Longitudinal seismic fragility analysis of utility tunnel structures based on IDA method

This study aims to propose a fragility analysis method for longitudinal seismic performance evaluation of long-line utility tunnel based on nonlinear incremental dynamic analysis (IDA). To this end, a simplified beam-spring model was established, which reasonably considered the mechanical properties of the joint and the soil-tunnel interaction. A series of 17 sets of ground motion records were selected and uniformly scaled to different intensity levels as the input of one-dimension free filed analyses to obtain the ground motions at the bottom slab of utility tunnel. Finally, seismic analysis of the utility tunnel considering wave passage effect was conducted. Based on the IDA results, the optimal intensity measure was selected. With the damage measure of peak joint opening, fragility curves of utility tunnel were established using the peak velocity at the bottom slab of tunnel and peak velocity at the ground surface as the intensity measures, respectively. The failure probability of the utility tunnel under different earthquake intensity levels was also obtained. The proposed fragility curves and failure probability of the utility tunnel in typical site II can provide an effective tool to estimate the seismic performance of this type underground structure and a reliable basis for predicting damage under different earthquake intensity levels.