The structural behaviour of a bolted, flanged connection subjected to a cyclic load

The results of an elastic-plastic bi-dimensional finite element analysis for a bolted flange in a boiling water reactor vessel are presented. The calculations were performed by the finite element program ADINA using the incremental-iteration technique. The aim was to follow the stress and the strain of a bolted flange subjected to a cyclic load, consisting of four steps: the bolt load; the pressure load with decreasing of bolt load; depressurisation with increasing bolt load; and, at the end, unbolting. Numerical analysis can clarify our knowledge in this field, where the ASME III Code NB-3228 rules are obtained from an analytical computation for simple structure, using over-simplified assumptions on material constitutive equations, such as perfect plasticity. (U.K.)