Seismic performance and fragility analysis of underground subway station with rubber bearings

In this paper, a comparative study of the seismic response and fragility of a station structure before and after being retrofitted with an LNB installed on the top of its columns is conducted to evaluate the effectiveness of retrofitting measures in reducing risk probability employing, for the first time, a probabilistic approach. The Daikai subway station was adopted as a case study, and two-dimensional finite element models of soil-structure system with and without LNB were established. Incremental dynamic analyses (IDA) of original and retrofitted structures were conducted to evaluate their seismic responses under different ground motion intensities and considering the uncertainty of ground motion. Further, the IDA curve cluster and quantile lines of station structure and rubber bearing were constructed. Finally, the seismic fragility curves of structure and LNB were established for the risk assessment under different performance levels based on the structural performance index. The results demonstrated that the horizontal deformation, shear force and bending moment of the central column fitted with rubber bearings are greatly reduced compared with the actual Daikai station structure, which is more pronounced for lower ground motion intensity. In addition, the failure probability of the retrofitted structure corresponding to different damage levels is much lower than that of the original structure under the same ground motion intensity. Meanwhile, the probability of moderate to severe damage for the underground station structure is greatly reduced after retrofitting with the rubber bearings. The overall seismic performance of the structure is significantly improved and post-earthquake repair-demand is greatly decreased.