seismic seismic behaviourbehaviourbehaviourof ooff of · pdf filesystems in rc buildings...

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Ductile Detailing of RC Structures
:: IS:13920-1993
Ductile Detailing of Ductile Detailing of RC StructuresRC Structures
:: IS:13920:: IS:13920--19931993
Short Course on Seismic Design of RC StructuresDurgesh C. RaiDepartment of Civil Engineering, IIT Kanpur
The material contained in this lecture handout is a property of Professors Durgesh C. Rai, Sudhir K. Jain and C.V.R.Murty of IIT Kanpur, and is for the sole and exclusive use of the participants enrolled in the short course on Seismic Design of RC Structures conducted at Ahmedabad during Nov 25-30, 2012. It is not to be sold, reproduced or generally distributed.
Seismic Seismic Seismic Seismic BehaviourBehaviourBehaviourBehaviour of of of of RC Shear Walls RC Shear Walls RC Shear Walls RC Shear Walls
Seismic Seismic Seismic Seismic BehaviourBehaviourBehaviourBehaviour of of of of RC Shear Walls RC Shear Walls RC Shear Walls RC Shear Walls
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Three common lateral load resisting systems in RC Buildings
Shear Wall Braced FrameMoment Resistant Frame
Front Views
of Buildings
Top Views
of Buildings
RC Building SYSTEMSRC Building SYSTEMS
55
shear wallshear wall
What is a Shear Wall?
Vertical plate-like RC Walls
Generally starts at foundation
Goes through full building height
RC Shear
Wall
Foundation
Co
lum
n Beam
Slab
6
RC Shear Wall Building
Shear Walls also called Structural Walls
RC
Walls
Plan
SHEAR WALLS...SHEAR WALLS...
RC Shear
Wall
Foundation
Co
lum
n Beam
Slab

2
7
Principal attributes
Large Strength
High Stiffness
Ductility
Shear wall can be detailed to have large ductility
7
0
Strength
Deformability
H RC Shear Wall Building
RC Frame Building
8
Role of Shear Walls
Smooth transfer of seismic forces
Vertically orientedwide beams
Earthquake-generated
forces at floor levels
Cumulative horizontal
force from above
increases downward
Floor Slab
F3
F2
F1
F3
F2
F1
F3
F3
Shear
Wall
F=F1+F2+F3
Shear
Wall
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Advantages of Shear Walls
Very good earthquake performance, if properly designed
In past earthquakes
Large number of RC frame buildings damaged or collapsed
Shear wall buildings performed very well
We cannot afford to build concrete buildings meant to resist severe earthquakes without shear walls:: Mark Fintel, a noted earthquake engineer in USA
We cannot afford to build concrete buildings meant to resist severe earthquakes without shear walls:: Mark Fintel, a noted earthquake engineer in USA
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Easy to construct
Straight-forward reinforcement detailing
Easily implemented at site
Effective in
Reducing construction cost
Minimising earthquake damage to Structural elements
Non-Structural elements
E.g., Glass Windows, Building Contents
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Lesser lateral displacement than frames
Lesser Damage to structural and non-structural elements
Shear Wall
small large
Moment Resistant Frame
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Current Use of Shear Walls
Popular choice in many earthquake prone countries
Chile, Canada, USA and New Zealand
In general, used in medium and high rise buildings 10 storeys and higher

3
13
Walls must be preferably in both directions
in planIf provided only in one direction, a proper moment resisting frame
must be provided in the other direction.
Architectural AspectsArchitectural Aspects
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If provided only in one direction, a proper moment resisting frame must be provided in the other direction.
Architectural Aspects...Architectural Aspects...
A D
1
4
B C
3
2Frame
Frame
Shear
Wall
Shear
Wall
Frame
Frame
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Shear wall can extend over the full width of building, or even over partial width
RC Wall of partial width
RC Wall of
full width 16
Walls should be throughout the height
Cannot be interrupted in lower levels
Best Option:
Wall all through!!
RC Wall
Discontinuity of
wall not desirable
RC Wall
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Walls should be throughout the height
Cannot be interrupted in upper levels
Best Option:
Wall all through!!
RC Wall
Discontinuity of
wall not desirable
RC Wall
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Walls should be along perimeter of building
Improves resistance to twist
Shear walls along
perimeter
are more efficient
Shear walls close to
center of building
are less efficient

4
19
Walls must be symmetrically placed in plan
Unsymmetric
location of shear walls not desirable
Symmetric location of
shear walls desirable
Shear Walls only along one direction
of the building
Symmetry of building in
plan about one axis
Symmetry of building in
plan about both axes
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Shear wall building should not be narrow
Earthquakes cause significant overturning effects
Special care is required in design of their foundations
Soil
Local failure of soil Soil
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Openings in walls must be
As few as possible
As small as possible
As symmetric as possible
Small and symmetrically
placed openings allowed
RC Wall
Large and randomly placed
openings not allowed
RC Wall
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Sliding Failure
Undesirable Modes of Failure
Vertical
Uplift
Horizontal
Slide
Inclined
Crack
Overturning Failure
Shear Failure
Seismic Seismic BehaviourBehaviour
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Undesirable Mode of Failure
Crushing
of
ConcreteFlexure Compression
Failure
Seismic Seismic BehaviourBehaviour......
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Desirable Mode of Failure
Horizontal
cracks and
yielding of
steel bars
Flexure Tension Failure

5
25
Shear demand is more in lower storeys
Earthquake-generated
forces at floor levels
Cumulative
horizontal force
from above
increases
downward
Floor
Slab
Shear Wall
Direct force flow through the wall
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Shear demand is more in lower storeys
Earthquake-induced
horizontal force at floor levels
Total Horizontal Force
Bu
ild
ing
Heig
ht
27
At each section along the height,shear wall carries
Axial Force P
Shear Force V
Bending Moment M
PV
V
M
M
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Region of Ductile Detailing
Lw
Hw
Ductile Response
Region:
Larger of Lw and Hw/6,
but need not be more
than 2Lw
(b) Yielding of
vertical steel bars
Actions in Ductile Response Region
(a) Formation of
horizontal cracks
Tensi
on
Com
pre
ssio
n
Seismic Design of RC WallsSeismic Design of RC Walls
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Possible Geometry of Walls
Hollow:: Walls around Elevators
C-Shaped
L-Shaped
Rectangular
Flanged
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Possible Geometry of Walls
Wall with two columns
built together
Wall with more than two columns built together
Barbell-Shaped

6
31
Primary Reinforcement in Walls
Maximum spacing of vertical
reinforcement not more than Lw/5, twor 450mm
Maximum
spacing of horizontal
reinforcement not more than
Lw/5, tw or 450mm
Proper anchoring of vertical
reinforcement into foundation
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Lapping of Vertical Reinforcement Bars
Lw
HwRegion over which
lapping should be avoided:
Larger of Lw and Hw/6, but need not be more
than 2Lw
Staggering lapping of
adjacent vertical bars:Minimum of 600mm
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Detailing of Vertical and Horizontal Bars
Closely spaced confining
reinforcement in boundary elements
Max. spacing of vertical reinforcement not
more than Lw/5, twor 450mm
Max. spacing of horizontal
reinforcement not more than
Lw/5, tw or 450mm
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Confining Steel in Boundary Elements

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