A Computer Program for Nonstationary Analysis and Simulation of Stong Motion Earthquake Records

The increasing need for a better understanding of the structural response to earthquake ground motion, has led to several structural analysis approaches. Among these, the equivalent static force approach and the response spectrum approach, although simple in concept and easy to implement, are known for not being accurate enough, especially if used for the design of very important and complex structures.

To account for the nonlinear behavior of structures, the only reliable and accurate method is the so-called "time history" approach. In this method, a complete acceleration-time history of the earthquake record is used as an input to a structural model. The structural model is assumed to behave non-linearly beyond the elastic limit. A finite-element (two- or three- dimensional) soil-structure model is usually developed for this purpose. The response is obtained by numerical integration. Even though this method provides a sufficiently sophisticated and accurate model of the soil- structural system, the input earthquake time history has considerable uncertainty. Therefore many researchers have developed analytical as well as numerical methods to simulate the earthquake time histories. Such models help to better understand the seismic phenomenon by itself and also give structural designers an option to evaluate the possible non-linear response of their structures due to a family of simulated earthquakes.

Several stationary and non-stationary models for earthquake simulation have been proposed (Cornell, 1964; Housner, 1964; Jennings, 1969; Ipek, 1980). It is generally recognized that due to the transient nature of the seismic input, a non-stationary simulation is far more reasonable, especially if one is dealing with non-linear structural behavior, which is the case for strong ground motions.

This program (Tilliouine, 1982) uses the concept of a physical spectrum (Mark, 1970). It can generate an ensemble of synthetic earthquakes having prescribed non-stationarities, both in the amplitude and frequency domains.