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

This study aims to propose a fragility analysis method for evaluating the longitudinal seismic performance of long-line utility tunnels based on nonlinear incremental dynamic analysis (IDA). To this end, a simplified beam-spring model is established, to reasonably consider the mechanical properties of the joint and the soil-tunnel interaction. A series of 17 sets of ground motion records are 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 a utility tunnel. Finally, the seismic analysis of the utility tunnel considering wave passage effects is conducted. Based on the IDA results, the optimal intensity measure is selected. With the damage measure of the peak joint opening, the fragility curves of the utility tunnel are established using the peak velocity at the bottom slab of the tunnel and the peak velocity at the ground surface as the intensity measures, respectively. The failure probability of the utility tunnel under different earthquake intensity levels is 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 of underground structures and a reliable basis for predicting damage under different earthquake intensity levels.