To evaluate the beneficial effect of rubber bearings on the seismic performance of underground station structures, three-dimensional finite element models of seismic soil-structural systems are established for a single-layer double span subway station. The seismic mitigation effect is investigated by employing the pushover analysis method. The obtained results indicated that the installation of rubber bearings can effectively alleviate stress concentration and damage degree of the central column, especially at its end area. Compared with the conventional column, the elastic and elastoplastic deformation capacity of the column fitted with rubber bearings both improved significantly. It was also found that the load bearing and deformation performance decrease with the increase of the axial pressure ratio. Furthermore, the lateral force distribution mechanism of the structural system fitted with the rubber bearings is significantly different from the original structure; the deformation and internal forces of central column of the seismic mitigation structure decreased substantially, but side walls' deformation and internal forces increased slightly. The proportion of shear force taken by the central column has decreased, while the side walls have taken larger share, i.e., the rubber bearings facilitated the transfer of seismic forces from the middle column to the side wall.

Cloud and incremental dynamic analysis (IDA) are the two most commonly used methods for seismic fragility analysis. The two methods differ significantly in the number of ground motions and whether these motions are scaled. This paper designed a random selection procedure to thoroughly discuss the influence of ground motion combinations encompassing different numbers of motions on the Cloud-based and IDA-based seismic fragility analysis for underground subway station structures. Focusing on a shallow-buried single-story station structure, a nonlinear dynamic time-history finite element analysis model of soil-structure interaction was developed. 400 ground motions were selected for random combination to perform Cloud-based seismic fragility analysis, and 20 ground motions were selected for random combination to perform IDA-based analysis. The results showed that the number of ground motions has a significant influence on the seismic fragility analysis in both Cloud and IDA, especially on the prediction of damage probability for higher seismic performance levels and when the PGA exceeded 0.3 g. In regions with a low probability of strong earthquakes, this paper recommended using no fewer than 10 and 220 ground motions in the IDA-based and Cloud-based seismic fragility analyses, respectively. In regions with a high probability of strong earthquakes, the optimal number of ground motions should be increased to 300 for Cloud-based analysis and 15 for IDA-based analysis.

The behavior of center columns in shallow-buried underground subway station structures resembles that of high-rise buildings. In both cases, these columns experience significant vertical loads during earthquake events and are susceptible to brittle failure due to inadequate deformation capacity. In this study, the design concept of split columns, commonly employed in high-rise structures, is adapted for application in a two-story, two-span subway station. Initially, a comparative analysis was conducted using quasi-static pushover analysis to assess the horizontal deformation characteristics of traditional and split columns under high axial loads. Subsequently, a comprehensive quasi-static pushover analysis model encompassing the soil-structure interaction was formulated. This model was employed to investigate differences in seismic performance between traditional and innovative underground structures, considering internal forces, deformation capacity, and plastic damage of crucial elements. The analysis results demonstrate that the incorporation of split columns in a two-story, two-span subway station enhances the overall seismic performance of the structure. This enhancement arises from the fact that split columns mitigate excessive shear forces while effectively utilizing their vertical support and horizontal deformation capacities.