then someone

should design it. Often they are GUESSED - THIS IS NOT GOOD ENOUGH.

We should, during our fee submissions, make quite clear what we believe our role and

responsibilities are. Too often Architects and others “assume responsibility” for

masonry but expect that the structural engineer will design it, especially for lateral

loads including wind and earthquake (often for no fee).

Our role can be:

• no design (dangerous)

• design advice in regard to wind loads, earthquakes with specification and drafting

by the Architect, and performance design by others (this requires checking of our

input).

• design and documentation including specification (the preferred approach if you

can be paid for it)

In the era of competitive fees, we need to clearly define what we have allowed for and

ensure that our competitors also allow for this. This matter is all about Risk

Management.

9.5.2. Design/Documentation

The actual design process of masonry is often poorly done and not well understood by

many structural engineers. It can involve seven basic processes, typically as for the

design of most structural elements. It also means preparation of calculations and

checking of drawings and specifications.

1. Calculation of all design loads including vertical and lateral loads including:

• dead and live loads.

• wind loads.

• earthquake loads.

• construction loads.

• other loads




2. Checking of the masonry element for the applied loads as per CI 4.3 of AS

3700 including:

• bending moments

• axial forces

• shear forces

• others actions

3. Designing of connections of masonry to the structure, ie. checking of the ties

with lateral loads (often nonexistent in poorly detailed structures).

4. Checking structure or other masonry elements for the applied loads from the

masonry including wind and earthquake (often nonexistent), ie. is the structure

capable of resisting the load applied to it?

5. Writing the specification for the masonry or checking the one written by the

Architect for structural content including lintels, control joints, characteristic

unconfined compressive strength, mortar type and allowable additives, etc.

6. Drafting of the structural details or checking the details on the Architectural

drawings where we have had input so that our design assumptions are

correctly interpreted.

7. Checking of our design (Quality Control).

In addition to the above, it is necessary to check the following items:

• Durability (reinforcement covers, tie selection)

• Robustness

• Fire resistance

• Control joint spacings

• Other requirements of AS 3700

Other items requiring consideration can include thermal and sound resistance and

prevention of moisture ingress. These are generally considered by the Architect.




9.5.3. Inspections

Routine site inspections by us should include checking of the masonry construction.

9.6. Loadings

9.6.1. Wind Loads

These are calculated in accordance with AS 1170.2. Often, internal walls are

designed for a nominal lateral load. These should be designed for a minimum ultimate

wind load of 0.4 kPa, or for other higher loads depending on the conditions.

In the case of air shafts and air plenums, the pressure or suction needs to be

obtained from the mechanical engineer. These loads can be several kPa. We are

aware of a number of cases where this pressure has caused failure of masonry walls

[Refer also Technical Note M95/14].

9.6.2. Earthquake Loads

These are calculated in accordance with AS 1170.4.

9.6.3. Vertical Loads

Masonry walls which need to be designed for vertical loads should be designed in

accordance with AS 3700.

9.6.4. Load Combinations

The load combinations for strength design are as specified in AS 1170.1, however the

earthquake combinations of AS 1170.4 take precedence over these in AS 1170.1. The

load combination which controls the design of a cross section in flexure may differ

from that which controls for axial compression or shear.

When considering overall stability, the loads tending to cause instability are factored

with the appropriate load factors whilst the design resistance effect shall be calculated

from 0.8 times the components of the unfactored loads tending to resist instability.

For example, when considering the stability of a cantilever retaining wall:

(a) Loads tending to cause instability




- Active earth pressure (Fep)

Use Factored Load......................1.5 Fep

(b) Loads resisting instability

- Dead Load of wall and footing plus

soil on heel (G)

Use Unfactored Load x 0.8........0.8G

(c) The resulting factor of safety against overturning

= 1.5 = 1.87

0.8

9.7. Design Details

9.7.1. Design of Control Joints

Control joints in masonry are provided for a number of purposes. These include

prevention of damage due to differential foundation movement, deflections in

supporting elements, shrinkage, axial shortening, growth, thermal movements, creep

or a combination of these. Cracked masonry is a very common problem and is often

the result of inadequate consideration of these items.

Designers should keep in mind that all burnt clay products including clay bricks have

a property known as “brick growth” (which is due to moisture absorption). It is real and

a significant problem where bricks expand or “grow”. It is often seen as vertical cracks

in walls where restraint is provided vertically. Unrestrained brick growth of up to

1mm/m is common and if brickwork is restrained it can shear off the restraints or

buckle the masonry element. It is one of the most common problems when inspecting

buildings where problems are reported with the masonry.

Calcium silicate bricks and concrete masonry units shrink with time.

Control joints break the continuity of the masonry and careful consideration must be

given to their spacing and their effect on not only the structural performance of the

elements but aesthetics and architectural matters.

Vertical control joints should be located at:




• major changes in wall height

• changes in wall thickness

• at large openings in walls

• near wall junctions

• near corners

The spacing of vertical control joints in long walls is dictated by many factors. For

example spacing may depend on whether the wall is reinforced or unreinforced,

exposed to weather or internal, supported on flexible slabs or beams and whether the

structure is supported on reactive or non-reactive foundation material. AS 3700 gives

no recommended spacing, however experience suggests that spacings should

generally not exceed 8-10m, with a preference for a spacing of around 6-8 metres.

Vertical control joints can be used to aid articulation of a wall supported on suspended

structure. Indeed, this technique should be used when there are incremental

deflections greater than Span/1000. The best locations for these joints are at the

points of maximum curvature, ie. midspan and over the supports. Panel sizes and

shapes should be examined to ensure that each element is capable of following the

floor deflection without creating local overstress points. This is particularly important

in walls with significant openings. Where possible, extend opening over doors up to

the underside of the structure over.

When openings and support deflections are considered, vertical joints may need to be

at 4 to 6 metres centres or less.

All joints should be the full height of the masonry and encompass the full width. Joints

in both skins of cavity walls need not be immediately opposite each other but can be

staggered to suit details. This needs to be co-ordinated with the architect for joints in

tiles, plasterboard and other finishes. Minimum joint width recommended is 12mm

which must be kept clean at all times.

Wall panels must not be mortared up hard to columns or other rigid elements or built

hard between beams or floors. Vertical joints approximately 12mm wide should be

provided with flexible ties, etc. creating the necessary support. Joints can be filled with

a compressible filler or be covered by a cover strip.




Special attention should be given to joints between different materials, ie brickwork to

concrete, where plaster or render is to be applied. It would appear that prevention of

cracks at these points are practically impossible and it is recommended that a cover

strip, recessed groove, etc. be provided.

Junctions of walls should not automatically be bonded together. Considerations of

differential movement between each wall meeting at a point must be considered. This

will frequently require specific vertical joints at or near junctions.

Horizontal control joints are required in cavity walls where the combined effect of

thermal and long term movement between the external leaf of masonry and the

supporting structure exceeds 0.3mm/m. Horizontal joints in the outer leaf should be

not more than 9 metres apart or every third floor, whichever is less. At such joints the

structure has to be designed to support the masonry panel above.

No panel masonry walls are to be built hard under the structure over. Horizontal joints

approximately 20mm wide should be left and if necessary filled with a compressible

filler, or fire rated compressible seal or similar if a fire rating is required.

Where a concrete nib supports an external panel walls, it is essential to create a

minimum clearance of 20mm below the nib to allow for vertical brick growth.

If restraint is required at the head of the wall for its stability, it can often be provided by

ceiling construction, however, it depends entirely upon the type of ceiling being used.

Alternatively steel brackets or flexible ties may be used which allow for the movement

in the structure.

For load-bearing walls it is recommended that a mortar layer be placed, finished off

with a steel trowel, and on the top place two layers of building paper (or similar) prior to

pouring the floor over. This is to ensure that no bond develops on the interface

between the wall and the concrete floor. This is necessary to ensure that differential

movements of the masonry and the concrete do not cause stress concentrations.

However, lateral restraint for earthquake loads will most probably be required.

Control joints in panel walls can generally be documented by marking locations on a

set of architectural plans. The locations are then shown by the architect in the final

documentation.




9.7.2. Design of Wall Ties

The Newcastle Earthquake provided some valuable information about masonry design

and detailing and the inadequacies of past practices. With respect to wall ties, it was

found that many of the ties used in walls in Newcastle had corroded and were

therefore rendered useless in the earthquake. Consequently, Newcastle City Council

requires that all masonry wall ties be manufactured from Grade 316 Stainless Steel.

In other council areas the requirements are different. In the United Kingdom now, only

stainless steel ties are permitted. Consideration should always be given to stainless

steel wall ties where the walls are external or located in a corrosive environment (ie an

industrial or near coastal environment).

The approximate costs of ties as at June 1997 are as follows:

Type of Tie (Abey) Stainless Steel Galvanised Steel

Expansion Tie (1) $0.80 $2.20

Expansion Tie (2) $1.12 $4.40

Tremor Tie $0.20 $0.65

Sheriff Face Tie $0.07 $0.25

Caltie $0.38 $0.98

While the cost of stainless steel is two to three times the cost of galvanised fixings, a

standard cavity wall costs about $120 m2, so using stainless steel ties at 600 x 600

centres would add about $4 /m2 ie 3% to the cost of a wall.

Stainless steel wall ties must be used within 1 km of the coast or 3 km of an industrial

area.

There are only a few masonry ties on the market which comply with AS 2669 the Code

for masonry wall ties. Most ties do not comply with this Code. Ties made by Abey

Australia Pty. Ltd and Brunswick Sales Pty. Ltd do comply and also have test data for

allowable loads. Both will provide samples if required. Note most Abey ties are only

medium duty. Most ties which do comply to AS 2669 have low load capacities. Most

ties in domestic work do not comply.




Also there is a considerable body of evidence now that galvanised ties are not suitable

mainly because the ties corrode where they are built into the masonry due to a

reaction with mortar.

The tie spacings given in the Masonry Code in C1 3.8 are MINIMUM requirements ie

maximum spacings. The maximum spacings given in the Code may not be adequate

and should be checked for all external wall panels data. Ties are designed to act in

either shear or tension/compression depending on the type of tie. The choice of the tie

must be consistent with the structural action and restraint required.

General tie spacing is 600mm in each direction but this may need to be reduced in

some terrain category 2 areas and cyclonic areas. Within 300mm of lateral supports,

control joints and openings, a line of ties is to be provided at an average spacing of

300mm with the maximum distance between any two ties of 400mm.

9.7.3. Fire Rating

The design of masonry walls for fire resistance is a particular area of masonry design

which is often neglected and is not well understood by many Architects. As design

engineers, we need to obtain from the Principal Consultant (which may be Connell

Wagner on occasions), the appropriate fire ratings all the structural elements including

load bearing masonry components, and also for non structural masonry elements.

This fire rating must include the fire resistance levels (FRL) required for each of the

following properties:

1. Structural adequacy

2. Integrity

3. Insulation

expressed in the form 90/60/30 ie. 90 min fire resistance level for structural adequacy,

60 min for integrity and 30 min for insulation. These values must conform with those

set out in the BCA.

The fire resistance level of a wall can be determined in two ways (as described in

Section 7 AS 3700):

1. Test results ie. testing of a prototype in accordance with AS 1530.4.




2. Using ‘Deemed to Comply’ clauses in AS 3700.

Failure in respect to structural adequacy occurs when the thermal expansion of the

face exposed to the fire causes bowing of the wall until it ultimately collapses due to

the resulting eccentricity. Both the thermal properties of the wall and its slenderness

influence the period to failure. Therefore, walls of different size and support conditions

must be checked separately. No relationship has been established between the load

on the wall and the time till failure.

9.8. Materials

9.8.1. Masonry

• Clay bricks - these are usually now extruded except for a few dry pressed bricks.

All clay bricks will suffer "brick growth" in all directions. There is both metric and

"imperial". The latter are most common 76 x 110 x 230.

• Concrete bricks - these are similar in shape to clay bricks but made from concrete.

They will shrink.

• Calcium silicate bricks - these are made from sand and lime and baked and are

finer than concrete bricks. They also will shrink.

• Concrete blocks - these are made from concrete and include solids and hollows.

They will shrink with time. These are either 90 mm, 140 mm or 190 mm wide. 290

mm blocks are generally not made as they are too heavy to lift.

9.8.2. Mortar

Mortar is used to provide a joint between units, bond for lateral loads, and even

bedding for units and a weathertight wall.

Four mortar classifications (M1, M2, M3, M4) are given in AS 3700 with mortar used for

reinforced or grouted masonry being of classification M3 or M4. Bond strength is the

important property of mortars because of its effect on the transverse strength of walls.

The use of excessively strong mortars is undesirable. Lime additives in the mortar




increase the ability of the mortar joint to accommodate strains within a wall and

therefore assist in the reduction of cracking.

In most applications the use of the mortar mix 1:1:6 (C:L:S) will suffice. This mortar is

a classification M3 in AS 3700. The average 28 day strength for this mortar when site

mixed is approximately 2.8 MPa.

If additional bond strength is required, this can be achieved by removing the lime from

the mix and using “Dynex” or a similar methyl cellulose water thickener to assist

workability. Do not use plasticising additives.

9.8.3. Grout

Grout used for the filling of cores in unreinforced and reinforced masonry should be of

pourable consistency. Maximum aggregate size is 10mm and slump should be

230mm ± 30mm.

AS 3700 stipulates that grout for reinforced masonry shall have a cement content of

not less than 300kg/m³ to ensure durability of the reinforcement. This cement content

will result in grout with a strength of approximately 25MPa, however, the design

strength of the grout is limited to 1.3 times the block strength.

Always use proprietary grouts where possible and allow "clean out" blocks for rodding

of mortar dags etc.

9.8.4. Masonry

Masonry is a two-part material consisting of the masonry units and mortar. The

properties of the whole masonry panel depend on the properties of the:

• masonry units.

• mortar.

• bonding patterns.

• workmanship.

9.8.5. Reinforcement

Reinforcement can be used to strengthen walls, piers etc. It can include:




• horizontal galvanised bed joint reinforcement of mesh or bars or bars in lintel units.

• Vertical reinforcement in block walls. (Use only 200 blocks for such walls as it is

almost impossible to get grout into smaller cores properly.

9.8.6. Accessories

These include:

• wall ties (of which there are a large number of types).

• damp proof courses, flashings etc.

• lintels




10. TIMBER DESIGN

10.1. Introduction

Timber is a natural, isotopic material ie different properties in different directions, and

its properties are affected by moisture and the environment. There is also a wide

range of species used in construction which have variations in these properties. As a

minimum the designer must be familiar with the strength grade, durability and

shrinkage characteristics of the timber to produce an economical durable structural

solution.

As the construction timbers may be drawn from a wide range of species with varying

standard sizes and lengths and within regions and states of Australia and New

Zealand as well as overseas, the designer must have a knowledge of the available

structural timbers in the region. Added to this must be an understanding of the

market’s ability to deliver the solution documented as larger, non domestic

construction or engineered timber structures are not common in many parts of

Australia. It is good practice to test the market place to determine the interest and the

level of expertise available.

This section of the manual is not intended to be an exhaustive and comprehensive

manual on timber properties and design principles but rather a summary and checklist

which will raise the designer level of awareness when designing in timber and point to

references or suggest courses which the designer should pursue to gain all required

details to produce a structure that is well detailed and will perform in the given

environment.

The Designer must understand the properties, characteristics and limitations before

embarking into timber design ie “Wood is good if understood”.

10.2. Codes

AS 2543 - Australian nomenclature

AS2878 - Classification into strength groups

AS1684 - Framing Code

AS1328 - Glue Laminated Code

AS1720.01 - Timber Structures Code : Design Code




AS1720.02 - Timber Structures Code : Properties

AS1720.04 - Timber Structures Code : Fire Resistance

AS2269 - Plywood - Structural

10.3. References

Wood in Australia by Keith .R. Bootle (McGraw Hill)

Timber Manuals Vol 1 & 2 by NAFI.


None

10.5. Availability

Timbers Grades in Order of Availability

Chief Areas of Use

Dry Timbers - Seasoned Radiata Pine (SD6) F5,F8,F11

(Radiata Pine is also marketed with grading MGP10, MGP12, and MGP15)

Victoria, New South Wales, Tasmania, Southern Coastal Queensland, South Australia, ACT, Western Australia

Alpine Ash (SD4) F17 Victoria, South Western New South Wales

Tasmanian Oak (SD4) F17 Tasmania, some areas of

Victoria Green Timbers - Unseasoned

Douglas Fir - Oregon (S5) F5, F7, F8 South Australia, Victoria Karri (from WA) (S3) F11, F14 Western Australia, South

Australia, Northern Territory, ACT

Jarrah (from WA) (S4) F8, F11 Western Australia, South

Australia, Northern Territory, ACT

General Hardwoods (S2, S3, S4)

F8, F11 New South Wales, Victoria, South Australia ACT, Tasmania




Timbers Grades in Order of Availability

Chief Areas of Use

F14, F17 Northern New South Wales,

Southern to central Queensland, Northern Territory

F17, F22 Northern Queensland

Cypress Pine (S5) F5, F7 Southern and South Western Queensland, North Western New South Wales

Engineered Timbers a) Laminated Beams • Radiata Pine - In various grades and laminated

thicknesses • Oregon - Generally F11 and imported

from America • Tasmanian Oak - Hardwood - available on

request. Refer to manufacturer for details

• Jarrah - " • Brush Box - " b) Laminated Veneer

Lumber (LVL) From Radiata

Pine

- Manufactured by various suppliers with various grades. Check local supplier

c) Plywood Generally only softwood

plywood is available in Grades F8, F11, F14, F17. (F11 is normally specified).

10.6. Timber Sizes

Timber Type Depth Width Max Length

Comments

Radiata Pine

70, 90, 120, 140, 190, 240

35, 45, 70 6.0 70 mm width members over 120 depth; check supplier

Oregon In 25 mm

Increments up to 500 mm

38, 50, 75, 100, 125, 150

10.0 m (check supplier)

Beware of shrinkage in deep members (>250 mm mm).




Timber Type Depth Width Max Length

Comments

K D Hardwood 100,150, 200

250, 300 50 5.2 m Larger size may be

“gangnailed” therefore, beware of appearance problem.

Green Hardwood

75, 100, 125, 150 175, 200, 250

38, 50 5.2 m Check availability.

Laminated Beams

Consult manufacturer literature.

Laminated Veneer Lumber

Consult manufacturer literature

Structural 1200 mm x 2400 mm Standard

Plywood 900 mm x 2400 mm Special Order

1500 mm x 1800 mm Special Order

1800 x 18000mm Special Order

Structural plywood constructions - pinus radiata

Identification Code Thickness Plys 1 2 3 4 5 6 7 8 9 4.5 - 15 - 3 4.5 1.6 1.6 1.6

7.5 - 25 - 3 7.5 2.5 2.5 2.5

9 - 32 - 3 9 3.2 3.2 3.2

12 - 25 - 5 12 2.5 2.5 2.5 2.5 2.5

15 - 32 - 5 15 3.2 3.2 3.2 3.2 3.2

17.5 - 25 - 7 17.5 2.5 2.5 2.5 2.5 2.5 2.5 2.5

20 - 32 - 7 20 3.2 3.2 2.5 3.2 2.5 3.2 3.2

25 - 32 - 25 3.2 2.5 3.2 2.5 3.2 2.5 3.2 2.5 3.2

Available in stress

grades:

F11 Standard as per AS 2269.

F14 Panels are all individually machine stress graded




and stamped as per AS 2269.

F17 Panels are all individually machine stress graded

and stamped as per AS 2269.

Other thickness and constructions are available upon enquiry.Hardwood plywood is

becoming increasingly more difficult to obtain due to raw material constraints. Face

grade of plywood should be nominated; ie Grade C for visual applications, Grade D for

non-visual and specification, therefore can be D-D, C-C or C-D, with one or both sides

finished for visual purposes.Characteristics in Timber

Structural timber is made up of, a base material which we refer to as wood plus knots

and other growth characteristics which reduce the strength of the clear wood.

Failure of timber structural members tend to be brittle when subject to bending or

tension.

When designing in timber it is also important to have an understanding of the

characteristics of timber which effect strength and serviceability. The main areas are:

• moisture content

• strength grading

• creep

• durability

• differing strength characteristics perpendicular and parallel to grain.

10.6.1.Moisture Content

Has an important effect on the strength and stability of wood. Wood usually increases

in strength as it dries, though this does not begin until “Fibre saturation” point is

achieved, below 26% - 30% moisture content. At 12% MC the modulus of rupture may

improved by 75 to 100%. Timber also begins to shrink once it falls below this fibre

saturation point. This shrinkage varies with species and varies in the orientation of

timber.

There is virtually no shrinkage longitudinal to the grain but it can be between 4 - 8%

radially. This shrinkage can cause considerable problems in joints and at supports




when it occurs, therefore it is good practice to specify seasoned timber ie MC between

12 & 15%, thereby negating the risk of shrinkage problems.

10.6.2.Strength Grading

There are many species and various types and sizes of strength-reducing defects in

these species. This has resulted in rationalising the way we assign strengths to

structural timber. This section does not go into detail on this subject, but rather refers

the reader to a more detailed reference. Eg Wood in Australia (K.R. Bootle). The

designer, should have a basic understanding of visual and mechanical stress grading

rules as set out in the relative Australian standards, so that when attending site to

provide a visual inspection of the timber structure, alarm bells will ring if it appears

outside the general rules set out in these standards for the specified strength group

and grade.

10.6.3.Creep

Timber continues to creep after loading. The amount of creep is dependant on:

• Initial moisture content. ie seasoned or green.

• Duration of load.

• Cyclication of the environmental humidity.

10.6.4.Durability

Classification of durability of a species is not a precise art because of the variability of

wood properties within a species, however, as a guide under Australian Conditions,

timber from a species is assigned one of four relative durability classes.

Class 1 Very Durable : (excess 25 years in ground)

Class 2 Durable : (between 15 and 25 years inground)

Class 3 Moderately Durable : (8 and 15 years in ground)

Class 4 Non Durable : (between 1 and 8 years inground).

A suitable service index has not been developed and accepted for timber which is

exposed to the weather but not in contact with the ground. The designer should rely on

broad locally accepted durability guidelines (refer to local Timber Association).




Softwood used for general structural timber in Australia, (Pinus Radiata or Oregon), is

not to be used in exposed conditions unless treated eg C.C.A or L.O.S.P.

10.6.5.Differing Strength Characteristics Perpendicular or Parallel to Grain

The following figures show schematically the ratio of tensile and compressive

strengths parallel and perpendicular to the grain.

45 45 1 1 10 10 1 1

Ratio of Tensile Strengths Ratio of Compressive Strengths

If a knot or defect is present in the section then sloping grain is produced around it

which results in a reduction of strength. In particular sloping grain has a pronounced

effect on tensile strength hence the reason for the very low allowable stress in the

code.

This variation also has a marked effect on bolt capacities perpendicular and parallel to

the grain and as a result drives the designer to avoid or to modify joints with bolts

acting perpendicular to the grain.

Bearing at joints also shows this same marked difference between loads

perpendicular and parallel to the grain.

An accepted way to model timber is the “hand full of straws” concept. If the designer

has this image firmly established many of the problems are easily conceptualised and

therefore more easily solved.

10.7. Designing Timber Structures

The current Australian Standard AS 1720.1 (1988) provides basic working stresses

which are then modified by factors that are appropriate to the design condition to

provide the Permissible Design stresses.




There are 38 modification factors in the code, however, only a few require regular

consideration. These are K1 to K12.

Currently there is a Draft revision of AS 1720.1 in a Limit States format and this is

expected to be released in the near future. This standard is set up similarly to the

permissible stress standard except that it provides characteristics properties which

are then modified by a capacity reduction factor and K factors, similar to the

permissible stress code.

10.7.1.Beams

In general serviceability requirements drive the size of beams especially if unseasoned

timber is used. If solid timber members are specified the designer should check the

available lengths and sizes and the availability of seasoned timber. Try not to use

unseasoned timber in anything but simplest domestic structures and beware of

shrinkage problems.

Manufactured beams like Glu-Lam and L.V.L provide best options for larger structural

beams.

10.7.2.Trusses

• Nail plate or Gang nail

Generally these are not designed by the structural consultant. The designer would

normally provide a plan that lays the trusses out and then provide a performance

specification for the design by the manufacturer. It is important that these trusses

are layed out with minimum bracing and tie down details shown, because if the

manufacture is left to lay them out, loads to the supporting structure are often

changed and some cases missed. The performance specification must specify

minimum serviceability requirements, because if it does not, manufacturers

‘camber out’ the initial deflections to get cheaper solutions. This often presents long

term serviceability problems, especially between parallel standard trusses and

girder trusses. Remember repetition is the key to an economical layout.

• Bolted Trusses




Architects often prefer this solution because of its more asthetic appeal, however,

they are very expensive compared to a similarly loaded gang nailed truss. They can

be 3 or four times more expensive due to increase in member sizes to

accommodate bolts, cost of fabrication and cost of connectors. If required there are

a number of easy ways to reduce number of bolts and therefore member sizes. by

using ‘nail on’ plates to non exposed faces of double chorded trusses then bolting

through these plates is a very effective way of transferring forces economically. The

load is transferred from nails to plate and then into the bolt which is a far more cost

effective solution.

Many designers forget to, or provide too little camber to bolted trusses. The bolt

‘take up’ at joints can provide final defections which are 2 or three times more than

calculated. There are a number of references which can assist the designer in this

regard, however, as a minimum, provide a camber to the truss which is twice the

expected long term deflection.

10.7.3.Fabricated Plywood Elements

Structural plywood possesses some physical properties that make it a engineered

building panel which is suitable for a diverse range of engineered applications. These

properties include:

• High strength and stiffness to weight ratio

• High panel shear strength

• Dimensional stability under changes of temperature and humidity.

Structural plywoods is a fully engineered panel manufactured to AS2269.

The designer needs to specify the face veneer grades which are defined in the

standard. C Grade veneer is usually specified for exposed faces and D Grade for

unexposed.

Section properties are calculated using an approach known as the parallel ply theory

and uses the parallel plies and the theorem of parallel axes to computate these

properties.

The most common structural uses of plywood include:




• T&G Flooring

• Formwork

• Panel shear bracing

• Stressed skin panels

• Plywood webbed beams

• Rigid Framed Structures

eg. (Plywood Portal Frames)

Like all wood products, plywood has a number of destructive enemies and treatments

are available using various preservatives.

There are many good references for the design of plywood structures and these can

be obtained through the Plywood Association of Australia which is located in

Queensland.

10.7.4.Joints

Numerous types of mechanical fasteners are available for the jointing and connection

of structural timber members.

To determine an appropriate connection, many considerations will apply and these

include:-

• fastener types

• timber species

• moisture content of the timber

• conditions of loading (duration)

• number of fasteners

• angle of load to the grain of the timber and the orientation of the fastener

• spacing of fasteners and edge and end distances

• critical section size

• eccentricity

• cost of fastener and assembly

• aesthetic value.




The designer must be aware of the timber properties when choosing/designing the

fastener and must not adopt steel joint layouts for timber.

General guidelines to follow include:

• use propriety fixings where possible.

• Try to use bearing type joints rather than fin plates

• use nails or small diameter screws before trying bolts.

Be aware of shrinkage if using large unseasoned sections. Eg if Bolts are 200mm

apart the section between the bolts may shrink up to 12mm and thus cause a large

split between the two bolts.

Don’t mix mechanical fixings with structural glue fixings (structural glue is rigid an will

fail before the mechanical fixing begins to work - exception is elastomeric glues which

are not structural but often used to improve instantaneous deflections).

Glued joints are not generally used except in some manufactured products like Glu-

Lam and L.V.L Glued joints a very sensitive to the quality of preparation, temperature

of curing and pressure, therefore, it is not recommended that glued structural joints be

used without considerable research and surity of delivery.

Elastomeric glues are often used in conjunction with nails to prevent squeaking in

joints and provide more rigidity for short term loads ie improve vibration performance

by considering the element as composite.




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11. GLASS AND CURTAIN WALL DESIGN

11.1. Introduction

Windows and curtain walls have traditionally been considered to be non-structural

elements and have been performance specified by architects and designed by the

specialist suppliers. However in recent times, structural engineers have become

involved in these areas due to a number of factors including:

• architects wanting to reduce their risk by having an independent, technically

capable engineering consultant involved in the design, specification and inspection

phases of glass and curtain wall elements; and

• architects and their clients not wanting to limit themselves to what the industry is

willing to provide.

Because these elements comprise the barrier which keeps the wind and rain out of

the building, any shortcomings quickly become apparent and a source of annoyance,

inconvenience or worse to the building occupiers. Faults can be difficult and therefore

expensive to fix.

A good quality curtain wall can cost as much as 50% of the cost of the building

structure and, besides being expensive, it is the face the building presents to the

world. Our involvement in this work must therefore be taken extremely seriously and

as a clearly identified extension to our normal structural engineering service. Our fees

must reflect this responsibility.

11.2. Codes and Standards

AS 1288, Glass in Buildings - Selection and Installation.

AS1664 SAA Aluminium Structures Code.

AS1665 Welding of Aluminium Structures.

AS1734 Aluminium and aluminium alloys - flat sheet, coiled sheet and plate.




2 of 28

AS1866 Aluminium and aluminium alloys - extruded rod, bar, solid and hollow shapes.

AS2047 Aluminium windows for buildings.

AS2048 Code of Practice for installation and maintenance of aluminium windows in

buildings.

AS/NZS 2208, Safety glazing Materials in buildings.

AS/NZS 4284, Testing of building facades.

AS1231 Aluminium and aluminium alloys - Anodised coatings for architectural

applications.

BS952 Glass for glazing.

ASTM C864 Specification for dense elastomeric compression seal gaskets, setting

blocks and spacers.

AAMA603.6 Performance requirements and test procedures for pigmented organic

coatings on extruded aluminium.

11.3. References

Glass and Glazing Federation. Glazing Manual. The Federation, London, January

1978.

Kneeland, A. Godfrey. Window Glass in Extreme Winds: Design for Flying Debris.

Civil engineering, January 1984.

Massey, and McGuire. Lateral Stability of Non-uniform Cantilevers. ASCE Journal of

Engineering Mechanics, June 1971.

Minor, J.E. Structural Engineering with Glass. Structural Engineering Practice, Vol. 2,

No. 1, 1983.




3 of 28

Minor, J.E. Design of Glass Against Breakage. In Second Century of the Skyscraper.

Council on Tall Buildings and Urban Habitat, Bethlehem, Penn., 1986.

Minor, J.E. and others. Laminated Glass Units Under Uniform Lateral Pressure. ASCE

Journal of Structural Engineering, May 1985.

PPG Glass Thickness Recommendations. 19 March 1981.

Selleys. Structural Glazing with Silicon Sealants. 21 September 1984.

Walker, G.E. and Minor, J.E. New Developments in the Structural Design of Cladding.

Institution of Engineers, Australia, Queensland Division, Technical Paper, Vol. 26, No.

11, May 1985.


None

11.5. Glass Design Principles

11.5.1.General

Glass is a solid which has cooled from a liquid state too rapidly for crystals to have

formed and which therefore becomes a solid with a liquid-like structure.

Most glasses are made from oxides, typical of which are SiO2, B2O3, GeO2, P205 and

Sb203. The glass most likely to be used for windows is soda lime glass which is

predominantly SiO2 and Na2O.

Window glass comes in three basic strength forms:

(a) Annealed glass (the normal untreated form).

(b) Heat strengthened glass (about twice as strong as annealed glass).




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(c) Toughened or tempered glass about four to five times as strong as annealed

glass).

Based on these glasses, other products are made such as laminated glass, tinted

glass, wired glass, heat absorbing glass etc.

11.5.2.Mechanical Properties

Type Young's Modulus

GPa

Density Kg/M3

Expansion Coefficient

°C-1

Allowable Bending

Stress MPa

Approx. UTS MPa

Annealed 70 2500 8 x 10-6 15.2 40

Heat strengthened

70 2500 8 x 10-6 24 80

Toughened 70 2500 8 x 10-6 37.5 170

Note: the tabulated allowable bending stresses are for wind loads in accordance with

Table 3.2, AS 1288.

11.5.3.Annealed Glass

Most glass used for engineered applications is made by the float process wherein the

molten glass is poured onto a bath of molten tin.

Annealed glass is not very strong and must not be used for doors or panels adjacent

to doors in all-glass assemblies. It characteristically breaks into sharp-edged shards.

It is available in thicknesses up to 25mm and in lengths up to 10m or more by a little

over 3m wide; however, glass this thick and large is available only from overseas

making delivery and replacement times quite long.

11.5.4.Toughened Glass

Annealed glass is made into toughened (or tempered) glass by heating it until it

becomes slightly soft then rapidly cooling the surfaces by jets of cold air. This shrinks

and hardens the surface inducing a compressive surface stress and a balancing

internal tensile stress. The surface compressive stress must exceed approximately

70 MPa.




5 of 28

Following toughening the glass may be bowed. The bow may be up to 1mm per

200mm of total measured at the point of maximum gap. Bowing becomes very visible

because of distortion of reflections.

Glass must be cut to size, drilled and shaped prior to undergoing toughening as the

slightest nick may cause toughened glass to shatter.

Edges of glass may be flat ground (machined with sharp edges removed), flat smooth

(ground smooth with sharp edges removed), or flat polished (highly polished smooth

edge).

Because the furnaces used to heat the glass are limited in size toughened glass can

be obtained only up to about 4m x 2m in size.

Toughened glass sometimes suffers spontaneous breakages due to nickel sulphide

impurity. For this reason heat strengthened glass should be used where broken glass

could fall on people below. (See Section 11.5.8.)

11.5.5.Heat Strengthened Glass

Heat strengthened glass was introduced in order to avoid the spontaneous breakage

problem of toughened glass. The lesser heat treatment creates a surface

compression which must be between about 24 and 70 MPa. The glass therefore

exhibits breakage characteristics anywhere from those of annealed glass at the 24

MPa end (most likely) to toughened glass at the 70 MPa end (less likely). Where

safety is a consideration, heat strengthened glass must be assumed to break in a

dangerous manner.

The main use of heat strengthened glass is in windows to high-rise buildings, either as

a single pane or as the outer pane of a sealed double glazed unit. (The inner pane

may be toughened glass for impact resistance and strength under wind loading).

11.5.6.Laminated Glass

Glass is laminated to make it more resistant to shattering under impact loading. Any

form of glass can be laminated but it is important that the surfaces be as flat as




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possible (this is achieved by selecting the best of the glass from a run). The interlayer

is usually polyvinyl butyral in one or more .38mm thick layers.

Because the shear modules of the interlayer is only about 1/10,000 that of the glass

the two glass layers act independently under sustained loading.

However, under transient loading (such as wind loads) at room temperature, testing

has demonstrated that laminated glass behaves as though it were monolithic glass of

the same overall thickness. At higher temperatures the interlayer softens until at about

70°C the laminated glass under transient loading behaves as two independent plates.

AS1288 takes this research into account (with an appropriate degree of

conservatism).

11.5.7.Available Glass thicknesses

Annealed glass is commonly available in thicknesses of 3, 4, 5, 6, 8, 10, 12, 15 and

19mm.

Toughened glass is usually 5, 6, 10, 12 and 15mm thick.

Laminated glass is listed by the total thickness of glass plus laminate, e.g. 6.38, 6.76,

8.38, etc. Glass suppliers are reluctant to supply laminated toughened glass as it is

not very flat and this could result in incomplete bonding of the glass to the interlayer.

Two layers (0.76mm) of the PVB are used if toughened glass must be laminated.

Thicker glass and larger sizes than those normally produced in Australia are available

from overseas.

Toughened glass and laminated glass may not be available from stock. Always seek

advice from suppliers regarding availability.

11.5.8.Considerations in Glass Selection

The following aspects should be considered:




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(a) Strength:

Often architectural considerations, such as an absence of stiffening mullions,

will dictate the use of toughened glass.

(b) Servicability:

For higher strength glass of a given thickness (eg heat strengthend versus

annealed), their is no increase in the stiffness of the glass; hence, no increase

in its resistance to out of plane deformation.

(c) Size:

Generally speaking, as soon as the length exceeds 4.2m and the width

exceeds 2.14m, annealed glass must be used unless a system of bolted metal

splice plates is used. A maximum handling mass of about 150 kg also needs

consideration. Check with suppliers for particular limitations, size and handling.

(d) Safety:

For overhead glazing either laminated glass or glass backed by a plastic safety

film which is locked into the glazing bars should be used. The later is not the

preferred approach. Straight toughened glass is unacceptable as it can

shatter but still fall en mass, subject to the criteria noted in AS/NZS 2208.

For glass in public areas it is wise to use toughened glass although thick (16 or

19mm) annealed glass is very difficult to break accidentally and may be

considered to be safe for some applications.

(e) Reliability:

All glass is brittle but its brittleness can be countered by laminating with a

plastic film. In regions where extreme storms are experienced and for

buildings in those regions where the loss of external windows will cause

internal damage with huge financial loss, the use of laminated glass should be

considered.

Toughened glass exhibits spontaneous breakage and for this reason heat

strengthened glass should be used for external panes in tall buildings.




8 of 28

Where strength requirements dictate the use of toughened glass (e.g. for

cantilevered glass balustrades) then only toughened glass which has been

heat soaked or scanned for nickel sulphide inclusions shall be used. Heat

soaking accelerates the expansion of the nickel sulphide, hopefully causing the

glass to fracture during that process. Unfortunately, the number of suppliers

offering this treatment is limited. Scanning involves the use of special optical

techniques to enable the nickel sulphide to be detected. The service is

available through some universities. It is a slow process and therefore

expensive.

11.5.9.Design of Glass for Wind Loading

The strength of glass, being a brittle material, is strongly influenced by the area of a

panel. The larger the area, the more fracture-inducing defects are likely to exist.

Hence, the results of a large number of tests can be expected to yield truer values of

strength than rational analysis. The AS1288 charts for 4-sided support are based on

many tests involving 20 to 30 repetitious for each geometry. However, the charts for

2-sided support have been derived from the 4-sided support tests assuming

maximum stresses at failure will be similar, which is not necessarily true for brittle

material.

Other factors also influence the strength of glass. Float glass is stronger than plate

(drawn and polished) glass due to tiny defects caused by polishing the plate glass; the

“air” side of float glass is stronger than the “tin” side (due to abrasion by the rollers

supporting the glass when it leaves the tin baths; but the most significant factor is

“weathering” which can reduce the tensile strength of glass by over 50% after a

number of years. (“Weathering” includes the effects of installation, regular cleaning,

as well as naturally occurring environmental effects.). The fact that numerous

breakages under wind loading as a result of “weathering” do not occur is probably

because design stresses are based on one minute duration loads whereas peak wind

loads typically have durations of fractions of a second.

Wind loads should be derived from AS1170.2 using the appropriate local pressure

coefficients unless a pressure tap model has been tested in a wind tunnel. Having

established the loads, the provisions of AS1288 can be applied to derive glass

thickness. Alternatively the more up to date design curves published by PPG can be

used. (Metricated versions of these are included at the end of this section.) As




9 of 28

previously stated, so called sophisticated design methods (FE analysis and the like)

will not yield more accurate results. Also, caution should be exercised when

extrapolating design charts published in the literature. Refer figure 11.4, 11.5, and 11.6

for design charts adapted from a PPG publication.

Deflections of glass at the maximum design wind load can be very significant

particularly for toughened glass. The deflection of a one-way span can be easily

calculated whereas the deflection of a two-way span is not easily obtained. Figure

11.7, adapted from a PPG publication, provides a suitably accurate estimate for all

practical purposes.

Laminated glass, when subjected to short duration loading, has been shown to behave

almost like monolithic glass of the same overall thickness up to a temperature of about

70°C. Over 70°C the plastic interlayer becomes soft and allows the two sheets of

glass to behave progressively more like separate elements. (Under sustained loading,

it must be treated as two separate elements). AS1288 now recognises this by the

adoption of a factor of 0.8 applied to the allowable stress when the two sheets are

treated as a monolithic element. (A factor of 1.0 would be unconservative.).

11.5.10.Gravity Loading

Glass is significantly weaker under sustained loading than under short term transient

loading. Allowable design stresses are therefore lower. AS1288 specifies a sustained

maximum stress which is half of that for wind loading.

For combined dead and wind load the code gives no direction. A conservative

approach would be to use 2G + W where the forces are additive and G-W where

subtractive in conjunction with the allowable wind load stress.

Design live loads for overhead glazing are clearly specified in the Code. These need

not be combined with wind loading. Live loads are usually considered to be transient

loads when determining allowable stresses.

11.5.11.Design for Human Impact




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Annealed glass is potentially lethal when broken. Stories abound of the dramatic

wounds caused by people falling/running through glass doors or windows. The Code

contains a set of complex, prescriptive rules governing the requirements for “safety

glass” and where it must be used. Essentially, any glass in a normal path of travel (a

door) and any immediately adjacent glass; and any glass in areas which may become

slippery (a bathroom for example) located such that it could be hazardous, must be

“safety glass”.

Safety glass can be toughened glass, laminated glass, wired glass or glass with an

adhered plastic safety film. Reference must be made to the Code when we have to

advise in this area as limitations apply to the panel areas and allowable locations for

different glass types and thicknesses.

11.5.12.All-Glass Assemblages

Nowadays it is common for building developers to request lobby glazing without metal

mullions or transoms reducing the transparency of the wall. Such systems usually

have glass mullions (fins) which may be full height or may be cantilevered from above

the ceiling. Proprietary systems using toughened glass connected by steel “patch”

plates exist. To avoid the use of steel plates in tall walls, annealed glass must be

used. Annealed glass 15mm and thicker is difficult to shatter and can be assumed to

be safe in terms of human impact.

The vision panel thickness should be derived from the Code or PPG charts for the

design wind load. The glass fins are designed as laterally slender, simply supported

beams subjected to loading from the vision panels. The code now has a section on

the buckling analysis of fins. For preliminary estimates of fin depth, the more simple

formula fb <15000/(d/t)² can be used.

Walls with cantilevered fins extending only part of the height of a glass wall are

extremely complex to design, and rational analysis will not necessarily give a true

result. We should therefore not offer to take responsibility for such a design.

The thickness of the fin is usually determined by the width needed to make the joint

between fin and vision panels using structural silicone.

Often these fins are poorly restrained as the seat or pocket must be capable of

restraining their appropriate load.




11 of 28

11.5.13.Jointing

(a) Silicone Joints

Structural glass is usually jointed using silicone. Although the types of silicone

used for glazing have ultimate tensile strengths of between 1 and 3 MPa, this is

achieved at an elongation of about 500% - well beyond any useful range.

Silicone suppliers recommend a design stress of 0.14 MPa for all silicones -

they will not guarantee the performance at any higher stresses. They also

recommend a dynamic movement range of ± 25%.

Thus it is a simple matter to derive the width of silicone needed to resist wind

forces on the glass.

It is not recommended that silicone is the sole means of resisting gravity

loading unless the silicone is in compression as in overhead glazing.

The connection of glass fins to the vision glass should be proportioned as

follows:

Fig. 11.1

The fins, being vertical beams, must be supported at their ends and the load

can be quite large. To avoid the need for bolting, and to allow rotation, a good

6




12 of 28

detail is to enclose the fin in a metal shoe suitably stiffened at each end to

resist the inward and outward reactions as shown in figure 11.2

Fig. 11.2

(b) Bolted Joints

When glass needs to be bolted, toughened glass should be used and a friction

grip joint designed. Oversize holes are drilled in the glass (before toughening)

and the metal plates and glass are separated by fibre or very hard neoprene.

The bolt torque must be specified and controlled.

Holes will have a ground surface with sharp edges removed. A maximum of 4

holes in one group is recommended with a minimum diameter of the glass

thickness. The distance between the edge of the hole and the edge of the

glass must be at least the glass thickness, preferable 1.5 times the glass

thickness. Where there are holes in a group, this distance should be 8 times

the glass thickness. The distance between edges of holes should be 4 times

the glass thickness for up to 4 holes in a group and 6 times for more than 4

holes.

11.5.14.Aquaria and Underwater Observation Panels

Where glass is used to contain water, because of the sustained high pressure and the

disastrous results should a breakage occur, particular attention must be given to the

selection of suitable glass and glazing systems.




13 of 28

Annealed glass rather than toughened glass should be used for the following reasons:

(a) The lower allowable stress means reduced deflections.

(b) In public areas, scratching of the glass whether accidental or due to vandalism,

could result in shattering of toughened glass.

(c) Should toughened glass break, it would break into numerous small pieces,

allowing the water to flood out whereas annealed glass may crack in such a

manner that it can still contain the water, giving time for remedial measures to

be taken.

Figure 11.3 gives the thickness of annealed glass for situations where the

water level is level with the top of the glass. Where the top of the glass is

below the water level, consideration must be given to the extra pressure of

water, the force exerted by as turning swimmer, the impact of a large fish, etc.

Fig. 11.3




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11.6. Curtain Wall Design Principles

11.6.1.Introduction

The design of curtain walls is NOT part of our normal design services but can be

offered as an additional service to our clients. Before any design of such elements is

considered, it must be discussed fully with the Principal responsible.

The design of such walls require specialised design beyond these Guidelines.

However, these Guidelines set out the general background for the design of these

walls.

Curtain walls are one of the most abused of building elements being subjected to wind

loading, temperature changes, building movements (short and long term), intense

sunlight, driven rain, atmospheric pollution and corrosion. It is particularly wind and

earthquake loading and building movements that has led to the Structural Engineer

becoming involved in the design of curtain walls.

It is not possible to design and document a curtain wall and then to have tenders

called on this. This is not the nature of the curtain wall industry where curtain wall

contractors are all manufacturers and developers of their own systems. However, the

Structural Engineer can advise the Architect when the performance specification and

documentation for the curtain wall is being prepared so that curtain wall contractors

tendering on a certain project are all working to the same standard of performance and

to a performance that is well understood by all parties and which can be monitored

during the design, fabrication and erection phase.

The first requirement of a curtain wall design is an understanding of the structural

behaviour of the building to which it is to be fixed. Buildings are not stationary but

undergo movement due to vertical load, shrinkage, creep, temperature, settlement and

wind loading. Curtain wall elements must be designed for stiffness as well as

strength, yet allow for building movements. Usually the element, once erected, cannot

be readily inspected so that deterioration is not visible until a failure takes place.

11.6.2.Factors Requiring Consideration




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The design of a curtain wall involves input from many parties.

All of these parties have a role that overlaps at some point and they will have to be

involved to ensure that the performance of the curtain wall is specified and

investigated in the following areas:

• Aesthetics

• Authority requirements and appeals

• Design loadings and structural systems

• Maintenance aspects and ability to repair damaged areas

• Material quality investigations and controls

• Glass type

• Surface finish of aluminium

• Prototype testing

• Limiting air leakage and water penetration

• Sealant detail, selection and installation

• Durability aspects

• Corrosion between dissimilar metals

Unless these matters are attended to, a curtain wall will not meet the expectations of

the Owner.

The curtain wall components must be designed for the self weight of the curtain wall

both during fabrication, erection and in its final location. It is considered good practice,

particularly for stiffness, to design members and their connections for an equivalent

load of two times the dead load.

It is important to consider the bending moments and torsions that arise when applied

loads do not coincide with the centre of members and in particular, connections.

These secondary forces are often overlooked and can result in excessive distortion or

connection failure. This is particularly so where connections are made to the building

where the theoretical eccentricities are greatly exceeded as a result of building

construction tolerances.

The curtain wall should be designed for wind load and earthquake loads if applicable.




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The wind loading to which curtain wall members are exposed can sometimes be

greater than the floor loading for which the actual building has been designed, allowing

for local pressures. Modern wind loading codes have based design loads on accurate

anemometer records and laboratory tests in wind tunnels. These have supplied

reliable data on wind pressures and in particular high local wind forces that occur near

corners and tops of buildings where local suctions can be up to two times average

wind pressures. AS 1170, Part 2 is particularly useful for the Structural Engineer to

assist in providing wind loading diagrams that should be included in the curtain wall

specification. These forces can be so great that the curtain wall system must be

designed by a competent Structural Engineer experienced in this type of work.

11.6.3.Building Movements

All materials deform under load and this increases with time as the building is

constructed or undergoes long-term shrinkage and creep. Material behaviour is now

sufficiently understood to enable the designer of a building to be able to predict with an

accuracy of ± 25% the amount that structural members will deflect in the short and

long term. Reinforced concrete columns and walls continue to shorten due to

shrinkage and creep, resulting in floor to floor heights being reduced up to 3mm to

4mm in a 3m height after the curtain wall has been installed. These deformations

must firstly be calculated and, then be specified in the curtain wall specification. Also,

the spandrel beams will deflect by various amounts depending on their span and load.

Concrete floors will shrink and, if prestressed, they will axially creep.

In addition the building undergoes movements due to temperature changes both on a

daily cycle and seasonal basis. As the temperature movement of the building is

usually considerably less than the curtain wall with its total exposure, differential

movements will result.

Under wind or earthquake loadings, a building will undergo lateral displacement the

magnitude of which is a direct function of the height of the building and its stiffness.

The fixing between curtain wall and building must be such that these movements are

not transmitted to the curtain wall. The curtain wall fixings must be able to

accommodate the total movement of the building without becoming overstressed or

such movements overstressing the curtain wall itself.

11.6.4.Building and Curtain Wall Tolerances




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It is the physical interface of curtain wall structure connected to the building where the

greatest problems occur during erection. This stems from the fact that the tolerances

of insitu concrete construction (AS 3600 and AS 3610) permit the building to be

vertically out of correct position by ± 10mm and laterally by ± 20mm. These

tolerances are an accumulation of setting out of particular floors, placement of

formwork and distortion of formwork during concrete placement, screeding off of floor

levels, as well as deflection of members due to distortion of formwork under wet

concrete and deflection of concrete members under superimposed load. However,

finished tolerances specified for curtain wall erection are ± 1mm for reflective glass

curtain walls where stricter tolerances are necessary to eliminate excessive distortion

of the reflected image.

It is essential that during documentation of the curtain wall, recognition of these

different tolerances is allowed for in detailing connections, cast in fixings and packers.

The structural design of the entire connection must recognise the maximum

eccentricity of load transfer from the curtain wall to the building.

11.6.5.Material Properties

Common materials used are:

• Aluminium

• Mild steel

• Stainless steel

• Masonry fixings

• Glass

• Silicone sealants

Structural design and material codes are in existence for each of these. It is important

that the particular materials used are clearly specified and limiting stresses and

particularly member deflections are specified. This is particularly important as the

water penetration and air leakage limitations require that joint movements and strains

on sealants do not exceed the material’s capacity to provide the amount of movement

over a period of many years.




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The Structural Engineer must recognise the properties of the materials he

intends to. Temperature movements of the various materials can differ dramatically,

e.g. the coefficient of thermal expansion of steel is one and half times that of glass, yet

aluminium has a coefficient three times that of glass, while polycarbonate sheeting

has a coefficient nearly ten times that of glass. Obviously this is a crucial factor in the

detailing of a curtain wall where many of these materials are in contact with each other

and meet at joints which have to accommodate these real movements.

11.6.6.Silicone Sealants

Silicone sealants are as varied in name as they are in properties. The correct material

has excellent properties of durability, movement and strength. It is exciting to be able

to squeeze a near liquid material out of a tube, to be able to mould it to almost any

shape, have it adhere to glass, aluminium, steel, masonry and concrete, then after

several days curing have a durable elastic material with considerable strength.

However, this requires the selection of the right silicone of the specific purpose, have it

applied to surfaces to which it is compatible and which have been prepared for the

material by cleaning and priming, have it applied at a limited date after manufacturing

of the silicone to ensure that it has not deteriorated, and then above all, have it cure

without the joining parts moving.

The latter, in particular, is difficult in situations where considerable temperature

movements take place from day to night.

11.6.7.Structural Silicone

Although structural silicone glazing is sometimes used, it is preferable that the glass is

mechanically restrained. The decision to use structural silicone glazing is driven by

architects and owners in the desire to see a flush and near continuous glass facade

on the outside of the building. Connell Wagner believes that once the owner and

architect wish to have structural silicone glazing, we can then assist in making this

less vulnerable to problems by input of structural engineering design and inspection.

We must put in writing each time that we do not recommend structural silicone

glazing for external panels and also point out the need to make provision in the design

for installing mechanical restraint at some future date if a total breakdown in silicone




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sealant adhesion occurs. We must further state in writing the need to continue to

carry out periodic inspection and maintenance and that this is a requirement of the

owner which must be transferred upon sale of the building.

We feel comfortable about giving advice on structural silicone but at the same time,

we must place the responsibility where it belongs; i.e. with the sealant manufacturer

for the product and the glazing contractor for its installation and the builder for overall

quality control.

We must not take responsibility for the manufacture and installation.

We must be critical of the manufacturer’s claims with the products and ensure testing

is carried out on the actual products and systems to have the material properties

demonstrated in the ‘as-built’ condition.

Our specification must be more detailed about what is wanted. We should specify the

limitation on voiding in the silicone, the adhesive strength which must be attained, the

deglazing testing that must be carried out and the replacement of faulty glazed units.

We must specify what is wanted and not accept alternatives without extensive proof

and warranties. Warranties must be checked by the Owners or Builders legal ????

We must continue to maintain high factors of safety. A factor of safety of five is the

minimum we should specify.

We must specify the amount of quality control testing and inspection plus technical

support required from the supplier of the silicone.

We must not claim to be experts at silicone and glazing, but must continue to put the

responsibility for this to the manufacturer and glazing contractor.

We must continue to specify and document that inspection and maintenance and

expected replacement of sealant is an inherent requirement of the use of structural

silicone. We must point out that there is a time limit on any sealant as per the

manufacturer’s warranty, and this has to be recognised, and above all, pointed out in

writing to the owner and architect of the building.




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We must continue to insist on factory glazing and avoid site sealant installation except

for special and isolated cases.

We must remain very cautious about structural silicone and alert everyone on the

risks.

We must not accept unsatisfactory practice.

Above all, have the client and the owner informed about potential problems and having

them share these risks.

Work towards having the building regulations cover the inspection and maintenance of

building facades (not just structural silicone glazing) so that the onus for this remains

with the owner whether he initially commissioned the design or purchases the building

later.

We must not put ourselves in the position of “accepting” materials on behalf of the

owner. The owner accepts materials and we should advise him appropriately.

We must be very careful with “new, unproven” products.

11.6.8.Curtain Wall Component Design

The Structural Engineer must work closely with the designer of the curtain wall who is

most often the curtain wall contractor who has developed and marketed his own

curtain wall system. This design most often is a typical panel solution and utilises

mullions, transoms, panels, joints and seals using members and details that are an

evolution of his own company’s practice. As most buildings are different in floor to

floor height, column grid, plan shape, structural and spandrel depth, it is necessary for

the basic system to be adapted and designed for each case.

The Structural Engineer’s role is to work with the creator and detailer of the curtain

wall to ensure that the load capacity of the component members, their stiffness and

connections are adequate for the loads and movements which must be

accommodated. When the Engineer carries out this design he needs to recognise the

tight limitations and fine detail work that is required of the curtain wall. He must have a




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sensitivity to the aesthetic requirements of the end product. The actual computations

of member sizes are not complex. It is the realisation of how the forces are

transmitted from member to member and back to the structure and how movement

provisions are created that test the skill of the Structural Engineer.

11.6.9.Structural Sealant Design

The basic process is to establish the joint spacing laterally and vertically, to calculate

the joint movements - both short term cyclical and long term, to calculate the forces

that have to be carried, the sealant type and sealant bead dimension. The materials to

be jointed influence the type of sealant selected as the first requirement is sealant

adhesion to the base material.

Experience with testing of silicone adhesion and strength has shown dramatic

differences between different silicones and the same silicones applied to different

materials. It is this characteristic of silicone sealants that is least appreciated by the

industry and which can lead to breakdown of the joint function and expensive repairs.

The adhesive and cohesive strength of silicone is a complex field and is the domain of

the silicone manufacturer and his chemists.

11.6.10.Structural Silicone Testing

This consists of two types of testing. Firstly, the testing carried out on the material by

the silicone manufacturer who batches the raw materials to strict formulation and

chemical composition. He carries out quality control testing on his product so that it

adheres to the specification that is set out in the technical literature he prepares and

circulates. This testing is carried out under laboratory conditions using freshly

formulated silicone and applied by experienced and conscientious testers. This is far

from what happens on a building site where often untrained personnel working on

swing scaffolds with limited access apply silicone of unknown age to partly cleaned

joints under all types of climatic conditions. Although laboratory tests are mandatory to

ensure that the product being used meets the specification, it is inadequate to rely on

these laboratory tests to ensure satisfactory performance of that silicone on the

curtain wall site.

Arrangements must be made to carry out prototype or even full scale tests on the

structural silicone applied under conditions simulating the real situation on site. The




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results obtained on such testing are often quite surprising when compared with the

technical literature. The specification for application of the silicone in the field must be

followed for the prototype testing and it must then be supervised on site.

11.6.11.Waterproofness

Connell Wagner is not an expert in waterproofness of curtain walls. Walls often leak

for many different reasons and the drained joint principle should be adhered to. We

must not accept responsibility for this area. There are a few skilled persons in

Australia (CSIRO and others) who will review drawings subject to testing on

manufacture and these MUST be consulted if the client requires assistance in the

area.

We should always recommend drawings be inspected PRIOR to fabrication as at

least 85% of the problems can be resolved at this stage.

11.7. Curtain Wall Prototype Testing

Because of the unique features that generally arise as a result of custom designing a

curtain wall system for a particular building facade, the extrapolation from past

experience is usually not satisfactory to guarantee a well performing curtain wall in

regards to structural response, air leakage and water penetration. This has led to

many of the major curtain wall installations in Australia having been subjected to full

scale prototype testing of a representative sample of curtain wall, attached to an exact

replica of the building.

This testing using the SIROWET rig has resulted in much improved knowledge on the

behaviour of curtain walls. This type of test usually does not cost more than $60,000

to 80,000 for an all-glass or glass and aluminium spandrel wall and $80,000 to

100,000 for a glass and granite wall, including the support structure. In many

instances, it has led to either joints, connections or seals being modified to meet the

performance specification. This type of testing must be written into the specification

and a sum of money to enable it to be carried out must be provided. There are many

curtain walls that do not perform satisfactorily but to our knowledge none that have

been subjected to full scale SIROWET testing. The test must, however, correctly

model all conditions, and not just a simple panel.




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11.8. Curtain Wall Fabrication and Erection

After the structural engineering input has been incorporated in the design carried out

by the curtain wall contractor, shop drawings are finalised and submitted for approval

by the Architect and Engineer. It is imperative that the curtain wall drawings cover not

only the typical panels and vertical and horizontal sections through panels, but also

non-typical areas and the intersection of panels and the resulting two-way joints that

occur. The treatment of panels where they pass around corners or join columns

and/or windows and doors must be drawn not only in section, but particularly in

elevation to ensure proper attention is paid to joints, flashing and sealing problems.

These drawings should also show the connection to the building and have provision

for packing to allow for the difference in tolerance between the structure and the

curtain wall. The purpose of shop drawings is to firstly, instruct the workmen in the

fabrication shop on how to build the curtain wall and secondly, to give the Architect and

Structural Engineer a further opportunity to review the design of the curtain wall.

Curtain wall drawings are often quite complex to read and this can lead to

misunderstanding between the parties and can detract from the quality of the end

product.

The erection of the curtain wall and its attachment to the structure should also be

documented to ensure that the procedure followed is understood by all parties. Quite

often the Builder does not understand the accuracy to which the curtain wall is to be

erected and the need for cast in fixings and structure to be accurately positioned to

permit fast erection. The curtain wall is inevitably on the critical path as it is the curtain

wall that weatherproofs floors and thereby permits the finishing trades to follow on.

It should be mandatory that a survey of structure and fixings is carried out in advance

of the curtain wall erection so that modification can be made to the erection procedure.

A good example of this is on a multi-storey structure where a survey for level and

lateral position of the fixing points up to six floors in advance of the curtain wall should

be carried out so that modifications may be made to joint widths on a distributed basis.

It is not uncommon to find that the curtain wall erector uses the nominal joints

documented for five or six floors in a row to only discover on the sixth floor that a




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nominal gap of 10mm has grown to 25mm or decreased to zero, at which stage

drastic action has to be taken which causes additional cost and above all delays to the

completion of the building. This often means a compromise solution that can result in

future -problems.

11.9. Quality Control and Inspection

The generally accepted quality control procedures that are normally carried out on the

building are the testing of materials to ensure that they meet material codes, and

inspection by Clerks of Works, Architects and Structural Engineers of quality of

workmanship. However, this degree of quality control and inspection is rarely provided

on facade elements that are required to perform a far more onerous task.

A fear of heights is a psychological barrier which many people cannot overcome and

as a result, inspections on the outside of a building are considerably less intense than

those carried out inside the building. This is not satisfactory and inspection must be

carried out even if it involves stepping into swinging scaffolds. Experience on many

buildings has shown that where inspections is not carried out by the most senior staff

the quality of workmanship deteriorates as well. This not only applies to curtain walls,

but to insitu concrete, brickwork, glass and any other work.

11.10.Future Inspection and Maintenance

The type of materials that are used on building facades and curtain walls often do not

have a sufficiently long history to warrant the lack of attention that is paid to them by

building owners.

An owner is quite happy to repaint his internal walls, replace carpet and other interior

furnishings on a regular basis and allows for this in his investment return studies.

However, he expects the facade to last forever, and exercises little control on whether

the facade, its joints and sealants are in good condition or not.

Alarm is raised only when water penetrates, pieces fall off, or other serious distress

occurs. Part of this problem is attributable to the designers who do not express

clearly the need to carry out inspection and possible maintenance of elements whose

manufacturers are rarely prepared to provide guarantees beyond ten years.




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Much litigation in the building industry is related to water penetration, break down of

sealants and distress in other facade elements. Much of this can be reduced or

eliminated by carrying out a regular inspections. Major buildings should be provided

with building maintenance units (not just window cleaning units) which provide people

with continued access to the facade to inspect the performance of the curtain wall and

also to permit minor maintenance and if necessary, repairs to be carried out. In most

instances an inspection, say six months after initial completion and then possibly at

two year intervals, should suffice. The cost if this is only a matter of a few hundred

dollars but can prevent major problems from occurring.

As part of a building handover, the owner should be instructed to carry out this type of

inspection and also be advised on the warranties and durability of some of the

products that he is wishfully thinking will last forever.

The Structural Engineer should be involved in the curtain wall design process and the

degree of involvement depends on the complexity of the curtain wall and the

uniqueness of the system.

He should be involved prior to the building structure being finalised as in some

instances curtain walls cannot be expected to function properly where the building

movements and deflections are beyond the limits to which a curtain wall can perform.

11.11.Curtain Walls - Connell Wagner’s Role

The following is an outline of how we envisage our detailed role. We generally act as

secondary consultants to the Architect, the prime consultant for the curtain wall. We

see ourselves providing support in structural areas throughout the documentation,

fabrication and erection period.

Our contribution is likely to be as described below:

1. Production of the structural content of the Performance Specification, involving

establishment of structural criteria.

2. Support and advice to the Architect during Design Development, including:




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Structural review and comments on curtain wall systems, jointing and

connection to the building; Authority requirements; facilitating passage of

Authority submissions and approvals; prototype testing to simulate conditions as

close as possible to the “as built” situation; identification of technical difficulties;

identification of inadequate or too conservative designs by potential curtain wall

contractors; guidance on the involvement of specialist consultants; related but

non structural aspects; eg. smoke barriers and recommending review of

drawings for waterproofing.

3. Reviewing submissions by the Sub-contractor and advising the Architect during

the Sub-contractor’s design, development, manufacture and erection.

This takes the form of:

3.1 Examining and checking shop drawings and computations for:

conformity with codes, manufacturer’s requirements and common

practice;

glass thicknesses, aluminium components and connections, fixing of

these components to the building frame, glass to aluminium and

aluminium to aluminium clearances at general and Building

Maintenance Unit (BMU) restraint locations; and

structural silicone bite size and locations.

3.2 Evaluation of structural silicone adhesion including:

glass coatings, aluminium finishes, adhesions to the chain of interfaces

and the compatibility of associated materials.

3.3 Reviewing quality control and testing procedures of the Builder and

Sub-contractor as they apply to structural matters, eg:

Aluminium supplier and fabricator.

Anodiser/Painter

Sealant Supplier and installer




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Erector

BMU supplier

This involves considering:

• Personnel qualifications and experience.

• Clerk of works and specialist inspections.

• Component testing where analysis is not appropriate, or where

confidence needs to be established.

• Structural silicone adhesion and glazing tests.

• Both fabrication and erection phases for structural matters.

It is important to note that Curtain Wall Contractor is the curtain wall

designer and Connell Wagner’s role is to structurally review that design.

4. Monitoring Quality Control Procedures during Construction

4.1 Reviewing material and system testing procedures

4.2 Reviewing test results

4.3 Making periodic inspections during fabrication glazing and deglazing,

installation and testing.

5. Post Installation or Maintenance Inspections and Reporting

including assistance in setting up the Maintenance Manual and monitoring its

production.

6. Extra Optional Services

• Engineering certification that we have checked the design prepared by the

Curtain Wall Contractor. This increases responsibility and the level of

engineering review.




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• A higher level than otherwise of quality control monitoring and periodic

inspections by Connell Wagner.

• An involvement in maintenance inspections.

The area of facade engineering can be both an area of increased risk and

rewards for Connell Wagner. Any involvement in this area requires detailed

discussions with the Principal responsible to ensure our responsibilities are

clearly understood.

11.12.Curtain Wall Problems

Below is a list of problem items and comments on curtain wall design, fabrication,

erection and post installation problems that we have encountered.

1. Lack of proper documentation in regard to shop drawings and specifications

for tender purposes.

2. Performance specifications suffering from lack of clear criteria, making it

difficult to assess whether the specification is met.

3. Authority requirements not established by suppliers so that “after contract”

approaches to authorities lead to cost increase and delays.

4. Suppliers providing minimum input at tender time and failing to answer

questions until a contract is signed. This places the owner at a disadvantage

and places the design team in the position of delaying the project and

recommending cost-increasing changes, argued to be unnecessary by the

Contractor.

5. Drawing approvals being made on early submissions which do not show up

problems until fabrication is well advanced and corrective action results in

delays.

6. Tolerances of structure, curtain wall elements and fixings not addressed at

documentation, thus leading to problems when erection takes place.




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7. Connection details of members being poorly documented, particularly

intersections, welding, studding and bolting.

8. Guarantees for performance are not alternatives for inadequate designs.

When they are provided it is after the event and give little comfort. We have

had examples where guarantees have been provided for work which was

clearly unsatisfactory.

9. Curtain wall contractors have disappeared with rapid frequency making after-

sales service difficult to get.

10. Inadequate site supervision ensures that fixings, connections, clearances,

drainage and corrosion protection are not inspected and are then out of sight.

Connell Wagner require supervision by inspectors on a full-time basis, both

inside and outside the building and during fabrication.

11. Damage during erection is difficult to rectify. Repairs results in compromise.

Protection procedures must be documented and carried out as work

proceeds.

12. Cleaning is a common problem as other trades are working overhead, e.g.

concreting and materials handling. It needs to be documented and priced as it

is a time consuming and expensive operation. The erector will scrimp on this if

it is included in the lump sum figure. It should be programmed and costed.

Remember it needs access on the exterior and this needs swing scaffolds.

Do not allow the BMU to be the means of access.

13. Having an appropriate means of protection is vital as there are instances

where the protection has resulted in major problems.

14. Corrosion protection, dissimilar materials, contaminated water, e.g, cement

products, rust, form oils and curing agents, can all lead to problems. Use

stainless steel or hot dip galvanised steel (after fabrication) for durability.




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15. It is difficult to replace damaged panels. Allowance for this should be part of

documentation. The BMU must have capacity to allow replacement where this

is not possible from within the building.

16. Incorporation of the BMU and its interfacing with curtain walls can lead to

delays and problems due to different responsibilities. Expansion joints can

lead to damage where “skates” lock into guides.

17. Expansion joints cause “noise” problems as thermal expansion causes

movement of metal parts in contact.

18. Provision of inadequate tolerance leads to on-site alterations with destruction

of corrosion protection, overloading of connections with excessive packing,

etc.

19. Prototype testing can only be carried out when dies are approved and

fabrication is well advanced. Progressive testing of components may be

preferable to confirm structural action when computations are inadequate to

prove structural criteria are met.

20. Knowledge of glass and understanding of its behaviour is limited.

21. Silicone material selection, fabrication, age, compatibility with glass, laminate,

aluminium, anodising, paint, concrete, bead size, backing rods, casing,

skinning over, etc., are all problems that must be overcome. Site sealing is to

be avoided. Durability of adhesion is vital.

22. Must test prototype joints with sealants and simulate actual conditions.

23. Recognise the large number of suppliers and contactors involved in the curtain

wall.

24. Large loads will require a structural connection well above “normal” restraints

provided in curtain walls.




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25. Erection should be preceded by site measurement of the structure to enable

tolerances to be adjusted progressively.

26. Historic problems -

• leaking windows

• noisy windows

• corroding brackets

• failing paint

• cracked glass (movement)

• disintegrating glass (inclusions)

• stained glass (acid, concrete washing)

• noisy panels

• silicone adhesion break down

• improper sealant installation (air pockets)

• inadequate glass thickness resulting in excessive deflection and

reflection

• inadequate bite of sealant

• loose dry seals

• sealing strip loosening

• panel corrosion

• water penetration

• improper sealing of glass leading to stress concentration and thermal

shock




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12. NATURAL STONE

12.1. Introduction

Stone is the oldest construction material used by mankind.

This is a specialised area of design. As with all materials an appreciation of both the

stone and the supporting material is vital to the understanding of the performance of

stone. Natural stone has properties determined by its geological history. The

performance of stone in place can often be determined by the way it is cut or fixed.

One cannot order stone to suit a design assumption like concrete, steel, timber etc.,

we must test the stone to establish the design criteria.

Stone can be either igneous, sedimentary or metaphoric. The main types of stone

include:

• Granite (Durable)

• Marble (Low to moderate durability)

• Sandstone (Low durability)

• Bluestone (Durable)

(or Basalt)

• Slate (Durable)

Stone is now used for:

• Veneer cladding to buildings (inside and outside - this is the area that CW are

most likely to be involved and this section concentrates on this type of cladding).

• Paving

• Joinery and furniture

• Monumental masonry

• Landscaping

• Traditional massive masonry.




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12.2. Codes

None

12.3. References

1 ASTM C99. Test Method for Modulus of Rupture of Natural Building Stone.

2 ASTM C880. Test Method for Flexural Strength of Natural Building Stone.

3 ASTM C120. Test Method for Modulus of Rupture of Slate Building Stone.

4 ASTM C121. Test Methods for Absorption and Specific Gravity of Slate

Building Stone.

5 ASTM C97. Test Methods for Absorption and Specific Gravity of Natural

Building Stones.

6 ASTM C170. Test Method for Compressive Strength of Natural Building

Stone.

7 ASTM C241. Test Method for Abrasion Resistance of Stone Subjected to Foot

Traffic.

8 ASTM C503. Standard Specification for Marble Building Stone (Exterior).

9 ASTM C568. Standard Specification for Limestone Building Stone.

10 ASTM C615. Standard Specification for Granite Building Stone.

11 ASTM C616. Standard Specification for Sandstone Building Stone.

12 ASTM C629. Standard Specification for Slate Building Stone.

13 Amrhein, J.E., and Merrigan, M.W., "Marble and Stone Slab Veneer", Masonry

Institute of America, 1986.




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14 "Marble Design Manual," Marble Institute of America, Farmington, MI, 1983.

15 "Specification for Architectural Granite," National Building Granite Quarries

Association, Inc., West Chelmsford, MA, 1986.

16 "New Stone Technology, Design and Construction for Exterior Wall Systems,

ASTM StP 996," Barry Donaldson, ed., 1987.

17 Sorensen, C.P., and Stephens, E.J., "Stone Veneer Cladding," Technical

Study No. 46, Department of Works Commonwealth Experimental Buiding

Station, Sydney, 1969.

18 Chin, I.R., Stecich, J.P., and Erlin, B, "Design of Thin Stone Veneers on

Buildings,"Proc of Third North American Masonry Conference, University of

Texas, Arlington, June 1985.

19 British Standard Code of Practice CP298:1972 "Natural Stone Cladding (Non-

load bearing)".

20 "Stone in Modern Buildings" Seminar, Sydney, October 1989.


None


12.5.1.General

There are two points of view in regards to who should carry out the design of the

facade system. Currently it is common for the architect to seek advice from the

industry and decide a design philosophy. This is then translated into indicative

details/performance specifications and is then issued for design/construct

submissions. This does have some advantages, not the least of which is the

opportunity for the main contractor to influence the choice of facade system to suit his

particular wishes. There are however many disadvantages. Not all specialist




4 of 17

subcontractors are particularly skilled in the use of stone and there is not much

experience in Australia in the use of pre-assembly systems. This method has great

risks for us particularly. If we provide a partial engineering service, the Project

manager and Architect will assume we take full responsibility when things go wrong .

This partial service should only be entered into with very clear definition of our role and

service and advice from Corporate office.

The other view is for specialist Facade Engineering companies or experienced

engineers such as ourselves to be involved in the design of stone cladding and to

carry out the complete design. There are also specialist firms with skills in the design

of stone cladding who can be engaged to assist us as sub consultants if required.

These specialists should be involved throughout the design development process

ensuring that ranges of options are investigated and thoroughly analysed and the

relative merits are clearly understood as well as the design, documentation and

construction phase.

There are a number of generic systems for the installation of stone on buildings and

infinite variation in the detail.

Having accepted a system and a subcontractor, it is important to continue the

involvement of the facade engineer in the scrutiny of the detailed design of the system

and the review of the shop drawings including component and material durability and

the construction phase.

Periodic inspections and testing if required needs to be incorporated in the facade

maintenance manual. Maintenance manuals are generally not well prepared. For

major facades, a dedicated manual should be prepared which will contain a minimum

of the following:

• Summary of Design Team, Builder, Subcontractor supplier;

• All relevant documents, including design drawings, shop drawings, site

instructions, calculations, etc.;

• Summary of design principles;




5 of 17

• Data sheet describing components, their purpose, materials, supplier and test

data as relevant;

• Details of inspection processes, sequence and frequency and proforma sheets

for recording findings and data;

With stone cladding, if we are involved, a full understanding of the whole process from

selection to final use is vital. Stone is normally chosen for its appearance. This

involvement will include:

• Quarrying and how the stone is extracted and finished.

• Evaluation and selection of stone. This may include:

- Aesthetic parameters, including colour, texture, finish, uniformity, massivity,

etc.

- A range of stones that satisfy architectural parameters and grade in order of

preference.

- Obtaining and evaluating data for physical properties, petrology, durability,

quarry source and performance in previous applications.

- Reporting on comparative quality of stone grade with preferences.

- For the preferred stone(s) we will need to visit the stone source and

evaluate the suitability of the geological disposition and the techniques used

to manufacture the stone from the quarry.

• variability of stone;

• historical data;

• quarry management, methods, blasting, cutting, etc;

• production rates and variations;

• block sizes;

• wastage rates;

• equipment;

• transportation requirements.

- Obtaining samples and carrying out a preliminary test programme to identify

stone properties including:




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• Modulus of Rupture

• Flexural Strength

• Compressive Strength

• Density

• Water Absorption

• Young's modulus

• Coefficient of linear expansion

• Petrology including thin section analysis and X-ray diffraction for

deleterious minerals

• Durability of accelerated ageing method.

- Investigating previous applications for:

• performance in-situ

• thickness vs panel size

• supplier performance

• Confirming suitability or not of preferred stone, and preparing a report

on design parameters, limitations etc.

Often stone is chosen prior to our involvement and it may be chosen by the architects

or developer on purely aesthetic grounds to fit in with a cloour scheme or other non-

engineering related criteria. If we are to get involved with the attachedment of stone

onto buildings we must make all aware of the engineering requirements as outlined

above for the particular stone concerned and ascertain its suitability for the intended

use, prior to large orders being placed. Quite often stones elected by those without

experience should not be used as cladding.

12.5.2.Natural Stone Facade Claddings

Natural stone facade cladding materials are used to enhance the external appearance

of buildings and to provide a durable finish. They are usually installed as one of the

following systems:

(i) "conventional" set stone on masonry backup;

(ii) stone in a glazed system of mullions, transoms, etc.; or




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(iii) stone fixed to prefabricated backup trusses or other steelwork.

The total facade must:

(i) withstand the anticipated design loads from gravity, wind and earthquake;

(ii) control air infiltration;

(iii) resist water penetration;

(iv) accommodate thermal movements;

(v) accommodate movements of the building frame.(sway, elastic deformation

and creep, shrinkage of structure and/or supporting back up walls, thermal

movements of structure and/or cladding).

(vi) have adequate connections to accommodate combinations of building

movements, fabrication and erection tolerances and economy of erection.

(vii) prevent corrosion of anchoring devices.

(vii) have adequate joint design.

(vii) meet transportation and handling requirements.

(viii) be coordinated with the requirements of adjoining trades.

(ix) meet the testing programme.

Natural stone has properties determined by its geological history. We cannot order

stone to suit a design assumption as we can with timber, steel or concrete; rather, we

must thoroughly test the selected stone to establish the design criteria.




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"Modern" stone technology is a product of the 1980's. Before this there had been little

change for a century. It is therefore not surprising that there is a scarcity of technical

information and that many in the industry are still using the old techniques.

Until recently, stone thicknesses were 50 to 100 mm, so different techniques are

obviously required for fixing the 30 mm stone used nowadays.

The trend to thin stone was driven by the cost savings in shipping and its support on

the building.

12.5.3.Stone Selection

Natural stone is usually selected for its appearance. Once a colour has been decided

upon, sources of supply are established. At this stage some broad parameters can

be investigated, eg:

(i) indicative landed costs;

(ii) amount available of the desired appearance;

(iii) flexural strength;

(iv) block size (to establish maximum stone panel size); and

(v) other buildings where that stone has been used.

Do not expect the stone supplier to be knowledgeable about the technical qualities of

the stone he supplies. It is up to the designer, to carry out the testing needed.

Once the choice has been narrowed down to one or two suppliers (quarries, not

agents who may be buying from the same quarry) it is important that the quarries and

fabrication plants are inspected to determine the quantity available, the capacity to

produce, the quality of the product and the quality control procedures that are in place.

By visiting the quarry and factory, the supplier sees that we are interested in quality

and we become real people, not merely an obscure source of correspondence from

another place.

Once a particular stone and its source of supply have been selected, comprehensive

testing should begin to confirm the suitability of the stone in all relevant aspects and to

confirm the thickness necessary (or the maximum allowable span).




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12.5.4.Properties of Building Stones

Because the properties of stone varies, there can be no rigid specification to control

quality. Therefore, comprehensive testing is always required. However, data for use

during the very early stages of a cladding project may be obtained from tables 12.1

and 12.2.

12.5.5.Testing

A range of tests on stone is necessary for all major projects. These include:

(i) petrographic tests to establish the true type of stone and its mineralogy,

particularly its susceptibility to weathering and staining;

(ii) mechanical strength testing, particularly for modulus of rupture (ASTM C99)

and flexural strength (ASTM C880);

(iii) permeability and absorption;

(iv) density; and

(v) abrasion resistance.

Testing should be divided into three phases:

(i) Initial testing, carried out before letting a contract and aimed at obtaining

reliable data for a range of possible stones.

(ii) Design testing, to establish design loads, factors of safety, etc.

(iii) Construction phase testing to ensure that the stone being delivered continues

to have the properties originally accepted.

Initial tests should include petrographic tests, modulus of rupture tests and flexural

strength tests.




10 of 17

Tests for compressive strength and absorption should also be done for some

materials.

Petrographic testing can best be carried out by a geological consultant from a local

university or geotechnical consultant.

Modulus of rupture tests are carried out on 57mm (2 1/4 inches) thick stone with a fine

abrasive finish to the face in tension.

Flexural tests to ASTM C880 are the most meaningful tests and should have the same

thickness and surface finish as intended for the project. Thinner stone is likely to

exhibit a lower rupture strength, particularly if it has relatively large crystals, that is, it is

"coarse grained".

Modulus of rupture and flexural strength testing should be carried out in both wet and

dry state and parallel to and perpendicular to the rift of the stone. (Rift is the direction

in which the stone splits most easily. Not having a rift is rare for any rock. Even

igneous rocks will usually split easier in one plane than in others. The quarry or

manufacturer should be required to mark the rift on the samples). At least five tests for

each of the four conditions should be carried out, ie. 20 modulus of rupture and 20

flexural strength tests. The lowest results (usually wet and perpendicular to the rift)

are used for design. Flexural strength test specimens should have the intended

surface finishes - polished, flamed, honed, etc., as these can have a significant effect

on the flexural strength. Thermal finishing (flaming, exfoliation) can cause a marked

reduction in flexural strength due to loss of thickness and micro cracking caused by

thermal shock from the surface heating. Reductions of between 5% and 35% have

been reported.

Natural stone exhibits flexural failure characteristics similar to glass in that larger

panels fail at lower stresses than smaller panels. (This is because the material is

brittle and non-uniform so that larger panels have a greater chance of containing a

significant defect than do smaller panels). Therefore, some flexural tests should be

carried out on full size panels.

All testing should be carried out where the designer is located to enable the designer

to observe the tests and so the results can be verified.




11 of 17

Design testing may involve wind tunnel testing to obtain facade pressures and

suctions, structural connection tests of the pin or kerf fixings, load tests of full size

panels fixed as they will be on the building and serviceability tests of a facade mock-up

to check for water penetration, air and water permeability, sealant performance, etc.

Construction phase testing involves regular load testing of randomly sampled panels,

either full size, or cut down for flexural testing to ASTM C880.

Other tests may be desirable; for instance, shear tests on a fixing pin within the stone.

This test is particularly important where it is proposed to place a pin close to the edge

of a stone panel or where the grain size is large compared to the thickness of the

panel.

12.5.6.Allowable Stresses (Working)

Design stresses can be ascertained only after carrying out sufficient tests. The tests

provide information on the ultimate strength that has to be modified by a safety factor

to give design strength. The safety factor should vary depending on the variability of

the test results and on the type of rock.

Recommended values are as follows:

Spread in Safety Factor Safety Factor

Test Results for Wind Load for Lateral

Anchorage

Igneous rock (eg. Granite)

Up to 10% 3 4.5

10% to 20% 4 6

over 20% 6 8

Metamorphic rock (eg. marble)

Up to 10% 4 6

10% to 20% 5 7.5




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over 20% 7 10

Sedimentary rock (eg. limestone)

Up to 10% 5 7.5

10 to 20% 6 9

over 20% 8 12

The spread of test results is a percentage of the average value of at least five tests. If

significantly more than five results are available, then the safety factors can possibly

be reduced.

When designing windows, the allowable stresses we use are based on a probability of

8 failures per 1000 panes at the design load. This represents a design factor of safety

of 2.5. People accept glass failures as a fact of life. It is a brittle substance. The

same rate of failure at the design load would not be readily accepted for stone cladding

as stone is considered to be strong, and it is not as easy to obtain matching

replacements as it is for glass. So design safety factors should be at least 3 for any

stone and probably higher.

12.5.7.Methods of Supporting Stone

Stone support can be divided into three types: conventional set stone on masonry

backup; stone in a glazed system; and stone fixed to backup trusses.

(a) Stone on Masonry Backup

This can be one of two forms, either stone fixed insitu to concrete, brick or

block walls, or stone with concrete poured against it to form a precast, stone

faced panel. In the latter case there should be a bond breaker between the

stone and the concrete.

Because of the high site labour cost and the weight of a masonry wall that

must be supported by the structure, stone fixed to insitu masonry is not

recommended as a first choice.

All steel should be grade 316 or 304 stainless. Kerf fixings are recommended

for their ease of aligning the panels. (A kerf is a slot cut into the edge of a




13 of 17

stone panel). The kerf is filled with a fast curing silicone before the panel is

positioned. This allows the panel to be aligned before the silicone sets and

leads to a flexible but firm connection.

(b) Stone in a Glazed System

There are three forms of fixing into a curtain wall or similar system; pin fixed,

kerf fixed, or fixed with clip-on aluminium extrusions.

The pin or kerf fixings may also include structural silicone as a continuous

fixing around the perimeter as a back up to the primary fixing.

For the aluminium extrusion method, the stone is fixed as if it were a glazing

unit as its thickness will be about the same as that of a double glazed window.

However, there is an aesthetic objection to this method. It results in aluminium

mullions and/or transoms exposed between adjacent stone panels.

The more usual approach of pin or kerf fixings results in only narrow sealed

joints between adjacent stone panels. The joint width depends on the

expected structural deformations, taking account of the allowable deformation

range of the sealant. The deformations to be considered include:

(i) lateral sway (perhaps 6 mm between adjacent floors);

(ii) axial column shortening (about 3-6 mm per storey);

(iii) differential spandrel beam deflection due to variations in live load, beam

stiffness, etc. (must be controlled to manageable values if the joint

width is not to be excessive).

It is normal practice to use a prefabricated panelised (or unitised) system

where the window units arrive on the site complete with stone and glass

already fixed in place. The unit size will depend on the window module but it is

usually around 2 m wide by the storey height.

(c) Stone Fixed to Backup Trusses




14 of 17

The advantage of this method is that the truss can usually span from column

to column, thereby eliminating one major source of differential movement

needing to be accommodated by the horizontal joints. A further advantage is

that the facade gravity load is applied to the columns directly rather than to the

spandrel beams. The wind load may be transferred to the structure between

columns using vertically flexible struts. The stone is fixed using kerfs or pins

The size of the trussed panel can vary from a spandrel height unit of about 1.2

m to a unit accommodating the window as well and therefore storey height.

However, unless the columns are very close together, such a unit cannot be

easily transported and its width may need to be less than the column spacing,

leading to the need to accommodate all the movements listed for the previous

system.

(d) Support Stiffness

Stone is a brittle material and, because it is much thicker than the glass used

in a facade, its allowable deflection is much less. The maximum deflection of

members restraining glass against out of place loading is usually limited to

span/150.

Facade manufacturers are accustomed to the member sizes that conform to

this requirement so that a design criterion of, say, span/1000 for the deflection

of a panel of stone can easily be overlooked. Therefore, the contract

documents must clearly explain such a requirement.

Suitable articulation and fixings of stone cladding can enable stringent

deflection limits to be reduced.

12.5.8.Considerations in Setting Up a Stone Supply Contract

The following points have come out of experience gained on several Australian

projects.




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- Never let a performance contract without requiring Client access to testing

results and supply details. Ensure that the Client has access to the

Contractor's design consultant.

- If we use a local (Australian) agent to import and handle the stone, we pay from

30 to 300% mark up for very little knowledge and experience.

- There are agents in Italy who buy stone blocks from quarries and on-sell to the

panel manufacturer. These agents are usually expert in stone selection.

- If we operate solely through a local (Australian) agent, we have no control over

the fabricator. The agent will negotiate the lowest price and we will get what he

pays for (which is probably not what our Client pays for).

- There is no point in making a curtain wall contractor responsible for the supply

and quality of stone, as a curtain wall contractor is unlikely to be knowledgeable

in that field.

- It is preferable that the selected stone to be imported by the Client, is tested,

cut, polished and provided to the fabricator/erector who must then take full

responsibility for its fixing.

- Prequalify all stone cutters/polishers from a selected tender list on the basis of

track record and financial soundness.

- Invite and evaluate bids on the basis of cost, sources of supply, stone

properties. Make clear whether cost or quality is the more important. Request

samples for petrographic and modulus of rupture testing.

- Inspect the quarries and fabrication plants. Obtain referees from previous

projects and check their satisfaction. Determine the details of the fabricator's

quality control procedures. (Do all this using a suitable CW person, do not use

an overseas agent, as it is important to establish a personal relationship to

facilitate communications).




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- Use an independent local (to the manufacturer) inspector to look after our

interests on a day to day basis during manufacture.

- Accept stone only after delivery and inspection. Pay on 90 day letter of credit,

payable after time for checking.

- Request sample panels to define the range of acceptability of blemishes,

colour and polish. Samples are to be cut from a larger panel with one part kept

at the factory and one at the building site.

- Select panels to avoid having opposite extremes of acceptability in adjacent

locations.

- For imported stone allow eleven months from completion of contract

documentation to stone fixed in place.

Prequalify manufacturers 3 weeks

Call tenders 1 week

Tender period 4 weeks

Evaluate tenders 2 weeks

Assess stone, inspect quarries, factories 4 weeks

Award tender 1 week

Manufacture first shipment 8 weeks

Shipping, customs, etc 9 weeks

Inspect and fix 2 weeks

Buffer period 12 weeks

The buffer period is to ensure time is allowed in the building programme for a

batch of stone to be rejected and a replacement obtained. Without this, we are

at the mercy of the supplier who knows we cannot afford to stop the job.

The shipping and buffer period could both be reduced for stone sourced from

within Australia or New Zealand.




17 of 17

Physical Property Type Of Building Stone And Applicable Astm Standard

Granite

Astm C615

Limestone

Astm C568

Marble

Astm C503

Sandstone

Astm C616

Slate

Astm C629

Astm Test

Method

Compressive

Strength, MPa

130 12 To 55 52 Sandstone14

Quartzitic

Sandstone69

Quartzitic138

C170

Modulus Of Rupture,

Mpa

10.3 2.8 To 6.9 6.9 Sandstone2.0

Quartzitic

Sandstone6.9

Quartzite13.8

50 To 62 C99

Slate C120

Density Kg/Cu.M. 2560 1760 To 2560 Calcite2590

Dolomite2800

Serpentine2690

Travertine2300

Sandstone2240

Quartzitic

Sandstone2400

Quartzite2560

C97

Absorption By

Weight %

0.4 12 To 3 0.75 Sandstone20

Quartzitic

Sandstone3

Quartzite1

0.25 C97

Slate C121

Abrasion Resistance 10 10 8 8 C241

Table 12.1 Minimum Physical Properties Of Commonly Used Building Stones.




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Type of Building Stone

Granite Limestone Marble Sandstone Slate

Modulus Of Elasticity

Mpa

40,000 To 56,000 23,000 To 37,000 13,500 To 102,000 13,000 To 53,000 67,000 To 124,000

Ultimate Tensile

Strength MPa

4 To 7 2 To 5 1 To 16 2 To 3 20 To 30

Ultimate Shear

Strength MPa

13 To 33 6 To 12 11 To 33 2 To 20 13 To 25

Coeff. Of Thermal

Expansion Per 0C

.000011 To .000016 .0000043 To

.0000054

.0000066 To .000022 .000009 To .000022 .000017 To .000022

Minimum Thickness*

(mm)

30 30 30 50 30

TABLE 12.2 Other physical properties of commonly used building stones.

* Thickness nominated is for cladding stonework. It is a guide only.




1 of 5

13. ALUMINIUM

13.1. Introduction

Aluminium and aluminium alloys find a place in structural design because of their

resistance to corrosion, high strength to weight ratio and ability to be readily extruded

into a wide range of shapes and sizes.

Although, at first glance, there seems to be a great number of alloys with meaningless

numbered designations, the designations are controlled by an international convention

based on the major alloying element as follows:

Pure (> 99%) aluminium 1 xxx

+ copper 2 xxx

+ copper/silicon 3 xxx

+ silicon 4 xxx

+ magnesium 5 xxx

+ magnesium/silicon 6 xxx

+ zinc 7 xxx

The other important designation is temper. This is a letter which follows the alloy

number and is one of the following:

F as fabricated (no control over properties)

O annealed (the lowest strength conditions)

H strain hardened (with or without thermal treatment)

T thermally treated (with or without strain hardening)

For example 5454-H34, a strain hardened aluminium-magnesium alloy used for

structural fabrication; and 6063-T5, a heat treated aluminium-magnesium-silicon alloy

widely used for producing extruded shapes.

Because it begins to lose strength at temperatures above about 100°C, aluminium is

unsuitable for high temperature applications but it is very suitable for low temperature

(cryogenic) applications when it may even exhibit improved ductility.




2 of 5

Aluminium is protected from corrosion under mild conditions by a surface film of oxide

which can be reinforced and decoratively enhanced by the anodising process.

Some properties of aluminium alloys are:

ultimate tensile strength 100MPa to 350MPa

Young’s modulus 69 to 73 x 10³ MPa

mass 2700kg/m³

coefficient of thermal expansion 24 x 10-6/°C

The following curves quite graphically illustrate the strength and ductility behaviour of

the common 6063-T5 alloy. Note how ductility improves below -100°C and strength

drops off above +100°C.

13.2. Codes

Standards Association of Australia AS 1664-1979 SAA Aluminium

Structures Code

Standards Association of Australia AS 1664 - 1997 SAA Aluminium

Structures code: Part 1 - Limit State

Design.

Standards Association of Australia AS 1664-1997 SAA Aluminium

Structures Code: Part 2 - Working

Design.

Standards Association of Australia AS 1665 Welding of Aluminium

Structures




3 of 5

Standards Association of Australia AS 1734 Aluminium and aluminium

alloys - flat sheet, coiled sheet and plate

Standards Association of Australia AS 1866 Aluminium and aluminium

alloys - extruded rod, bar, solid and

hollow shapes

13.3. References

The Aluminium Development Council of Australia (Limited), Engineers Handbook

Aluminium, February 1979


13.5. Design principles

Before designing any aluminium member, the alloy must be selected or identified.

Selection will usually be made on the basis of availability and cost as well as suitability

for the application required. This may include weldability, bendability, castability,

machinability, etc.

13.5.1.Allowable Stresses

AS 1664-1979 (superseded) tabulates the allowable stresses for 21 different alloys.

Single values are given for tension and bearing for the welded and unwelded

conditions and formulae are given for compression and web shear for a significant

number of different shapes.

The allowable stresses are based on the formulae contained within section 5.3 of AS

1664. For the case of a single web laterally unbraced beam (such as a curtain wall

split mullion), the tabulated values can possibly under estaimate the beam’s strength.

A more precise value for the maximum permissible stress can be obtained using

section 5.5 of AS 1664. In the special case of a split mullion, it is standard industry

practice for the Iy of the combined section to be used as both extrusions have been

found to buckle laterally together under testing.




4 of 5

Maximum allowable stresses are able to factored up, depending on the nature of the

member, for wind loads as specified under section 3.2.4 of AS 1664 - 1979.

Welding results in a large reduction in permissible stress as it destroys the temper of

the alloy. Rules are provided in the Code for assessing the loss of strength of

compression members depending on the location of the welds.

A 1997 edition of AS 1664 has recently been released - Part 1: Limit State and Part 2:

Working.

13.5.2.Fatigue

Fabricated aluminium, like steel, must be designed for fatigue when frequent load

fluctuations exist. AS 1664 has a large section on fatigue for 9 classes of

construction. The classes are defined by the welding/bolting/rivetting details.

13.5.3.Thermal Movement

The coefficient of thermal expansion of aluminium is twice that of steel, a factor which

must not be overlooked when detailing aluminium in association with other materials,

particularly steel. Ignoring this could, where the aluminium is restrained, lead to

buckling or severe overstress.

13.5.4.Connections

Joints in fabricated aluminium are commonly effected by welding, bolting, rivetting,

screwing and gluing. AS 1664 and AS 1665 cover the welding of aluminium.

Bolting and rivetting are covered in AS 1664 in respect of spacings and edge

distances, bearing and shear stresses. Because of the wide variety of conditions

encountered, the load capacities of self tapping screws are not specified and must be

established by testing particular joint arrangements.

Gluing of aluminium is becoming increasingly common in the aeronautical and bus

and train manufacture industries but will probably not often be applied in building

structures. When its use does arise, reference should be made to adhesive

manufacturers or suppliers for recommendations and design data.




5 of 5

13.5.5.Dissimilar Materials

Aluminium will react readily with dissimilar metals in the presence of moisture.

However, grade 304 or 316 stainless steel, which like aluminium, also has a strong

protective oxide layer, has been found to perform satisfactorily without added

protection unless in a marine or industrially polluted environment.

Where aluminium is in contact with mild steel, both the aluminium and the steel should

be coated with a suitable paint to separate the two metals. (As the available types of

paint tend to change with the passage of time, advice as to which to use should be

sought from the Aluminium Development Council or another expert source.)

Aluminium in contact with moist concrete must be avoided as the concrete is highly

alkaline. A thick paint coating or thin plastic separating film should be used to avoid

corrosion.

Timber should be considered similarly to concrete as timber contains many

compounds, some of which will react with aluminium.

13.5.6.Chemical Corrosion Resistance

Aluminium reacts strongly with all strong acids and alkalis and less strongly with weak

acids and alkalis. Other chemicals may react with aluminium to varying degrees.

Reference should be made to the Engineers Handbook Aluminium which contains an

extensive listing and, in cases of doubt, to major aluminium suppliers.

Available Forms

Aluminium is available in a wide range of forms including:

• Extruded sections by various manufactures;

• Plate and sheet;

• Corrugated sheeting for roofs etc; and

• Castings and forgings.




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14. TENSILE MEMBRANE STRUCTURES

14.1. Introduction

Tensile Membrane Structures are a specialised area and differ from other building

systems in that they have significantly greater span to weight ratio and the principal

structural forms are all doubly curved surfaces. The equilibrium of the system under

different loading conditions is maintained primarily by changes in the geometry of the

structure. Tensile Membrane structures are also known as fabric structures and can

be divided into two distinct categories:

• Air supported structures

• Tensile structures

Air supported structures are conclastic surfaces in which the interior is pressurised to

support the fabric roof. The tensile structures basic form is the hyperbolic paraboloid

and the hyperboloid which are anticlastic shapes (double curved, with the curvatures

opposing each other from a single intersecting point). There are a number of families

of tensile structures. These are hypars, barrel arches, crossed arches, folded plate

and conical forms, which are illustrated below.

Tensile membrane structure fabric can be divided into three main groups - films,

meshes and fabrics. The last group is by far the largest and the one where we are

most likely to be involved. In that group there are two materials predominantly used in

the industry. These are polyester laminated or coated with polyvinyl chloride (PVC)

and woven fibre glass coated with polytetrafluoroethylene (PTFE, better known by its

trade name, Teflon).

Films are transparent polymers supplied in sheet form and are not laminated or

coated. Examples include clear vinyl, polyester or polyethylene. These films are

cheaper than textiles but they are not as strong or durable as them.

Meshes are porous fabrics, typically available as polyester weaves lightly coated with

vinyl or as a knitted fabric using high density polyethylene, polypropylene or acrylic

yarn. Being porous they do not provide rain shelter, but they are inexpensive, require




2 of 15

little engineering, or patterning and have become very popular as temporary sun shade

structures.

The starting point for the design of a tensile membrane structure is the definition of an

acceptable surface geometry. Tensile structures are typically minimal surface

structures with curved formations with the smallest achievable surface area within the

defined closed boundary. The shape of the surface is its structure, thus geometry is a

vital element of our work. In days past, stocking models were the stock of trade of the

tensile membrane designer. These can still be a valuable design tool however for

anything but the very simplest of structures computer-aided design is essential. A

membrane mesh is developed on the computer representing the doubly curved

surface as a grid of lines. Initial formfinding is then carried out, followed by analysis for

external loads, such as wind, rain and snow, as applicable. When the analysis is

completed, maximum membrane stresses are determined. These in turn are used to

select the fabric and calculate component forces and reactions used to design the

components, the supporting structure and foundations.

As can be seen the design of tensile membrane structures is a highly specialised area

and it is recommended that all design enquiries should be referred to the Melbourne

Office. We have access to the "TENSYL" computer program for the form finding,

analysis and patterning of tensile membrane structures. Samples of our structures to

date are shown in Connell Wagner's Lightweight Structures Brochure.

14.2. Codes

There are no Australian Standards for the design of the fabric surface. A set of factors

of safety have been developed over the last decade for use in the design of these

structures.

14.3. References

B K Dean "Computer Modelling - The Key to Successful Fabric Structures"

MSAA Conference, July 1989

P Lim, B K Dean "The Influence of Geometry on Wind Pressure Coefficients on

Conical Structures" MSAA Conference, July 1990




3 of 15

S Fernando,

P N Georgiou "Wind Tunnel Testing for Membrane Structures"

and R L Dutton MSAA Conference, August 1991

P Lim "The Development of Structural Fabrics and Foils"

MSAA Conference, August 1991

I Knox "Criteria for Selection for Shade and Tensile Structures"

LSAA Conference, September 1996

Buro Happold - Patterns 5


None

14.5. Components

14.5.1.Membrane Material

There are three main groups of membrane materials:

Films: Transparent polymers supplied in sheet form which are not laminated or

coated. Not as durable or strong as fabric, rarely used.

Meshes: Porous fabrics typically available as polyester weaves lightly coated with

vinyl or as a knitted fabric using high density polyethylene, polypropylene

or acrylic yarn.

Fabric: There are two materials predominantly used in the industry:

Polyvinyl chloride (PVC) coated polyester yarn.

Polyvinyl chloride (PVC) coated polyester yarn is strong, inexpensive and easy to

fabricate. It can be translucent or opaque and coloured. However, it has a limited life

span (10 to 20 years), and is fire-resistant but not non-combustible. It has been used




4 of 15

in a large number of projects including the 10,000m² Australian Bicentennial Exhibition

and the 40,000m² Expo '88 structure.

It key features are:

• Flammability rating in accordance with AS1530 part 2 and 3 which has enabled its

use in Class 9 structures. The latest fabrics include fire retardants which eliminate

the spread of flames. It was successfully used as a petrol station canopy at the

Shell Westgate project.

• Available in 4 strength grades and a variety of colours.

• The PVC can be provided with a top coat to improve self cleaning nature of surface

and lengthen life. Four different types of top coats are available. Fluoropolymer

lacquer is the preferred top coating as it gives better reduction in dirt adherence

compared with other lacquers whilst not affecting fabrication techniques as does

the otherwise superior tedlar top coat lamination.

Fluorocarbon (PTFE) coated glass fibre fabric

Fluorocarbon (PTFE) coated glass fibre fabric was developed for use in permanent

structures. Its Teflon coating, being inert, suffers very gradually from any of the usual

degrading effects to which plastics are subjected. Its life span is projected as being in

the order of 20 years plus. Its surface coating does not allow attachment of pollutants

and accordingly it is relatively self-cleaning in rain. Teflon/Glass as a material is

classified as non-flammable and is available in 3 strength grades.

It is always coloured off-white (starts off-beige in colour and bleaches to off-white over

a 3-6 month period on exposure to sunlight), has a translucency between 8 to 15%

depending on the grade, and comes with a 10 year warranty.

There are only 4 producers of these fabrics in the world, including Verseidag in

Germany and Chemfab in USA. In Australia there are only two fabricators/erectors of

these products, Spacetech Pty Ltd based in Melbourne and Permafab Pty Ltd based in

Sydney.

Data of a typical range of fabrics is given below.




5 of 15

PVC COATED WOVEN POLYESTER

Property Grade of fabric

Type i Type ii Type iii Type iv Standard

Tensile strength: Warp(kN/m) Weft(kN/m)

60 55

88 79

115 102

149 128

Din 53354

" " Tear strength: Warp(N) Weft(N)

310 350

520 580

800 950

1100 1400

Din 53363

" " Adhesion (kN/m) 30 30 2.5 3.0 Din 53357

Strength of standard seam at 70°C(kN/m)

48 57 67 92 -

Weight coated (gm/m²) 800 900 1050 1300 Din 60001

Support cloth Pes Pes Pes Pes Din 60001

Weave L1/1 Panama 2/2

Panama 2/2

Panama 3/3

61101

Type of Coating PVC PVC PVC PVC -

Yarn(dtex) 1100 1100 1670 1670 Din 53830 Note:Data based on Verseidag - Indutex Duraskin fabric

Warp = Lenghtwise thread/direction in a roll of fabricWeft = crosswise thread/direction in fabric

PTFE COATED WOVEN FIBRE GLASS

Property Grade Of Fabric

B 18039 Gf B 18089 Gf B 18059 Gf Standard

Tensile Strength:

Warp(kN/m)

Weft(kN/m)

76

70

116

116

160

130

Din 53354

" "

Tear Resistance:

Warp(N)

Weft(N)

300

300

500

500

600

600

Din 53363

" "

Adhesion(kN/m) 1.6 1.6 1.6 Din 53363

Weight (Incl Coating) (gm/M²) 800 1150 1550 Din 53352

Support Cloth Glas Ec3 Glas Ec3 Glas Ec3 Din 60001

Type Of Coating Ptfe Ptfe Ptfe -

Yarn(Dtex) 1360 Dtex 2040 Dtex 4080 Dtex Din 53830

Translucency 15% 13% 8% - Note:Data based on Verseidag-Indutex Duraskin fabric




6 of 15

It is recommended that the fabric be chosen to have a factor of safety in the range of 4

to 6 of its tensile strength against the maximum working stress. The factor of safety

chosen for a particular project will depend on the accuracy of determining the

maximum stress in the fabric, the degree of concentration of load within the fabric at

support points, and the consequence of failure of the fabric material.

14.5.2.Cables

Cables are used along free edges and ridge lines of tensile membrane structures, as

supports of flying masts and as tiebacks of perimeter masts to the foundations.

Galvanised steel cables are used in most structures. Stainless steel and kevlar

cables can be used if required for appearance, durability or weight. Cables are

available in a range of construction, each having different stiffness, strength and suited

to different tasks.

For more detailed information on cables, their properties and design considerations

refer to the cable structures technical report Appendix B

Strand

This is the best material for guying purposes as it is the stiffest type of cable available.

Connections are available using the full range of terminations, including thimble and

ferrule, swage and drop forget sockets.

Wire Core Wire Rope

This is stiffer than fibre core wire rope. It is less susceptible to damage - particularly

due to crushing forces on drums. However, the greater stiffness means that greater

drum and sheave diameters must be used. Nobles have cables generally available off

the shelf 8, 11 and 16mm dia galvanised cable of 2070MPa grade (construction 6x19,

6x25 or 6x36) and 9mm to 36mm diameter black 1770MPa grade. BHP Lifting

Products have a similar range of cables readily available.

Connections are available using the full range of terminations, including thimble and

ferrule, swage or drop forge socket. Wire core wire ropes are typically used for edge

cables.




7 of 15

Fibre Core Wire Rope

Most readily available type of rope in 1570MPa (6 x 24) constructions. It is readily

available galvanised in the full range of sizes from 3mm to 32mm diameter. Thimble

and ferrule connections only can be used due to the greater flexibility of the core.

Swaged end connections cannot be used.

Stainless Steel Wire Rope

Stainless steel wire ropes are all manufactured outside Australia. Most of the

stainless steel ropes are made to imperial sizes. They are available in Grade 304 and

316 stainless steel. Grade 316 is only marginally more expensive than Grade 304,

has superior corrosion resistance and appearance but has generally a slightly lower

load capacity. The wire rope is produced in 1x19, 7x7 and 7x19 construction. 1x19 is

preferred for all structural applications due to its higher strength and stiffness.

Ronstan and Austress Freyssinet (with Guy Linking System) are the two main

suppliers of stainless steel wire rope in Australia. Both have cables readily available in

sizes from 2.5 to 26mm (1 inch).

Other sizes/grades/construction of cables are available, with a longer waiting period, a

cost penalty and generally with some sort of minimum order (fairly large). Size, for

size higher strength rope is more expensive, although on a strength basis, it may be

slightly cheaper. On the basis of cables always being under tension, and not being

exposed to shock loadings, a factor of safety against the minimum breaking load of the

cable of 2.5 is generally used. Right hand ordinary lay ropes are generally used.

Some other lay ropes are available in a limited range of sizes if required.

Cable Manufacturers catalogues are the principal source of information on cables. A

summary of main types of cables available follows:

Nobles 1 x 19, 1 x 37, 1 x 61 and 1 x 91 Strand Cables

• Minimum Tensile Stress 1570 MPa.




8 of 15

Strand Diameter (mm)

Construction Mass (kg/m) Minimum breaking load (kN)

13

14

16

18

20

22

24

26

28

32

36

40

44

48

52

1 x 19

1 x 19

1 x 19

1 x 19

1 x 19

1 x 19

1 x 19

1 x 37

1 x 37

1 x 37

1 x 61

1 x 61

1 x 91

1 x 91

1 x 91

0.827

1.10

1.33

1.68

2.14

2.55

2.99

3.43

4.15

5.22

7.05

8.83

10.6

12.8

14.8

144

173

217

274

350

416

487

564

680

855

1130

1410

1540

1830

2150

Guy Linking 7 x 19 Cable 1 x 19 strand, Compact Strand - Grade 316

Typical Young's Modulus:

• Compact: 133 x 103 MPa

• 1 x 19 strand: 107 x 103 MPa

• 7 x 19 cable: 85 x 103 MPa




9 of 15

7 x 19 Cable 1 x 19 strand Compact strand (Dyform)

Nominal Diameter

(mm)

Minimum breaking load (kN)

Approx. weight (kg/m)

Minimum breaking load (kN)

Approx. Weight (kg/m)

Minimum Breaking load (kN)

Approx. weight (kg/m)

3

5

6

8

10

12

14

16

19

22

26

5

13.9

20

35.6

55.6

80

0.03

0.10

0.14

0.24

0.38

0.54

7.1

19.6

28.2

45.5

71.1

102

139

182

212

286

398

.04

.12

.18

.31

.49

.70

.96

1.25

1.76

2.36

3.30

23.9

34.8

60.3

95.0

141

189

251

313

0.14

0.20

0.35

0.54

0.81

1.15

1.47

2.06

Ronstan Grade 304 and 316 1 x 19 Stainless Steel Cables

1x19 Grade 304 1x19 Grade 316

Diameter

(mm) (Inches)

Breaking Load (kN)

Breaking Load (kN)

Approx. Mass

(kg/m)

2.40

3.20

4.00

4.75

5.55

6.35

7.15

7.95

9.50

12.7

16.0

3/32

1/8

5/32

3/16

7/32

1/4

9/32

5/16

3/8

1/2

5/8

5.4

9.5

14.9

21.3

28.6

37.2

47.2

56.7

79.4

136

213

4.9

8.6

13.4

19.3

25.4

34.4

43.5

53.8

75.8

142

215

.028

.050

.078

.113

.145

.198

.239

.310

.410

.750

1.20




10 of 15

14.5.3.Webbings

Webbing is used in two locations in tensioned membrane structures. The first is that

they are sewn along the seam of the edge cable sleeves to carry the tangential forces

that arise from the differential loads in the edge cable along its length. The second is

where it is used as a ridge cable. It is recommended that a factor of safety against

minimum breaking load of the webbing of 4.0 be adopted.

Webbings are typically constructed from polyester belt material, such as used for car

seat belts, but thicker and stronger.

14.5.4.Fittings

Fittings are used to connect the fabric to the supporting structure and form part of the

tieback cables to perimeter masts. They provide flexible and adjustable connections.

The principal types of fittings used within tensile membrane structures are swaged

ends, shackles, rigging screws and turnbuckles. These items should be designed to

comply with the following Australian Standards.

i) Shackles - AS 2741

ii) Rigging Screws and Turnbuckles - AS 2319

Shackles are readily available, galvanised, in grades L, M, P and S. In general, alloy

bow shackles quality grade S (fu = 630MPa) are most economical (and highest

strength). Shackle pins are readily available in either screw-in pin or hexagonal nut

and safety pin types. Other pin types are special items. It is not economical to buy

loose shackle pins. Grade T shackles are approximately 4 times as expensive and

not carried in stock. Note that shackle sizes are generally quoted as the body

diameter for galvanised shackles, not the pin diameter. Bow shackles are generally

used in preference to dee shackles. Note that Ronstan stainless steel shackles are

referred to by their pin diameter.

Rigging screws and turnbuckles are readily available, galvanised in Grades L and P.

The stronger grade P (fu = 630MPa) is generally used. Any end combinations of clevis

end, round and elongated eye is permissible. Drilled eye fittings are a special item

which have a longer lead time. Rigging screws can be made to order with non

standard overall lengths.




11 of 15

On the basis of fittings always being under tension and not being exposed to shock

loadings, a factor of safety against the minimum breaking load of the fitting of 3.0 is

generally used.

Manufacturers catalogues are again the principal source of information on these

elements.

14.5.5.Structural Steelwork

Tensile membrane structures are generally supported by steelwork. Steel is the most

efficient way to carry the axial loads from the fabric, can be detailed to handle the

tensioning and tolerance requirements and is typically more architecturally

sympathetic with the structure. Support is provided in many arrangements from free

standing masts, flying masts to continuous gutter supports of the edge of the fabric.

All steelwork should be designed to Australian Standard AS 4100 - Steel Structures.

14.5.6.Foundations

This component of the structure is not always included in the area of responsibility of

the tensile membrane structure designer. If it is not, design loads from the structure

(including magnitude, direction and the variability of the forces) will need to be issued

to the relevant engineers. If included within the scope of work the foundations shall be

designed with relevant Australia standards.


When considering the design of Tensile Membrane Structures the primary principles

to be aware of are:

1. The fabric acts as both the primary structure and the finished surface, both

external and internal.

2. The structures have minimum structural weight with loads being resisted by

changes in geometry and stress level within the shape of the fabric.




12 of 15

Tensile membrane structures often appear deceivingly simple. They are however

complex structures which are not cheap to engineer. The design process for a tensile

membrane structure requires a large number of items to be considered. These

include:

• formfinding the fabric to have sufficient curvatures to enable the structure to have

reasonable prestress loads and acceptable movements under loadings, avoiding

uniaxial stress areas, (which implies wrinkles in the fabric) and sufficient slope for

drainage.

• checking magnitude of movements, especially near to fixed structures out of the

plane of the structure.

• method of erection and tensioning of structure.

• design of 3D connection details, and set out geometry.

• specialist fabric structure connections, such as connections to supporting

structure, fabric splices, cone top rings.

14.6.1.Approximate Calculation Methods

1. Cylindrical membrane strip or unit width under pressure loading.

w = load/unit length

R = Radius of Arc

T = Tension

T = w x R

2. Forces in hanging cable under uniform vertical loading.




13 of 15

H =wL8S

2

V =wL2

T = H +V2 2

For a cable, sag remains relatively unchanged under different loadings. Typical S/L =

10

For a fabric strip, the sag can increase significantly under loading, reducing the radius

of curvature and thus the tension in the fabric.

3. Doubly curved surfaces

1

1

2

2

TR

+TR

= P

P = Pressure

loading

The principal radii of curvature are the maximum and minimum and follow lines at right

angles to each other on the surface.

With anti-clastic surfaces (as being considered here as opposed to pneumatic

structures), the centres of curvature are on opposite sides and R1 and R2 have

opposite signs.

Hence for prestress equilibrium condition

T T




14 of 15

1

1

2

2

TR

+TR

= 0

Under load P from above T1 will increase while T2 will decrease. In the extreme case

T2 will become slack when T1 = P x R1, or in other words the downwards load on a

hypar structure is carried by an increase in the stress in the fabric between the high

points, and a decrease in the direction of the low points.

Indicative Fabric Stress Levels

For a PVC coated polyester fibre fabric, prestress loads would be in the order of

50kg/m width.

In non-cyclonic areas, loads in fabric under design wind loads could be a factor of 10

times the prestress, whilst an edge cable load might be expected to increase by a

factor of 4 to 5 on its prestress force.

These loads cannot be generalised due to dependence of forces generated within a

structure on its shape.

14.6.2.Formfinding

Formfinding of the structure is carried out on a specialist computer program. A model

detailed enough to properly define that shape of the fabric surface and edge cables is

required. The initial model may be used to provide data to make a physical model for

wind tunnel testing. Key criteria to be considered during this process are:

• sufficient 2 way curvature

• no water ponding problems

• aesthetics

• axis/es of symmetry

• sufficient angle between cables into membrane plates

• sufficient drape in edge cables (notionally span/10)

• clearances

• fabric forces/stresses

• erectability




15 of 15

14.6.3.Design Loads

In Australia, the principal load acting on a tensile membrane structure is wind. The

gust dynamic wind pressure (qz) should be determined in accordance with Australian

Standards AS 1170.2 - Wind Loads. The determination of relevant pressure

coefficients for the structure is complicated by the doubly curved surfaces. The wind

loading code pressure coefficients for free roofs are adequate for preliminary design of

large structures or for design of small structures. The curved shape of the fabric

surface and its movement under load both tend to reduce the overall loading on the

structure. Thus the code values generally significantly overestimate the actual wind

loads on the structure.

14.6.4.Analysis/Detailed Design/Patterning

Loading analysis can be carried out on a specialist computer program and detailed

design of the various components of the structure (including fabric, cables, steelwork

and foundations) can be carried out .

Production of cutting pattern data for the fabrication of the structure is required and

usually will form part of the design task.

Depending on the computer software a new model may be required in order to get

cloth width within the roll width supplied.




1 of 10

15. GRC

15.1. Introduction

GRC, because of its versatility, has been used for a number of years to produce a

wide range of products including building facades as well as structural elements such

as pits, kerbs etc.

Like all materials, it is important that the designer has an overall appreciation and

understanding of the material and how it will perform with other materials during its life.

Do not be afraid to visit a factory and see how it is made.

15.2. Codes

A Code of Practice for the design and manufacture of glass reinforced cement

products, GRC Association of Australia Approx. 1980.

15.3. References

Design Guide for GRC, Pilkintons UK 2nd Ed 1979.


None


15.5.1.Materials

Glass reinforced cement (GRC) materials are normally a mixture of 5% to 6% Alkali-

Resistant Glass Fibres by weight (4-4.5% by volume) and have been developed to

replace conventional steel reinforcement mixed with Portland cement, sand and water.

The resultant material is normally of 3-12 mm in thickness. The glass fibres provide

the tensile reinforcement and strength of the material in combination with the sand and

cement.

The material can be produced by a variety of methods including spraying, vibrating,

casting, spinning, extruding and pressing. Each method gives varying characteristics




2 of 10

to the end product. The most commonly used method is spraying (spray up), either

by hand equipment or mechanically on a production line. The spray-up method is

often used where size, strength and appearance are important such as cladding

panels.

Premix casting techniques from the precast concrete industry are often used in

smaller standardised products such as pits, sumps etc.

The physical properties of GRC are largely dependent on the ratio and length of fibres

to cement and sand and the rate of drying. The rate of drying is controlled by the

curing process. The total curing period recommended is approximately one month

with 7 days wet curing. Polymer modification of the cement matrix can be used

instead of wet curing but this technique requires specialist control.

The material used for the moulds varies depending on the required finish, shape and

number of panels. Materials used include plywood, fibreglass, metal, rubber, plastic

and even GRC itself.

The quality of the moulds sets the standards of the finished surface of the product.

Like precast concrete, moulds are expensive and repetition and reuse is essential for

reducing overall costs. Too often, designers, in trying to create a finished building,

ignore the complexity of shapes and mould costs as part of the total cost of the

project.

15.5.2.Glass Fibres

GRC was initially made from commercial fibres of E-Glass as used in glass reinforced

plastics (GRP), and High Alumna cement, however, this was too expensive.

Problems occurred when E-Glass and Portland cement were used due to the

reaction between the fine glass fibres and the high alkaline environment of the cement

matrix which resulted in degradation of the glass fibres.

In the late 1960's, the UK Building Research Establishment produced a fibre

containing zirconium oxide which can resist alkali attack when mixed with a Portland

cement matrix. The Building Research Establishment's work was patented by the

National Research Development Corporation which joined with Pilkington Brothers to




3 of 10

develop it. Pilkington took up the commercial development under the licence of the

National Research Development Corporation.

The current product is the result of many years of research and development by

Pilkington, the UK Building Research Establishment and the National Research

Development Corporation. A slow chemical reaction still occurs between the glass

fibres and the Portland cement which results in an eventual reduction of strength, and

some loss of ductility. This material is known as CEM-FIL. Alkali resistant glass fibre

is also available from Nippon Electric Glass of Japan.

15.5.3.Quality Control

The properties of GRC and therefore the allowable stress levels for design, are

dependent on the particular mix chosen, the method of production and the curing

conditions.

This situation is common to many building materials. The Engineer can refer to codes

and design handbooks and a large amount of experience for design information.

Initially, to provide quality control, Pilkington restricted the sale of Cem-Fil AR Glass

Fibre to companies considered suitable for entering into a Licence Agreement.

Pilkington also helped the formation of the Glassfibre Reinforced Cement Association

that allows for a pooling of information and the sponsor of standards and codes of

practice.

This 'Incorporation Licence Agreement' requires Pilkington to sell Cem-Fil AR

Glassfibre, provide long-term test data and assist in the design, manufacture, testing

and marketing of GRC products. The licensees in return, were to consult with

Pilkington on potential GRC products in terms of design, specification, formulation,

test methods, results and quality control procedures. This procedure is no longer

used. Doubt has been expressed whether Pilkington has maintained sufficient control

over quality, but it did at least ensure some form of quality control.

The Glass Reinforced Cement Association of Australia (SRCAA) has been active in

recent years and only recognises member firms who follow Stringent Quality Control

Procedures. This has been taken up by the SRCAA who will not admit companies

who cannot prove quality control.




4 of 10

Most of the licensees in Australia are capable of undertaking reasonably sized projects

and some have the experience, expertise and the capability to undertake larger

projects. There are few companies with the expertise to undertake a project the size of

Capita as discussed in the second part of this paper.

There is no substitute (or cheap alternative) to providing proper design, detail and

quality control and all designers have an obligation to satisfy themselves on these

matters.

15.5.4.Production Methods

In the simplest form of spray process, a combined spray of mortar slurry and chopped

glassfibre are deposited from a hand-held spray gun into or onto a suitable mould.

Mortar spray is fed to the spray gun from a metering pump unit and is atomised by

compressed air. Glass fibre is fed to a chopper and a feeder unit mounted on the

same gun assembly.

The thickness of the GRC deposited is monitored by pin gauges. Roller compaction

by hand ensures filling and a true reproduction to the mould surface and removes any

entrapped air.

Products are normally removed from the mould the following day and are then cured.

Adequate curing is necessary to achieve optimum mechanical properties.

The quality of the finished product is dependent on the operator and the whole process

is very labour intensive.

15.5.5.Methods of Transportation and On-site Handling

In the flat sheet form the methods of transporting and handling GRC are no different

from those for cellulose fibre or similar materials.

Moulded shapes are treated similarly to those of precast concrete members.

However, because of the light weight of GRC, handling and transport is more

economic.




5 of 10

Some care is required in the handling of GRC, particularly in the removal from moulds

to minimise damage.

15.5.6.Mechanical and Physical Properties

There is a wide range of technical information available on glass reinforced cement.

There is a list of the written literature available on the product at the end of this paper

including the Code of Practice for the Design and Manufacture of Glass Reinforced

Cement Products by the GRCAA.

In addition, organisations such as the Concrete Institute of Australia, have written

literature available. Specific properties which must be consiered include:

i) Compressive and Shear Strength, Creep and Stress Rupture, Fatigue

Performance

In the external walling system or similar, the loads and stresses in the GRC

are relatively low. The GRC is usually used as a "nonstructural" element of

the system.

The material possesses adequate structural strength and stiffness for this

purpose. There is a significant loss of strength and ductility in the long term,

but this is overcome by adopting low design stresses as set out in the design

codes.

ii) Movement

GRC has a high coefficient of expansion shrinkage and movement due to

moisture and these factors have caused design problems. Correct detailing

with proper allowances for this movement overcomes these problems.

Manufacturers of GRC usually recommend surface coating of both sides of the

GRC product to stabilise the sheet and balance the surface tension.

iii) Fire Properties, Chemical Resistance, and Water Permeance

Problems are not normally encountered in these areas. Fire tests on GRC

have been carried out in Australia and the UK, however, GRC panels with a




6 of 10

steel sub-frame are unlikely to provide the necessary fire separation under the

Building Code of Australia.

It should be noted that the physical properties of GRC are quite different to

concrete.

Coeff of Thermal

Expansion

Sinkage Moisture induced

movements

GRC

Concrete

7 to 12 x 10 -6/°C

12 x 10 -6/°C

750 x 10 -6

mm/mm

600 x 10-6

mm/mm

1000 x 10 -6

mm/mm

-

.

15.5.7.Fixings

Several methods of fixing the GRC skin are commonly used. Methods used for other

materials such as concrete, timber, stone, steel or cellulose fibre cement can be used

or adapted to suit GRC thus providing a range of alternatives

The fixing details should always be designed to ensure the force transmitted through

the fixing is distributed over a as large an area of GRC as possible. This is done by

either encapsulating the fixing in GRC during production, or by using load-spreading

washers, plates or similar.

There is little published test data on pull out and shear values of fixings and in critical

cases, simple testing is advised. Some manufacturers can provide their own test

data.

Only cast-in fixings should be used for structural connections because of the difficulty

of accurately controlling hole diameters when drilling GRC on site and to ensure

adequate load capacity is achieved. The following rules should be followed when

designing large building elements such as cladding panels in GRC:

i) The weight of the unit should be supported at two locations, this is normally at

the bottom, or as close to it as possible. Fixings at the top of the panel provide




7 of 10

the lateral restraint. This is the same principle as non-load bearing precast

concrete cladding panels.

ii) The centre of gravity of the unit should be as close as possible to the support

frame points, ie to limit rotation away from the building face. This is particularly

important where panels are fixed to steel framing with limited torsional or lateral

strength.

iii) The top fixings are used for restraint only, not for supporting dead loads and

must be designed accordingly.

iv) The fixing system should make allowance for site and manufacture tolerances

for thermal, moisture and structural movements.

For cladding panels these provisions for movement are usually accommodated

in the top restraint fixings as slotted or oversize holes. It is not uncommon for

site tolerances to be as much as 30 mm vertically between floor slabs and

panels should be designed to allow for this.

v) Oversize washers are recommended to avoid local compressive failure of GRC

when the fixings are tightened on site.

vi) Frictionless washers or bearings of neoprene must be incorporated to allow the

component parts of a fixing to slide.

vii) Panels must be supplied floor by floor so that axial shortening, creep deflections,

shrinkage and other building movements do not impose additional stresses in

the panels.

If these rules are followed, the panel will only carry its self weight. The GRC and sub-

frame should be designed to resist wind, earthquake, and other applied loadings as

required.

For the major restraint fixings stainless steel or nonferrous metals such as galvanised

materials should always be used.




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Most large panels of GRC are designed with a light metal sub-frame, reducing the

framing required and simplifying on-site fixing and handling. This system was

originally developed in the USA. Detailing, however, can be based on GRC sheets

being fixed to a separate steel framed wall. In this case, the best method of fixing the

panels is to cast in lugs that would be fixed to the steel frame. This method eliminates

exposed fixings and therefore would help in achieving the required finish, but

movements in the panels may not be properly accommodated.

Fixings should be not exposed. Where this cannot be avoided, the problems of

exposed fixings can be overcome by:

i) Patching over fixings and coating. This includes a bond breaker to the head of

the fixing before patching and final sanding prior to coating.

ii) Fixing the back of the panel to a steel frame with lugs.

iii) Casting a steel frame into the back of the panel.

Either (ii) or (iii) are preferable.

In summary, the fixings required for GRC panels in a cladding situation do not present

insurmountable problems if the Designer is aware of movement tolerances etc.

15.5.8.Surface Finishes

GRC can be painted or left unpainted.

GRC when produced from grey Portland cement or integral colours (and left

unpainted) will show variation in colour due to variations in hydration as for precast

concrete and which it becomes exaggerated after rain.

Other finishes can include highly profiled or moulded surfaces or integrally cast

aggregate finishes.

These finishes can be lightly acid washed or sand blasted as required. Polishing is

not recommended.




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With the many high-class paint systems on the market, there is a wide range of

appropriate finishes that can be applied. However, with such finishes, the preparation

and application must be of the highest quality to achieve the final finish, and these do

not have an infinite life.

The following properties are important in determining the suitability of applied finishes

for use on GRC:

i) Resistance to Alkalinity.

ii) Moisture Compatibility.

iii) Moisture Permeability.

iv) Weathering Characteristics.

v) Mechanical Flexibility

Particular care should be taken when using a finish with very low moisture

permeability such as polyurethane, epoxies or fluorocarbon finishes since moisture

already present in the panel or entering from the back face may migrate to the

paint/GRC interface where it may cause flaking, peeling, or bubbling.

Permeable finishes should be used whenever possible but where an impermeable

finish is necessary, the following precautions will reduce these problems.

i) All traces of mould release oils on the panel should be removed during surface

preparation for the coating system.

ii) Ensure the panel is sufficiently dry before coating, and check the PH level is

correct.

iii) Seal the back face of the panel with a material of similar or low permeability.

Because of the smooth dense finish that can be achieved with GRC, surface

preparation to allow adhesion of the coating is recommended.




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Care should be taken when choosing a colour as dark colours have a tendency to fade

and attract a heavy heat load. In addition, high-gloss dark finishes show all

imperfections, however small.

15.5.9.Waterproofness

Where a GRC panel forms part of a wall system or similar, a complete design solution

must be developed for waterproofing the wall.

The joint detail must recognise that even with the best workmanship, some failure is

possible and as with precast concrete on curtain walls, should have an appropriate

back up drainage system with the so-called "drained joint" principle adopted for curtain

walls.

For high-rise buildings, some form of "Sirowet" or panel testing may be appropriate.

15.5.10.Composite Panels

Designers and Architects have, in the USA in particular, attempted to use composite

panels with separate facings or materials such as ceramic tiles, brick tiles etc. fully

bonded to the GRC panels. These practices have been tried in the precast concrete

panel industries with often poor results because of dissimilar materials and it is

suggested that similar results will occur if used on GRC.

15.6. General Summary of Material

Advantages

• Ease and flexibility in manufacture.

• Ease of fabrication to complex shapes.

• The thin and lightweight sections enable ease of handling and low transport and

fixing costs.

• High early impact strength - this is valuable during manufacturing, handling,

transport, erection.




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• Non-combustibility and high fire resistance.

• Good resistance to corrosion and insect or biological attack.

• Safe to manufacture and handle.

• Good Acoustic properties.

• Ready availability of raw materials.

• Flexible and tensile strength levels which allow economic component design.

• Cheaper than equivalent precast units.

Disadvantages

• Loss of strength, long term.

• Loss of ductility, long term.

• High coefficient of expansion.

• Considerable movement due to moisture and drying.

• An unpainted surface gives an uneven colour variation.

• Expensive due to moulds and labour content to manufacture.




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16. TEMPORARY WORKS DESIGN

16.1. Introduction

Temporary works design should only be carried out by experienced Engineers with

considerable expertise in this area and a good background in building construction and

ground conditions. Engineers should always discuss such designs with their

responsible Associate/Principal, and if necessary, review works with others in the

office. This is a high risk area and must be carefully carried out.

In building works, temporary works design can include underpinning, site retention,

shoring of excavations, temporary support of existing walls to be retained, crane base

design and site gantries and other forms of temporary construction.

There is a potential conflict of interest if we carry out designs for both the Client and

the Contractor on the same project particularly when it is a hard money contract. This

means we are working for two clients on the same job. Before carrying out any design

work where this occurs, we must get the Client's approval in writing and advise the

Contractor that in case of any problem, we would have to act on the behalf of our

Client.

Where the documents call for specific items to be designed by other Engineers, we

must carefully decide during our documentation, if we really want to inspect their

drawings and computations. If we take this course, then we accept some

responsibility for the design, so think carefully!

When involved in work in the ground, very careful assessment of ground conditions is

essential. Conditions vary enormously in both New Zealand and Australia and local

experience is essential in these matters.

As with any other design, the production of computations, sketches and drawings and

checking are to communicate the final correct solution.

16.2. Codes

1. Facade retention code of practice by Work Cover Authority of NSW.

2. AS 2601, The Demolition of Structures.




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16.3. References

References:

1. Handbook of Temporary Structures in Construction - Robert Ratay

2. Design and Construction of Deep Basements - I Struc E 1975

3. Earth Retaining Structures - Draft Australian Standard


None.


16.5.1.Design Considerations

The following general matters need to be considered for all temporary works designs:

• Planning and site considerations.

• Geotechnical information required.

• Experienced designers.

• Adequate time to design.

• Proven techniques.

• Sequence of construction.

• Experience of construction personnel.

• Simple and constructible details.

• Attention to detail.

• Wall displacement/movement monitoring.

• Sensitivity of adjacent properties and dilapidation surveys.

• Loadings.

• Lateral restraint/ground anchors.

• Water inflow.

• Types of occupancy in basements.

• Drained or undrained construction.

• Contractor’s capabilities.

• Speed of construction/programme.

• Cost.




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Underpinning

The underpining method should be designed to limit possible movements to

acceptable levels. In any event, as a result of the nature of this type of work on site, the

possibility exists that excessive movements could occur which may damage finishes.

The client should be advised to allow for repairs to finishes and his agreement sought

before proceeding with the work.

Underpinning is usually carried out under adjoining properties where the excavation for

our project such as for a basement will interfere with and reduce the bearing capacity

of an existing adjoining wall or column footing.

The usual procedure for a continuous wall footing is initially to excavate to about the

level of the existing footings. Then carry out individual excavations 1200-1500 mm in

length in a hit and miss fashion for the full width of the wall footing down to a level that

will be below the cut level of the final excavation. A similar procedure can be used for

pad footings but be careful that sufficient bearing is provided. Temporary propping may

be required.

The excavated section is then filled with concrete and reinforcement is required and

the process repeated in a systematic procedure usually with every fourth section

being excavated at the same time.

The following points must be noted:

1 Because underpinning is usually on an adjoining property, full details of the

proposal must be submitted to the adjoining owner in strict accordance with

the Building Code of Australia or Local Building Regulations. The work must

not proceed without the adjoining owners written consent.

2 The bearing of the lower level must be equal to or greater than that where the

existing foundation is currently founded.

3 The underpinning will need to be laterally propped if lateral pressures can

occur or the existing footing can move laterally.




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4 Designers should refer to either previous projects, where underpinning has

been carried out, or other experienced engineers.

5 Before excavating even to the level of existing footings, check whether the

existing wall will have to retain backfill and whether temporary lateral support

will be required to enable this.

16.5.2.Shoring

Shoring refers to retaining ground for excavation. This work is sometimes carried out

by other Engineers for the Contractor. Sometimes it is part of our work.

Shoring can consist of vertical members (often steel or concrete "soldiers")

cantilevered with horizontal members (usually timber "whalers"). Sometimes the

vertical members are propped back or tied with ground anchors. Soldiers can also

include permanent bored piers, sprayed walls, the Connell Arch and other systems.

Where shoring is carried out adjacent to the street alignment, approval of the local

Council or Building Authority will be required. It is normally a requirement that the

shoring is removed when construction is complete and it should be designed to enable

this.

Where a road pavement abuts or is close to the excavation, a surcharge must be

allowed. Refer to the recent draft code for retaining structures.

The following design points will help designers in this area.

• The maximum depth of vertical excavated face is usually 2.5 m between horizontal

lines of props, ground anchors and the like but this will depend on geotechnical

information and advice.

• All walls should be drained with granular back filling or drainage behind.

• Where shores are strutted, failure can occur with uplift of the struts. (if they are too

close to vertical).




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Shoring should be designed where possible to provide an open and uncluttered

basement excavation area. Movement of the wall may result in some cracking in

adjacent pavements and clients must be aware of this.

The design pressures should be determined from the Geotechnical Report with

assistance from the draft code on retaining structures if required.

16.5.3.Retaining Walls

There are many types of retaining walls. These can be either permanent or

temporary. Matters to be considered by designers will include:

• Piled walls of bored piers, grout injected piles etc. with infill walls and ground

anchors.

• Contiguous wall.

• Soldiers with infill panels.

• Concrete - precast, insitu, sprayed.

• Free standing, ie batters.

• Bentonite displacement walls, ie diaphragm walls.

• Rock bolting.

16.5.4.Temporary Supports (for Walls)

Temporary wall supports can often be incorporated as part of the final design.

The usual design procedures should be followed.

Design loads will include:

a) Dead Load

b) Construction Load

c) Wind Load

d) Earthquake Load




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16.5.5.Crane Bases and Ties

The Contractor may have us design the crane bases.

Crane bases can be incorporated as part of footings for the building (if they exist), a

separate pad footing or separate pier or pile foundations under each leg.

Many designs have been carried out by various offices and these should be referred

to. The forces in the crane legs can be calculated by the computer program

"FAVCO". The wind loads may NOT be adequate for high buildings.

Crane ties can involve significant design and thought and again, reference should be

made to previous designs.

16.5.6.Site Gantries

We are often asked to help the Contractor with design of site gantries for site offices

etc. on larger projects.

The design should follow normal design procedures, but always be aware of the need

for lateral stability.

16.5.7.Demolition

This is an area that is potentially risky and review with others in the office who are

appropriately experienced.

Where an end span of beams or slabs is demolished, remember that continuity over

the next support will no longer exist and moments in the next span could be

unacceptably increased.

Particular care is required in the demolition of pre- and post-tensioned structures.

Appendix C of AS 2601 contains useful notes on the subject and should be read an

fully understood before proceeding with work in this area.


APPENDIX A

TECHNICAL REPORT TR96-1

EARTHQUAKE DESIGN TO AS 1170.4


APPENDIX B


CABLE STRUCTURES


APPENDIX C


THE DEVELOPMENT OF A

PREFABRICATED STEEL FRAMED HOUSING SYSTEM


APPENDIX D


INTRODUCTION TO STRUCTURAL ASPECTS OF FIRE

ENGINEERING

CROWN CASINO EXPERIENCE


APPENDIX E


CONCRETE FACADE REPAIRS AND MAINTENANCE

Documents

CW Manual