The selection of representative ground motion intensity measure (IM) and structural engineering demand parameter (EDP) is the crucial prerequisite for evaluating structural seismic performance within the performance-based earthquake engineering (PBEE) framework. This study focuses on this crucial step in developing the probabilistic seismic demand model for two-story and three-span subway stations exposed to transverse seismic loadings in three different ground conditions. The equivalent linearization approach is used to simulate the shear modulus degradation and the increase in damping characteristics of the soil under seismic excitation. Nonlinear fiber beam-column elements are adopted to characterize the nonlinear hysteretic degradation of the subway station structure during seismic events. A total of 21 far-field ground motions are selected from the PEER strong ground motion database. Nonlinear incremental dynamic analyses (IDAs) are conducted to evaluate the seismic response of the subway station. A suite of 23 ground motion IMs is evaluated using the criteria of correlation, efficiency, practicality, and proficiency. Then, a multi-level fuzzy evaluation method is employed to integrate these evaluation criteria and determine the optimal ground motion IMs in different ground conditions. The peak ground acceleration and sustained maximum acceleration are demonstrated to be the optimal ground motion IM candidates for shallowly buried rectangular underground structures in site classes I, II, and III, while the root-mean-square displacement and compound displacement are found to be not suitable for this purpose.

Large diameter shield tunnels traversing liquefiable soil-rock strata are highly susceptible to seismic hazards, as earthquake-induced soil liquefaction significantly reduces soil strength and stiffness. Therefore, it is crucial to accurately assess the seismic performance of these tunnels. This study first establishes a numerical model for tunnel seismic response analysis, considering soil liquefaction, segment nonlinearity, and joint deformation. The validity of the model is affirmed through experimental, theoretical, and additional numerical simulations. The probabilistic seismic demand models are established employing the seismic database consisting of 120 ground motion records. Subsequently, a quantitative selection method for the optimal Intensity Measure (IM) based on fuzzy comprehensive evaluation is proposed, identifying Velocity Spectrum Intensity (VSI) as the most suitable among 29 commonly used IMs, and the IMs related to duration exhibit poor performance. The study then categorizes tunnel damage into three states: minor, moderate, and extensive, using joint opening as the damage measure. Finally, seismic fragility analysis is employed to assess seismic performance of tunnel, and fragility curves derived using VSI and Peak Ground Acceleration (PGA) is compared. The results indicate that PGA, a commonly used IM, significantly underestimates the probability of damage to the tunnel, with a maximum underestimation of 22.4%.