Study on Restoring Force Models of Nonlinear Uplift Behavior of Unanchored Oil Storage Tank Under Strong Seismic Excitation

It had been reported that some unanchored oil storage tanks had serious damages due to its uplift behavior during strong seismic excitation. In some past studies, the uplift behavior of tank was generally simulated using elastic-plastic hysteresis models. But recently, a static FEM analysis for the cyclic uplift behavior of the shell-to-bottom joint of tank has shown that the hysteresis loop of the uplift force and uplift displacement is similar to S-curve with a narrow loop area. In order to investigate the effects of S-curve Restoring Force Model (SRFM) on the nonlinear response when it is used to simulate the tank’s uplift action, in this paper, the seismic response analyses of tank are carried out by using three kinds of restoring force models including SRFM, the Elastic-Perfectly Plastic Model (EPPM) and the Bilinear Elastic-Plastic Model (BEPM), and their results are compared with each other to examine the differences. In the analyses, the tank is modeled with an equivalent mass-spring model, and three recorded earthquake accelerations scaled to 0.6G are taken as the representation of strong motions. Consequently, this paper shows that SRFM gives the maximum response displacement and ductility respectively among the three restoring force models.