Finite Element Analysis for Bifurcation Buckling of Conical Roof Shells Subjected to Dynamic Internal Pressure

摘要

Cylindrical tanks with conical roof shells are utilized as oil storage tanks and for some containment vessels. It is known that conical roof shells and torispherical shells subjected to static internal pressure buckle into a displaced shape with circumferential waves caused by an instability condition commonly called bifurcation buckling [1]. It can be important to obtain the dynamic bifurcation buckling load in designing conical roof shells. We calculated the bifurcation buckling pressure for dynamic pressure during accident conditions as characterized by step pressure loading, ramp pressure loading and pulse pressure loading. The minimum bifurcation buckling pressure was shown to be a linear function of radius-to-thickness ratio R/h of the shell in a linear fashion on a logarithmic scale. It is important to calculate dynamic buckling pressure for designing the storage tanks. A lot of conical roof shells are designed by the equation based on the American Petroleum Institute (API) standard 650.In the present paper, the finite element analyses of the minimum bifurcation buckling pressure for effects of a yield stress, a radius-to-thickness ratio and an angle of roof are performed. The shells of revolution for bifurcation buckling are formulated in the FE analysis. We compare the numerical results with calculated results based on the American Petroleum Institute (API) standard 650. It is consider that the failure internal pressure of API 650 and the results of FEM are related across each other. Then both safe and unsafe pressures for dynamic analysis are given by the equation of the API 650 for designing the storage tanks.