Download Seismic Behaviour of RC Shear Walls

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Vol.03,Issue.18
August-2014,
Pages:3878-3886
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Seismic Behaviour of RC Shear Walls
MAHDI HOSSEINI1, AHMED NAJM ABDULLAH AL-ASKARI2, PROF, N.V. RAMANA RAO3
1
PG Scholar, Dept of Civil Engineering, JNTUH, Hyderabad, India, E-mail: [email protected].
2
PG Scholar, Dept of Civil Engineering, JNTUH, Hyderabad, India & Ministry of Municipalities &
Public Works, Iraq, E-mail: [email protected].
3
Professor, Dept of Civil Engineering, JNTUH, Hyderabad, India, E-mail: [email protected].
Abstract: Shear walls are a type of structural system that provides lateral resistance to a building or structure. They resist inplane loads that are applied along its height. The applied load is generally transferred to the wall by a diaphragm or collector
or drag member. The performance of the framed buildings depends on the structural system adopted for the structure The
term structural system or structural frame in structural engineering refers to load-resisting sub-system of a structure. The
structural system transfers loads through interconnected structural components or members. These structural systems need to be
chosen based on its height and loads and need to be carried out, etc. The selection of appropriate structural systems for building
must satisfy both strength and stiffness requirements. The structural system must be adequate to resist lateral and gravity loads
that cause horizontal shear deformation and overturning deformation. Other important issues that must be considered in
planning the structural schemes and layouts are the requirements for architectural details, building services like vertical
transportation and fire safety among others. Each of the structural system will be having its own prospects and considerations.
The efficiency of a structural system is measured in terms of their ability to resist lateral load, which increases with the height
of the frame. A building can be considered as tall when the effect of lateral loads is reflected in the design. Lateral deflections
of framed buildings should be limited to prevent damage to both structural and nonstructural elements.
Keywords: RC Structure, Seismic Load ,Wind Load, RC Shear Wall, Structural System.
I. INTRODUCTION
A. 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.
B. Wind Load
Wind load is really the result of wind pressures acting on
the building surfaces during a wind event. This wind pressure
is primarily a function of the wind speed because the pressure
or load increases with the square of the wind velocity (i.e.,
doubling of wind speed results in a four-fold increase in wind
load or pressure). Wind load during a hurricane can last hours
and a building experiences sustained wind load and short
wind impacts (gusts). While the wind pressures are treated as
a “static” (do not vary with time) or constant load for
purposes of design, the real loads actually fluctuate
dramatically with gustiness of wind as well as wind direction.
Two fundamental wind effects are of a concern: (1) localized
“spikes” in wind pressure that act on small areas of a building
to cause damage to items such as roof panels or siding
(known as components and cladding wind loads in
engineering terms) and (2) averaged wind loads that act on
larger areas of the building which the entire structure must
resist(known in engineering terms as main wind force
resisting system loads).
C. Earthquake Load
Earthquake forces experienced by a building result from
ground motions (accelerations) which are also fluctuating or
dynamic in nature, in fact they reverse direction somewhat
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
theory rests on the simplicity and validity of Newton’s law of
physics: F = m x a, where ‘F’ represents force, ‘m’ represents
mass or weight, and ‘a’ represents acceleration. For example,
as a car accelerates forward, a force is imparted to the driver
through the seat to push him forward with the car(this force is
equivalent to the weight of the driver multiplied by the
Copyright @ 2014 SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.
MAHDI HOSSEINI, AHMED NAJM ABDULLAH AL-ASKARI, PROF, N.V. RAMANA RAO
acceleration or rate of change in speed of the car). As the
prevent racking of the studs in domino fashion as the floor or
brake is applied, the car is decelerated and a force is imparted
roof diaphragm above transfers shear (racking) forces into
to the driver by the seat-belt to push him back toward the
the plane (length direction) of a braced wall line (braced wall
seat. Similarly, as the ground accelerates back and forth
line is explained latter in the text). In general, only braced
during an earthquake it imparts back-and-forth(cyclic) forces
wall lines parallel to a given lateral load direction are
to a building through its foundation which is forced to move
considered in providing racking resistance. However, even
with the ground. One can imagine a very light structure such
the interior and transverse walls (Figure 1b) participate in
as fabric tent that will be undamaged in almost any
load transfer and overall stiffness providing that they too are
earthquake but it will not survive high wind. The reason is
adequately connected to the floor or roof diaphragm system
the low mass (weight) of the tent. Therefore, residential
above. This three-dimensional action is not explicitly
buildings generally perform reasonably well in earthquakes
considered in the current IRC bracing provisions and requires
but are more vulnerable in high-wind load prone areas.
the services of a design professional to implement. In
Regardless, the proper amount of bracing is required in both
addition, the portion of the lateral load imparted to each shear
cases.
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
D. What parts of a structure resist lateral loads?
The lateral resistance of the residential structure is almost
lateral load as compared to the less stiff wall (3). Unlike
entirely provided by a system of shear walls and diaphragms.
water, structural loads tend to follow the path of greatest
These two parts of the lateral force resisting system (bracing
resistance or stiffness until that path is “broken” or
system) of a home are discussed below.
weakened.
Fig1. Concept of shear walls and diaphragms. All walls
contribute to the house stiffness.(a) Schematic, (b) Wall
participation is the force transfer.
1. Diaphragm
A diaphragm is a structural term that simply refers to a
horizontal plate-like system (i.e., a sheathed floor, ceiling or
a roof assembly) that distributes lateral loads acting on the
building to shear walls (or braced wall lines) that support a
floor or roof diaphragm and prevent it from excessive
sideways movement leading to potential collapse. Thus, a
floor or roof diaphragm serves an important role of tying the
light-frame building together (Figure 1). The basic concept is
to collect all the loads and transfer them to the foundation. In
the IRC, construction of floor and roof systems (diaphragms)
is addressed in separate chapters of the code (Chapters 5 and
8)
2. 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
Fig2. Schematic of the deformations of the structure due
to the lateral loads.
This means, for example, that a wall with large opening
will attract fewer loads 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
system but will not, by itself, be sufficient in providing
lateral resistance of the building. An entire system and load
path must be established (e.g., diaphragms connected to shear
walls, shear walls connected to floors/foundation, etc.).
Consequently, the IRC provides basic connection
requirements for framing (floor, wall, and roof construction)
to provide such a system for the limited design wind and
earthquake conditions addressed directly in the code. For
extremely hazards areas (hurricane-prone regions) and near
fault areas in seismic zones, an engineered design is required.
Alternatively, a prescriptive design in accordance with
reference standards in Section R301 of the IRC may be used.
In Pennsylvania, such high hazard wind or seismic conditions
do not exist. When a building is subjected to wind or
earthquake load, various types of failure must be prevented:
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886
Seismic Behaviour of RC Shear Walls
effects of twist in buildings. They could be placed
 Slipping off the foundation (sliding)
symmetrically along one or both directions in plan. Shear
 Overturning and uplift (anchorage failure)
walls are more effective when located along exterior
 Shear distortion (drift or racking deflection)
perimeter of the building such a layout increases resistance of
 Collapse (excessive racking deflection)
the building to twisting.
The first three types of failure are schematically shown in
B. Function of Shear Wall
the Figure2 Clearly, the entire system must be tied together to
Shear walls must provide the necessary lateral strength to
prevent building collapse or significant deformation.
resist horizontal earthquake forces. When shear walls are
strong enough, they will transfer these horizontal forces to
II. METHODOLOGY WHY ARE BUILDINGS WITH
the next element in the load path below them Shear walls also
SHEAR WALLS PREFERRED IN SEISMIC ZONES?
provide lateral stiffness to prevent the roof or floor above
Generally shear wall can be defined as structural vertical
from excessive sides way. When shear walls are stiff enough,
member that is able to resist combination of shear, moment
they will prevent floor and roof framing members from
and axial load induced by lateral load and gravity load
moving off their supports. Also, buildings that are
transfer to the wall from other structural member. Reinforced
sufficiently stiff will usually suffer less nonstructural
concrete walls, which include lift wells or shear walls, are the
damage. Reinforced concrete building structures can be
usual requirements of Multi Storey Buildings. Design by
classified as:
coinciding centroid and mass center of the building is the
1. Structural Frame Systems: The structural system consist
ideal for a Structure. An introduction of shear wall represents
of frames. Floor slabs, beams and columns are the basic
a structurally efficient solution to stiffen a building structural
elements of the structural system. Such frames can carry
system because the main function of a shear wall is to
gravity loads while providing adequate stiffness.
increase the rigidity for lateral load resistance. In modern tall
2. Structural Wall Systems: In this type of structures, all the
buildings, shear walls are commonly used as a vertical
vertical members are made of structural walls, generally
structural element for resisting the lateral loads that may be
called shear walls.
induced by the effect of wind and earthquakes which cause
3.
Shear Wall–Frame Systems (Dual Systems): The system
the failure of structure as shown in figure Shear walls of
consists of reinforced concrete frames interacting with
varying cross sections i.e. rectangular shapes to more
reinforced concrete shear walls.
irregular cores such as channel, T, L, barbell shape, box etc.
can be used. Provision of walls helps to divide an enclose
In the lateral load analysis of building structures having
space, whereas of cores to contain and convey services such
shear walls, proper methods should be used for modeling
as elevator. The use of shear wall structure has gained
planar and no planar shear wall assemblies. Shear wall
popularity in high rise building structure, especially in the
models in the literature can be divided into two:
construction of service apartment or office/ commercial
1. Models developed for elastic analysis of building
tower. It has been proven that this system provides efficient
structures.
structural system for multi storey building in the range of 302.
Models developed for nonlinear analysis of building
35 storey’s (MARSONO & SUBEDI, 2000). In the past 30
structures.
years of the record service history of tall building containing
shear wall element, none has collapsed during strong winds
C. Shear Walls: Stiffness
and earthquakes (FINTEL, 1995).
A. 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 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.” as said by Mark Fintel, a noted consulting
engineer in USA. RC shear walls provide large strength and
stiffness to buildings in the direction of their orientation,
which significantly reduces lateral sway of the building and
thereby reduces damage to structure and its contents. Since
shear walls carry large horizontal earthquake forces, the
overturning effects on them are large. Shear walls in
buildings must be symmetrically located in plan to reduce ill-
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.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886
MAHDI HOSSEINI, AHMED NAJM ABDULLAH AL-ASKARI, PROF, N.V. RAMANA RAO
Real wall is probably between two cases; diaphragm provides
some Shear Walls 9 rotational restraint, but not full fixity.
D. Maximum reinforcing
No limits on maximum reinforcing for following case
Reinforcement limits: Calculated using Maximum stress in
steel of fy Axial forces taken from load combination
D+0.75L+0.525QE Compression reinforcement, with or
without lateral ties, permitted to be included for calculation
of maximum flexural tensile reinforcement
Fig1.
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886
Seismic Behaviour of RC Shear Walls
III.SEISMIC BEHAVIOUR OF SHEAR WALL
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886
MAHDI HOSSEINI, AHMED NAJM ABDULLAH AL-ASKARI, PROF, N.V. RAMANA RAO
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886
Seismic Behaviour of RC Shear Walls
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886
MAHDI HOSSEINI, AHMED NAJM ABDULLAH AL-ASKARI, PROF, N.V. RAMANA RAO
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.
[2] “Review on Shear wall for soft storey high rise building,
Misam Abidi and Mangulkar Madhuri N. ,International
Journal of Civil and Advance Technology, ISSN 22498958,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.
[10] Öztorun, N. K., “Computer Analysis of Multi-Storey
Building Structures”, Ph.D. Thesis, Middle East Technical
University, 1994.
IV. CONCLUSIONS
[11] “Response of Buildings to Lateral Forces”, ACI
Properly designed and detailed buildings with shear walls
Committee Report, SP-97, American Concrete Institute,
have shown very good performance in past earthquakes. The
Detroit, 1985: 21-46.
overwhelming success of buildings with shear walls in
resisting strong earthquakes is summarized in the quote: We
Author’s Profile:
cannot afford to build concrete buildings meant to resist
Mahdi Hosseini,
Post
Graduate
severe earthquakes without shear walls. However, in past
Student, Dept. of Civil Engineering,
earthquakes, even buildings with sufficient amount of walls
Jawaharlal
Nehru
Technological
that were not specially detailed for seismic performance (but
University
Hyderabad
(JNTUH),
had enough well-distributed reinforcement) were saved from
Hyderabad, Andhra Pradesh, India.
collapse. Shear wall buildings are a popular choice in many
Email: [email protected].
earthquake prone countries, like Chile, New Zealand and
USA. Shear walls are easy to construct, because
reinforcement detailing of walls is relatively straight-forward
Ahmed Najm Abdullah Al-Askari,
and therefore easily implemented at site. Shear walls are
Ministry of Municipalities and Public
efficient; both in terms of construction cost properly designed
Works-IRAQ, Post Graduate Student,
and detailed buildings with Shear walls have shown very
Dept. of Civil Engineering, Jawaharlal
good performance in past earthquakes. The overwhelming
Nehru
Technological
University
success of buildings with shear walls in resisting strong
Hyderabad
(JNTUH),
Hyderabad,
earthquakes is summarized in the quote: And effectiveness in
Andhra Pradesh, India.
minimizing earthquake damage in structural and nonEmail: [email protected],
Structural elements (like glass windows and building
[email protected].
contents).
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886
Seismic Behaviour of RC Shear Walls
Prof.N.V.Ramana Rao, Professor,
Dept. of Civil Engineering, Jawaharlal
Nehru
Technological
University
Hyderabad (JNTUH), Hyderabad,
Andhra Pradesh, India.
Email: [email protected].
International Journal of Scientific Engineering and Technology Research
Volume.03, IssueNo.18, August-2014, Pages: 3878-3886