The reliability of structural systems undergoing progressive fatigue damage at several joints is investigated. Two methods for fatigue system reliability are proposed. The first method is based on failure path approach. The failure sequences leading to system failure are initially identified and system failure probability is computed as the probability of the union of all these sequences. The second method uses order statistics to determine the smallest failure time of the system thus eliminating the many permutations and repetitive calculations necessary in the previous method.; The developed methods are applied to study the fatigue reliability of Tension Leg Platform (TLP) tendon system. TLP collapse due to progressive failure of a group of tendons without repair program, as well as progressive failure of tendons during and after repair of first failed tendon is considered. The effects on system safety of uncertainties and correlation of joint fatigue lives, redundancy and system configuration (number of tendons per leg, and number of joints per tendon) are studied.; Inspections of selected joints are also included in the analysis in order to evaluate its impact on system reliability. Two approximate methods based on order statistics are presented for evaluating the updated system failure probability based on information obtained from inspections of several joints.; Finally, a 3-D model of a TLP is used to investigated the effect of interaction between tendon failures in different legs, and of long term wind and wave directionality. Uncertainties in the environmental model are included in the analysis and order statistics combined wih failure path method are applied in the solution of the problem.
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