Systems Reliability Approach to Fatigue of Structures

In structural reliability under fatigue, the basic event is section failure. It is defined in terms of the time to develop a through-thickness crack at the critical hot spot in the section. Correction factors account for the fact that the crack may occur at a site other than the critical hot spot and that section failure occurs sometime after development of a through-thickness crack. After failure, the section is assumed to be "severed." The branch-and-bound algorithm is used to identify important sequences of section failures leading to collapse, and structure failure is approximated as the event that one of these important sequences occurs. Efficient first-order reliability methods are used for probability computations. The procedure is applied to an offshore platform. Significant systems effects are observed, i.e., the probability of structure collapse is much smaller than the probability of failure of an individual section. The use of inspection observations in updating reliability estimates also is presented.