Seismic Vulnerability Assessment of Existing Ground-Supported Liquid Storage Tanks with Deformed Shells

This study presents a novel methodology for the seismic vulnerability assessment of ground-supported liquid storage tanks, with a particular emphasis on tanks exhibiting deformed shells. The framework is built around the development of a simplified two-degree-of-freedom (2DoF) system, specifically designed to enable efficient probabilistic analysis through incremental dynamic analysis. The 2DoF model is calibrated using detailed nonlinear finite element simulations, which account for fluid-structure interaction and complex geometric effects. This approach allows for a significant reduction in computational effort while maintaining a high level of accuracy in predicting seismic fragility. A key feature of the proposed methodology is the explicit inclusion of deformed tank geometries, which are often encountered in real cases and can critically impact seismic performance. The study identifies and quantifies the effects of these deformations on various damage states, such as local buckling, overturning, and liquid overspill. Fragility curves are developed to characterize the probability of exceeding these damage states under different levels of seismic intensity. The proposed methodology is validated through a representative case study, demonstrating its ability to capture the key features of tank behavior and provide robust fragility estimates. The results highlight the potential of the 2DoF system to serve as a practical tool for seismic risk assessment, enabling engineers and researchers to evaluate tank vulnerabilities more efficiently.