Study on Behaviour of Rc Structure with Infill Walls Due to Seismic Loads

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395 -0056
Volume: 04 Issue: 06 | June -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 2494
STUDY ON BEHAVIOUR OF RC STRUCTURE WITH INFILL WALLS DUE TO
SEISMIC LOADS
Yadunandan C1, Kiran Kuldeep K N2
1 P.G. Student, Civil Engineering Department, Sri Jagadguru Balagangadharanatha Institute of Technology,
Bengaluru - 560060, Karnataka, India
2
Assistant Professor, Civil Engineering Department, Sri Jagadguru Balagangadharanatha Institute of Technology,
Bengaluru - 560060, Karnataka, India
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Abstract –Since long masonry infill are being usedtofillup
the voids between the horizontal and vertical structural
elements such as beams and columns. Theyaretreatedasnon-
structural elements and they are not considered during the
analysis and design of the structure. But, whenlaterallyloaded
they tends to interact with the RC frame, changing the
structural behaviour. However, infill walls contribute to
lateral stiffness and seismic resistance to the building. In this
study, an attempt is being made to incorporate the masonry
infill in the form of Equivalent diagonal strut whose width is
calculated using the various relations proposed by the
researches. A general review of the relations proposed by the
researches in calculating the width of the Equivalentdiagonal
strut is being made and compared. The paper also focuses to
study the behaviour of bare frame and infilled frame. The aim
of this research work is to present a comparative study and
analysis of G+3 story building with and without opening and
soft story by performing linear dynamic analysis using ETABS
software .Results for base shear, story drift, lateralloads, story
displacement, column forces andtimeperiodarecomparedfor
different models.
Key Words: Masonry infill, Infill opening, Soft story,
Equivalent diagonal strut Response spectrum analysis.
1. INTRODUCTION
RC moment resisting frame buildings are themostpreferred
type of construction in developing countries like India. RC
moment resisting frame buildings consist of moment
resisting frame with masonry wall as Infill’s. These wallsare
considered as nonstructural elements in construction
practices. In present day practice of building design,
buildings are designed as framed structures while effect of
infill masonry walls is ignored and considered as
nonstructural elements. Due to the above reason, buildings
behave in different manner with infill wall when compared
with only moment resisting frames. In past four decades,
through lots of analytical and experimental studies
importance of brick infill has been recognized however its
strength and stiffness contribution has been neglected by
considering it as nonstructural elements.
Another importantaspectconcernsthe numerical simulation
of the infilled frames. The structural model can be idealized
by different techniques and can be divided into micro model
and macro model. In the present paper the masonry infill
wall is modeled has “Equivalent diagonal strut” considering
the strength and stiffness of brick masonryinfill .Thisstrutis
designed in such a manner that it only carries compression.
2. OBJECTIVES
 To study the behaviour of RC frame with brick infill by
modeling infill as a diagonal strut.
 Understand the suitability of different macro models
available for considering the infill effects in reinforced
concrete infilled frames.
 Investigate the contribution of masonry infill walls to
lateral strength and lateral stiffness of the building.
 To study the effect of opening and soft story on the
performance of masonry infilled RC framed structures.
3. METHODOLOGY
 In the present study, the RC members and masonry
infill Walls are modeled using ETABS software.
 The analytical macro modelsaremodeledandanalyzed
for linear dynamic analysis.
 Response spectrum method of analysis is adopted for
the analysis of infilled frame with and without opening
and soft story and the results are compared.
4. REVIEW OF MACRO MODELS
4.1 EQUIVALENT DIAGONAL STRUT MODEL
The existence of infill influences the distribution of lateral
loads on the framed structures due to the increase in
stiffness. The investigation ofinteractionofinfill withframes
has been endeavored by utilizing many analyses like theory
of elasticity or finite element analysis.Becauseofcomplexity
and uncertainty in defining the interaction between infills
and the frames, several approximate methods are being
developed. A prominent among the most prevalent and
known approaches is by replacing masonry infill by
equivalent diagonal struts, the thickness of which is equal to
the thickness of masonry infills. The primary issue with this

approach is to find the effective width. Numerous Scientists
have proposed different techniques for determining the
width of equivalent diagonal strut. Strut width leans on the
length of contact between the columns and thewall (αh)and
between the beam and wall (αL).
Fig -1: Equivalent diagonal strut model
4.1.1 Holmes Model
Holmes (1963) took the idea from Polyakov (1956) and
stated that infilled walls can be replaced by a equivalent
diagonal strut which has the same thickness and material as
the infill wall.
bw = dw/3
Where, dw= Diagonal length of the panel
4.1.2 Stafford Smith and Carter model
Stafford Smithand Carter(1969)haveproposedatheoretical
relationship forthe width of the diagonal strut onthebasisof
relative stiffness of infill and frame.
w = 0.58 ( (λh Hinf)0.335.d
inf
λh =
t = Infill wall thickness,
Hinf = Height of the infill,
Einf = Modulus of elasticity of the infill,
Ec = Modulus of elasticity of the column,
Ic = Moment of inertia of the columns,
H = Total frame height,
θ = Angle between diagonal of the horizontaland theinfill,
λh = Dimensionless parameter.
4.1.3 Mainstone model
Mainstone (1971) performedtests on frameswithbrickinfill
walls and gave equivalent diagonalstrutmodelthisapproach
takes into contribution of both InfilledFramestiffnessandits
ultimate strength.
w = 0.16 dinf ((λh Hinf)-0.3
λh =
4.1.4 Paulay and Preistley model
Paulay and Preistley (1992) stated that higher estimation of
width(w) will effect in a stiffer structure and potentially
superior seismic reaction.
w =0.25 dinf
Where, dinf = Diagonal length of the infill
4.1.5 Hendry model
Hendry (1998) has also presented equivalent strut width
that would represent the masonry that actually contributes
in resisting the lateral force in the composite structure
w = 0.5
h =
L =
αh, αL = Contact length between wall and column at the time
of initial failure ofwall.
Ib = Moment of inertia of the beam
Linf = Length of the infill i.e. Clear distance betweencolumns.
4.1.6 FEMA model
FEMA (1998) proposed that infill wall thickness which is
represented has equivalent strut can be obtained by
w = 0.175 dinf ((λh Hinf)-0.4
λh =

Table -1: Equivalent diagonal strut Width
Sl No Model Equivalent strut width
(m)
1 Holmes 1.73
2 Smith and Carter 4.91
3 Mainstone 0.54
4 Paulay and Preistley
Paulay and Preistley
model
Paulay and Preistley
model
1.32
5 Hendry 0.68
6 FEMA 273 0.52
With reference to various literature reviews, Mainstone's
relation was widely used for most of the experimental and
analytical works, as it predicted the value of the width of the
Diagonal strut which was very near/close to the Romanian
code and it was commonly adopted because of its simplicity.
4.2 PERFORMANCE OF INFILL FRAME WITH CENTRAL
OPENING
Asteris et al. (2011) presented the analytical results of the
influence of opening size on the seismic response of
masonry infilled frames with central opening. Fig. shows
the variation of the ‘λ’ factor as a function of the opening %
for the case of an opening on the compressed diagonal of
the infill wall.
Opening % (αw) =
Width of strut with opening = Stiffness Reduction
factor as per Figure x w without opening
Fig -2: Stiffness reduction factor for Infill with opening
Table -2: Stiffness reduction factor and width of strut for
different percentage of opening
% of
opening
Stiffness
reduction
factor , λ
Width of
strut, m
0 - 0.540
10 0.45 0.267
20 0.32 0.173
30 0.21 0.113
40 0.13 0.071
5. BUILDING DESCRIPTION
Table -3: Description of the model
Table -4: Parameters of G+ 3 storey Diagonal strut model

Fig -3: Plan layout of G+3 story building model
Fig -4: Elevation of bare frame and infilled frame
Fig -5: Elevation of 20% and 40% opening infilled
frame
Fig -6: Elevation of soft story at ground floor and third
floor
6. RESULTS AND DISCUSSIONS
6.1. Comparision with bare frame, infilled frame and
infilled frame with 20 and 40% opening
6.1.1 BASE SHEAR
The Base shear is more in infilled frame than bare frame
because it depends on the stiffness in the frame. Due to the
presence of infill (strut) the stiffness of the frame is
increased resulting in increased sesmic forces than bare
frame.
Chart -1: Bar graph showing variation of base shear
6.1.2 STORY DRIFT
Introduction of infill in the building structure reduces the
seismic demands of the building both in terms of storeydrift
and the horizontal displacement. Story drift is more in bare
frame than 20% and 40% infill.

Chart -2: Variation of story drift
6.1.3 LATERAL LOADS
Infilled frame has highest lateral load when compared with
bare and infilled frame with openings. As the percentage of
infill wall decreases the lateral load also decreases .
Chart -3: Bar graph showing lateral loads
6.1.4 STORY DISPLACEMENT
Bare frame structure has a maximum story or roof
displacement whencomparedwithinfilledframeandframes
with opening. This is because infill wall increases strength
and stiffness in moment resisiting RC frames.
Chart -4: Comparision of story displacement
6.1.5 COLUMN FORCES
Outer columns are taken for the comparision because it will
be greater than the inner columns. Due to the action of strut,
frame action is changed to truss actionresultinginreduction
of bending moment.
It is noted that the decrease in bending moment is more in
the smaller openings becauseofthefactthatsmalleropening
has more infill effective i.e. the impact of infill is high in
small openings.
Table -5: Corner Column Forces
6.1.6 TIME PERIOD
The presence of infill has found to reduce the time period of
bare frame and enhances stiffness of the structure. Bare
frame has high time period when compared with infilled
frame and infilled frame with 20 and 40% opening.
Chart -5: Bar graph showing variation in base shear

6.2. Comparision with bare frame, infilled frame,soft
stories at ground and third floor
6.2.1 BASE SHEAR
Base shear is more in infilled frame when compared with
bare frame and soft story frames. Here the soft story at GF
and soft story at TF is compared and its base shear obtained
is almost same.
Chart -6: Bar graph showing variation in base shear
6.2.2 STORY DRIFT
Story drift is maximum in bare frame and minimum in
infilled frame.The behaviour of story drift in the soft stories
at GF and TF shows that maximum story drift occurs near
the soft stories
Chart -7: Variation of story drift
6.2.3 LATERAL LOADS
The soft story at TF has highest lateral load at top story
whereas soft story at GF has least lateral load at top story.
Fig below shows the variation of lateral loads among
different models
Chart -8: Bar graph showing lateral loads
6.2.4 STORY DISPLACEMENT
The presence of infill reduces the lateral displacement
because of increase in rigidity of the structure. The bare
frame has maximum displacement while infilled frame has
least displacement.
Chart -9: Comparision of story displacement
6.2.5 COLUMN FORCES
The compared results shows that bare frame has highest
axial force and bending moment. Whereas soft story at TF
has higher value of axial force and lesser bending moment.
Table -6: Corner Column Forces:

6.2.6 TIME PERIOD
In soft story models time period is dependingonthelocation
of soft story provided.Here the soft story at GF has higher
time period than soft story at TF.
Chart -10: Bar graph showing time period
7. CONCLUSIONS
1. The infill wall predominantly changesthebehaviourofthe
structure and it is essential to considerinfill wallsforseismic
analysis of structure.
2. Introduction of infill panels in the RC frame reduces the
time period of bare frames and also enhances the stiffnessof
the structure. The fully infilled frame has the lowest storey
drift value and the highest base shear value.
3. The percentage of opening and the soft story influencethe
fundamental period of infill frame and the period increases
as the percentage of opening increases.
4. The effect of infill on the lateral stiffness of the infilled
frame may be ignored if the area of opening exceeds 40% of
the area of the infill and the frame is analyzed as bare frame.
5. Deflection is very large in case of bare frame as compared
to that of infill frame with opening and deflection will
increase as the percentages of opening increases.
6. The story displacement and time period of soft story at
third floor is less when compared with soft story at ground
floor.
7. Infill increases the initial stiffness of thestructureandalso
increases the base shear carrying capacity of the structure.
REFERENCES
[1]. Haroon Rasheed Tamboli and Umesh N Karadi (2012)
“Seismic analysis of RC frame structure with and
without masonry infill walls” Indian Journal of Natural
Sciences, ISSN: 0976-0997, Volume 3, Issue 14.
[2]. Wakchaure M.R, Ped S. P (2012)“EarthquakeAnalysisof
High Rise Building with and Without In filled Walls”
International Journal of Engineering and Innovative
Technology, ISSN: 2277-3754, Volume 2, Issue 2.
[3]. Vishal P. Jamnekar and Chaudhari D.J.(2013), “Effect of
brick masonry infill in seismic evaluation of an existing
RC building”, The Indian Concrete Journal, Volume 87.
[4]. Manju G (2014) “Dynamic analysis of infills on RC
framed structures”, International journal of innovative
research in science, engineering and technology. ISSN:
2319-8753,Volume 2,Issue 2.
[5]. C.Rajesh, Ramancharla Pradeep Kumar and Suresh
Kandru (2014) “Seismic Performance of Reinforced
Concrete Framed Buildings With & Without Infill Walls”
International Journal of Engineering Research &
Technology, Volume 3, Issue 10
[6]. Paveen Rathod, S.S.Dyavanal (2014)“SeismicEvaluation
of Multistorey RC Building with openings in
Unreinforced Masonry Infill Walls with User Defined
Hinges” International Journal of Mechanical and
Production Engineering, Volume 2, Issue10
[7]. Jaykumar R. Gaikwad, Rahul D. Pandit, Dr.Abhijeet P.
Wadekar (2016) “Analysis of sesmic behavior of infill
frame structures with shear wall for lifts by etabs
software” International Journal of Science Technology
and Management, Volume 5, Issue 1.
[8]. Deshmuk Vishwajeet, Shrirang Tande (2016) “Analysis
of masonry infill in multi story structure” International
journal of latest trends in engineering and technology,
Volume 7, Issue 1.
[9]. IS 1893 (part 1) “Criteria for earthquake design of
structure”. General provisions and buildings, Bureau of
Indian standards.

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