Study on Collapse Characteristics of Cylinder-to-Cylinder Intersections by Inelastic Finite Element Analysis

It is known that the collapse strength of complex three-dimensional structures cannot be evaluated accurately with elastic analysis, and more accurate results require the use of inelastic analysis. A typical example is cylinder-to-cylinder intersection. In this paper, the relationship of collapse loads and local primary membrane stresses of cylinder-to-cylinder intersections was examined. First, elastic analysis of the cylinder-to-cylinder intersections with various combinations of diameter and thickness under internal pressure was conducted. The local primary membrane stress (P_L) obtained from the analysis was normalized by the general primary membrane stress (P_m) the ratio of P_L/P_m defining the Stress Intensification Factor (SIF). The results revealed that SIF was directly influenced by the geometries. Secondly, limit load analysis was conducted on the same structures and the collapse pressure was obtained. The Collapse Strength Reduction Factor (CSRF) defined as the ratio of the run pipe collapse pressure to the cylinder-to-cylinder collapse pressure was proposed. The CSRF was also found to be influenced by the geometries. Comparing the result of SIF with CSRF, it is clear that the evaluation by SIF is overly-conservative and the proposed concept of CSRF provides more accurate evaluation of the cylinder-to-cylinder intersections. Furthermore, the basic data for the intersections with uniform thickness can also be applied to the reinforced intersections.