Seismic fragility assessment of storage tanks considering different sources of uncertainty

Liquid storage tanks are critical facilities in petroleum depots that must remain intact and functional following an earthquake. The seismic fragility function is a useful tool for quantifying structural vulnerability. This study accordingly explored the effects of different uncertainties on the seismic fragility of a case study floating-roof storage tank by applying an appropriate approach to seismic fragility analysis. First, an orthogonal sensitivity analysis was performed using a finite element model to determine the random model variables most affecting the seismic responses of the storage tank. Considering the different sources of uncertainty, seismic fragility was subsequently evaluated by combining a cloud analysis with model sampling. Then, the seismic fragility curves of the storage tank system were developed by studying the correlations among multiple failure modes. The results indicate that the computational requirements of the present method were significantly less demanding than those of direct Monte Carlo simulation. Geometric uncertainty was found to exert the greatest impact on the seismic responses. The maximum difference among the fragility function parameters for different sources of uncertainty was 28.9%. The damage assessment of the tank system was shown to be more reasonable when considering the correlations among multiple failure modes. This analysis technique can accordingly provide practical guidance for the seismic design of vertical floating-roof storage tanks.