Topic : Common Structural Forms for High-rise Buildings …bst1.cityu.edu.hk/e-learning/building...Structural_forms_Sep10.pdf · Topic : Common Structural Forms for High-rise Buildings

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Topic :

Common Structural Forms for High-rise Buildings in Hong Kong

Prepared by Raymond Wong

wind

Building bends or deflects under lateral force

The more rigid of a building structure, the less it deflects

Deflection is a comfort consideration for building users. Building regulation has a basic criteria on deflection.

The structure of a building should be so designed to have a deflection less than 1/500 of its height

The problems of tall and slim building

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Various deflection modes under wind tunnel test

Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK1. Column and beam (framed) structure in RC

sometimes called framed buildings which are structures formed by the framed elements usually in the form of columns and beams, as well as further strengthened as necessary by the introduction of rigid floor membranes and external walls. - Simple formwork is required- lower cost of construction- easy to satisfy various spatial arrangement and shapes- may not be very able to cater for the structural needs of

tall and slim buildings- more suitable to construction low-rise or horizontal-

spread buildings such as schools, podium or carparkstructures

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Example of layout design evolution from a 5 x 3 grid system

Example of In-situ RC frame building

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Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK

2. Load bearing wall (shear wall) structure in RC- More complicated formwork is required- cost of construction may increase especially for

building with more internal walls or in complicated shape

- the load bearing walls can strengthen the rigidity of the building and able to resist building against deflection

- building examples: public buildings such as theHarmony Blocks

Example of load-bearing wall structures

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Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK3. Load bearing wall plus core wall structure

- Complicated formwork is often required especially in forming the core

- cost of construction is higher, especially for buildings with complicated shape (e.g. lots of set-back or light wells

- has very strong rigidity to resist deflection- this is the most common structural form for use in HK’s

residential buildings due to:. walls between residential flats can be best used as a

load bearing wall (fire resistance is one reason). To fulfill building regulation for prescribed window

areas. To satisfy the rigidity of high-rise buildings

Example of load-bearing wall structures with building area below 500 sq m

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Example of load-bearing wall structures of building area around 800 – 1000 sq m

Example of load-bearing wall structures with several blocks linked together to form a connected structure

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Structures inload-bearing wall with a RC core

Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK4. RC Centre core plus a RC frame structure

- Confine to more regularly shaped or building with simpler layout, such as usual tower type buildings- fair rigidity performance but may not be sufficient for building higher than, say 50 storeys.- rigidity can be improved by the adding in of other stiffening members- plenty of window areas (it is only a frame in the external face the building)- The internal core may have difficulty in getting natural ventilation or sunlight.

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Example of cored structure with an external frame for tower-type office building

Various layout arrangement for building using core and outer frame structure

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Various layout arrangement for building using core and outer frame structure

Example of cored structure with an external frame –Central Plaza in Wanchai

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Example of cored structure with an external frame –Langham Place in Mong Kok

It is sometimes quite difficult and costly to construct the RC core

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5. Center core plus a outer core structure (tube in tube)- Formwork usually very complicated with the floor

added in at a second stage- building shape confined to tubular forms- area of windows limited due to the provision of a

structurally strong external tube (wall)- quite strong in rigidity and be able to construct to

very tall structure- building examples – Hopewell Center (HK) or the

previous World Trade Center in New York

Examples of tube-in-tube structures – Jardin House in Central

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Hopewell Centre in Wanchai

Examples of a framing plan showing the location/layout of walls, columns and beams

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Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK6. Steel frame structure

- building is lighter than usual RC structure due to the relative higher weight/strength ration of steel

- construction cost is lower especially for buildings adopting high level of standardization

- building is weak in rigidity due to steel is a more flexible (elastic) material when compare to RC

- additional stiffening elements in the form of internal/external trusses, out-rigger or bracing members are often required to make the building structure more rigid

- addition work is required to fire-protect the steel structure

- building examples: The Center, China Bank Building

Examples of building constructed in pure structural steel frame

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Construction of Structural steel frame building


7. Composite structure (RC Core plus steel frame, hybrid structure)- building can be lighter than usual RC structure but

with a more acceptable rigidity than pure steel buildings

- construction cost is higher for the adding in of a RC core which requires a complicated formwork system

- it is time consuming and more complicated to make connections between the RC and steel elements

- It is even more difficult and costly if stiffening members are introduced into the building in order to make it more rigid to resist deflection

- Building examples: Time square, Manual Life Tower, Cheung Kong Center, IFC 1 and 2

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Examples of composite structures

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More examples of composite structures

More examples of composite structures

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Complicated stiffening elements incorporated in steel or composite building to improve the rigidity of the structure

The IFC 2

Outrigger system used in Cheung Kong Center

Cheung Kong Center

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The Cheung Kong Center

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Cost idea of using RC, Steel and composite method in constructing tall buildings

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How to construct various forms of BuildingsHow to construct various forms of Buildings

Buildings can be constructed or formed in a number of ways, such as:

1. In-situ manner using formwork – for all reinforced concrete buildings

2. Prefabricated manner – for using part or all in precast concrete elements

3. Prefabricated manner – using structural steel elements

4. Hybrid manner – making combination of any of the above systems

Construction of in-situ RC buildings

Forming the wall structure using aluminum moulds

Forming the wall structure using manual-type timber formwork

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Forming the structure using large panel-type forms for walls or columns


Forming the wall structure using mechanical-operated formwork systems

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Forming the floor structure using timber formwork systems


Forming the floor structure using table formwork – most suitable for office buildings

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Forming the floor structure using table formwork – floor being strengthened by tensioning technique

Construction of prefabricated frame building

Headquarters building of Hong Kong Jockey Club

Podium – KCR Kowloon Station

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Construction of prefabricated frame building

Using precast elements as part of the external walls as well as the permanent formwork for load-bearing walls

An external view of building –majority of external walls are constructed in precast manner

Advantageous features of framed structureAdvantageous features of framed structure1. Speedy construction due to simplicity in geometry –

consist of only columns and beams (or partially by the floor slab) as the main structural elements

2. Very rigid and stable – able to resist tremendous vertical (dead load) and lateral loads (wind)

3. Reduced dead load – absent of thick shear wall etc.

4. Roofed over at an earlier stage – every floor slab being finished becomes an cover to protect the lower floors from sun and rain

5. Offer large unobstructed floor areas – without obstacle between columns

6. Flexible utilization of space

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AdvanAdvan. features of framed structure (continued). features of framed structure (continued)7. Adaptable to almost any shape8. Easily altered within limits of frame

– regular or non-regular grid system is very adaptable in spatial arrangement

9. Offsite preparation possible – especially for prefabricated construction using precast concrete or structural steel elements

10. May be designed to accommodate movement11. Acceptable distribution of natural light – window openings

can be provided easily on eternal walls12. Easy to design structurally including computer design – again,

due to simple geometry

Principle factors affecting choice of framePrinciple factors affecting choice of frame

Production considerationAvailability of materials, labour and plantSpeed of constructionAvailability of mechanical plants

Architectural Design considerationSize and shape of siteConditions of siteIntegration of mechanical elementsArchitectural or aesthetic requirements

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Principle factors affecting choice of framePrinciple factors affecting choice of frame

Structural Design considerationFoundation considerationStandardization of members or designSpan and floor loadsFire resistance requirementMaintenance considerationIntegration of architectural & structural elements

Features of InFeatures of In--situ concrete frame constructionsitu concrete frame construction

Construction aspects1. Insitu concrete is inconsistent in quality in performance –

mixing, delivery, placing and compacting of concrete require very tight quality control

2. Overlapping formwork, steel fixing and concreting process make site operations more difficult – these works are to be done almost at the same time at the same location

3. Formwork erection is often timely, expensive, environmental unfriendly and labour intensive

4. Increase a lot of wet-work – difficult to maintain site in a clean and tidy environment

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Features of InFeatures of In--situ concrete frame constructionsitu concrete frame constructionConstruction aspects – examples of problem

Improper placing and compaction will serious lower the strength of concrete


Finishing the concrete surface after placing – improper finish will affect the size and dimension of member

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It is difficult to maintain a clean and tidy site using in-situ concrete structure for the casting process is wet and dirty

Exterior environment Interior environment

Features of InFeatures of In--situ RC frame constructionsitu RC frame constructionConstruction aspects (continue)5. Easier to allow for dimensional discrepancy – formwork

can relatively easy to provide any ready dimension and shape

6. Concrete is cheap, easy available and can be cast into complicated shape

7. Frame erection affected seriously by climatic condition – in windy day it is difficult to erect formwork nor to place concrete

8. Durability affect by heat, moisture or environmental factors – concrete is not so durable as most person think

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Features of inFeatures of in--situ RC frame construction (cont.)situ RC frame construction (cont.)

Structural characteristics and design aspects1. Concrete design more flexible and accurate than steel

because of non dependence on standard sections2. Concrete frame easily damaged by building movements3. Problems of creep & shrinkage (cause damage to finishes)4. Higher dead load and bigger structural elements5. Better fire resistance6. Durability sensitive to workmanship7. Overloading cause irreversible structural damages8. Flexible in layout and shape

Typical case using traditional timber formwork for frame structure in RC with load-bearing walls

The CCCU Building of CityU

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Features of structural steel construction Features of structural steel construction

Structural characteristics1. Steel has lower dead load (unless encased in concrete)2. Steel frame can easily to have the layout changed to suit

new design than concrete, especially requiring alteration after completion of the building.

3. Easily accommodate building movements for steel is a relatively flexible material and have greater adaptability to take up strain and deformation

4. However, it is weaker in fire resistance for steel will lose strength and deform serious at higher temperature (at 600oC or above). This can be improved by applying fire resistant plaster

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Features of structural steel construction Features of structural steel construction

Structural characteristics (continue)5. Beams usually shallower in size than for concrete Beams6. Sections in various convenient type and size thus

economical in design and uses – refer to standard steel sections

7. Produce larger deflection & deformation (Bend) under wind – this will cause uncomfort to users of building

8. Steel has higher thermal expansion value9. Rusting or corrosion problems – very strict anti-corrosion

treatment has to be applied

Features of structural steel construction (cont.)Features of structural steel construction (cont.)

Construction aspects1. Quicker to erect and can be prepared offsite – in

workshop/factory environment with good production and quality control

2. Erection on site less affected by climatic conditions –without placing of concrete

3. Longer and highly coordinated planning – require long time to make structural design, fabrication and delivery

4. Higher requirement in the control of dimensional accuracy before and during construction (in fabrication and in erection

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Features of structural steel construction (cont.)Features of structural steel construction (cont.)

Construction aspects5. Demand greater transportation or cranages provision6. Complicated quality assurance procedures – especially in

the control of welding connection7. Difficult to make connection with rigid structures –

especially in composite structure in which RC core structure is involved

8. More complex when building become more gigantic and taller – due to the huge number of structural members, some may be of very heavy section

9. Induce more works at higher altitude

Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems

Delivery of structural steel member by ship

Large member delivery to site waiting to hoisting up for erection

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Hoisting of the structural steel member to the upper floor


Connecting steel members with RC element – an anchor frame may be required for making strong connection

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To connect floor to core wall –starter bars are to be provided within the core structure

Constructing the composite floor in steel/RC composite structure


Very large component often in complicated shape

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Huge amount of structural members make erection very complicated


Very complex and gigantic framework as stiffening members to the overall structure – Belt truss system, the IFC II

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Very complex and gigantic framework as stiffening members to the overall structure –Outrigger, Cheung Kong Center


The existence of very complicated jointing in steel structure

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Required to perform works at very high altitude


Workers work at high altitude

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Connecting large and complicate shaped components can be very difficult


Examples of location where unmatched dimension causing problem

Concrete has to be trimmed to allow steel to pass through

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Examples of location where unmatched dimension causing problem

Roof truss and the decking not on the same level

Documents

Topic : Common Structural Forms for High-rise Buildings …bst1.cityu.edu.hk/e-learning/building...Structural_forms_Sep10.pdf · Topic : Common Structural Forms for High-rise Buildings