What are the advantages of the response spectra method in seismic analysis?

The response spectra method is widely preferred due to its significantly lower computational demands compared to other methods, such as the time history method. Here is why.

Assume the system for which the seismic analysis is going to be performed has N degrees of freedom. The first step in performing seismic analysis is to write the equation of motion for the given system. By default, the equations of motion are coupled with each other. Now, for linear elastic systems, the modal orthogonality principle can be applied. By applying the modal orthogonality principle, the N degrees freedom system is decoupled into N number of single-degree freedom systems. To get the total response of a structure, the N number of single-degree freedom system equations should be solved.

In the response spectra method, the peak responses for each single-degree freedom system are easily obtained from the response spectrum curve. Similarly, responses for all other (N-1) equations are obtained from the response spectrum curve corresponding to the N number of natural frequencies of the system. Hence without solving the decoupled equation, the solution is obtained for all the N numbers of single-degree freedom systems equations. Hence there are no computationally intensive calculations as of like time history method.