Shear wall

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

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Provide large strength and stiffness in the direction of orientation Significantly reduces lateral swayEasy construction and implementation Efficient in terms of construction cost and effectiveness in minimizing earthquake damage

ADVANTAGES OF SHEAR WALLS

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5

PLACEMENT OF SHEAR WALLS

Located symmetrically to reduce ill effects of twistSymmetry can be along one or both the directionsCan be located at exterior or interiorMore effective when located along exterior perimeter of building


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7Fig. 2 Reinforced concrete shear wall (Murthy C.V.R. ,2005)

X

Y

Located symmetrically to avoid ill effects of twistingSymmetry can be along one or both the directionsCan be located at exterior or interiorMore effective when located along exterior perimeter of building


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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

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Thickness 150 – 400 mmMinimum reinforcement 0.25% of gross area in each directionDiameter shall not exceed 1/10 th thickness of sectionReinforcement provided in two curtains when:

Factored shear stress exceeds orWall thickness exceeds 200 mm

DESIGN CONSIDERATIONS

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0.25 ckf

Nominal shear stress,

SHEAR STRENGTH OF WALLS

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v

uv

w w

Vt 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 wus

v

f A dV

S

SHEAR STRENGTH OF WALLS CONTD…

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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

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u u

w w

x xl l

2 2

2

11 0.416 0.1682 3

uv u u

ck w w w w

M x xf t l l l

2 0.36u

w

xl

0.00350.87

0.0035

u

yw

xfl

Es

0.87 y

ck

ff

u

ck w w

Pf t l

0.870.0035

y

s

fE

st

w w

At l

FLEXURAL STRENGTH CONTD…

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For 1u u

w w

x xl l

2

1 2 32 2uv u u

ck w w w w

M x xf t l l l

10.36 12 2

2 10.15 12 2 3

1 3

6 /u wx l

ux depth of NA from extreme compression fibre*

ux balanced depth of NA

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Portions along edges of shear wall strengthened by longitudinal and transverse reinforcement Can have same or greater thickness compared to wall Develop good flexural strengthShould have adequate axial load carrying capacityVertical reinforcement range between 0.8 and 6%

BOUNDARY ELEMENTS

Factors governing seismic behavior of shear walls:

DuctilityStiffnessSoil structure interaction effectsPeriod of structure

SEISMIC BEHAVIOUR OF WALLS

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DuctilityRatio of displacement at maximum load to that at yield Highly desirable property for shear walls

StiffnessProperty of element to resist displacementMore stiffer wall need more force to deflect it

SEISMIC BEHAVIOUR CONTD…

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Soil- structure interactionStructural damage directly related to depth of soil overlying the rock and period of vibration of soilUnderstanding relationship between period of vibrations of soil and structure is important


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Period of a buildingImportant index that identifies vulnerability to excessive driftA simple approximation to period of building:

(Mete a Sozen, 2004)

m = unit mass (total mass divided with height )


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4

2

3.5w

c w

w

TE Imh

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]


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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]


CASE STUDY 1

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Three specimens W1, W2, W3Represent slender shear wallsAspect ratio 4Axial 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]

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24

wh

wl

Fig. 3 A shear wall

w

w

hl

11 2

2

SquatIntermediateSlender

Aspect ratio =

Three specimens W1, W2, W3Represent tall slender shear wallsAspect ratio 4Axial 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]

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applied axial load axial load capacity at a

section

AXIAL LOAD RATIO

25

Axial load ratio =

'u

c g

PALRf A

compressive strength of concretegross cross section of the wall

'cf gA

TESTING METHODOLOGY

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Fig.4 Testing rig (R.K.L. Su and S.M. Wong, 2006)

Specimens placed in a steel loading frameCompressive axial force applied from bottom simulated gravity loadPush and pull forces to the flange beam represented lateral seismic loads

TESTING METHODOLOGY CONTD…

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28Fig. 5 Testing rig and load application (Su and Wong, 2006)

Specimens placed in a steel loading frameCompressive axial force applied from bottom simulated gravity loadPush and pull forces to the flange beam represented lateral seismic loads


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28Testing rig and load application (Su and Wong, 2006)

W1 exhibited flexural ductile failureCracks developed at early stagePropagated inwards to the core of the section

OBSERVATIONS

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Fig. 6 Failure pattern of specimen W1

(Su and Wong, 2006)

W2 and W3 exhibited brittle compression failureSpalling of concrete observed due to high ALR

OBSERVATIONS CONTD…

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Fig.7 Failure pattern of specimens W2 and W3(Su and Wong, 2006)

ALR affect failureHigh ALR has a suppressive effect on ductilityAs ALR increases energy dissipation decreasesAxial stiffness reduces with increasing lateral deformation

Leads to reduction in applied axial loadWith high ALR faster and greater reduction

SUMMARY

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

2006)

High ALR affect failureHigh ALR has a suppressive effect on ductilityAs ALR increases energy dissipation decreasesAxial stiffness reduces with increasing lateral deformation

Leads to reduction in applied axial loadWith high ALR faster and greater reduction

SUMMARY

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

CASE STUDY 2

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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)

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Wall without opening




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Wall without opening Staggered openings




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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 displacementsBehaviour of specimens monitored by transducers, strain gauges etc.


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OBSERVATIONS

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ModelInitial

crackingPlasticized

concreteCrushed 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 rigidWith 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

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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

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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

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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…

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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…

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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…

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THANK YOU…

Shear wall

Engineering

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