Application of Elastic-Plastic Hinge Method to Up-lift Behavior of Flat-Bottom of Cylindrical Tank subject to Seismic Excitation: 5th Report

Oil storage tanks are usually constructed directly on tank foundations without anchors. In such a flat-bottom cylindrical tank subject to seismic horizontal force, a part of the bottom plate adjacent to the shell will be lifted off the tank foundation by the overturning moment, and excessive plastic strain cyclically occurs at the toe of the inside fillet weld of the shell-to-bottom joint. Previously, expanding the basic theory of Elastic-Plastic Hinge Method (E.P.H.M.) to uplift behavior of flat-bottom of cylindrical tank, the authors proposed the analytical method to evaluate the integrity of annular plate adjacent to the shell from the viewpoint of seismic design, and calculations were carried out for a 32,000kl oil storage tank of high strength steel SPV490Q2)6). Furthermore, the equilibrium equations in consideration of 2 elastic-plastic hinges of uplifted bottom plate for the elastic sidewall tank were formulated, considering nonlinear M～ϕ relationship based on elastic-plastic beam theory (Relation-Ⅰ). Then, calculations are carried out for 32,000kl/18,200kl oil storage tanks, and the effectiveness of this method was shown by comparing it with results of FEM non-linear axisymmetric analysis7)8). In this paper, the effect of large deflection of uplifted bottom plate is taken into consideration based on the finite deformation theory of strap, and the method (E.P.H.M.) is expanded for the analysis on uplift behavior of flat-bottom of tank with large deflection.