Influence of Earthquake Frequency Nonstationarity on Seismic Structural Response

Abstract

Earthquake ground acceleration records exhibit nonstationarity in both amplitude and frequency content. In order to simplify the random vibration analysis, most earthquake models have often neglected the temporal variation of the frequency content. This is partly because it is difficult to incorporate this variation in ground motion models and also partly because it was believed that it had no substantial effect on structure response. The aim of this paper is to identify the temporal variation in frequency content effects, characterizing the earthquake strong ground motions, on structures. Two comparative stochastic earthquake ground motion models based on the concept of physical spectrum are used to characterize and simulate from a selected ground acceleration record two sets of artificial earthquakes exhibiting similar phases distribution and different frequency contents: the first set presents a time-variant frequency content, and the second has a time-invariant frequency content. Three hysteretic models have been considered, elasto-plastic model (bilinear), Clough’s stiffness degrading model and maximum point-oriented bilinear model. Comparative results are presented to quantify the effects of the time-variant frequency content of earthquake ground motion on the structural response of elastic and inelastic simple systems. It is found that the characteristics of elastic and inelastic structural response depend strongly on the time variation of the frequency content in the seismic input.