A method for generating fully nonstationary spectrum-compatible earthquakes

摘要

Seismic analysis of ordinary structures is usually performed via the design response spectrum. For structures that exibits nonlinear behaviour the direct integration of equation of motion in conjunction with the simulation of appropriate time-histories is usually preferred. Unfortunately, international seismic codes do not give a method for generating the earthquake time-histories furnishing only the spectrum-compatible criteria that have to be satisfied. As a consequence, several methods have been proposed in literature coping with the generation of spectrum-compatible accelerograms. Most common approaches rely on the modeling the seismic action as a realization of a stationary or quasi-stationary stochastic process. On the other hand, it is well known that the dynamic response of nonlinear structures is highly influenced by the nonstationary behavior of the input. Thus, more reliable simulations would take into account the time variability of both intensity and frequency content of the ground motion. These aspects have been dealt with by various procedures. In this paper a handy method for generating fully nonstationary spectrum-compatible earthquakes is proposed. The method assumes that the ground motion is modeled by the superposition of two contributions: the first one is a fully-nonstationary counterpart modeled by a recorded or, alternatively, by a simulated earthquake that takes into account the time variability of both intensity and frequency content; the second one is a corrective term represented by a stationary process that adjust the response spectrum of the nonstationary signal in order to make it spectrum-compatible. Interestingly, via the proposed approach the evolutionary spectrum-compatible power spectral density has been also derived. Several examples show the accuracy and the efficiency of the proposed method.