Response Spectra

Abstract

In this chapter, we introduce the concept of response spectrum, which in recent years has gained wide acceptance in structural dynamic practice, particularly in earthquake engineering design. Stated brief, the response spectrum is a plot of the maximum response (maximum displacement, velocity, acceleration, or any other quantity of interest) to a specified load function for all possible single-degree-of-freedom systems. The abscissa of the spectrum is the natural frequency (or period) of the system, and the ordinate the maximum response. A plot of this type is shown in Fig. 5.1, in which a one-story building is subject to a ground displacement indicated by the function u_s (t). The response spectral curve shown in Fig. 5.1a gives, for any single-degree-of-freedom system, the maximum displacement of the response from an available spectral chart, for a specified excitation, we need only to know the natural frequency of the system.