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8/4/2019 Building Design b

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Integrated Civil EngineeringDesign Project

(Building Structure Design)

CIVL 395

HKUST

By : Ir. K.S. Kwan

Date: 3/07


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Content

1. Building Control in Hong Kong

2. Design Criteria

3. Structural Form (Residential Building)

4. Hong Kong Wind Loading

5. Computer Modeling6. Design Example


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STRUCTURAL FORMfor Residential Building

Tower

Podium Structure

Building adjacent to slope


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Lintel beam

To identify the wall as structuralelement and link them together by lintel

beam to provide sufficient lateralstiffness

Slab

Wall


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Slab DesignSlab Design

Concrete gradeConcrete gradeGrade 30 to 35 (too high concrete grade may lead to thermal craGrade 30 to 35 (too high concrete grade may lead to thermal crackckduring large pour of concrete)during large pour of concrete)

Steel reinforcement percentageSteel reinforcement percentageDesign as HKDesign as HK CoPCoP 2004 for structural use of concrete2004 for structural use of concrete

Average steel ratio is around 120~140 Kg/mAverage steel ratio is around 120~140 Kg/m33

Preliminary slab size estimationPreliminary slab size estimation

About 100mm~400mm depending on theAbout 100mm~400mm depending on the span of slabspan of slab ( to minimize( to minimizethe number of different slab thickness, say 2 ~3 types, at typicthe number of different slab thickness, say 2 ~3 types, at typical flooral floor

forfor buildabilitybuildability considerationconsideration

To consider the following loadingTo consider the following loading

Self weightSelf weight

Finishes (domestic area/toilet/kitchen) (25mm to 80mm thick)Finishes (domestic area/toilet/kitchen) (25mm to 80mm thick) PartitionPartition


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Slab is designed asone-way or two waysslab


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Wall DesignWall Design

Concrete gradeConcrete gradeGrade 30, 40, 60 or more is commonly used. By usingGrade 30, 40, 60 or more is commonly used. By using high strengthhigh strengthconcreteconcrete, it can optimize the wall thickness and increase the lateral, it can optimize the wall thickness and increase the lateralstiffness of wall. The concrete grade will also bestiffness of wall. The concrete grade will also be changed along thechanged along theheight of buildingheight of building e.g. from Grade 60 at lower floor to Grade 30 at tope.g. from Grade 60 at lower floor to Grade 30 at top

roof.roof.

TheThe thicknessthickness will bewill be trimmedtrimmed down along the height of building e.g.down along the height of building e.g.from 400 at 1/F and gradually changed to 200 at top floor. Thefrom 400 at 1/F and gradually changed to 200 at top floor. Thethickness will be changed every 10 ~20 storey to minimize thethickness will be changed every 10 ~20 storey to minimize the

disturbance on construction.disturbance on construction.

Steel reinforcement percentageSteel reinforcement percentageDesign as HKDesign as HK CoPCoP 20042004

Average steel ratio is around 100~150Kg/mAverage steel ratio is around 100~150Kg/m33

Preliminary wall size estimationPreliminary wall size estimationGravity LoadGravity Loadby tributary methodby tributary method

Wind LoadWind Loadby simple computer modelby simple computer model


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3-D

Vertical Element Gravity Load Estimation byVertical Element Gravity Load Estimation byTributary Area MethodTributary Area Method

Plan

W2

W1W1

W3

C1

250250 200 26252625

200

3900


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TRIBUTARY AREA METHODTRIBUTARY AREA METHOD

No. of storey = 20

Storey height = 2800

Slab thickness = 150

Beam size = 400x200 (ext.)

Beam size = 450x250 (int.)

Dead Load = 10KPa

Live Load = 3KPa

AssumptionAssumption


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Plan

1266W3

2568W2

2264W1

1686C1

(KN)

W2

W1W1

W3

C1

250250 20026252625

200

3900

TRIBUTARY AREA METHODTRIBUTARY AREA METHOD


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Lintel Beam DesignLintel Beam Design (where linking shear(where linking shearwall together to transmit wind shear force)wall together to transmit wind shear force)

SizeSizeWidth as wall thicknessWidth as wall thickness

Depth controlled by headroom (min.Depth controlled by headroom (min.under side of beam i.e. 2100 at doorunder side of beam i.e. 2100 at doorand 2300 under beamand 2300 under beam

Concrete grade same as floor slabConcrete grade same as floor slabfor easy concrete pour with slab orfor easy concrete pour with slab ormore if requiredmore if required

Steel reinforcement percentageSteel reinforcement percentageDesign as HKDesign as HK CoPCoP 20042004

Average steel ratio is around 120Average steel ratio is around 120~160 Kg/m~160 Kg/m33

Preliminary lintel size estimationPreliminary lintel size estimationWind LoadWind Loadby simple computerby simple computer

model; the size is always controlledmodel; the size is always controlledby wind shear transmission (in someby wind shear transmission (in somecritical case, steel plate will be usedcritical case, steel plate will be usedto replaceto replace r.cr.c. design to enhance the. design to enhance thewind shear transmission)wind shear transmission)

Gravity LoadGravity Loadby tributary methodby tributary method

(not the controlled case)(not the controlled case)

LintelBeam

Steel plate at lintelbeam


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TransferStructure

Podium(Plate Structure)

Tower(Shear Wall system)

Supporting Column

(Rigid Frame)


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Transfer Girder Structure

The behavior is similar to deep beam whenthe wall extending to columns such as case a,

b & c.


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Transfer Plate StructureShear WallStructure atTower above

Transfer Plate

ColumnStructure belowTransfer Plate

Thick plate structure

to support all wallstructures above


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Transfer Plate


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Transfer Structure Design (Plate or Girder)Transfer Structure Design (Plate or Girder)

Design similar toDesign similar to pilecappilecap or beamor beam

Closed column spacing under the transfer structure to allow trusClosed column spacing under the transfer structure to allow truss effects effect

at transfer structure to minimize the deformation of transfer stat transfer structure to minimize the deformation of transfer structureructure

((PrestressedPrestressedtransfer structure is required for large span )transfer structure is required for large span )

Steel reinforcement percentageSteel reinforcement percentage

Design as HKDesign as HK CoPCoP 20042004Average steel ratio is around 240~280 Kg/mAverage steel ratio is around 240~280 Kg/m33

Preliminary size estimation (1.5m ~5m)Preliminary size estimation (1.5m ~5m)

Depend on the spacing of columns and tower loadingDepend on the spacing of columns and tower loading

Gravity loadGravity loadas the wall load transmitted tower load to plate levelas the wall load transmitted tower load to plate level

Wind loadWind loadthe platethe plate behaviourbehaviour as frame structure integrated with columnsas frame structure integrated with columns

belowbelow

Normally, the thickness is controlled by shear stressNormally, the thickness is controlled by shear stress


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Loading from towerincluding:

(P) Axial Load(M) Moment

(V) Shear

Transfer Plate Design

To cater for gravity load andwind load from tower

structure including axial load,moment and shear

The transfer plate with

column below to form a rigidframe structure

All loadings are transmitted

to foundation by shear,moment and axial force.

Podium

Structure

Behavior


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Transfer Plate withPrestressed Tendon


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Building DevelopmentAdjacent to Slope

Retaining structure isrequired for buildingnear the slope

The extent ofexcavation willdepend on the subsoil

condition of slope i.e.Rock / Soil

????

????

???


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Building Developmentnear Slope

Column undertransfer structure

Transfer Plate

Walls at Tower

Large Diameter

Bored Pile Pile Cap


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Retaining Wall Structure

Pile Cap


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Retaining structure forsemi-basement

construction


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Retaining WallStructure with

deep excavationrequired


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Two levels

basement toreduce the deep

excavation


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HONG KONG

WIND LOAD

Wind Load

Assessment Procedure


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Wind Responses of a Building

Static

Dynamic

No movement Wind direction

- Along wind

response

- Cross wind

response

- Torsional wind

response

EquivalentStatic Load

WC 2004

Gust Factor

Method

WC 2004

Literature/ Wind Tunnel Test

WC 2004

Wi L A t P


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Win Loa Assessment Proce ure

(1)

(i) Open frame with significantresonant dynamic response, or

(ii) f natural < 0.2Hz, or

(iii) Significant cross wind /

torsional resonant response

(i) fnatural 5 x Min (B, D); or

H > 100m

(i) fnatural > 1Hz; or

(ii) H


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Buildingheight (H)

Building leasthorizontal dimension(B,D)

B

Building on plan

To determine building

height (H) and width

(B,D)


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h

B

H

b

To define the heightand least dimension

of building

Sec A-A

Sec B-B

A-A

B-B


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Wind Load Assessment Procedure (2)

Calculate Force Coefficients (Cf)

Height Aspect Factor, ChShape Factor, Cs

[Appendix D, p.14~15]

Calculate Force Coefficients (Cf)

Height Aspect Factor, ChShape Factor, Cs

Reduction Factor, RA[Appendix D, p.14~16]

4

Calculate Gust Response Factor (G)

[Appendix F, p.19~21]

2b

Calculate Total Along-Wind Force

F = G. Cf . qz .Az[Eqn (3), p. 4]

Calculate Topography Factor

[Appendix C, p.10~13]

Calculate Design Hourly Mean Wind

Pressure

[Table 2, p.5]

Method 2 Slightly Dynamic Building

Calculate Total Wind Force

F = Cf. qz .Az[Eqn (1), p. 3]

5

Calculate Topography Factor

[Appendix C, p.10~13]

3

Calculate Design Wind Pressure

(3-sec. gust pressure)

[Table 1, p.3]

2a

Method 1 Static BuildingStep

Steps 2 - 5


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Wind Code 2004 Only One Terrain

Open Sea Terrain

Step 2a Design Wind Pressure/ DesignHourly Mean Wind Pressure


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Wind Profiles Below 200m

Wind Pressure Profile Under 200m

0

50

100

150

200

250

0.00 1.00 2.00 3.00 4.00 5.00

Pressure (KPa)

Heig

ht(m)

1983

1983

(Stepwise)

PNAP150

2004

Step 2b Along Wind Dynamic


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The original method was developed by Davenport

(1967) and Vickery (1966 and 1971)

In Wind Code 2004, the equation is simplified to:

(Refer to Wind Code 2004 Appendix F for

description of the other variables)

Step 2b - Along Wind Dynamic

Resonant Response by Gust Factor

Method (1)

SEgBgIG fvh

2

221 ++=

St 2b Al Wi d D i R t


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Dynamic resonant response is dependant on the

magnitude of the fluctuating load as well as its size

(or scale) in relation to the size of the structure

The size reduction factor, S, accounts for the

correlation of pressures over a building and is equal

to

The reduction factor, RA, in Table D3 (p.16) does

not apply to the Gust Factor Method in

Appendix F

+

+

h

a

h

a

V

bn

V

hn 41

5.31

1

Step 2b - Along Wind Dynamic Resonant

Response by Gust Factor Method (2)

h/

b/

representsthe size of the

wind gust


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Step 3 Topography Factor (1)

Wind Code 2004 Speed up ratio adopted from BS6399-2:1995

except that the altitude factor in BS6399-2 wasexcluded

(In BS6399-2, altitude factor is used to adjust

the basic wind speed for the altitude of the siteabove seal level.)

St 3 T h F t (2)


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St 3 T h F t (3)


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St 3 T h F t (4)


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St 3 T h F t (5)


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These examples are taken

from British reference bookbased on British Code. Due tothe different requirements in

British Code and Hong KongCode regarding the idealization

of the hill/slope, the actualhill/slope shall be differentlyidealized under the two Codes.

These examples from Britishwere for illustration only and

the method of idealizing thehill/slope should not be copiedfor application to Hong Kong

Code.




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Comment: Idealized slope (a) may be more appropriate for Hong Kong Code.


Topography FactorTopography Factor (App. C of HK Wind Code)(App. C of HK Wind Code)


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opog ap y actop g p y ( pp C C )( pp )


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Forces on Buildings1. Total Force on a Building

F = Cf qz Azwhere Cf= force coefficient

qz = design wind pressure at height z

Az = effective projected area of that part of the

building corresponding to qz

2. The effective projected area of an enclosed building shallbe the frontal projected area

3. The effect projected area of an open framework buildingshall be the aggregate projected area of all members on aplane normal to the direction of the wind

4. Each building shall be designed for the effects of windpressures acting along each of the critical directions


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Force CoefficeintsA. For Enclosed Building

a) Cf = Ch x Cs

b) From other international codes accetped byBA

c) For building with isolated blocks projecting

above a general roof level, individual forcecoefficients corresponding to the heightand shape of each block shall be applied.

d) For building composed of similar contiguousstructures separated by expansion joints,the force coefficients shall be applied tothe entire building.


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Height Aspect Ratio Ch

Height Aspect Factor Ch

1.21.210.0

1.4-20.0 and over

1.11.16.0

1.051.054.0

1.01.02.0

0.950.951.0 or less

20041983

HeightBreadth

Remark: Linear Interpolation to obtain intermediate values


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Shape Factors Cs for Enclosed Building

1.33.0 and over

1.12.0

1.01.0 or less

Csb/dPlan Shape

d

b

wind

Remark: Interpolate linearly

Rectangular

b

d

Cs for buildingswith closed

spacing


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Shape Factors Cs for Enclosed Building

wind

Cs for the Respective enclosingrectangular shape in the direction ofthe wind

Other Shapes

0.75

Circular

CsPlan Shape

Note:When the actual shape of a building renders it to become sensitiveto wind acting not perpendicular to its face, the diagonal windeffects and torsional wind effects should be considered

Reduction Factor RA


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Reduction Factor RA

Gusts are the results of eddies and vortices

The speed of gust is a function of its duration

The smaller the size of the gust, the shorter will be its duration and thehigher will be the gust speed

The larger the size of gust, the longer will be its duration and the lower theaverage gust speed

A small gust can only create high wind loading on a small local area of thestructure

The whole structure should be designed with the speed of a gust which isjust big enough to affect the whole structure simultaneously

A 3 second gust can normally engulf a building with frontal area of 300 to800m2, a longer duration gust is required to be effective on the whole ofthe structure

A reduction factor is therefore applied when designing buildings of largerdimensions

(E.C.C.Choi Commentary on 1983 wind codes)

Not applicable for buildings with significant resonant dynamic responsedesigned by using hourly mean wind pressure

Reduction Factor RA for Enclosed


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Reduction Factor RA for Enclosed

Buildings

0.8015000 and over

0.8410000

0.868000

0.8950000.923000

0.961000

0.978001.00500 or less

2004

Reduction Factor RAFrontal Projected Area m2

Note : Linear Interpolation may be used to obtain intermediate values


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Wind Load Case

X & Y directions are commonly accepted

Additional wind direction (e.g. diagonal wind

for Y-shape building) is required For large frontal area building (say >50m),

additional torsional wind load (10% of long

face dimension) is required


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Wind Load Distribution

at Building

Wind Load Calculation as HK CoP


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(Building is considered as significant resonant dynamic structure)

Wind load


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Wind loadcalculation at each

floor for a building with40 storey (with 3 floorsabove domestic floor)and the building width

is 40.23m

Building structure as

significant resonantdynamic structure \

Sa=topography

factor


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(Building is not considered as significant resonant dynamic structure)

Wind loadcalculation at each


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calculation at eachfloor for a building

with 40 storey (with 3floors abovedomestic floor) andthe building width is

40.23m

Building structure

not considered assignificant resonant

dynamic structure

(Note: Total wind

shear is larger basedon static wind loadapproach for buildingaspect ratio just

greater than 5)

Sa = topographyfactor


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COMPUTER MODELING

Common Structural AnalysisCommon Structural Analysis


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Common Structural AnalysisCommon Structural Analysis

Software used in Hong KongSoftware used in Hong Kong

ETABSETABS

SAP2000SAP2000

SAFESAFE

SADSSADS

GSAGSA STARIIISTARIII

GTSTRUDLGTSTRUDL

PAFECPAFEC

STANSTAN

Tall Building Modelling AssumptionsTall Building Modelling Assumptions


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1.1. MaterialMaterialAll structuralAll structuralcomponents behavecomponents behavelinearly elastically.linearly elastically.

2.2. ParticipatingParticipatingComponentsComponentsonly theonly theprimary structuralprimary structural

componentscomponents participateparticipatein the overall behaviourin the overall behaviour

3.3. Floor slabsFloor slabsFloor slabFloor slab

are assumed to beare assumed to be rigidrigidin planein plane unless theyunless theycontain large openingscontain large openingsor are long and narrowor are long and narrow

in planin plan

Only the primary

structuralcomponents are

put in model

Rigid in plane



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g g pg g p

4.4. Negligible stiffnessNegligible stiffnesscomponent stiffness ofcomponent stiffness ofrelatively small magnituderelatively small magnitude

are assumed negligibleare assumed negligible

5.5. Negligible deformationsNegligible deformationsdeformations that aredeformations that are

relatively small and of littlerelatively small and of littleinfluence are neglected.influence are neglected.

6.6. CrackingCrackingthe effects ofthe effects ofcracking in reinforcedcracking in reinforcedconcrete members toconcrete members toflexural tensile stresses mayflexural tensile stresses maybe represented by abe represented by areduced stiffnessreduced stiffness

This line should be astraight line in

assumption due to thesmall deformation

How to apply wind loading inHow to apply wind loading incomputer model?computer model?

V


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computer model?computer model?In common building shape

with the rigid diaphragmassumption, the wind loadshould be applied at the

geometry centre of each floor

Windload

appliedat floor

Wind load applied at

centre of frontal area

What can you find inWhat can you find in

computer modeling?computer modeling?


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computer modeling?computer modeling?

Seismic, wind and gravitySeismic, wind and gravity

analysisanalysis

Deformation of buildingDeformation of buildingunder different loadingunder different loading

conditionsconditions

Member force underMember force underdifferent loading conditionsdifferent loading conditions

Deflection of building at topfloor including the X & Y

displacement and Z direction


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d sp ace e t a d d ect o

rotation


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Q & AIf you have any questions about the structural design, pleaseforward email (with your Name and Student ID no.)

to :[email protected]

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