1. Fundamental of Tall Buildings

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FUNDAMENTAL OF TALL BUILDINGSDr. Henry LUK


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Why tall buildings?

What is tall buildings?

How to design a tall buildings?

Source: en.wikipedia.org


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Ancient Tall Structures

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Ancient pyramids of Egypt El Castillo, Mayan pyramid

The ancient tall structures, which can be considered as prototypes of

present-day high-rise buildings, were protective or symbolic in nature and

were infrequently used as human habitats.

Ancient structures such as the Egyptian pyramids and the Mayan temples

primarily served more as monuments than as space enclosures.


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The Pyramid of Cheops was built by piling huge masonry blocks

one on top of another to a peak of 146.7 m, equivalent to amodern 40-story office building.

Ancient structures were constructed using masonry or timber

owing to limitation on available building materials.

Limitations: The spans that timber and stone could bridge, either as beams, lintels, or

arches, were limited.

Wood was neither strong enough for large structures, nor did it possess

fire-resisting characteristics.

Brick and stone masonry, in spite of their excellent strength and fireresistance, suffered from the drawback of weight.

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Monadnock Building

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Location: Chicago, USA

Completion: 1893

Number of storeys: 17

Height: 60 m

Status: Completed

Materials: Masonry

Architect: Holabird & Roche; Burnham & Root

Main Contractor: George A. Fuller Co.

o Around 2 m thick load-bearing masonry

walls at the ground floor were used.

o Low net usable area was achieved owing

to the excess dead loads and wide cross-

sections.


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Tall Buildings Development

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Home Insurance Building

10+2 storey(55 m)

Steel frame

Chicago, USA

1885 / 1890

First skyscraper

Demolished

Empire State Building

102 storey (381 m)

Braced steel frame

New York

1931

Tallest in the world from 1931 to 1970

Technological developments

1. Construction materials

2. Vertical transportation

system - elevator

3. Construction technique

4. Structural form

5. Computer simulation


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Why Tall Buildings

The growth in modern tall building constructions has been

largely for commercialand residentialpurposes.

Tall commercial buildings are primarily a response to the

demand by business activities to be as close as possible.

They form distinctive landmarks so that they are frequently

developed in city centres as prestige symbols for corporate

organisation.

The rapid growth of the urban populationand the consequent

pressure on limited space have considerably influenced city

residential development.

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What is Tall Buildings

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http://www.ctbuh.org/

Council on Tall Buildings and Urban Habitat (CTBUH)

Height

Number of storey

Wind effect

Tall building / High-rise building / Skyscraper

Construction technology


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CTBUH, Council on Tall Buildings and Urban Habitat, Illinois Institute of Technology,

http://www.ctbuh.org/TallBuildings/HeightStatistics/Criteria/tabid/446/language/en-US/Default.aspx

a) Height relative to context

A tall building is not just about the height, but

about the contextin which it exists.

b) Proportion

A tall building is not just about height but also

about proportion(aspect ratio).

c) Tall building technologies

If a building contains technologieswhich may

attributed as being a product of tall (e.g., specific

vertical transport technologies, structural wind

bracing, etc.), then this building can be classified as

a tall building.

A building of perhaps 14 or more stories, or more

than 50 metres in height, could perhaps be used as

a threshold for considering its a tall building.


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Tall buildings Buildings of 14 storeys or 50 metres height

Super-tall buildings Buildings of 300 metres height

Mega-tall buildings Building of 600 metres height

CTBUH

Emporis Standards

High-rise buildings Buildings of 12 storeys or 35 metres height

Skyscrapers Buildings of 100 metres height

Ali and Armstrong (Architecture of Tall Buildings, 1995)

The tall building can be described as a multi-storey buildings generally

constructed using a structural frame, provided with high-speed elevators,

and combining extraordinary height with ordinary room spaces such as

could be found in low-building. In aggregate, it is a physical, economic, and

technological expression of the citys power base, representing its private

and public investments.


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Tall Buildings in the World

10 tallest completedbuildings in the world (Skyscrapercenter, Jan 2016)

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http://skyscrapercenter.com


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Tall Buildings in the World

10 tallest completed buildings/buildings under construction in the world

(Skyscrapercenter, Jan 2016)

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Name:Burj Khalifa

Location: Dubai, United Arab Emirates

Completion: 2010


Height: 828 m

Status: Completed

Materials:Steel/Concrete


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Name:Shanghai Tower

Location: China

Completion: 2015


Height: 632 m

Status: Completed

Materials:Composite


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Name:Makkah Royal Clock Tower

Location: Mecca, Saudi Arabia

Completion: 2012


Height: 601 m

Status: Completed

Materials:Steel/Concrete


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One World Trade Center

New York, 2014

541.3 m

94 storey

Taipei 101

Taipei, 2004

508 m

101 storey

International Commerce

Centre

Hong Kong, 2010

484 m

108 storey


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Height of Buildings

CTBUH recognises to measure tall building height in three

categories:

1. Height to architectural top

2. Highest occupied floor

3. Height to tip

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1. Height to Architectural Top(widely used)

Height is measured from the level of the lowest, significant, open-air,

pedestrian entrance to the architectural top of the building, including

spires, but not including antennae, signage, flag poles or other

functional-technical equipment.

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CTBUH, Council on Tall Buildings and Urban Habitat, Illinois Institute of Technology

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2. Highest Occupied Floor


pedestrian entrance to the finished floor level of the highest occupied

floor within the building.

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3. Height of tip


pedestrian entrance to the highest point of the building, irrespective of

material or function of the highest element (i.e., including antennae,

flagpoles, signage, and other functional-technical equipment).

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Tall Buildings in Hong Kong

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10 tallest completedbuildings in the HK (Skyscrapercenter, Jan 2015)


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International Commerce Centre

Kowloon, 2010

484 m

Bank of China Tower

Central, 1990

367.4 m

Central Plaza

Wan Chai, 1992

373.9 m


HSBC Main

Building

Central, 1985

178.8 m


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BEHAVIOUR OF TALL BUILDINGS

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Tall Buildings

A tall building may be defined as one that, because of its

height, is affected by lateral forces due to wind or earthquake

actions to an extent that they play an important role in the

structural design.

The influence of these actions must therefore be considered

from the very beginning of the design process.

High-rise behaviour:

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A high-rise building behaves as a

vertical cantilever

Subjected to

1. Vertical loading by gravity

2. Transverse loading by wind or

earthquake

G

P

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The key idea in conceptualising the structural system for a

narrow tall building is to think it as a beam cantilevering from

the earth.

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The laterally directed force generatedeither due to windor seismicactionstends both to snap it (shear), and

push it over (bending).

Therefore, the building must have a

structural system to resist shear as

well as bending.

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Tall building under lateral loads (UDL)

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w

L

= = /2

L/3

= /3 = /18

At the base

At i-th storey

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Point load at the top

Point loads at every storey

Triangular loading

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Effects of Gravity Loading

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G G

G

G

G

G

G

=

Loading transfer: Slab -> Vertical walls and columns -> Foundations

3

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Effects of Horizontal Loading

Single storey frame

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Multi-storey frame

P

P

3P

Shear

6

Deflection

P

P

P

Ph

6Ph

Moment

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For an n-storey building:

Axial load n

Lateral shear n

Overturning moment n2/2

Lateral drift n2

This is why the emphasis of tall building analysis and design

should be placed on the structural behaviour of the systems

under lateral loading.

Storey

Force/Displace

ment

Force

Moment

Drift


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STRUCTURAL FORM AND FLOOR

SYSTEMS

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Common Structural Forms

Frame structures

Rigid frames

Braced frames

Infilled frames

Shear wall structures

Linked shear walls

Coupled shear walls

Wall-frame structures

Outrigger-braced systems

Core wall structures

Tubular structures

Framed-tube structures

Tube-in-tube structures

Exterior diagonal tube

Bundled tube

Mega-braced framed systems

Transfer structures

Hybrid systems

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Rigid Frames

A rigid frame structure consist of columnsand girdersjoined by

moment-resisting connections.

The lateral stiffness is governed mainly by the bending stiffness

of columns, girders and connections in the plane of the bent.

Rigid framing is generally economic

for buildings of up to about 25

storeys.

Beam/girder

Column

Beam-column

joints

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Braced Frames

Braced frames may be considered as vertical trusses resisting

lateral loads primarily through the axial stiffness of columns

and braces.Chord members

Web members

Single diagonal

bracing

Double diagonal

Chevron

Storey-height

knee

The columns act as the

chords in resisting the

overturning moment.

The diagonals work as

web members resisting

the horizontal shear inaxial compression or

tension.

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Shear Walls

Concrete continuous vertical walls may serve both

architecturallyas partitions and structurallyto carry gravity and

lateral loads.

Their very high in-plane stiffness

and strength make them ideallysuited for tall building structures.

A shear wall structure may be

economically up to about 35

storeys.

Shear walls

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Wall-frame Structures

A wall-frame structure consists of shear wall structure and rigid

frame structures.

The walls and the frames are

constrained to adopted a common

deflected shape by the horizontal

rigidity of the girders and slabs.

It Is appropriate for building in the

40 to 60-storeyrange.

Shear walls

Rigid frames

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Outrigger-braced Structures

An outrigger structure consists of a central core (braced frames

or shear walls), with horizontal cantilever outriggertrusses or

girders connecting the core and the outer columns.

Outrigger

trusses

Braced

core

The outriggers are made

one or often two stories

deep.

It have been used for

buildings from 40 to 70

storeysheight.

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Framed-tube Structures

The lateral resistance is provided by very stiff moment-resisting

frames that form a tubearound the perimeter of building.

It has been used for buildings ranging from 40 to 100-storeys.

Core (inner tube)

Hull (outer tube)

Framed-tube Tube-in-tube

Columns to carry

gravity loads

Framed-tube to

carry gravity and

lateral loading

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Mega Frame/Trussed Systems

Mega frame/trussed systems consist of RC or composite

columns, braces, and/or shear walls with much larger cross-

sections than normal, running continuously throughout the

height of the building.

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Common Floor Systems

Reinforced concrete floor systems:

One-way slabs

Two-way slabs

Flat slabs

Waffle flat slabs

Steel framing floor system

One-way beam system

Two-way beam system

Three-way beam system

Concrete-steel composite floor systems

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Reinforced Concrete Floor Systems

One-way slab Two-way slab

Flat slab Waffle flat slab

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Steel Floor Systems

One-way beam system

Two-way beam system

Three-way beam system

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Concrete-Steel Composite Floor Systems

Steel decking composite slab

Composite frame system

Composite frame and steel decking

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Typical Structural Form

Plan of office block Residential block

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Foundations

Shallow foundations

Pad footing

Strip footing

Raft footing

Deep foundations/Pile foundations Steel H-piles/Steel tubular piles

Socketed steel H-piles

Precast prestressed spun concrete piles

Driven cast-in-place concrete piles Bored piles

Mini-piles

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Weight of Materials in Tall Building

The materials weight (and thus

cost) increases non-linearly with

increasing building height due to

the influence of lateral loads.

Appropriate structural form should

be selected to reduce the cost.

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Construction Materials

Common construction materials

Concrete

Steel

Composite

Timber

Masonry

http://en.wikipedia.org


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DESIGN CONSIDERATIONS

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Aims of Structural Design

Safetyand Serviceability

Not only must a structure safely support the loads to which it is

subjected, but is must support them in such a manner that serviceability

issues are not so great as to frighten the occupants or cause structural

damages.

Cost

The designer must always bear in mind to lower cost without sacrifice of

strength. Savings can be achieved by minimising material weight,

construction time, maintenance cost and maximising structural

performance. The structural cost typically accounts for 20%30% of the overall building

cost.

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Practicality

The designed structure must be fabricated and erected without great

problems arising both in construction and in future maintenance. The

engineer should understand fully the method of construction and the

availability of manpower and construction facilities.

Probability

Uncertainties in loading conditions, material properties and structuralbehaviour do exist in constructed facilities. Whilst it is certainly the

desire of the engineer to provide a safe and serviceable structure, there

is always a risk element in the design decision making process that does

not guarantee 100% safety resulting in risk free structures.

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OverallDe

signpro

cess

System level design

Member level design

Design for structural systemsDifficult task which requires

creativity, originality and

experience of the engineer

Design for structural members

Routine and time consuming

task which often an iterative

process.

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Structural System Design

A structural system is an assemblageof structural members.

These members are interconnected to each other to transfer

forces from top to the foundation.

http://en.wikipedia.org/wiki/File:Skyscraper_structure.png

Decision of making a

structural system depends on

1. understanding of the

system level behaviours;

2. limitations of all possiblealternatives; and

3. design requirements.

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Factors of Consideration

Functionof the building

Number of storey / Height of building

The spansinvolved

Special consideration is necessary if there is a requirement for long spans

or large, clear floor areas.

The verticalloading

The presence of heavy point loads on floors or the need to accommodate

cranes.

The horizontalloading Attention must be given to the way in which horizontal loading is to be

resisted. This aspect of design is of particular importance for very tall

building.

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The servicerequired

These include water, electricity and gas and often nowadays significant

computing facilities, and are usually accommodated under the floors.

In situations where large volume of services are needed (e.g. hospitals),

special forms of flooring permitting easy incorporation of the necessary

pipework and ducting may be necessary.

The groundcondition Clearly the type of ground on which the building is to be erected will

dictate the form of foundation that must be used and this in turn must be

taken into consideration when selecting the super-structure.

The structural performance, practicalityand cost.

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Structural Member Design

Once a structural system is defined, the detailed design is then

performed on the member level.

Given the geometric layout of a structural framework, a

structural analysis is then carried out to obtained its structural

responses.

Depending on the internal force action on each individual

member, a specific size of each member is then estimated and

designed in according with a design standard.

Beam member Beam-column

member

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Structural Analysis

Internal forces (axial, shear, moment, torsion) in each structural

members can be obtained via structural analysis.

1. Classical analytical approach

2. Approximate approach

3. Computer simulation (Finite element method / FEM)

Braced frame structure Rigid frame structure

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Design Standards in HK

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Structural Elements

Reinforced Concrete Design

Beams

Slabs

Short columns

Walls Footings

Pilecaps

Steel Design

Tension members

Compression members

Beams

Beam-columns Steel connections

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Limit State Design

A structural engineer has to design structures that are both

safeand economic.

It is difficult to assess at the design stage how safe and

economic a proposed design will actually be in practice since

there are too many uncertainties.

Uncertaintiesfall roughly into groups:

Loading;

Material strength; and

Structural behaviour.

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Limit state design is a modern approach for structural design

based on the concept of probability.

It aims to ensure an acceptable probability that a structure will

perform satisfactorily during its design life.

Two main limit states

Ultimate limit state (ULS)Ultimate limit states concern the safety of the whole or part of the

structure at ultimate loading conditions.

Serviceability limit state (SLS)Serviceability limit states correspond to limits beyond which the

whole or part of the structure becomes unserviceable under working

loads.

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It requires that a member be designed such that

The above approach is for ULS checking. On the other hands,

SLS checking in principle uses mean values instead of

characteristic values and almost always does not apply partial

factor of safety.

CapacityDesignLoadDesign

Capacity/Load)( mf

where f and

m reflect the degree of uncertainties in the

various loads and the resistance.

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Design Load Characteristic load= magnitude of load that issufficiently larger than the average load so thatonly a very low probability it will be exceeded

during the design life. Design load= Characteristic Load x

f

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Design Capacity Characteristic strength= value of the strengthof the material that is sufficiently lower thanthe mean value so that only a small portion of

the materials in the structure is expected tofall below it.

Design strength= Characteristic Strength / m

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References

Bryan Stafford Smith, Alex Coull (1991). Tall Building Structures: Analysis and Design. JohnWiley & Soons, Inc.

Bungale S. Taranath (2004). Wind and Earthquake Resistant Buildings: Structural Analysis and

Design. CRC Press, Taylor & Francis Group.

Bungale S. Taranath (2010). Reinforced Concrete Design of Tall Buildings. CRC Press, Taylor &

Francis Group.

Bungale S. Taranath (2012). Structural Analysis and Design of Tall Buildings, Steel andComposite Construction. CRC Press, Taylor & Francis Group.

Lin, T.Y. and Stotesbury Sidney D. (1981). Structural Concepts and Systems for Architects and

Engineering, 2nded. Van Nostrand Reinhold.

Mark Sarkisian (2012). Designing Tall Buildings, Structure as Architecture. Routledge, Taylor &

Francis Group.

Mehmet Halis Gnel and Hseyin Emre Ilgin (2014). Tall Buildings Structural Systems andAerodynamic Form. Routledge, Taylor & Francis Group.

Dave Parker and Antony Wood (2013). The Tall Buildings Reference Book. Routledge, Taylor &

Francis Group.

Documents

1. Fundamental of Tall Buildings