Elastic-Plastic Buckling Of Ring-Stiffened Cone-Cylinder Intersections Under Internal Pressure

Cone large end-to-cylinder intersections, simply referred to as cone-cylinder intersections, are commonly used in pressure vessels and piping. The intersection is subject to a large circumferential compressive force under internal pressure. It is often convenient and necessary to reinforce these intersections using an annular plate ring stiffener. Under this large circumferential compression, these intersections may fail by elastic buckling, plastic buckling or plastic collapse. This thesis investigates the elastic-plastic buckling behavior and practical calculation method of ring-stiffened cone-cylinder intersections under internal pressure.Reasonable finite element models were established using the commercial finite-element package ANSYS. Linear eigenvalue buckling analyses (LEA) were performed to study the bifurcation buckling loads and buckling modes of the intersections using the whole model. Geometrically and materially nonlinear analyses (GMNA) were carried out to examine the load-deformation response of the intersection using half-wave sector model. A method for the determination of plastic bifurcation buckling load was proposed based on the load-deformation response curves of several key nodes.The elastic-plastic buckling behavior of ring-stiffened cone-cylinder intersections under internal pressure have been thoroughly investigated. Some geometric parameters have obvious effects to elastic-plastic buckling strength and buckling mode of ring-stiffened cone-cylinder intersections, such as the radius-to-thickness ratios of the shell, the width-to-thickness ratios of the annular plate ring, and the cone apex half angle. Two buckling modes are identified through a wide range of parametric analyses: a shell mode for thin intersections with a shallow cone (a cone with its apex half angleapproaching 90°) and/or a relatively stocky ring stiffener, and a ring mode for other cases. An existing plastic buckling approximation for annular plate rings in steel silos is found to be applicable to the intersection when it buckles in the ring mode. New approximate design equations are also established for the shell mode based on the effective area method.The effects of the non-uniform thickness intersections and initial geometrical imperfections to the strength of ring-stiffened cone-cylinder intersections were also carried out. As the ring thickness increases, the ring buckling strength enhances and the buckling mode changes from shell mode to ring mode. Eigenmode-affine imperfections were introduced in GMNA of ring-stiffened cone-cylinder intersections to examine the effects of initial geometrical imperfections on the stability behavior of the structure. In general, the ring-stiffened cone-cylinder intersections are not sensitive to eigenmode-affine imperfections but the effect is unfavourable.