Accuracy of equivalent linear models for bilinear oscillators under pulse-like ground motion

Nonlinear dynamic analysis is the most reliable approach for the assessment of structures under earthquake, provided that implemented computational method and adopted mechanical models are able to simulate properly material and geometrical nonlinearities. Nonetheless, several guidelines and codes also strive to include simplified methodologies for use in practice. In this perspective, several equivalent linear models have been proposed so far in order to allow a rapid analysis of oscillators with bilinear-type response, but none of the existing studies has yet examined systematically their reliability in case of pulse-like ground motion. Therefore, this paper presents the results of an extensive numerical investigation that aims at assessing whether existing equivalent linear models can be exploited in order to estimate the maximum displacement of bilinear oscillators under pulse-like near-fault ground motion. Several nonlinear dynamic analyses have been performed and final results demonstrate that the accuracy of current equivalent linear models depends on the ratio between the elastic period of the bilinear oscillator and the pulse period of the seismic excitation.