ON BOUNDS AND APPROXIMATIONS IN STRUCTURAL SYSTEMS RELIABILITY

Four aspects of structural systems reliability are considered. These are: (a) bounds on structural systems reliability for systems loaded with a sequence of independent loadings. It is found the the Ditlevsen bounds for a structure under one set of loads can be extended to a sequence of loadings; (b) the use of the static theorem of plasticity to evaluate system reliability using first order, second moment theory. It is shown that unless all equilibrium equations are considered, the correct solution for system reliability will not be obtained; (c) the use of the static theorem of plasticity to evaluate system reliability using a simplification obtained by assuming that plastic moment capacities are perfectly correlated. It is demonstrated that this is not a gross assumption for a simple structure; (d) an approximate systems reliability calculation procedure based on integrating in the load space using the observation that the hyper volume over which integration is to be performed is usually fairly regular in shape. This then leads to two suggested avenues of approach for simplified analysis. (Author/TRRL)