Seismic Performance Evaluation of Two-story and Three-span Subway Station in Different Engineering Sites

This study firstly investigates the seismic intensity measures (IMs) from the existing scalar ones that are suitable for the prediction of seismic response of shallowly buried rectangular underground structures. The peak acceleration and peak velocity at the ground surface are identified as the optimal IMs based on their efficiency, practicality, and proficiency. A series of seismic fragility curves are then developed for a two-story and three-span underground subway station embedded in three different typical engineering sites using nonlinear incremental dynamic analyses. In this study, the input ground motions at the level of engineering bedrock for the underground structure-soil interaction system are obtained through one-dimensional equivalent linear site response analysis according to the one-dimensional wave propagation theory. Comparison of the numerical results in this paper with the previous empirical and numerical fragility curves shows that the fragility analysis method in this paper is feasible, which can quantitatively give the failure probability of structures at different performance levels, and can provide reference for seismic design of underground structures. The numerical results indicate that both the characteristics of ground motions and the site profile have significant influence on the seismic fragility curves of underground structures. Underground subway stations are generally more vulnerable to seismic damage when embedded in engineering sites with lower average shear velocity. Moreover, seismic damage margin ratios are proposed for the underground structure in different site classes to show the confidence levels of its seismic performance when subjected to different levels of earthquake events, and can be used as a preliminary index for the earthquake risk assessment of subway station.

Automated summary

This study explores optimal seismic intensity measures for predicting the seismic response of shallowly buried rectangular underground structures and develops seismic fragility curves for two-story and three-span underground subway stations. It is found that both ground motion characteristics and site profiles significantly influence the seismic fragility curves of underground structures, with underground subway stations being more vulnerable in engineering sites with lower shear velocity. Furthermore, seismic damage margin ratios are proposed as a preliminary index for earthquake risk assessment of subway stations.