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)
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