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Chapter 6 Seismic Design of Reinforced Concrete Buildings

Chapter 6

6.1 Introduction

6.2 Earthquake Damage in Reinforce Concrete Buildings

6.3 Structural System and Seismic Grading for Structures

6.4 Seismic design of RC frames

6.5 Seismic design of RC walls

6.6 Detailing

6.7 Dual system

6.8 Case Study

6.1 Introduction

RC structural system

Frame structure

Structural wall

Dual system

Mega structure

钢筋混凝土框架

钢筋混凝土框架梁柱楼板配筋

梁柱节点钢筋连接

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梁柱节点钢筋连接

梁柱节点钢筋连接

一、现行设计能实现强柱弱梁吗 6.2 Earthquake Damage in Reinforce Concrete Buildings

Sources: China Southwest Architecture Design Institute Co., Ltd

Con’d

现行设计能实现强柱弱梁吗

Sources: China Southwest Architecture Design Institute Co., Ltd

Weak Column

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Con’d

现行设计能实现强柱弱梁吗

Sources: China Southwest Architecture Design Institute Co., Ltd

如何考虑框架、框剪结构中填充墙对整体结构的刚度贡献

Con’d

Sources: China Southwest Architecture Design

Institute Co., Ltd

如何考虑框架、框剪结构中填充墙对整体结构的刚度贡献

Con’d

Sources: China Southwest Architecture Design Institute Co., Ltd

怎样合理设计框架、框剪结构中的填充墙

Con’d

Sources: China Southwest Architecture

Design Institute Co., Ltd

建议提高竖向构件的最低配筋水准

Con’d

Sources: China Southwest Architecture Design Institute Co., Ltd

箍筋设置问题 Damage regarding to stirrups

建筑材料、施工管理问题

Con’d

Sources: China Southwest Architecture Design Institute Co., Ltd

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十六、重视角柱、加腋梁柱的抗震设计

Photo by Prof. Xiong Haibei, 2008.7

Photo by Prof. Xiong Haibei, 2008.7 Photo by Prof. Xiong Haibei, 2008.7

Key lessons from 5.12 earthquake

From the earthquake vulnerability of RC Frames, we

learnt:

• Vulnerability of corner columns was worse than other exterior and

interior columns

• Column’s failure were more occurred and more severe than beam’s.

• All elements must be detailed so that they can respond to strong

earthquakes in a ductile mode.

• Non-ductile modes such as shear and bond fai lures must be

avoided.

• A high degree of structural redundancy should be provided.

6.3 Structural System and Seismic Grading for Structures

Conceptual Design for RC frame structures

Height

Structural System

Seismic Fortification Intensity Grading

Requirements in Design

Configuration

Calculation

Details

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The appropriate maximum height for R/C buildings (m)

(Table 6.1.1 in GB50011-2010)

Notes: the height in () is the value listed in GB 50011-2008

Structure Types System Seismic Fortification Intensity

6 7 8 (0.2g) 8 (0.3g) 9

Frame System 60 50 (55) 40 (45) 35 24 (25)

Frame-Wall System 130 120 100 80 50

Structural Wall System 140 120 100 80 60

Frame supported Wall System

120 100 80 50 N.A

Frame- Tube System 150 130 100 90 70

Tube in Tube System 180 150 120 100 80

Slab-Column and Wall System

80(40) 70(35) 55(30) 40 N.A

Seismic grading for reinforced concrete buildings

(Table 6.1.2 in GB50011-2010)

Types of structure Seismic fortification intensity

6 7 8 9

Fram structure

Height (m) ≤24 >24 ≤24 >24 ≤24 >24 ≤24

Frames 4th 3rd 3rd 2nd 2nd 1st 1st

Large span frames

3rd 2nd 1st 1st

Wall-Frame

structure

Height (m) ≤60 >60 ≤24 25~60 >60 ≤24 25~60 >60 ≤24 25~60

Frames 4th 3rd 4th 3rd 2nd 3rd 2nd 1st 2nd 1st

Structural walls

3rd 3rd 2nd 2nd 1st 1st

Structural wall

structure

Height (m) ≤80 >80 ≤24 25~80 >80 ≤24 25~80 >80 ≤24 25~60

Structural walls

4th 3rd 4th 3rd 2nd 3rd 2nd 1st 2nd 1st

be continued

Types of structure Seismic fortification intensity

6 7 8 9

Frame -supported

wall structure

Height (m) ≤80 >80 ≤24 25~80

>80 ≤24 25~80

Struc-tural walls

General 4th 3rd 4th 3rd 2nd 3rd 2nd

Streng-thening

3rd 2nd 3rd 2nd 1stI 2nd 1st

Frames that supporting

walls

2nd 2nd 1st 1st

Framed-tube structure

Frame 3rd 2nd 1st 1st

Tube 2nd 2nd 1st 1st

Tube in tube structure

Exterior tube 3rd 2nd 1st 1st

Interior tube 3rd 2nd 1st 1st

Slab-column-wall structure

Height (m) ≤35 >35 ≤35 >35 ≤35 >35

Columns 3rd 2nd 2nd 2nd 1st

Walls 2nd 2nd 2nd 1st 2nd 1st

(Table 6.1.2 in GB50011-2010)

Seismic design flow chart

6.4 Seismic design of RC

frames

Earthquake action and responses

22

Three kinds of Calculation method

• Base Shear Method

• Response Spectrum Method

• Time History Analysys Method

To get the lateral force to every storey of

the building struture, then

To get the shear force of every storey of

the building struture

The Min Value of story shear force

Determination of story shear force

(GB 50011-2010, 5.2.5) The horizontal seismic shear force at each floor level of structure shall be comply with the requirement of the following equations:

n

ij

jeki GV

6 7 8 9

Structures with obvious torsion effect or fundermental period is less than 3.5s

0.008 0.016

(0.024)

0.032

(0.048)

0.064

Structures with fundermental period greater than 5s

0.006 0.012

(0.018)

0.024

(0.036)

0.048

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the shear force of the k-th column in i-th floor

where

Vik is the horizontal shear force induced in column k on i th story;

Dik is relative shear stiffness of column k on i th story;

in

k

ik

ikik V

D

DV

1

(5.7)

n

k

ikD1

is summation of relative shear stiffness of

total columns on i th story.

D Value methods 2

c

h

i12D

Determine the internal forces of

lateral-force-resisting frames :

Determine flexural stiffness for beam and column;

Calculate D value;

Determine shear force for each column;

Determine the position of the point of contra-flexure in column;

Calculate column moments, then derive the beam moments based on

equilibrium of beam to column joint, and distribution of beam stiffness

/hVM ikkl (5.11)

)( /hhVM ikku (5.12)

6.4 Seismic design of RC frames

6.4.1 Principle of seismic design

Three Principles of seismic design

strong shear - weak flexure

strong column - weak beam

strong joints - weak members

M-φ Curve

Lesson from this Diagram

M-φ Curve of a beam

Lesson from this Curve

Ductility and compress ratio

Lesson from these picture

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6.4.2 Shear resistance of members

Members in a Frame:

BEAM, COLUMN, and JOINT

What's different from beam and column?

A member subjected to an axial force of 0.1fc Ag or less can be treated as a beam (Ag = the gross area of the section, fc = design compression strength for concrete).

To dirtermin size of a member's section we should:

),,(0 ccRE fVfbh

• Shear compression ratio : defined as nominal shear stress

divided by design compression strength of concrete (cylinder

strength), or V/fcbh0, to quantify a nominal shear stress across a

beam section

• To ensure that premature diagonal compression failure not

occur before the onset of yielding of shear reinforcement, the

diagonal compression principal stress should be limited.

6.4.2 Shear resistance of members

For Beam：If ratio of span to depth (跨高比) is greater than 2.5,

For Column and Wall：If shear span ratio (剪跨比) is greater than 2,

the design shear force should satisfy the following equation:

ccREccRE

cc

RE

fVfVbh

bhfV

/50.20/

)20.0(1

0

0

6.4.2 Shear resistance of members

)15.0(1

0bhfV cc

RE

For Beam：If ratio of span to depth (跨高比) is NOT greater than 2.5,

For Column and Wall：If shear span ratio (剪跨比) is NOT greater

than 2, the design shear force should satisfy the following equation:

)30.0(1

jjcj

RE

j hbfV

(5.46) For Joint：

6.4.2 Shear resistance of members

To ensure ductile flexural failure and prevent brittle shear failure, a principle of “strong shear—weak flexure” should be followed in seismic design of reinforced concrete beams.

Gb

n

r

b

l

bvb V

l

MMV

6.4.3 strong shear—weak flexure

For beams in grade 1 frames, is 1.3.

For beams in grade 2 frames, is 1.2.

For beams in grade 3 frames, is 1.1. vbvb

vb

Gb

n

r

bua

l

bua Vl

MMV

1.1

For beams in grade 1 and earhtquake intensity 9,the beam

and lintel may not be adjusted,but it should satisfy the

following requirement.

Shear strength of beams

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Considering shear strength reduction in the diagonal plan of

beam under the repeated reversal loading, the shear strength in

diagonal plan should be checked as the follows

)25.142.0(1

00 hs

AfbhfV sv

yvt

RE

b

)1

05.1(

100 h

s

AfbhfV sv

yvt

RE

b

Shear strength of beams

Principle of strong shear and weak flexure

To ensure ductile flexural failure and prevent brittle

shear failure

n

b

c

t

cvc

H

MMV

(5.37)

Shear strength of columns

For columns in grade 1 frames, is 1.5, the others are 1.4

For columns in grade 2 frames, is 1.3. 1.2

For columns in grade 3 frames, is 1.2. 1.1

For columns in grade 4 frames, is 1.1. 1.1

vc

vc

vc

vc

n

t

cua

b

cua

H

MMV

2.1

For columns in grade 1 and earhtquake intensity 9, the

columns may not be adjusted, but it should satisfy the

following requirement.

Shear strength of columns shear resistance of columns

)056.0

1

05.1(

100

Nhs

AfhbfV

c

sv

yvcct

RE

col

)2.01

05.1(

100

Nhs

AfhbfV

c

sv

yvcct

RE

col

Design value of bending moments of members around a

beam-column joint should satisfy the following requirements:

bcc MM

For frame structures in grades 1,2,3 and 4, is 1.7,1.5,1.3 and 1.2;

For other types of frame, is 1.4 in grade 1,1.2 in grade 2,1.1 in grade 3and 4.

c c c c

cc

c

6.4.5 strong column—weak beam

Mc,up

Mc,low

Mb,r

Mb,l

Vc,up

Vb,l

Vb,r

Nc,up

Nc,low

Vc,low Vc,low

Vc,low

Beam

Column

buac MM 2.1

For frame structures in grade 1 and earhtquake intensity 9, the

design value of combined bending moment of menbers

should satisfy the following requirement.

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6.4.5 strong joints-weak members

(1) Design of beam-column joints

The design of beam-column joints is primarily

aimed at:

(i) preserving the integrity of the joint so that the strength

and deformation capacity of the connected beams and

columns can be developed and substantially maintained.

(ii) preventing significant degradation of the joint stiffness

due to cracking of the joint and loss of bond between

concrete and the longitudinal column and beam

reinforcement or anchorage failure of beam reinforcement.

bc

sbo

sb

bjb

jhH

ah

ah

MV

/

/

0

1 (5.41)

bc

sbo

sb

bua

jhH

ah

ah

MV

/

/

0

115.1

(5.42)

(2) Design value of shear force

(b) Shear strength checking of beam-column joint

s

ahAf

b

bNhbfV sb

svjyv

c

j

jjjtj

RE

j05.01.1

1

47.5

(3) Seismic shear strength checking of joint core

s

ahAfhbfV sb

svjyvjjtj

RE

j09.0

1

48.5

6.4.6 Lateral deflection evaluation

• Drift, or inter-story displacement should be limited

(causes non-structural damage and human discomfort

and secondary stress in the main structure)

• To provent the structure collapsed.

(1) Checking elastic floor drifts under frequently accured earthquake,

(2) Checking plastic floor drifts under rare accured earthquake,

A simplified equation to calculate elastic-plastic story drift is the follows:

hu pp (5.50)

epp uu (5.51)

hu ee