building design

(1)

Integrated Civil Engineering

Design Project

(Building Structure Design)

CIVL 395

HKUST

By : Ir. K.S. Kwan Date: 3/07

(2)

Content

1. Building Control in Hong Kong

2. Design Criteria

3. Structural Form

(Residential Building)

4. Hong Kong Wind Loading

5. Computer Modeling

(3)

STRUCTURAL FORM

for Residential Building

•Tower

•Podium Structure

(4)

Lintel beam

To identify the wall as structural

element and link them together by lintel beam to provide sufficient lateral

stiffness

Slab

(5)

Slab Design

–

Concrete grade

Grade 30 to 35 (too high concrete grade may lead to thermal cra

ck

during large pour of concrete)

–

Steel reinforcement percentage

Design as HK

CoP

2004 for structural use of concrete

Average steel ratio is around 120~140 Kg/m

33

–

Preliminary slab size estimation

About 100mm~400mm depending on the

span of slab

( to minimize

the number of different slab thickness, say 2 ~3 types, at typic

al floor

for

buildability

consideration

To 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) –

(6)

Slab is designed as one-way or two ways slab

(7)

Wall Design

–

Concrete grade

Grade 30, 40, 60 or more is commonly used. By using

high strength

concrete

, it can optimize the wall thickness and increase the lateral

stiffness of wall. The concrete grade will also be

changed along the

height of building

e.g. from Grade 60 at lower floor to Grade 30 at top

roof.

The

thickness

will be

trimmed

down along the height of building e.g.

from 400 at 1/F and gradually changed to 200 at top floor. The

thickness will be changed every 10 ~20 storey to minimize the

disturbance on construction.

–

Steel reinforcement percentage

Design as HK

CoP

2004

Average steel ratio is around 100~150Kg/m

33

–

Preliminary wall size estimation

Gravity Load

–

by tributary method

Wind Load

(8)

3-D

Vertical Element Gravity Load Estimation by

Tributary Area Method

Plan

W2 W1 W1 W3 C1 250 250 2625 200 2625 200 3900

(9)

TRIBUTARY 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

Assumption

(10)

Plan

1266 W3 2568 W2 2264 W1 1686 C1 (KN) W2 W1 W1 W3 C1 250 250 2625 200 2625 200 3900

TRIBUTARY AREA METHOD

(11)

Lintel Beam Design

(where linking shear (where linking shear wall together to transmit wind shear force)

wall together to transmit wind shear force)

–

Size

Width as wall thickness

Depth controlled by headroom (min.

under side of beam i.e. 2100 at door

and 2300 under beam

Concrete grade same as floor slab

for easy concrete pour with slab or

more if required

–

Steel reinforcement percentage

Design as HK

Design as HK CoPCoP2004 2004

Average steel ratio is around 120

~160 Kg/m

~160 Kg/m33

–

Preliminary lintel size estimation

Wind Load

Wind Load –– by simple computer by simple computer model; the size is always controlled

model; the size is always controlled

by wind shear transmission (in some

critical case, steel plate will be used

to replace

to replace r.cr.c. design to enhance the . design to enhance the wind shear transmission)

wind shear transmission)

Gravity Load

Gravity Load –– by tributary method by tributary method (not the controlled case)

(not the controlled case)

Lintel Beam

Steel plate at lintel beam

(12)

Transfer

Structure

Podium

(Plate Structure)

Tower

(Shear Wall system)

Supporting Column (Rigid Frame)

(13)

Transfer Girder Structure

The behavior is similar to deep beam when the wall extending to columns such as case a, b & c.

(14)

Transfer Plate Structure

Shear Wall Structure at Tower above Transfer Plate Column Structure below Transfer Plate

Thick plate structure to support all wall

(15)

(16)

(17)

Transfer Structure Design (Plate or Girder)

–

Design similar to

pilecap

or beam

–

Closed column spacing under the transfer structure to allow trus

s effect

at transfer structure to minimize the deformation of transfer st

ructure

(

Prestressed

transfer structure is required for large span )

–

Steel reinforcement percentage

Design as HK

Design as HK CoPCoP2004 2004

Average steel ratio is around 240~280 Kg/m

Average steel ratio is around 240~280 Kg/m33

–

Preliminary size estimation (1.5m ~5m)

Depend on the spacing of columns and tower loading

Gravity load

Gravity load –– as the wall load transmitted tower load to plate level as the wall load transmitted tower load to plate level Wind load

Wind load –– the plate the plate behaviourbehaviour as frame structure integrated with columns as frame structure integrated with columns below

below

Normally, the thickness is controlled by shear stress

(18)

Loading from tower including:

(P) Axial Load (M) Moment (V) Shear

Transfer Plate Design

To cater for gravity load and

wind load from tower

structure including axial load, moment and shear

The transfer plate with

column below to form a rigid frame structure

All loadings are transmitted

to foundation by shear, moment and axial force. Podium

Structure Behavior

(19)

(20)

Transfer Plate with Prestressed Tendon

(21)

Building Development

Adjacent to Slope

Retaining structure is

required for building

near the slope

The extent of

excavation will

depend on the subsoil

condition of slope i.e.

Rock / Soil

????

????? ??

(22)

Building Development near Slope Column under transfer structure Transfer Plate Walls at Tower Large Diameter

(23)

Retaining Wall Structure

(24)

Retaining structure for semi-basement

(25)

Retaining Wall Structure with deep excavation

(26)

Two levels basement to reduce the deep

(27)

HONG KONG

WIND LOAD

Wind Load

(28)

Wind Responses of a Building

• Static

• Dynamic

No movement Wind direction

- Along wind response - Cross wind response - Torsional wind response • Equivalent Static Load • WC 2004 • Gust Factor Method • WC 2004

• Literature/ Wind Tunnel Test • WC 2004

(29)

Wind Load Assessment Procedure

(1)

(i) Open frame with significant resonant dynamic response, or (ii) f_natural < 0.2Hz, or

(iii) Significant cross wind / torsional resonant response (i) f_natural <= 1Hz; and

(ii) H > 5 x Min (B, D); or H > 100m

(i) f_natural > 1Hz; or

(ii) H <= 5 x Min (B, D); and H <= 100m

Signpost in Wind Code 2004

• Susceptible to dynamic

excitation

• Recommendation from

literature/ Dynamic wind tunnel test [App. A, p.7] III

• Susceptible to along wind

resonant response

• Gust Factor Method

[Cl. 7, p.4] II

• No significant resonant

dynamic response

• Equivalent Static Load

Method [Cl. 5, p.3] I

Characteristic Method

Step 1 – Determine Method of Calculation

• Determine method of calculation according to the signpost in Cl. 3.3 (p.2) and Cl. 7.6 (p.5).

(30)

Building height (H) Building least horizontal dimension (B,D) B Building on plan To determine building height (H) and width (B,D)

(31)

h

B H

b To define the height

and least dimension of building

Sec A-A

Sec B-B A-A

(32)

Wind Load Assessment Procedure (2)

• Calculate Force Coefficients (Cf)

– Height Aspect Factor, C_h – Shape Factor, C_s

[Appendix D, p.14~15]

• Calculate Force Coefficients (Cf)

– Height Aspect Factor, C_h – Shape Factor, C_s

– Reduction Factor, R_A

[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 .Σ 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. Σ 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 Building Step

Steps 2 - 5

(33)

• Wind Code 2004

– Only One Terrain

• Open Sea Terrain

Step 2a – Design Wind Pressure/ Design

Hourly Mean Wind Pressure

(34)

(35)

(36)

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) He ig h t ( m ) 1983 1983 (Stepwise) PNAP150 2004

(37)

• 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)

ς

SE

g

B

g

I

G

_h _v f 2 2

2

1 +

+

=

(38)

• 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, R

_A

, in Table D3 (p.16) does

not apply to the Gust Factor Method in

Appendix F

⎥

⎦

⎤

⎢

⎣

⎡

+

⎥

⎦

⎤

⎢

⎣

⎡

+

h a h a

V

b

n

V

h

n

4

1

5 .

3

1

1 Step 2b - Along Wind Dynamic Resonant

Response by Gust Factor Method (2)

h/λ

b/λ

λ represents

the size of the

wind gust

(39)

Step 3 – Topography Factor (1)

• Wind Code 2004

– Speed up ratio adopted from BS6399-2:1995

except that the altitude factor in BS6399-2 was

excluded

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

the basic wind speed for the altitude of the site

above seal level.)

(40)

(41)

(42)

(43)

These examples are taken from British reference book based on British Code. Due to the different requirements in British Code and Hong Kong Code regarding the idealization of the hill/slope, the actual

hill/slope shall be differently idealized under the two Codes. These examples from British were for illustration only and the method of idealizing the hill/slope should not be copied for application to Hong Kong Code.

(44)

(45)

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

(46)

Topography Factor

(47)

Forces on Buildings

1. Total Force on a Building

F = C

_f

Σ q

_z

A

_z

where C

f

= force coefficient

q

z

= design wind pressure at height z

A

z

= effective projected area of that part of the

building corresponding to qz

2. The effective projected area of an enclosed building shall

be the frontal projected area

3. The effect projected area of an open framework building

shall be the aggregate projected area of all members on a

plane normal to the direction of the wind

4. Each building shall be designed for the effects of wind

pressures acting

along each of the critical directions

(48)

Force Coefficeints

A. For Enclosed Building

a) C

f

= C

h

x C

s

b) From

other international codes

accetped by

BA

c) For building with isolated blocks projecting

above a general roof level, individual force

coefficients corresponding to the height

and shape of each block shall be applied.

d)

For building composed of similar contiguous

structures separated by expansion joints,

the force coefficients shall be applied to

the entire building.

(49)

Height Aspect Ratio C

_h

Height Aspect Factor Ch

1.2

10.0

1.4 -20.0 and over

1.1

6.0

1.05

4.0

1.0

2.0

0.95

0.95 1.0 or less

2004

1983

Height

Breadth

(50)

Shape Factors Cs for Enclosed Building

1.3

3.0 and over

1.1

2.0

1.0

1.0 or less

C

_s

b/d

Plan Shape

d b wind

Remark: Interpolate linearly Rectangular b d Cs for buildings with closed spacing

(51)

Shape Factors Cs for Enclosed Building

wind

Cs for the Respective enclosing

rectangular shape in the direction of

the wind

Other Shapes

0.75 Circular

Cs

Plan Shape

Note:

When the actual shape of a building renders it to become sensitive to wind acting not perpendicular to its face, the diagonal wind

(52)

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 the higher will be the gust speed

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

• A small gust can only create high wind loading on a small local area of the structure

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

• A 3 second gust can normally engulf a building with frontal area of 300 to 800m2, a longer duration gust is required to be effective on the whole of the structure

• A reduction factor is therefore applied when designing buildings of larger dimensions

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

• Not applicable for buildings with significant resonant dynamic response designed by using hourly mean wind pressure

(53)

Reduction Factor RA for Enclosed

Buildings

0.80 15000 and over

0.84 10000

0.86 8000

0.89 5000

0.92 3000

0.96 1000

0.97

800

1.00 500 or less

2004

Reduction Factor RA

Frontal Projected Area m2

(54)

• 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

(55)

Wind Load Distribution

at Building

(56)

Wind Load Calculation as HK CoP

(57)

Wind load

calculation at each floor for a building with 40 storey (with 3 floors above domestic floor) and the building width is 40.23m Building structure as significant resonant dynamic structure \ Sa=topography factor

(58)

(59)

Wind Load Calculation as HK CoP

(60)

Wind load

calculation at each floor for a building with 40 storey (with 3 floors above

domestic floor) and the building width is 40.23m

Building structure not considered as significant resonant dynamic structure (Note: Total wind shear is larger based on static wind load approach for building aspect ratio just

greater than 5) Sa = topography factor

(61)

(62)

Common Structural Analysis

Software used in Hong Kong

ETABS

SAP2000

SAFE

SADS

GSA

_GSA

STARIII

_STARIII

GTSTRUDL

_GTSTRUDL

PAFEC

_PAFEC

STAN

_STAN

(63)

Tall Building Modelling Assumptions

1.

1. Material

Material

–

All structural

components behave

linearly elastically.

2.

2. Participating

Participating

Components

–

only the

primary structural

components

participate

in the overall behaviour

3.

3. Floor slabs

Floor slabs

–

Floor slab

are assumed to be

rigid

in plane

unless they

contain large openings

or are long and narrow

in plan

Only the primary structural components are

put in model

(64)

Tall Building Modelling Assumptions

4.

4. Negligible stiffness

Negligible stiffness

–

component stiffness of

relatively small magnitude

are assumed negligible

5.

5. Negligible deformations

Negligible deformations

–

deformations that are

relatively small and of little

influence are neglected.

6.

6. Cracking

Cracking

–

the effects of

cracking in reinforced

concrete members to

flexural tensile stresses may

be represented by a

reduced stiffness

This line should be a straight line in assumption due to the

(65)

How to apply wind loading in

computer model?

V

In common building shape with the rigid diaphragm assumption, the wind load should be applied at the

geometry centre of each floor

Wind load applied at floor

Wind load applied at centre of frontal area

(66)

What can you find in

computer modeling?

–

Seismic, wind and gravity

analysis

–

Deformation of building

under different loading

conditions

–

Member force under

different loading conditions

(67)

Deflection of building at top floor including the X & Y

displacement and Z direction rotation

(68)

(69)

Q

&

A

If you have any questions about the structural design, please forward email (with your Name and Student ID no.)