A significant fire and explosion accident on spherical storage tanks for Liquefied Petroleum Gas (LPG) at Chiba prefecture in Japan were occurred due to the strong ground motion of the 2011 Great East Japan Earthquake. The braces made of steel pipe for supporting columns of a spherical tank, which was filled with water for purging air at that time, were broken by the strong seismic inertia force. Then, buckling of columns was occurred by the aftershock. To clarify the failure mechanism of the pipe braces of its supporting frame of a spherical tank, the elastic and elastic-plastic finite element analysis (FEA) was performed. From FEA results, the failure mechanism of the pipe brace was revealed as follows; (1) high stress was generated in the intersection of long and short braces due to the structural discontinuities, (2) the generated high stress was a trigger of the failure initiation of the damage of the supporting frame, (3) the breakage of the intersection of the long and short braces of the supporting frame was caused overturn of the spherical tank at the aftershock of predominant earthquake. In this paper, the fracture mechanism of the spherical storage tank was clarified for prevention of the same type accidents, and the effective reinforcement method of pipe braces of spherical tanks was proposed for securing safety.

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