Longitudinal seismic fragility analysis of long tunnels under multiple support excitation

Abstract

Probability-based seismic fragility analysis can quantitatively evaluate the seismic performance of structures. This study proposes a longitudinal fragility analysis method for long tunnels under multiple support excitation (MSE). Firstly, 10 MSEs are synthesised based on the spatially correlated ground motion simulation method. Then, the two-dimensional free-field model is established, and incremental dynamic analysis under MSE is performed. On the basis of the generalised response displacement method, the soil–tunnel model is established and the seismic response is analysed. The maximum opening width of the tunnel circumferential joint and the peak ground acceleration (PGA) are selected as the damage measure and the intensity measure in the fragility analysis, and fragility curves are generated. The obtained results are compared with the identical support excitation (ISE) results. Findings show that the proposed method is suitable for fragility assessment. The seismic response under MSE is larger than that under ISE, and the results of the former are more accurate. The fragility results further indicate that the damage probability of the tunnel is higher under MSE. The seismic design safety of the tunnel can be improved with more reliable MSE results.