Seismic fragility curves for shallow buried subway station using pushover-based method

Numerical methods are widely used to establish seismic fragility curves in the performance-based seismic design for buildings. However, non-linear dynamic analyses for large soil-structure systems are computationally demanding and alternative methods are sought to establish seismic fragility curves for buried structures. This paper proposes a simplified pushover method to calculate the non-linear response of underground structure. The pushover-based fragility analysis method can establish the conditional probability of the structure relevant to certain limits states by conducting a series of free-filed response analyses and one pushover static analysis. To verify the applicability of the method, two different subway stations designed for static loads only are used as examples for vulnerability assessment using the proposed method as well as the conventional incremental dynamic analysis (IDA) method. The structure capacity limits are associated with the inter-story drift ratio and the earthquake intensity measure is represented by the earthquake peak ground acceleration (PGA). The fragility curves predicted employing the pushover-based method are compared with those obtained from the IDA method. The comparison indicated that the probabilistic approach integrated with pushover-based strategies is an effective tool for rational and quantitative seismic fragility assessment of underground structures.