APPLICATION OF STRUCTURAL SYSTEM RELIABILITY ANALYSIS TO OFFSHORE STRUCTURES (PROBABILITY, FAILURE)

Structural reliability analysis has significantly evolved during the last decade. In particular, the so-called First Order Reliability Methods have proven to be useful tools, and they now form the basis of most recently developed structural codes. However, those applications deal mainly with structural components reliability as opposed to structural system reliability.; The focus of this thesis is on the applicability of new First Order System Reliability Methods to the analysis and design of structural systems, in particular offshore structures, under extreme loading conditions. After a review of those methods and a presentation of the probabilistic environmental model used for extreme loading definition, the applicability is demonstrated on two different types of offshore structures. The first type is the Tension Leg Platform, a new type of platform for which experience is almost totally lacking, especially regarding its critical tensioning system. The second type of structure is the steel jacket platform, currently the most common type of offshore structure, for which our main concern is the truss system supporting the platform. A special Branch and Bound search algorithm is developed to find the most likely failure modes of such a system.; In both cases the applicability is demonstrated by showing that structural system reliability analysis can successfully be used: (1) to compare alternatives and perform parametric studies that can help a designer make decisions based on reliability considerations, (2) to identify critical components and study the effective redundancy of a structure, (3) to assess the overall reliability of a given structure.; Most important of all is that, by allowing failure modes correlation to be accounted for, First Order System Reliability Methods lead to a good understanding of structural redundancy, a key element in structural analysis and design. In particular the common belief that adding components in parallel increases the redundancy is put in perspective.