Seismic Behaviour of Multistorey Shear Wall Frame Versus Braced

International Journal of Advanced Mechanical Engineering.
ISSN 2250-3234 Volume 4, Number 3 (2014), pp. 323-330
© Research India Publications
http://www.ripublication.com/ijame.htm
Seismic Behaviour of Multistorey Shear Wall
Frame Versus Braced Concrete Frames
S.R. Thorat and P.J. Salunke
MGM College of Engineering and Technology, Kamothe, Navi Mumbai.
Abstract
It is observed that there is a need the study of structural systems for
R.C.C framed structure, which resist the lateral loads due to seismic
effect. Safety and minimum damage level of a structure could be the
prime requirement of tall buildings. To meet these requirements, the
structure should have adequate lateral strength, lateral stiffness and
sufficient ductility. Among the various structural systems, shear wall
frame or braced concrete frame could be a point of choice for designer.
Therefore, it attracts to review and observe the behaviour of these
structural systems under seismic effect. Hence, it is proposed to study
the dynamic behaviour of reinforced concrete frame with and without
shear wall and concrete braced frame. The purpose of this study is to
compare the seismic response of above structural systems. Axial forces
and moments in members and floor displacements will be compared.
Keywords: Shear wall, Bracing, Lateral force, Building structure.
1. Introduction
A Tall buildings are the demand of present situation. As the height of structure
increases, lateral forces due to seismic becomes predominant. The major portion of
these shall be resisted by the structural elements. Out of different structural systems,
shear wall frames and Concrete braced frames are two principal structural systems
used in reinforced concrete buildings to resist earthquake forces.
Reinforced concrete shear-walls are mostly used in buildings due to betterobserved performance in recent past. In areas of high seismic risk, RC shear walls have
been widely used as main lateral load resisting system in medium & high rise buildings
because of their high lateral stiffness. Recent earthquake have shown that only
properly designed shear walls can withstand strong earthquake forces with minor
324
S.R. Thorat & P.J. Salunke
damage. The function of shear wall is to resist the effect of lateral and gravity forces
and to provide lateral stability to a tall building. Reinforced concrete shear walls are
relatively easy to construct because their reinforcing details are straight-forward, at
least when compared to those of moment frames.
The most effective and practical method of enhancing the seismic resistance is to
increase the energy absorption capacity of structures by combining bracing elements in
the frame. The braced frame can absorb a greater degree of energy exerted by
earthquakes. In braced frame reduces the column and girder bending moments. The
shear is primarily absorbed by diagonals and not by girders. The diagonals carry the
lateral forces directly in predominantly axial action, providing for nearly pure
cantilever behavior. Bracing members are widely used in steel structures to reduce
lateral displacements and dissipate energy during strong ground motions. This concept
is extended to concrete frames. The various aspects such as size and shape of building,
location of shear wall and bracing in building, distribution of mass, distribution of
stiffness greatly affect the behavior of structures. These aspects need to be well
understood and should be considered during design of structure.
Seismic response of braced concrete frames is compared with that of shear frames.
The parameters studied are width of shear wall and bracing patterns-namely X, K and
inverted V(IV) shaped. It observed that location of shear wall and brace elements have
significant effect on performance of frame and there appear some advantages in using
reinforced concrete braced frames over shear wall frames as former results in lesser
member moments and floor displacements.
2. Method of Seismic Analysis
The code IS: 1893-2002 provides both static (seismic coefficient method) and dynamic
(response spectrum method) procedures for the determination of seismic design forces
for buildings. The code generally requires that the design for horizontal seismic forces
be considered only in any one direction at a time. In both the seismic coefficient and
the response spectrum methods, consideration is given to the seismic zone where the
structure is located (The building is assumed to be located in seismic zone ‘III’),
importance of the structure, soil-foundation system ductility of construction, flexibility
of the structure, and weight of the building.The STAAD-PRO V8i are used for
dynamic analysis and stiffness analysis.
Load Calculation:
1) Dead Load :- Dead load on frame includes self-weight of beams, shear-walls,
brace elements, slabs, exterior walls and is calculated for center grid from assumed
dimensions.
Unit weight of concrete = 25kN/m3
Unit weight of brick masonry= 20kN/m3
2) Live Load :- Live load intensity is adopted as 3 kN/m2, at each storey level &
for roof level 1.5 kN/m2. (At roof, no live load is to be lumped)
Seissmic Behaviiour of Multtistorey Sheear Wall Fra
ame Versuss Braced Cooncrete
325
3) Seismic Load:
Dessign base shhear
V B = A h W ……………
…
…
Distributionn of seismicc force alongg height of building
b
W h2
Q = VB i − n i i
Wi h i
∑
i =1
………
………………
.(A)
.(B)
Calculate Design
D
basee shear (V B ) by using
g equation A and distrribute along
g the
heigght of buildiing at each floor
f
by using equation
n B.
3. Selection of Structture
To study
s
the beehavior of shear-wall
s
fr
frame
and brraced concrete frame, aan building with
simpple symmetric plan haaving threee bays in bo
oth the direections is sselected(Fig
g. 1),
Diffferent shearr wall framees and braceed concrete frames are developed
d
bby placing shear
s
walls and bracced elementts at variouss selected locations
l
inn 15-storey building. Itt has
totaal eight planne frames inn both the all direction
ns. Four coolumn locatiions ( a, b, c, d
resppectively) of each planne frame aree treated as shear-wall locations aand three baays (
B1, B2, B3 respectively) are
a treated as
a brace elem
ment locatioons. Solid ccantilever sh
hearwalls having width
w
1.5m in
i rectangullar section are
a adoptedd. The X, K
K, IV-type brace
b
pattterns are adoopted. In alll a total of 24
2 frames haave been annalysed.
Fig. 1: Plan of bu
uilding.
Preliminaryy data:
Size of all beams
b
= 2330 x 450 mm
m
Size of all columns
c
= 300 x 6000 mm
3266
S Thoratt & P.J. Salu
S.R.
unke
Size of sheaar-walls = 300 x 15000 mm
Size of braccings = 230 x 450 mm
Storey heigght
= 4500 mm
Frame Spaccing in bothh direction = 6000 mm
Slab thicknness = 1500 mm
Wall thicknness = 120 mm (Brickk masonry)
4. Shear-waall frame Systems
In these
t
system
ms, shear-w
wall is proovided in different
d
maanners at vvarious seleected
locaations from
m bottom flloor to topp floor. Acccordingly different
d
syystems (fram
mes)
developed are as
a follows.
• Placingg shear-wall at one locaation out off four locatioons at a tim
me and repeaating
it for reemaining loccations, thuss four system
ms are deveeloped
• Placingg shear-wall at two locaations out of
o four locaations at a tiime in diffeerent
mannerr, another foour systems are develop
ped
• Placingg shear-wall at first threee locations, only one syystem is devveloped
• Placingg shear-wall at all locatiions, anotheer one system
m is developped
• In all, total
t
10 sysstems are developed. These
T
ten syystems are used for sh
hearwall width ‘1.5 m’ resulting 10 systems with
w constannt width from
m bottom to
o top
floor (F
Fig.2).
F 2: Secttion of Sheaar wall Fram
Fig.
me.
Fig. 3: Secction of Bracce Frame.
( X, K & IV
V respectiveely)
5. Braced Concrete
C
F
Frame
Syystems
In thhese system
ms, brace ellements are provided in
n different manner
m
at vvarious seleected
locaations from bottom flooor to top flooor. Accord
dingly differrent system
ms developed
d are
as follows.
fo
Placing braace X and K type elemeents at one location out of three loccations at a time
and repeating itt for remainning locationns, thus Six system are developed
Placing braace X, K andd IV type ellements at tw
wo locationns out of threee locationss at a
timee in differennt manner, another
a
six systems
s
are developed
Seismic Behaviour of Multistorey Shear Wall Frame Versus Braced Concrete
327
Placing brace X and K type elements at all locations, two more system is
developed.
In all, 6 systems are developed each for X and K-type brace patterns (total 12
systems). Placing brace elements in two adjacent bays to form ‘inverted V-type’ brace
pattern in different manner, thus two additional systems are developed (Fig.3).
6. Result
Response of Shear-wall Frame Versus Braced Concrete Frame:
When column axial force of above system is compared, it is observed that more
column axial force is induced in braced frame than shear wall frame. Column moments
induced in braced frame are much less than shear wall frame. Beam moments induced
in braced frame are less than shear-wall frame the drift induced in braced frame is less
than shear wall frame.
The even column axial force induced in braced frame is more than shear-wall
frame and plane frame, but column and beam moment are very small with less drift,
hence braced frame is advisable.
The result of the analysis are presented in form of table. The 15-story building
frame results are presented in tabulated form.
Abbreviated Name of Various Systems in table:
SWF
Shear-wall frame
BR
Braced Concrete Frames
‘A’
Shear wall or brace elements are provided at all locations
‘X,K,IV’ Type of bracing pattern provided
‘a, b, c, d’
Locations where shear-wall is provided (Example:- SWFa, SWFbc,
SWFabc, SWFA)
‘B1,B2,B3’ Locations where brace elements are provided(Example:- BRXB1,
BRKB2B3, BRIVB1B2, BRXA)
Summary of result and Discussion
Frame Name
Comment
SWFa
Notrecommended
SWFb
Recommended
SWFc
Recommended
SWFd
Notrecommended
Notrecommended
Recommended
SWFad
SWFbc
Reason
More actions (axial force,
shear, moment) & more drift
Less actions (axial force, shear,
moment) & less drift
Less actions (axial force, shear,
moment) & less drift
More actions (axial force,
shear, moment) & more drift
More actions (axial force,
shear, moment) & more drift
Less actions (axial force, shear,
moment) & less drift
Remark
1st priority
1st priority
1st priority
328
S.R. Thorat & P.J. Salunke
SWFab
Recommended
SWFac
SWFabc
Recommended
Notrecommended
SWFA
Notrecommended
BRXB1
BRXB2
BRXB3
BRXB1B2
BRXB1B3
Recommended
Recommended
Recommended
Recommended
Notrecommended
Recommended
BRXA
BRKB1
BRKB2
BRKB3
BRKB1B2
BRKB1B3
BRKA
BRIVB1B2
BRIVB2B3
Notrecommended
Recommended
Notrecommended
Recommended
Notrecommended
Recommended
Notrecommended
Recommended
Less column shear , moment &
less drift
Less column axial force
Not equally effective in
reducing actions & drift as
compared with one & two
shear wall locations
Not equally effective in
reducing actions & drift as
compared with one & two
shear wall locations
Slightly more actions & drift
Less actions & drift
Slightly more actions & drift
Less actions & drift
More actions & drift
2nd priority
3rd priority
-
Symmetrical
Distribution
of
mass & stiffness
2nd priority
1st priority
2nd priority
1st priority
-
Equally effective in reducing 1st priority
actions & drift
More actions & drift
Less actions & drift
More actions & drift
2nd priority
-
Less actions & drift
More actions & drift
1st priority
-
Equally effective in reducing 2nd priority
actions & drift
More actions & more drift
Less actions & less drift
1st priority
7. Concluding Remarks
1. The location of shear-wall and brace member has significant effect on the
seismic response of the shear-wall frame and braced frame respectively. The
central location of shear-wall and brace member are favorable as they are
effective in reducing actions induced in frame with less horizontal deflection
and drift.
2. Addition of shear-walls at all or unfavorable locations do not effectively in
reduce the actions induced in frame. Hence it is advisable to provide
3. one shear-wall in frame instead of multiple shear-walls.
Seismic Behaviour of Multistorey Shear Wall Frame Versus Braced Concrete
329
4. IV & X-type brace pattern are most efficient out of studied pattern, as less
actions are induced in frame with less floor displacement and drift. The K-type
brace pattern can be adopted as second choice. X-type brace pattern induces
less drift and lateral deflection in frame out of various brace pattern considered
in the present study.
5. Instead of providing brace elements in alternate bays, it is advisable to place
them adjacent bays. Addition of brace elements equally reduces the actions,
horizontal deflection and drift induced in the frame. Braced frame offers most
of the resistance through axial action in term of column and brace axial force;
hence moments induced in frame are very less.
6. Brace elements are very much efficient in reducing lateral displacement of
frame as drift and horizontal deflection induced in braced frame are much less
than that induced in shear-wall frame and plane frame. Though column axial
force induced in braced frame is more than that in shear-wall frame and plane
frame, however, the column and beam moments, and drift induced in braced
frame are very less. Hence, braced frame is very efficient in resisting seismic
force than shear-wall frame and plane frame.
References
[1]
Jain A.K. “Reinforced Concrete Design(Limit State Design)” Nem Chand and
Bros Roorkee(2002).
[2] Paz M. “Structural Dynamics” CBS Publication(1992).
[3] Park and Pauley, “Reinforced Concrete Structures” A Wiley Inter-science
Publication, John Wiley and sons(1999).
[4] SP22: (S&T)-1982, “Explanatory Hand Book on Earthquake Resistant Design
and Construction”. Bureau of Indian Standards New Delhi.
[5] IS 1893-1984 and 2002(Part I), “Criteria for Earthquake Resistant Design of
Structure”, Bureau of Indian Standards New Delhi.
[6] IS 456-2000, “Plain and Reinforced Concrete-Code of Practice”, Bureau of
Indian Standards New Delhi.
[7] Goel S.C. “Seismic Behavior of Multistorey K-braced Frame under Combined
Horizontal and Vertical Ground Motion”, 7th World Conference Proceeding
Earthquake Engg. Symposium London vol.2-1977, pp-1172-1177.
[8] Kapur V. and Jain A. K. “Seismic Response of Shear wall Frames Versus
Braced Concrete Frames”, Indian Concrete Journal, April-1983, pp-107-114.
[9] Xu Shan-Hua and Niu Di-Tao “Seismic Behavior of Reinforced Concrete
Braced Frame”, ACI Structural Journal / January-February 2003, pp-120-125.
[10] A.R.Khaloo and M. Mahdi Moseni “Nonlinear Seismic Behavior of RC
Frames With RC Braced”, Asian Journal of Civil Engineering (Building And
Housing) Vol. 9 , No. 6 (2008) Pages 577-592.
330
S.R. Thorat & P.J. Salunke
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