Efficient seismic fragility of underground structures using endurance time analysis method

The feasibility of efficient seismic fragility analysis of underground structures using the endurance time analysis (ETA) method is investigated. A typical two-story three-span subway station embedded in the site class Ⅲ is used as the prototype. To effectively consider the inherent dispersion of as-recorded earthquake ground motions during the simulation of endurance time acceleration functions, the 16%, 50% and 84% quantiles of response spectra of the as-recorded ground motions at the engineering bedrock are used as the target response spectra to generate three endurance time acceleration functions using the quantile regression method in the incremental dynamic analysis (IDA) for reference as the input motions for the nonlinear soil-structure interaction system, respectively. The seismic fragility evaluation of the underground structures is performed based on the ETA results and the IDA results. It can be seen from the numerical results that the seismic fragility curves obtained by the ETA are in good agreement with those obtained by the IDA. Therefore, the proposed ETA with full consideration of the dispersion of ground motions can significantly reduce the number of nonlinear dynamic analyses, and ensure high accuracy of the computed results. Moreover, the proposed ETA using a series of discrete ETAFs by the quantiles of response spectra of the as-recorded ground motions is a feasible alternative for the seismic fragility analysis of underground structures.