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1. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 7, July (2014), pp. 81-88 © IAEME
INTERNATIONAL JOURNAL OF CIVIL ENGINEERING
AND TECHNOLOGY (IJCIET)
ISSN 0976 – 6308 (Print)
ISSN 0976 – 6316(Online)
Volume 5, Issue 7, July (2014), pp. 81-88
© IAEME: www.iaeme.com/ijciet.asp
Journal Impact Factor (2014): 7.9290 (Calculated by GISI)
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81
IJCIET
©IAEME
PARAMETRIC INVESTIGATION OF THE EFFECT ON BASE SHEAR OF
MULTISTORIED REINFORCED CONCRETE FRAMES
RahmathullaNoufal E.*
Assistant Professor in Civil Engineering
Department of Civil Engineering, Government Engineering College, Kozhikode-673005
ABSTRACT
Multistoried buildings should be designed such that they offer sufficient stiffness against
lateral displacement and should have the strength to resist inertial forces imposed by the ground
motion arising from earth quakes. Seismic forces in buildings are greatest at the base of the building.
Hence one of the key factors to be considered in designing seismic resistant buildings is the base
shear. Base shear is an estimate of the maximum expected lateral force that will occur due to seismic
ground motion at the base of a structure. In this manuscript we perform a detailed study of the values
of base shear for bare frame as well as infilled frame multi bay, multistoried structures using Free
Vibration analysis in SAP 2000 as well as pseudostatic analysis presented in I.S. 1893(Part I)-2002.
Keywords: Base Shear, Infilled Frames, Multistoried Structures, Free Vibration Analysis,
Pseudostatic Analysis.
1. INTRODUCTION
Vertical loads such as dead or live loads do not pose much problem in multistoried buildings,
whereas lateral loads arising from seismic ground motion are matter of great concern and need
special considerations in the design of buildings [1]. These lateral forces can produce critical stress in
a structure and may produce undesirable vibrations. In addition to vibrations, it can also lead to
lateral sway of the structure. Hence special care need to be taken in the design of multistoried
buildings so that they offer sufficient stiffness against lateral displacement and should have the
strength to resist inertial forces imposed by the ground motion arising from earth quakes.
Constructing infilled frames, where the reinforced concrete skeleton frames are filled with brick or
concrete block masonry walls in multistoried buildings to meet the architectural and functional
requirements, could be a practical solution to increase the overall strength and lateral resistance of a
building. But infilled walls, like any other structures, should be designed to withstand lateral forces

2. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 7, July (2014), pp. 81-88 © IAEME
that can result from seismic ground motion as they behave as a constituent part of the structural
system and determine overall behavior of the structure, especially when it is subjected to lateral loads
[2].
82
Seismic forces in buildings are greatest at the base of the building and earth quakes often
damage buildings at this level. Hence one of the key factors to be considered in designing seismic
resistant buildings is the base shear which estimates the maximum expected lateral force that will
occur due to seismic ground motion at the base of a structure. It depends on the soil conditions at the
site, proximity to potential sources of seismic activity (such as geological faults), probability of
significant seismic ground motion, the level of ductility and overstrength associated with various
structural configurations and the total weight of the structure, the fundamental (natural) period of
vibration of the structure when subjected to dynamic loading etc. [3]. In this manuscript we perform
a detailed study of the values of base shear for bare frame as well as infilled frame single bay to four
bay, one to ten storied structures using Free Vibration analysis in SAP 2000 as well as pseudostatic
analysis presented in I.S. 1893(Part I)-2002 [4, 5].
2. FORMULATION
The objective here is to estimate the changes in base shear for multibay, multistoried bare
frame and infilled frame structures using Free Vibration analysis in SAP 2000 as well as pseudostatic
analysis presented in I.S. 1893(Part I)-2002. Here the infilled wall is modelled by using the concept
of equivalent diagonal strut presented by Smith (1966) and subsequent modification by Khan and
Ekramul (2006) [6, 7].The natural period of vibrations is evaluated using FVA as well as by using
the empirical expressions presented in IS code. Using the natural periods thus obtained the design
lateral forces will be evaluated by using pseudo static method presented in I.S. 1893(Part I)-2002.
The structure will be analyzed and designed for these lateral forces considering it to be a bare frame
and infilled frame. Using the above attained values, we evaluated the spectral acceleration ratio
depending up on the soil condition and the time period which was subsequently used for estimating
the values of base shear [5]. The dynamic analysis is also carried out for single bay, ten storied to
four bay, ten storied frames and the results are compared with the psuedo static analysis.
3. RESULTS AND DISCUSSION
Estimation of base shear is performed based on the values of natural period evaluated by
dynamic analysis and also by I.S. 1893-2002 (part- I) provisions and a comparison of the two values
are performed [5]. Base shear is evaluated for single bay, one storey to four bay, ten-storey frames.
3.1 Effect on base shear for multi-storey frames
Sample calculations of base shear evaluation are presented below for four bay, five-storey
frames as shown in Figure 1.
Following data has been assumed for this purpose.
Seismic zone = III
Soil condition – medium strata
Importance factor = 1
Response reduction factor = 5 (Special moment resisting RC frame.)

3. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 7, July (2014), pp. 81-88 © IAEME
Figure.1: Four bay five-storey frame considered for sample calculations.
3.2 Seismic weight calculations
Seismic weight is calculated as follows.
Storey 5 (Terrace):
Floor slab = 16.896 x 6 x 4 = 405.504 kN
Reaction from secondary beams = 19.896 x 5 = 99.48 kN
Weight of beam = 0.23 x 0.53 x 25 x 6 x 4 = 73.14 kN
Weight of column = 0.3 x 0.3 x 25 x 1.5 x 5 = 16.875 kN
83
-----------------
Total weight (W5) 594.999 kN
Storey 4:
Floor slab = 30.09312 x 6 x 4 = 722.235 kN
Reaction from secondary beams = 41.454 x 5 = 207.725 kN
Weight of beam = 0.23 x 0.53 x 25 x 6 x 4 = 73.14kN
---------------
1003.1 kN
Weight of column = 0.3 x 0.3 x 25 x 1.5 x 5 + 16.875 = 38.25 kN
Total weight (W4) 1041.35 kN
Storey 3:
Total weight (W3) = 1003.1 + 2.58 x 1.5 x 5 + 3.375 x 1.5 x 5 = 1047.763 kN
Storey 2:
Total weight (W2) = 1003.1 + 3.975 x 1.5 x 5 + 3.375 x 1.5 x 5 = 1058.225 kN
Storey 1:
Total weight (W1) = 1003.1 + 3.975 x 3 x 5 = 1062.725 kN
Seismic weight of the entire frame (W) = 4805.062 kN
The seismic weight of the floor is lumped weight, which acts at respective floor level at the
centre of mass of the floor.

4. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 7, July (2014), pp. 81-88 © IAEME
3.3 Design seismic load calculation
Base shear is calculated first for bare frame by using the period given in the I.S. 1893-2002 (part-
I).The fundamental natural period of vibration in seconds, Ta, is given by
Ta= 0.075 x h 0.75[IS 1893 (part I): 2002, clause 7.6.1] where h = height of building in meters
= 0.075 x 15 0.75= 0.5716 sec.
Zone factor, Z = 0.16 for Zone III [IS 1893 (part I): 2002, Table 2]
Importance factor = 1
Sa/g represents the Spectral Acceleration ratio which depends on the natural period of vibration,
damping of the structure and type of the soil.
For medium soil site
84
=
= 2.38IS 1893 (part I): 2002, Figure 2
Ductile detailing is assumed for the structure. Hence, Response reduction factor, R, is taken
equal to 5.0.
Hence,
Ah=

5. = 0.03808,where Ah = design horizontal seismic coefficient,
z = zone factor, I = Importance factor and m = mass
Base shear, VB = AhxW= 0.03808 x 4805.062 = 182.976 kN.
From Free Vibration Analysis,we get Ta= 0.9535 sec.
= 1.426
Hence Ah= 0.0228 and VB= 0.0228 x 4805.062 = 109.63 kN
Similarly for infilled frame,
Ta =
where d = base dimension of the building at the plinth level in meters along the
considered direction of the lateral force
= 0.27556 sec.(h= 15 m, d = 24 m)
From Free Vibration Analysis, we get Ta= 0.3466 sec.
Hence
= 2.5 for both cases as obtained from IS 1893 (part I): 2002, Figure 2 [5]
Therefore we get Ah=
= 0.04 and VB= 0.04 x 4805.062= 192.202 kN.
Using above procedure base shear is calculated for all frames of 3m floor height and 6m span
length and corresponding graphs are plotted showing the variation of base shear with the number of
storeys.
Table I summarizes the values of base shear obtained for a single bay with the number of
storeys varying from one to ten for bare frame (BF) and infilled frame (IF) obtained from Free
Vibration analysis (FVA) as well as IS code and the corresponding graph is shown in Figure 2.
Table I: Base shear for a single bay with the number of storeys varying from one to ten
NO. OF STOREY’S 1 2 3 4 5 6 7 8 9 10
BASE SHEAR BF(FVA) 4.516 10.01 16.121 19.01 22.51 25.91 26.51 25.32 26.01 26.03
BS. BF(IS 1893) 4.514 10.04 16.141 22.51 27.42 30.01 32.12 34.13 36.22 37.13
BS. IF (FVA) 6.011 17.51 30.01 42.51 54.91 68.01 80.01 75.05 73.92 72.01
BS. IF (IS 1893) 6.014 17.52 30.11 42.53 54.93 55.02 57.11 57.51 57.91 59

6. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976
ISSN 0976 – 6316(Online), Volume 5, Issue
Base shear kN
Number of stories

7. Figure 2: Variation of base shear for a single bay with the number of storeys varying
The graph clearly suggests that in the case of the bare frame the values obtained from the
Free Vibration analysis as well as IS code show lower values for base shear as c
infilled frames. In the case of infilled frames, the values of b
eventually saturating for higher stories.
code.
Variation in base shear with number of stories
and infilled frame (IF) obtained from Free Vibration analysis (FVA) as well as IS code
three bay and four bays are shown in Figures 3, 4 and 5, respectively.
Base shear (kN)

8. Number of stories
Figure 3: Variation of base shear for
7, July (2014), pp. 81-88 © IAEME
85
base shear increases linearly initially
This trend is followed both in the case of FVA as well as IS
varying from one to ten for bare frame (BF)
two bays with the number of storeys varying
– 6308 (Print),
from one to ten
compared to the
ncreases for two bay,
h from one to ten

9. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976
ISSN 0976 – 6316(Online), Volume 5, Issue
Base shear (kN)
7, July (2014), pp. 81-88 © IAEME

10. Number of stories
Figure 4: Variation of base shear for three bay
Base shear (kN)
– 6308 (Print),
bays with the number of storeys varying from one to ten
Numberof stories

11. Figure 5: Variation of base shear for four bays with the number of storeys varying from
one to ten
The above figures representing the variation of base shear with storey height suggests that the
trends suggested by the FVA as well as IS code are similar, similar
both in the case of bare frames as well as
infilled frames. In the case of bare frames, for all the bays the base shear value increases linearly
upto about three storeys and then reaches saturation/a slight increase beyond that. In the case of
infilled frames for two bays the base shear values obtained from FVA increases linearly upto
seven
storeys and reaches a saturation beyond that, whereas for three and four bays the saturation is
attained beyond eight storeys, below which the linear trend is being fol
lowed. code analysis of the infilled frame structures, for
that of FVA even though the saturation base shear values are lower than that obtained from FVA. A
distinct trend could be observed for four bay infilled frames, where the base shear values continues
to increase linearly upto ten storeys as seen from codal analysis.
The general trend of large increase in base shear values for infilled frame as compared to the
bare frames possibly arises from the fact that with infilled walls, mass and stiffness of the structure
increases, hence the natural period of vibration decreases which leads to large increase in base shear
[8, 9]. With increasing number of bays, the base width
86
ames followed. However, from IS
single and two bays the trend followed is similar to
ved rises ith d increases leading ing to an increasing stiffness

12. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 7, July (2014), pp. 81-88 © IAEME
of the structure, which means the lateral displacement should decrease. Hence as we increase the
number of bays as well as the number of storeys (which means the height h is also increasing), a
proportional increase in k and m occurs which might be reflecting in the natural period. In the IS
code evaluation the height and the base width is proportionally increasing, which might be leading to
a linear increase in base shear values initially. Similarly in FVA, the mass and stiffness matrices are
influenced proportionally which could result in a linear increase initially and a saturation thereafter.
Table II shows the percentage decrease in base shear obtained from FVA as compared to those
evaluated by codal provisions.
87
Table II: Decrease in base shear calculated by FVA as compared to I.S. code.
SR. NO. FRAME SINGLE BAY TWO BAYS THREE BAYS FOUR BAYS
1 BARE FRAME 0 TO 30% 0 TO 24% 0 TO23% 0 TO 27%
2 INFILLED
FRAME
0 TO (-40)% 0 TO (-4)% 0 TO (11)% 0 TO (26)%
In the case of bare frame, for all the bays, there is about 0 to 30% decrease in base shear
values obtained from FVA as compared to codal expressions suggesting that codal provisions leads
to higher estimation of seismic forces for bare frames which is on very conservative side. On the
other hand, the overestimation of period by codal expressions for single and two bay infilled frame
represents a flexible structure, which in turn leads to underestimation of seismic forces [10].
4. CONCLUSIONS
Considering the importance of understanding the values of base shear in the designing of
seismic resistant buildings, we have carried out detailed investigations of the changes in base shear
for multibay, multistoried bare frame and infilled frame structures using Free Vibration analysis in
SAP 2000 in comparison with the pseudostatic analysis presented in I.S. 1893(Part I)-2002. The
results point out that the trends suggested by the FVA as well as codal expressions are similar, both
in the case of bare frames as well as infilled frames. Also, there exists large increase in base shear
values for infilled frame as compared to the bare frames possibly arising from the fact that with
infilled walls, mass and stiffness of the structure increases, hence the natural period of vibration
decreases which leads to large increase in base shear.
5. REFERENCES
[1] D. Das, C. V. R. Murty, “Brick masonry infills in seismic design of RC framed
buildings”The Indian Concrete Journal, 7, 2004, pp. 39-43.
[2] Rahmathulla Noufal E., “A solution for the analysis of R C Framed structure with infilled
frames under dynamic load”, International Journal of Engineering Research and Technology,
3, 2014, pp. 569-575.
[3] M. R.Wakchaure, S. P. Ped, “Earthquake analysis of high rise building with and without in
filled walls”, International Journal of Engineering and Innovative Technology, 2, 2012, pp.
89-94.
[4] SAP 2000 software.
[5] I.S. 1893(Part I)-2002, “Criteria for Earthquake Resistant Design of Structure, General
Provisions and Buildings”, Bureau of Indian Standards, New Delhi.
[6] B. S. Smith, “Behaviour of square infilled frames”, Journal of structural Division, American
Society of Civil Engineering, 92, 1966, pp. 381-403.

13. International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),
ISSN 0976 – 6316(Online), Volume 5, Issue 7, July (2014), pp. 81-88 © IAEME
88
[7] Mahmud Amanat Khan, Hoque Ekramul, “A rationale for determining the natural period of
RC building frames having infill”, Engineering Structures, 28, 2006, pp. 495-502.
[8] Rahmathulla Noufal E., “Effect of infills in the dynamic responses of RC framed structures”,
Unpublished results.
[9] Bryan Stafford Smith, “Methods for Predicting the Lateral Stiffness and Strength of Multi-
Storey Infilled Frames, Building and science”, 1967, 2, pp. 247-257.
[10] M. Sobaih and M. M. Abdin, “Seismic analysis of infilled reinforced concrete frames,
Computers and structures” 1988, 3, pp. 457-464.
[11] Dr. Suchita Hirde and Dhanshri Bhoite, “Effect of Modeling of Infill Walls on Performance
of Multi Story Rc Building”, International Journal of Civil Engineering Technology
(IJCIET), Volume 4, Issue 4, 2013, pp. 243 - 250, ISSN Print: 0976 – 6308, ISSN Online:
0976 – 6316.
[12] Misam.A and Mangulkar Madhuri.N., “Structural Response of Soft Story-High Rise
Buildings under Different Shear Wall Location”, International Journal of Civil Engineering
Technology (IJCIET), Volume 3, Issue 2, 2012, pp. 169 - 180, ISSN Print: 0976 – 6308,
ISSN Online: 0976 – 6316.
[13] Dr. Suchita Hirde and Dhanshri Bhoite, “Effect of Modeling of Infill Walls on Performance
of Multi Story RC Building”, International Journal of Civil Engineering Technology
(IJCIET), Volume 4, Issue 4, 2013, pp. 243 - 250, ISSN Print: 0976 – 6308, ISSN Online:
0976 – 6316.