Evaluation of seismic resistance capacity on pipe braced supporting frame of spherical tank by shaking experiment

Abstract

Significant fire and explosion accident on spherical tanks for Liquefied Petroleum Gas (LPG) storage was induced by the strong ground motion of the 2011 Great East Japan Earthquake. Steel pipe braces were broken due to the strong seismic inertia force, and then buckling of support legs occurred. To prevent recurrence, reinforcing the intersection of braces was needed. Currently, in the Japanese seismic resistance design standard for high pressure equipment including spherical tanks for storage, when subjected to a large earthquake, it is allowed to occur a certain degree of plastic deformation, witch way not lead to release high pressure gases. When receiving a high-level seismic motion, seismic response of high pressure equipment could be non-linear due to plastic deformation and the mechanical damping could be increased as well. On the other hand, a vibration test for spherical tank has not conducted in the past. Deformation behavior of the spherical tank and pipe braces was not clear against real ground motion. In addition, there are not many precedent studies done on the effectiveness of the reinforcement of pipe braced supporting frame against high-level ground motion. In this study, we conducted vibration tests using small models of spherical tank and examined non-linear response characteristics and failure mode due to plastic deformation. From the test results, it was concluded the effectiveness of reinforcement and the response characteristic of the pipe braced supporting frame of a spherical tank as follows; (1) The natural frequency indicates substantially the same value with or without reinforcement, because a large difference in the response characteristics of the whole structure was not observed. (2) In a case of brace intersection was reinforced, the maximum response acceleration increased at collapse. (3) In a case of brace intersection was reinforced there is no reinforcement to brace intersection, structural strength indicated the lowest at the load direction acting tensile force on long brace, cross section of long brace were deformed largely.