Explanatory Examples on Indian Seismic Code IS 1893

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Problem Statement:
Consider a four-storey reinforced concrete office building shown in Fig. 1.1. The building is located in
Shillong (seismic zone V). The soil conditions are medium stiff and the entire building is supported on a raft
foundation. The R. C. frames are infilled with brick-masonry. The lumped weight due to dead loads is 12
kN/m2 on floors and 10 kN/m2 on the roof. The floors are to cater for a live load of 4 kN/m2 on floors and
1.5 kN/m2 on the roof. Determine design seismic load on the structure as per new code.


Design Parameters:
For seismic zone V, the zone factor Z is 0.36
(Table 2 of IS: 1893). Being an office building,
the importance factor, I, is 1.0 (Table 6 of IS:
1893). Building is required to be provided with
moment resisting frames detailed as per IS:
13920-1993. Hence, the response reduction
factor, R, is 5.


Force Distribution with Building Height:
The design base shear is to be distributed with
height as per clause 7.7.1. Table 1.1 gives the
calculations. Fig. 1.2(a) shows the design seismic
force in X-direction for the entire building.


Problem Statement:
For the building of Example 1, the dynamic properties (natural periods, and mode shapes) for vibration in
the X-direction have been obtained by carrying out a free vibration analysis (Table 2.1). Obtain the design
seismic force in the X-direction by the dynamic analysis method outlined in cl. 7.8.4.5 and distribute it with
building height.