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Code Name IS 1893(Part 1):2002
( Criteria for Earthquake Resistant Design of structures )
Issued by Bureau of Indian Standard
Revision Fifth Revision
Horizontal Base Shear


W = Seismic weight that is full dead load  + Appropriate percentage of imposed load (see Table 1)
Ah = Design horizontal acceleration spectrum value

Design horizontal Seismic coefficient


Z = Zone factor (see Table 2),
I = Importance factor (see Table 3),
R = Responce reduction factor as given in, I/R shall not be greater than 1.0 (see Table 4)
= Average responce acceleration coefficient (see Fig. 1) for rock and soil site and based on fundamental natural periods and damping (see table-5) of the structures. These curves represent free field ground motion.

Fundamental natural period (Ta) For moment resisting frames without brick infill panels may be estimated as below,

     Ta   = 0.075 h 0.75    for R. C. Framed building
           = 0.085 h 0.75    for Steel Framed building
                        h is height of the building in m.

For others building may be estimated as below,

     @Ta  = 0.09 /(d) 
                         d (in m) is base dimension of building at plinth                          level along the  considered direction of the lateral                         forces.