A simple and efficient model for seismic response and low-cycle fatigue assessment of uplifting liquid storage tanks

Abstract

Ground-supported unanchored liquid-storage cylindrical tanks, when subjected to strong seismic loading may exhibit uplifting of their bottom plate, which may have significant effects on their dynamic behavior and structural integrity. In particular, due to uplifting, a substantial amount of plastic deformation develops at the vicinity of the welded connection between the tank shell and the bottom plate that may cause failure of the welded connection due to fracture or fatigue, associated with loss of tank containment. The present study focuses on the base uplifting mechanism and tank performance with respect to the shell/plate welded connection through a numerical simple and efficient methodology that employs primarily a simplified modeling of the tank as a spring-mass system for dynamic analysis, enhanced by a nonlinear spring at its base to account for the effects of uplifting, supported by a detailed finite element model of the tank for incremental static analysis. The latter model is capable of describing with accuracy the state of stress and deformation at different levels of lateral loading, in order to obtain the overturning moment-rocking angle relationship to be used in the simplified model. The methodology is applied in two cylindrical liquid storage tanks of different aspect ratios focusing on local performance of the welded connection, towards assessing the strength of the welded connection. The numerical results provide better understanding of tank uplifting mechanics and strength against failure of the welded connection at the tank bottom. Furthermore, the proposed methodology can be used for efficient assessment of uplifting effects on tank structural safety, towards minimizing seismic risk in industrial facilities. © 2017 Elsevier Ltd