Definition of shear wall

Position

Design provisions

Behavior

Case studies

PRESENTATION OUTLINE

1

2Fig. 1 A reinforced concrete wall

Known as shear walls

Designed to resist lateral forces

Excellent structural system to resist earthquake

Provided throughout the entire height of wall

Practicing from 1960s for medium and high rise

buildings (4 to 35 stories high)

RC STRUCTURAL WALLS

3

Provide large strength and stiffness in the

direction of orientation

Significantly reduces lateral sway

Easy construction and implementation

Efficient in terms of construction cost and

effectiveness in minimizing earthquake damage

ADVANTAGES OF SHEAR WALLS

4

PLACEMENT OF SHEAR WALLS

5

Located symmetrically to reduce ill effects of twist

Symmetry can be along one or both the directions

Can be located at exterior or interior

More effective when located along exterior

perimeter of building

PLACEMENT OF SHEAR WALLS

6

7Fig. 2 Reinforced concrete shear wall (Murthy C.V.R.

,2005)

Located symmetrically to avoid ill effects of

twisting

Symmetry can be along one or both the directions

Can be located at exterior or interior

More effective when located along exterior

perimeter of building

PLACEMENT OF SHEAR WALLS

6

Widely used design approaches for shear walls

ACI method (ACI 318-1995)

IS 13920:1993 - Indian Standard Ductile

Detailing of RC members

Code provides a ductile design to give

adequate toughness and ductility to resist

severe earthquakes

CODES FOR DESIGN OF SHEAR

WALLS

8

Thickness 150 – 400 mm

Minimum reinforcement 0.25% of gross area in

each direction

Diameter shall not exceed 1/10 th thickness of

section

Reinforcement provided in two curtains when:

Factored shear stress exceeds or

Wall thickness exceeds 200 mm

DESIGN CONSIDERATIONS

9

0.25 ckf

Nominal shear stress,

SHEAR STRENGTH OF WALLS

10

v

uv

w w

V

t d

Factored shear

force

Thickness of wall

section

Effective depth of wall

section = for

rectangular sections 0.8 wl

Design shear stress, from table 19 of IS

456:2000

If < minimum shear reinforcement

If > shear reinforcement is designed

for excess shear force of

SHEAR STRENGTH OF WALLS CONTD…

11

v

v c

c

c

usV

0.87 y h w

us

v

f A dV

S

SHEAR STRENGTH OF WALLS CONTD…

12

c w wVu t d

= characteristic strength of steel

= effective depth of wall section

yf

wd

Area of horizontal shear

reinforcement

Vertical

spacing

For

where,

FLEXURAL STRENGTH

13

u u

w w

x x

l l

22

2

11 0.416 0.168

2 3

uv u u

ck w w w w

M x x

f t l l l

2 0.36

u

w

x

l

0.0035

0.870.0035

u

yw

x

fl

Es

0.87 y

ck

f

f

u

ck w w

P

f t l 0.87

0.0035

y

s

f

E st

w w

A

t l

FLEXURAL STRENGTH CONTD…

14

For 1u u

w w

x x

l l

2

1 2 32 2

uv u u

ck w w w w

M x x

f t l l l

10.36 1

2 2

2 10.15 1

2 2 3

1

36 /u wx l

ux depth of NA from extreme compression fibre*

ux balanced depth of NA

Portions along edges of shear wall strengthened

by longitudinal and transverse reinforcement

Can have same or greater thickness compared

to wall

Develop good flexural strength

Should have adequate axial load carrying

capacity

Vertical reinforcement range between 0.8 and

BOUNDARY ELEMENTS

16

Factors governing seismic behavior of shear

walls:

Ductility

Stiffness

Soil structure interaction effects

Period of structure

SEISMIC BEHAVIOUR OF WALLS

15

Ductility

Ratio of displacement at maximum load to

that at yield

Highly desirable property for shear walls

Stiffness

Property of element to resist displacement

More stiffer wall need more force to deflect it

SEISMIC BEHAVIOUR CONTD…

16

Soil- structure interaction

Structural damage directly related to depth

of soil overlying the rock and period of

vibration of soil

Understanding relationship between period

of vibrations of soil and structure is

important

SEISMIC BEHAVIOUR CONTD…

18

Period of a building

Important index that identifies vulnerability to

excessive drift

A simple approximation to period of building:

(Mete a Sozen,

2004)

m = unit mass (total mass divided with height )

SEISMIC BEHAVIOUR CONTD…

19

4

2

3.5

w

c w

w

TE I

mh

Some important conclusions from extensive

experimental studies on seismic behaviour of

shear walls:

High axial load ratio is undesirable for structures

[7]

Damage always initiate from top of splices. So

splice impacts seismic performance [1]

SEISMIC BEHAVIOUR CONTD…

20

For accurate evaluation of seismic

demands soil structure interaction must

also be considered [8]

Shear walls with staggered openings

produce better results in earthquakes [4]

SEISMIC BEHAVIOUR CONTD…

22

CASE STUDY 1

22

Three specimens

W1, W2, W3

Represent slender shear walls

Aspect ratio 4

Axial load ratios (ALR) 0.25,0.5,0.5 resp.

BEHAVIOUR OF SHEAR WALLS UNDER

HIGH AXIAL LOAD RATIO

[R.K.L. Su and S.M. Wong]

23

24

wh

wl

Fig. 3 A shear wall

w

w

h

l

1

1 2

2

Squat

Intermediate

Slender

Aspect ratio =

Three specimens

W1, W2, W3

Represent tall slender shear walls

Aspect ratio 4

Axial load ratios (ALR) 0.25,0.5,0.5 resp.

BEHAVIOUR OF SHEAR WALLS

UNDER HIGH AXIAL LOAD RATIO

[R.K.L. Su and S.M. Wong]

23

applied axial load

axial load capacity at a section

AXIAL LOAD RATIO

25

Axial load ratio =

'

u

c g

PALR

f A

compressive strength of concrete

gross cross section of the wall

'

cf

gA

TESTING METHODOLOGY

26Fig.4 Testing rig (R.K.L. Su and S.M. Wong,

2006)

Specimens placed in a steel loading frame

Compressive axial force applied from bottom

simulated gravity load

Push and pull forces to the flange beam

represented lateral seismic loads

TESTING METHODOLOGY CONTD…

27

28Fig. 5 Testing rig and load application (Su and Wong,

2006)

Specimens placed in a steel loading frame

Compressive axial force applied from bottom

simulated gravity load

Push and pull forces to the flange beam

represented lateral seismic loads

TESTING METHODOLOGY CONTD…

27

28Testing rig and load application (Su and Wong,

2006)

W1 exhibited flexural

ductile failure

Cracks developed at

early stage

Propagated inwards

to the core of the

section

OBSERVATIONS

29

Fig. 6 Failure pattern of specimen

W1

(Su and Wong, 2006)

W2 and W3 exhibited brittle compression failure

Spalling of concrete observed due to high ALR

OBSERVATIONS CONTD…

30

Fig.7 Failure pattern of specimens W2 and W3

(Su and Wong, 2006)

ALR affect failure

High ALR has a suppressive effect on ductility

As ALR increases energy dissipation decreases

Axial stiffness reduces with increasing lateral

deformation

Leads to reduction in applied axial load

With high ALR faster and greater reduction

SUMMARY

31

32Fig. 8 Energy dissipation of specimens (Su and Wong, 2006)

High ALR affect failure

High ALR has a suppressive effect on ductility

As ALR increases energy dissipation decreases

Axial stiffness reduces with increasing lateral

deformation

Leads to reduction in applied axial load

With high ALR faster and greater reduction

SUMMARY

31

33Fig. 9 Reduction in ALR (Su and Wong, 2006)

CASE STUDY 2

34

To study effect of staggered openings

5 specimens with same amount of reinforcement

Represented 4 storey rectangular walls

Specimen W1 without opening

W2,W3,W4 with staggered openings

W5 with regular openings

SEISMIC PERFORMANCE OF SHEAR

WALLS

(MOSOARCA MARIUS, 2013)

35

36

Wall without opening

To study effect of staggered openings

5 specimens with same amount of reinforcement

Represented 5 storey rectangular walls

Specimen W1 without opening

W2,W3,W4 with staggered openings

W5 with regular openings

SEISMIC PERFORMANCE OF SHEAR

WALLS

(MOSOARCA MARIUS, 2013)

35

36

Wall without opening Staggered openings

To study effect of staggered openings

5 specimens with same amount of reinforcement

Represented 5 storey rectangular walls

Specimen W1 without opening

W2,W3,W4 with staggered openings

W5 with regular openings

SEISMIC PERFORMANCE OF SHEAR

WALLS

(MOSOARCA MARIUS, 2013)

35

36

Wall without opening Staggered openings Regular

openings

TESTING METHODOLOGY

37Fig. 10 The test bench (Mosoarca Marius, 2013)

Reversed cyclic lateral loads

A constant vertical force

Seismic behaviour studied for different

horizontal displacements

Behaviour of specimens monitored by

transducers, strain gauges etc.

TESTING METHODOLOGY CONTD…

38

OBSERVATIONS

39

Model

Initial

cracking

Plasticized

concrete

Crushed

concrete

P (kN) P (kN) P (kN)

W1 29.33 113.63 114.43

W2 25.12 100.12 103.72

W3 25.13 88.63 92.03

W4 25.15 88.40 95.90

W5 17.7 69.70 73.80

Walls with staggered openings were more rigid

With same amount of reinforcement ductile failure

observed for staggered opening walls and brittle

failure for regular opening walls

Staggered opening walls failed at higher seismic

forces and horizontal displacements

SUMMARY

40

Shear walls are efficient in resisting earthquakes

More efficient with increased ductility

Soil structure interaction studies are important

ALR ratio has adverse influence on seismic

performance of shear walls

Shear walls with staggered openings are more

effective than walls with regular openings

CONCLUSIONS

41

1. Anna Birely and Dawn Lehman (2008).

“Investigation of the seismic behavior and

analysis of reinforced concrete structural walls”.

The 14th World Conference on Earthquake

Engineering, Beijing, China.

2. Lepage, A (1994). “Seismic Drift Estimates for

RC Structures”. Eleventh World Conference on

Earthquake Engineering, Acapulco, Mexico.

REFERENCES

42

3. Murty, C.V.R.(2005). “Earthquake Tips. Learning

Earthquake design and Construction”. IIT Kanpur

4. Mosoarca Marius (2013). “Seismic behavior of

reinforced concrete shear walls with regular and

staggered openings after the strong earthquakes

between 2009 and 2011”. Journal of Engineering

Failure Analysis.

REFERENCES CONTD…

43

5. Mete A. Sozen, (2004) “Earthquake Engineering

from engineering seismology to Performance

based Engineering”. Second Edition, CRC Press.

6. Shimazaki and Sozen, M.A., (1984).”Seismic

drift of reinforced conctrete structures”. Technical

Research Report of Hazana- Gumi, Tokyo. Vol. 5,

ISSN 0385- 7123.

REFERENCES CONTD…

44

7. Su, R.K.L. Wong, S.M. (2006). “Seismic behavior

of slender reinforced concrete shears walls under

high axial load ratio”. Journal of Engineering

Structures, 29 (2007) 1957-1965.

8. Yuchuan Tang and Jian Zhang (2010).

“Probabilistic seismic demand analysis of a slender

RC shear wall considering soil- structure interaction

effects”. Journal of Engineering Structures, 33

(2011) 218-229.

REFERENCES CONTD…

45

THANK YOU…