
Calculate Earthquake Forces on Buildings and Structures
First step to calculate earthquake loads on structure is to identify the earthquake zone for which structure needs to be designed. This earthquake zones are displayed in a map on page – 6 of the code. After earthquake zone has been identified, the following steps are followed: 1. Calculate design horizontal seismic coefficient, Ah, which is given by (cl. 6.4.2 of IS1893 – 2002:Example:
Consider a two-bay two-storied building for which earthquake forces need to be calculated. Consider total weight of the building as 1000 kN. Top roof has the weight of 200 kN and both floors have weight of 400 kN as shown in figure below. The calculation of earthquake seismic forces will be as shown below:
Total Weight of the Structure |
Wi = |
1000 |
kN |
|||
Zone Factor (Zone IV) |
Z = |
0.24 |
||||
Importance factor (Table6) |
I = |
1 |
||||
Response Reduction Factor |
R = |
3 |
||||
Average response acceleration coefficient |
||||||
Let time period |
 T |
0.373358 |
(Cl. 7.6) |
|||
Sa/g |
2.5 |
|||||
Design Horizontal Seismic coefficient Ah |
0.10 |
|||||
Base Shear |
100 |
kN |
||||
Storey |
Base Shear |
Height |
Wi |
Wixhi2 |
Qi |
Design Force |
3 |
100 |
8.5 |
200 |
14450 |
57.00197 |
9.50 |
2 |
100 |
5 |
400 |
10000 |
39.44773 |
6.57 |
1 |
100 |
1.5 |
400 |
900 |
3.550296 |
0.59 |
Total |
25350 |
(in kN) |