Failure analysis of an un-anchored steel oil tank damaged during the Silakhor earthquake of 2006 in Iran

On March 31, 2006, a destructive earthquake (Mw = 6.1) occurred in western Iran. Because of the earthquake, some of the old un-anchored cylindrical steel fuel storage tanks were damaged. The damaged tanks experienced the horizontal peak ground acceleration (PGA) of 0.44g. During the earthquake, the most affected tank experienced shell uplift. Because of the tank-to-foundation impact, the concrete cover of the tank foundation was damaged. In addition, the evidences of slight buckling were observable on tank shell. In this study, failure analysis was performed on the most affected tank. In order to evaluate the seismic performance of the studied tank, existing analytical relations were carried out as well as the inelastic response history analysis. To this end, the accelerogram of the recorded earthquake at a station close to the selected tank was used. Numerical analysis was performed using ABAQUS software. In addition, a parametric study was carried out to evaluate the effect of amount of stored liquid on seismic behavior and performance of the studied tank. Results of this study revealed that the numerical model is capable of estimating the actual performance of the tank. It was shown that the critical PGA of the dynamic buckling of the considered tank is 0.285g. Additionally, the uplift threshold PGA is 0.23g.