A response spectrum is created by performing a transient analysis of a certain ground motion time-history on a set of 1-degree-of-freedom oscillators of varying frequency. The peak response of each oscillator over the duration of the transient becomes a point on the response spectrum graph vs. the frequency or period of the oscillator that produced it.
What makes a response spectrum so useful is that the peak response of a single mode of a multi-dof model to a transient excitation can be computed from the peak response of a single dof oscillator of the same frequency. This property allows Response Spectrum Analysis to be a simplified alternative to the more complex time-domain transient analysis for the prediction of a structure’s response to shock or seismic load.
