Response Spectrum Wizard : IS 1893 (Part 1) (2002)

The IS 1893 (Part 1) : 2002 spectrum is defined by a set of parameters defined in the code.

Seismic Zone

The seismic zones are defined as II, III, IV or V (See Fig. 1 and Annex E).

Soil Type

Sites are classed depending on the soil type as one of Type I (rock or hard soil), Type II (medium soil) or Type III (soft soil).

Importance Factor

For most buildings the importance factor is 1 but this can increase to 1.5. Determine the importance factor (I) from Table 6.

Response Reduction Factor

Depending on the structure type a different response reduction factor can be used. Determine the response reduction factor (R) from Table 7.

Structure Damping Ratio ()

The spectrum values to use depend on the level of damping in the structure as expressed in the damping ratio. (See Table 3). This value will normally be adjusted during an analysis.

Factor for Vertical Excitation

Clause 6.4.5 recommends that the spectral values for vertical excitation be ⅔ of that used for horizontal excitation. Checking this option applied the ⅔ factor for the vertical direction.

Ignore Short Period Force Reduction

It may be unconservative to reduce spectral values for low periods. This option ignores the reduction and extends the plateau to cover the low periods.