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SEISMIC BEHAVIOUR OF RC SHEAR WALLS
Mahdi hosseini1, Ahmed Najm Abdullah Al-Askari2,Prof.N.V.Ramana Rao3
1
Post Graduate Student, Dept. of Civil Engineering, Jawaharlal Nehru Technological University Hyderabad
(JNTUH), Hyderabad, Andhra Pradesh, India
Email: civil.mahdi.hosseini@gmail.com
2
Post Graduate Student, Dept. of Civil Engineering, Jawaharlal Nehru Technological University Hyderabad
(JNTUH), Hyderabad, Andhra Pradesh, India
Email: ahmednajim1985@gmail.com
3
Professor, Dept. of Civil Engineering, Jawaharlal Nehru Technological University Hyderabad (JNTUH),
Hyderabad, Andhra Pradesh, India
Email: rao.nvr@gmail.com
important issues that must be considered in planning the
ABSTRACT
structural schemes and layouts are the requirements for
Shear walls are a type of structural system that provides
architectural details, building services like vertical
lateral resistance to a building or structure. They resist
transportation and fire safety among others. Each of the
in-plane loads that are applied along its height. The
structural system will be having its own prospects and
applied load is generally transferred to the wall by
considerations. The efficiency of a structural system is
a diaphragm or
The
measured in terms of their ability to resist lateral load,
performance of the framed buildings depends on the
which increases with the height of the frame. A building
structural system adopted for the structure The
can be considered as tall when the effect of lateral loads
term structural system or structural frame in structural
is reflected in the design. Lateral deflections of framed
engineering refers
buildings should be limited to prevent damage to both
collector
or drag member.
to load-resisting sub-system of
a
structure. The structural system transfers loads through
interconnected structural
components or
structural and nonstructural elements.
members.
These structural systems need to be chosen based on its
height and loads and need to be carried out, etc. The
Keywords:, RC structure, seismic load ,wind load, RC
shear wall, structural system
selection of appropriate structural systems for building
I. INTRODUCTION
must satisfy both strength and stiffness requirements.
The structural system must be adequate to resist lateral
and
gravity
loads
that
cause
horizontal
deformation and overturning deformation. Other
shear
What Causes Lateral Loads?
Lateral loads result from wind or earthquake actions and
both can cause a collapse of improperly braced building.
The way that wind or earthquake loads act on a building is
completely different, but they have the same general effect.
These two sources of lateral load are discussed below.
Wind Load
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Wind load is really the result of wind pressures acting on the
with the car(this force is equivalent to the weight of the
building surfaces during a wind event. This wind pressure is
driver multiplied by the acceleration or rate of change in
primarily a function of the wind speed because the pressure
speed of the car). As the brake is applied, the car is
or load increases with the square of the wind velocity (i.e.,
decelerated and a force is imparted to the driver by the seat-
doubling of wind speed results in a four-fold increase in
belt to push him back toward the seat. Similarly, as the
wind load or pressure). Wind load during a hurricane can
ground accelerates back and forth during an earthquake it
last hours and a building experiences sustained wind load
imparts back-and-forth(cyclic) forces to a building through
and short wind impacts (gusts). While the wind pressures are
its foundation which is forced to move with the ground. One
treated as a “static” (do not vary with time) or constant load
can imagine a very light structure such as fabric tent that will
for purposes of design, the real loads actually fluctuate
be undamaged in almost any earthquake but it will not
dramatically with gustiness of wind as well as wind
survive high wind. The reason is the low mass (weight) of
direction. Two fundamental wind effects are of a concern:
the tent. Therefore, residential buildings generally perform
(1)localized “spikes” in wind pressure that act on small
reasonably well in earthquakes but are more vulnerable in
areas of a building to cause damage to items such as roof
high-wind load prone areas. Regardless, the proper amount
panels or siding (known as components and cladding wind
of bracing is required in both cases.
loads in engineering terms) and (2)averaged wind loads that
What parts of a structure resist lateral loads?
act on larger areas of the building which the entire structure
The lateral resistance of the residential structure is almost
must resist(known in engineering terms as main wind force
entirely provided by a system of shear walls and
resisting system loads).
diaphragms. These two parts of the lateral force resisting
Earthquake Load
system (bracing system) of a home are discussed below.
Earthquake forces experienced by a building result from
ground motions (accelerations) which are also fluctuating or
dynamic in nature, in fact they reverse direction some what
chaotically. The magnitude of an earthquake force depends
on the magnitude of an earthquake, distance from the
earthquake source(epicenter), local ground conditions that
may amplify ground shaking (or dampen it), the weight(or
mass) of the structure, and the type of structural system and
its ability to with stand abusive cyclic loading. In theory and
practice, the lateral force that a building experiences from an
earthquake
increases
in
direct
proportion
with
the
acceleration of ground motion at the building site and the
mass of the building (i.e., a doubling in ground motion
acceleration or building mass will double the load).This
Fig 1.8 Concept of shear walls and diaphragms. All walls
contribute to the house stiffness.(a) Schematic, (b) Wall
participation is the force transfer
Diaphragm
A diaphragm is a structural term that simply refers to a
theory rests on the simplicity and validity of Newton’s law
horizontal plate-like system (i.e., a sheathed floor, ceiling or
of physics: F = m x a, where ‘F’ represents force, ‘m’
a roof assembly) that distributes lateral loads acting on the
represents mass or weight, and ‘a’ represents acceleration.
building to shear walls (or braced wall lines) that support a
For example, as a car accelerates forward, a force is
imparted to the driver through the seat to push him forward
floor or roof diaphragm and prevent it from excessive
sideways movement leading to potential collapse. Thus, a
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floor or roof diaphragm serves an important role of tying the
to provide such a system for the limited design wind and
light-frame building together (Figure 1). The basic concept
earthquake conditions addressed directly in the code. For
is to collect all the loads and transfer them to the foundation.
extremely hazards areas (hurricane-prone regions) and near
In the IRC, construction of floor and roof systems
fault areas in seismic zones, an engineered design is
(diaphragms) is addressed in separate chapters of the code
required. Alternatively, a prescriptive design in accordance
(Chapters 5 and 8)
with reference standards in Section R301 of the IRC may be
used. In Pennsylvania, such high hazard wind or seismic
Shear Wall
A shear wall is a structural term for a wall or portion of a
wall line (i.e., braced wall panel) that is specifically braced
to prevent racking of the studs in domino fashion as the floor
or roof diaphragm above transfers shear (racking) forces
into the plane (length direction) of a braced wall line (braced
wall line is explained latter in the text). In general, only
braced wall lines parallel to a given lateral load direction are
considered in providing racking resistance. However, even
the interior and transverse walls (Figure 1b) participate in
load transfer and overall stiffness providing that they too are
conditions do not exist. When a building is subjected to
wind or earthquake load, various types of failure must be
prevented:
• slipping off the foundation (sliding)
• overturning and uplift (anchorage failure)
• shear distortion (drift or racking deflection)
• collapse (excessive racking deflection)
The first three types of failure are schematically shown in
the Figure 1.8 Clearly, the entire system must be tied
together to prevent building collapse or significant
deformation.
adequately connected to the floor or roof diaphragm system
above. This three-dimensional action is not explicitly
considered in the current IRC bracing provisions and
requires the services of a design professional to implement.
In addition, the portion of the lateral load imparted to each
shear wall or braced wall line by a floor or roof diaphragm
depends on various factors but, in general, a stiffer wall
(stronger and more rigid bracing) will attract a larger portion
of the total lateral load as compared to the less stiff wall (3).
Unlike water, structural loads tend to follow the path of
greatest resistance or stiffness until that path is “broken” or
weakened. This means, for example, that a wall with large
opening will attract less load compared to a wall of the same
size and construction with small or no opening. As discussed
above, “wall bracing” is an important part of the bracing
Fig 1.8 Schematic of the deformations of the structure
due to the lateral loads
system but will not, by itself, be sufficient in providing
II. METHODOLOGY
lateral resistance of the building. An entire system and load
WHY ARE BUILDINGS WITH SHEAR WALLS
path must be established (e.g., diaphragms connected to
PREFERRED IN SEISMIC ZONES?
shear walls, shear walls connected to floors/foundation,
etc.). Consequently, the IRC provides basic connection
requirements for framing (floor, wall, and roof construction)
Generally shear wall can be defined as structural vertical
member that is able to resist combination of shear, moment
and axial load induced by lateral load and gravity load
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transfer to the wall from other structural member.
orientation, which significantly reduces lateral sway of the
Reinforced concrete walls, which include lift wells or shear
building and thereby reduces damage to structure and its
walls, are the usual requirements of Multi Storey Buildings.
contents. Since shear walls carry large horizontal earthquake
Design by coinciding centroid and mass center of the
forces, the overturning effects on them are large. Shear walls
building is the ideal for a Structure. An introduction of shear
in buildings must be symmetrically located in plan to reduce
wall represents a structurally efficient solution to stiffen a
ill-effects of twist in buildings. They could be placed
building structural system because the main function of a
symmetrically along one or both directions in plan. Shear
shear wall is to increase the rigidity for lateral load
walls are more effective when located along exterior
resistance. In modern tall buildings, shear walls are
perimeter of the building such a layout increases resistance
commonly used as a vertical structural element for resisting
of the building to twisting.
the lateral loads that may be induced by the effect of wind
and earthquakes which cause the failure of structure as
Function of Shear Wall
shown in figure Shear walls of varying cross sections i.e.
Shear walls must provide the necessary lateral strength to
rectangular shapes to more irregular cores such as channel,
resist horizontal earthquake forces. When shear walls are
T, L, barbell shape, box etc. can be used. Provision of walls
strong enough, they will transfer these horizontal forces to
helps to divide an enclose space, whereas of cores to contain
the next element in the load path below them Shear walls
and convey services such as elevator. The use of shear wall
also provide lateral stiffness to prevent the roof or floor
structure has gained popularity in high rise building
above from excessive sides way. When shear walls are stiff
structure, especially in the construction of service apartment
enough, they will prevent floor and roof framing members
or office/ commercial tower. It has been proven that this
from moving off their supports. Also, buildings that are
system provides efficient structural system for multi storey
sufficiently stiff will usually suffer less nonstructural
building in the range of 30-35 storey’s (MARSONO &
damage. Reinforced concrete building structures can be
SUBEDI, 2000). In the past 30 years of the record service
classified as:
history of tall building containing shear wall element, none
1. Structural Frame Systems: The structural system consist
has collapsed during strong winds and earthquakes
of frames. Floor slabs, beams and columns are the basic
(FINTEL, 1995).
elements of the structural system. Such frames can carry
RC Shear Wall
Reinforced concrete (RC) buildings often have vertical
plate-like RC walls called Shear Walls in addition to slabs,
beams and columns. These walls generally start at
foundation level and are continuous throughout the building
height. Their thickness can be as low as 150mm, or as high
as 400mm in high rise buildings. The overwhelming success
gravity loads while providing adequate stiffness.
2. Structural Wall Systems: In this type of structures, all the
vertical members are made of structural walls, generally
called shear walls.
3. Shear Wall–Frame Systems (Dual Systems): The system
consists of reinforced concrete frames interacting with
reinforced concrete shear walls.
of buildings with shear walls in resisting strong earthquakes
In the lateral load analysis of building structures having
is summarized in the quote, “We cannot afford to build
shear walls, proper methods should be used for modeling
concrete buildings meant to resist severe earthquakes
planar and no planar shear wall assemblies. Shear wall
without shear walls.” as said by Mark Fintel, a noted
models in the literature can be divided into two:
consulting engineer in USA. RC shear walls provide large
strength and stiffness to buildings in the direction of their
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1. Models developed for elastic analysis of building
structures.
2. Models developed for nonlinear analysis of building
structures.
Shear Walls: Stiffness
Reinforcement limits: Calculated using Maximum stress in
steel of fy Axial forces taken from load combination
Deflection calculations shall be based on cracked section
properties. Assumed properties shall not exceed half of
gross section properties, unless a cracked-section analysis is
performed.
Real wall is probably between two cases; diaphragm
provides some Shear Walls 9 rotational restraint, but not full
fixity.
Maximum reinforcing
No limits on maximum reinforcing for following case
D+0.75L+0.525QE Compression reinforcement, with or
without lateral ties, permitted to be included for calculation
of maximum flexural tensile reinforcement
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III.SEISMIC BEHAVIOUR OF SHEAR
WALL
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IV. CONCLUSIONS
Properly designed and detailed buildings with shear walls
have shown very good performance in past earthquakes. The
overwhelming success of buildings with shear walls in
resisting strong earthquakes is summarized in the quote: We
cannot afford to build concrete buildings meant to resist
severe earthquakes without shear walls. However, in past
earthquakes, even buildings with sufficient amount of walls
that were not specially detailed for seismic performance (but
had enough well-distributed reinforcement) were saved from
collapse. Shear wall buildings are a popular choice in many
earthquake prone countries, like Chile, New Zealand and
USA.
Shear
walls are easy to construct, because
reinforcement detailing of walls is relatively straightforward and therefore easily implemented at site. Shear
walls are efficient; both in terms of construction cost
properly designed and detailed buildings with Shear walls
have shown very good performance in past earthquakes. The
overwhelming success of buildings with shear walls in
resisting strong earthquakes is summarized in the quote: And
effectiveness in minimizing earthquake damage in structural
and non-
Structural elements (like glass windows and
building contents).
V. REFERENCES
[1] Solution of shear wall in multi-storey building”,
Anshuman,
Dipendu
Bhunia,
Bhavin
Ramjiyani,
International journal of civil and structural engineering,
Volume 2, no.2, 2011.
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[2] “Review on Shear wall for soft storey high rise building,
[10] Öztorun, N. K., “Computer Analysis of Multi-Storey
Misam Abidi and Mangulkar Madhuri N. ,International
Building Structures”, Ph.D. Thesis, Middle East Technical
Journal of Civil and Advance Technology, ISSN 2249-
University, 1994.
8958,Volume-1,Issue-6, August 2012
[3] “Effect of change in shear wall location on storey drift
of multi-storey residential building subjected to lateral
load”, Ashish S. Agrawal and S. D. Charkha, International
journal of Engineering Research and Applications, Volume
2, Issue 3,may-june 2012, pp.1786-1793.
[4] “Configuration of multi-storey building subjected to
lateral forces”, M Ashraf, Z. A. Siddiqui, M. A. Javed,
Asian journal of civil engineering ,vol. 9,no.5, pp. 525-535,
2008.
[5] Y. L. Mo and C. J. Kuo. 1998. Structural behavior of
reinforced concrete frame-wall components, department of
civil engineering, national Cheng kung University, Tainan,
701, Taiwan.
[6] Chen Qin and Qian Jiaru .2002.Sstatic inelastic analysis
of RC shear walls, department of civil engineering, Tsinghua
University, Beijing 100084, China. Article ID: 16713664(2002) 01-0094-06.
[7] Y. L. Mo and S.D. Jost .1993.Seismic response of
multistory framed shear walls, department of Civil
Engineering, National Cheng Kung University, Taiwan
70101, Taiwan.
[8] Arnaldo T. Derecho and M. Reza Kianoush, seismic
Design of reinforced concrete structures, Professor, Ryerson
Polytechnic University, Ontario, Canada.
[9] Taranath, B. S., Structural Analysis and Design of Tall
Buildings, McGraw-Hill Company, 1988.
[11] “Response of Buildings to Lateral Forces”, ACI
Committee Report, SP-97, American Concrete Institute,
Detroit, 1985: 21-46.