Earthquake analysis on 2 d rc frames with different

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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IC-RICE Conference Issue | Nov-2013, Available @ http://www.ijret.org 18
EARTHQUAKE ANALYSIS ON 2D RC FRAMES WITH DIFFERENT
ASPECT RATIOS OF MASONRY INFILL AND MONOLITHIC PANEL
Md.Khaja.M1
, Chethan.K2
, Ramesh Babu3
1
Department of Civil Engineering, B.K.I.T, Bhalki, mohammed_khajarec@yahoo.com
2
Assistant Professor Department of Civil Engineering, U.V.C.E, Bangalore, k.chethu@gmail.com
3
Additional Director, E.V.R.C CPRI, Bangalore, rbabu@cpri.in
Abstract
RC structures are one of the most famous and most utilized types of construction throughout the world. The wall panels for this type of
structures usually are made of masonry infill or monolithic RC panels. In this paper, earthquake analysis of a typical 2D-RC frame is
carried out. Masonry infill is modeled as equivalent diagonal strut and monolithic panel is modeled as shell element. Modal analysis
is carried out on the models and the results are compared with the shake table tests conducted at Central Power Research Institute
(CPRI), Bangalore to validate the models. Earthquake analysis is continued with equivalent static, response spectrum and time history
analyses for all the zones (II-V) as per IS: 1893(Part-1):2002. The analysis results such as natural frequency, displacement, inter-
storey drift and acceleration are tabulated, compared and conclusions are drawn.
Key words: 2D-RC Frame, Masonry Infill, Monolithic wall, Shake table, Natural Frequency, Modal analysis, Response
spectrum, Equivalent Diagonal Strut, Time History, Inter-Storey drift.
--------------------------------------------------------------------***----------------------------------------------------------------------
1. INTRODUCTION
Reinforced concrete frame buildings with masonry infill
panels are generally regarded as „Earthquake Risk‟ buildings.
As such there is a growing need to carry out an evaluation of
their level of seismic performance. In recent years there has
been a good deal of research in the area of infill-masonry
buildings. Guidelines have also been published recently for the
seismic evaluation of these structures. A literature review
indicated that the current „state-of-the-art‟ in practice is to
account for infill panels by including an equivalent strut to
represent the stiffness of the panels. There are however a
range of proposed modeling methods. The earthquake damage
of the in filled frame structures usually results from ignoring
the stiffening effect of the infill, which is reported to increase
the stiffness of the bare frame 4 to 20 times, [Comite Euro-
International Du Beton, (1996)].
2. MODELING OF MASONRY INFILL
In the case of an infill wall located in a lateral load resisting
frame the stiffness and strength contribution of the infill are
considered by modeling the infill as a an equivalent
compression strut. The infill parameters are effective width,
elastic modulus and strength were calculated using the method
recommended by Chethan.K the length of the strut is given by
the diagonal distance “d” of the panel and thickness is given
by the thickness of the infill wall. The estimation of the width
of the strut is given in equation 1. Parameters α
h
and α
l
are
given below are used to calculate the effective width
2 2
L hw    ---- (1.0)
Here,
2
h



 ---- (1.1)
4
4
2sin
hIE
tE
cc
m 
 
---- (1.2)
Beam contact length „αL‟ is taken approximately half of its
span.
Where, t, h, l and d, are respectively the thickness, height,
length and diagonal length of MI; Em, Ec, and EL are the
Modulus of elasticity of MI, column and beam respectively; Ic
and IL are Moment of inertia of the column and beam
respectively. The slope of infill diagonal to horizontal is θ =
tan-1
(h/L). Also, λh is coefficient used to determine equivalent
θ = tan-1
(h/L) width of infill strut, λL is empirical parameter
expressing the relative stiffness of the beam to the infill and αh
is the relative stiffness of the infill to frame
3. ANALYTICAL MODELLING
The 2D RC Frames used for analysis are of one-bay, one to
five storey with different aspect ratios of 0.7, 1.0 and 1.3. The
length of beams is 2.4m for all frames and the length of
columns are 1.68m, 2.4m and 3.12m respectively. The
boundary condition is fixed. Table 1 shows member properties
and structural details. Fig.1 shows the model details

__________________________________________________________________________________________
Table.1: Member Properties and Structural Details
Member Properties Structural Details
Member Diameter
of bar
Number
of Bars
Cross-section
in mm
Main Reinforcement Stirrups/Lateral Ties
Column 12 mm 6 115mmx230mm 6-12mm bars
throughout the length
of the column
2 legged 6 mm @ a
spacing of 75 mm c/c
throughout
Beam 12 mm 4 115mmx230mm 4-12mm bars
throughout the length
of the beam
2 legged 6 mm @ a
spacing of 75 mm c/c
throughout
Masonry 115mm --- ---
Fig.1: 2D RC frame with detailed dimensions for different
Aspect Ratios
The different configurations of Bare Frame (BF), Masonry
Infill (MI), Masonry Infill with Soft Storey (SMI), Monolithic
Panel (MP) and Monolithic Panel with soft Storey (SMP) are
analyzed. Results obtained for model with one bay and one
storey for BF and MI are validated with the Shake table
results.
4. LOADS
Analysis of the frames is done using SAP 2000 software. Dead
load and Earthquake load are considered for analysis.
i) Dead load (DL)
The dead load is considered as per IS 875-1987 (Part I-Dead
loads)
 Unit weight of Reinforced Concrete = 25 kN/m3
 Unit weight of Brick = 19.2 kN/m3
ii) Earthquake Load (EL)
The earthquake load is considered as per the IS 1893(Part 1):
2002 the factors considered are
 Zone factors = 0.10, 0.16, 0.24, 0.36
(zone II-zone V)
 Importance factor = 1.0
 Response reduction
factor =5.0 (S.C.R)
 Soil condition = Soft soil
 Damping = 5%
5. GENERATION OF TIME HISTORY AND
RESPONSE SPECTRA
Design response spectrums are developed for zone II, III, IV
and V for the two axes and are fed into the Desired File
Generator (DFG) software. The DFG software converts the
required response spectrum into the time history, which is in
terms of acceleration. Typical time history for zone-II is as
shown in Fig.2.
Fig 2: Time history for Seismic Zone-II
Fig.3: Design Spectrum for Seismic Zone-II

__________________________________________________________________________________________
For analyzing the 2D-RC frame subjected to seismic loading,
the design response spectra is obtained as per the
recommendations of IS 1893 (Part1): 2002 titled “Criteria for
Earthquake Resistant Design of Structures”. The typical
design response spectrum for seismic Zone-II is as shown in
Fig.3.
6. RESULTS AND DISCUSSIONS
Nonlinear static analysis is performed to determine the lateral
load resisting capacity of the structure and nonlinear dynamic
analysis is performed to evaluate seismic performance of bare,
infill frame and monolithic panel model.
From this analysis the modal parameters such as natural
frequencies and mode shapes are obtained. Sine sweep tests
are conducted on the RC frames using shake table to evaluate
the natural frequencies experimentally which are later
analyzed using software for validation. The natural
frequencies obtained using shake table and software for
different models are compared in Table.2.
Table.2. Comparison of Natural Frequency
From the above Table 2, it is observed that the natural
frequency obtained from modal analysis matches well with the
shake table test results and hence the models are validated and
the models so developed are further analyzed for different
configurations. The number of storey of all the models is
increase from one storey to five storeys.
a) Natural Frequency in In-Plane Direction
(a)
(b)
Fig.4: In-Plane Natural frequency (Hz)
From above graphs as the number of storeys increases the
natural frequency of the frame decreases, also when the aspect
ratio increases natural frequency decreases due to the increase
in the mass of the frame. The natural frequency of frame SMI
decreases by 30% compare to bare frame which are nearly
equal in SMP, whereas the natural frequency of MP frame is
more than double the frequency of the BF. The MP has the
highest natural frequency followed by MI, SMP and SMI as
the masonry in fills and the monolithic panel adds stiffness to
the structure. As the stiffness increases in the in-plane
direction, the natural frequency increases. Hence it is clearly
observed that the MI has a role in the earthquake response of
the structure.
0
20
40
60
1 2 3 4 5
Frequency(Hz)
Number of Storey
Aspect Ratio 0.7
BF
MI
SMI
MP
0
5
10
15
0.7 1 1.3
Frequency(Hz)
Aspect Ratio
For 1B5S
BF
MI
SMI
FOR BARE FRAME
Aspect
ratio
In- plane Out of plane
Shake
Table
Modal
Analysis
Shake
Table
Modal
Analysis
0.7 24.00 24.773 7.00 7.188
1.0 14.00 14.789 3.75 4.166
1.3 10.25 10.865 2.00 2.726
FOR MASONRY INFILL FRAME (MI)
Aspect
ratio
In- plane Out of plane
Shake
Table
Modal
Analysis
Shake
Table
Modal
Analysis
0.7 29.00 30.77 4.00 4.800
1.0 22.00 22.75 2.00 2.581
1.3 15.00 15.78 1.25 1.612

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7. EARTHQUAKE RESPONSE OF 2D-RC FRAME
To determine the earthquake response of the 2D-RC frame for
different configuration it is analyzed for the all seismic zones
as specified by the IS:1893(Part-1):2002. The models have
been analysed by Equivalent Static Analysis from which the
Static base shear have been extracted, then by Response
Spectrum Analysis the Dynamic base shear have been
obtained for a scale factor of 1. Inter-Storey drift is calculated
using the following formula,
SDi = ∆i - ∆i-1
Where, ∆i - ∆i-1 =horizontal displacement
hi= floor height the values obtained for inter-storey dirft are
tabulated and compared
a) Displacement in In-Plane direction
(a) (b)
Fig.5: Comparison of In-Plane Displacement (mm)
From Fig.5, it is observed that the displacement in the soft
storey is maximum in the lower storeys as compared to the
other two conditions (i.e. MI and MP) which show its
criticality in the earthquake resistant design. As the mass
increases, displacement decreases. As the aspect ratio increase
from 0.7 to 1.0, displacement of the frame increases by 32% in
BF, SMI and SMP, whereas it increases by 43% in MI and
MP. When the aspect ratio changes from 1.0 to 1.3,
displacement increases by 45% in BF, SMI and SMP, which
also increases by 36% in MI and MP. This indicates that the
BF is having maximum displacement because of less stiffness.
SMI, SMP, MI and MP are having less displacement values
because of more stiffness.
b) Out of Plane Inter-Storey Drift
Fig.6: Comparison of Inter-storey drift (mm) for Aspect Ratio
0.7
It is observed that the inter-storey drift in the MI are higher
compared to BF and MP, but less than SMI and SMP. Due to
the presence of soft storey in first floor, the inter-storey drift of
SMI and SMP is maximum in the third floor as compared to
BF, MI and MP which has the maximum inter-storey drift at
second storey. As the aspect ratio increase from 0.7 to 1.3 the
inter-storey drift decreases by 16%.
c) Acceleration in In-Plane direction
(a)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 2 4 6
Displacementin
mm
Number of Storey
Aspect Ratio 0.7
BF
MI
SMI
MP
SMP
0
5
10
15
0.6 0.8 1 1.2 1.4Displacementin
mm
Aspect Ratio
1B5S BF
MI
SMI
MP
SMP
1
2
3
4
5
0 5 10 15
NumberofStorey
Inter-Storey drift in mm
BF
MI
SMI
MP
SMP
0
0.5
1
1.5
2
2.5
1 2 3 4 5
Accelerationinmm/sec²
Number of Storey
Aspect Ratio 0.7
BF
MI
SMI
MP
SMP

__________________________________________________________________________________________
(b)
Fig.7: Comparison of In-Plane Acceleration
It indicates that the acceleration increases with increase in the
number of storey for all configurations. But when the aspect
ratio increases the acceleration decreases. BF is having high
acceleration value because of less mass. SMP is having less
acceleration value followed by SMI, MP and MI because of
more mass. When the frame is provided with soft storey (i.e.
SMP, SMI) the acceleration is nearly equal. When the aspect
ratio increases from 0.7 to 1.0 the acceleration decreases by
14%, whereas when it increases from 1.0 to 1.3 the
acceleration decreases by 9%.
8. TIME HISTORY ANALYSIS RESULTS
The Time History is from response spectrum as per IS:
1893(Part- 1):2002 by using DFG software and used for
analysis. The Displacements and Accelerations obtained from
the Time History Analysis for Zone-V compared in Fig.1.8.
a) Displacement in the In-plane direction
(a)
(b)
Fig.8: Comparison of In-Plane Displacement (mm)
It is observed that the BF is having maximum displacement
because of less stiffness, followed with SMI and SMP
compare to MI and MP. With the increase in the number of
storeys, the displacement of the frame increases by 7%, also
when the aspect ratio increases the displacement increases. As
the aspect ratio increase from 0.7 to 1.0, displacement of the
frame increases by 5% in all configurations whereas when the
aspect ratio changes from 1.0 to 1.3, displacement increases by
20%. MI and MP are having minimum displacement values
because of more stiffness. From this we can clearly understand
that the displacement decreases as the stiffness increases.
b) Acceleration in the In-plane direction
(a)
(b)
Fig9: Comparison of In-Plane Acceleration (mm/sec2
)
It is observed that as number of storey increase the
acceleration increases for all configurations. The BF is having
high acceleration value because of less mass, whereas SMP is
having least acceleration value followed by MP, SMI and MI
0
0.5
1
1.5
2
2.5
0.7 1 1.3
Accelerationinmm/sec²
Aspect Ratio
1B5S
BF
MI
SMI
MP
SMP
0.135
0.14
0.145
0.15
0.155
0 2 4 6
Displacementin
mm
Number of Storey
Aspect Ratio 0.7
BF
MI
SMI
MP
SMP
0.135
0.185
0.235
0.6 1.1 1.6
Displacementin
mm
Number of Storey
1B5S BF
MI
SMI
MP
SMP
0
5
10
15
1 2 3 4 5
Accelerationin
mm/sec²
Number of Storey
Aspect Ratio 0.7 BF
MI
SMI
MP
SMP
-4
1
6
11
16
0.7 1 1.3
Accelerationin
mm/sec²
Number of Storey
1B5S
BF
MI
SMI
MP
SMP

__________________________________________________________________________________________
because of more mass. With the increase in the aspect ratio
from 0.7 to 1.0 the acceleration decreases in all models,
whereas when aspect ratio increase from 1.0 to 1.3
acceleration increases in BF and MI only. MP is having less
acceleration value because of its mass.
9. CONCLUSIONS
1) From the modal analysis, it is found that the natural
frequencies of the infill frame are around twice when
compared to bare frames.
2) As the aspect ratio increases the natural frequency
decreases in both in-plane and out of plane direction,
due to increase in the mass of the frame.
3) The inter-storey drift in the first storey are large for
soft storey compared to BF, and SMI frame which
shows the sudden change in slope of drift, this is due
to the abrupt change in storey stiffness, whereas the
MI, MP and SMP frame shows a smooth profile.
4) From time history analysis, it is found that the large
displacement occurs in the soft storey compared to
bare frame and infill frames due to the abrupt change
in storey stiffness.
5) Of all seismic zones considered (Zone II to Zone V),
Zone-V is the critical zone with highest base shear,
acceleration and displacement.
REFERENCES
[1] Amit V Khandve, Seismic Response of RC Frame
Buildings with Soft Storeys, IJERA, Vol. 4 (3), May-
Jun 2012, pp.2100-2108.
[2] Chethan K, Study on Dynamic Characteristics of 3D
Reinforced Concrete Frame with Masonry Infill,
Journal of CPRI, Vol 5 (2), September 2009, pp. 11-18
[3] Sharany Haque and Khan Mahmud Amana, Strength
and drift demand of columns of RC framed buildings
with soft ground story, IEB, Vol. 37, January 2009 (2),
pp 99-110.
[4] Smith B S and Carter C, A method of analysis for
infilled frames, Proceedings of the Institute of Civil
Engineers, Vol. 44, 1969, pp. 31-48.

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