Ground Motion Intensity Measures for Seismic Vulnerability Assessment of Steel Storage Tanks with Unanchored Support Conditions

This paper aims to comprehensively evaluate the performance of a series of ground motion intensity measures (IMs) used in the seismic vulnerability assessment of steel storage tanks with unanchored support conditions. Sixteen well-known IMs are thus selected, which are classified into amplitude-, frequency-, and time-based categories. A comparative study is then performed on four different unanchored steel storage tanks subjected to a suite of 140 ground motion records that is comprised of seven different bins of records with different hazard levels. In this regard, the tanks are appropriately modeled based on a simplified approach, whose uplift and sliding nonlinear behaviors are properly implemented based on a three-dimensional nonlinear pushover analysis of the tanks. Four characteristics of the examined IMs including efficiency, practicality, proficiency, and sufficiency are evaluated based on a probabilistic seismic demand model of two critical failure modes of the tanks, i.e., plastic rotation of the shell-to-bottom connection and elephant's foot buckling of the shell plate. According to the comparative study, frequency-based IMs demonstrate their superior performance for all criteria compared with other groups; in particular, the average spectral acceleration gains the highest ranking. Finally, an appropriate range of the upper period considered in the average spectral acceleration IM is then proposed to optimize the efficiency of this IM for the examined tanks.