Seismic fragility assessment of the Daikai subway station in layered soil

A numerical method based on nonlinear incremental dynamic analysis is proposed in this paper to develop seismic fragility curves for rectangular subway station buried in layered soil and subjected to transverse seismic excitations. The proposed method primarily consists of four parts, namely, model verification, damage quantification, ground motion processing, and seismic performance assessment. The main section of the Daikai subway station collapsed during the Kobe Earthquake is used as an example to demonstrate the detailed procedure of the proposed method in construction of seismic fragility curves for underground structures. Results from the nonlinear soil-structure interaction model in this paper is firstly verified against the results from existing literature. The threshold values of different damage states of the underground structure are quantified by interstory drift ratio obtained from the nonlinear static pushover analysis of the soil-structure interaction system. Based on the results of the incremental dynamic analysis, it is found that the peak acceleration at the ground surface is an efficient and appropriate intensity measure of the ground motions for shallowly buried underground structure. The proposed method is validated by comparing with the existing empirical and numerical seismic fragility curves of buried rectangular underground structures and can be used as an effective approach in the development of seismic fragility database for underground structures.