Chapter 4

Response Spectrum Method
 

The quantity Spa is related to the maximum value of base shear as

  
(4.12)

The relations between different response spectrum quantities is shown in the Table 4.1.
As limiting case consider a rigid system i.e. or , the values of various response spectra are

(4.13)

(4.14)

(4.15)

The three spectra i.e. displacement, pseudo velocity and pseudo acceleration provide the same information on the structural response. However, each one of them provides a physically meaningful quantity (refer equations (4.11) and (4.12)) and therefore, all three spectra are useful in understanding the nature of an earthquake and its influence on the design. A combined plot showing all three of the spectral quantities is possible because of the relationship that exists between these three quantities. Taking the log of equations (4.8) and (4.9)