The reliability of offshore structures under ultimate load conditions is considered under a potentially diverse load process scenario. An "outcrossing" formulation in which. the loads are modeled as processes rather than only as random variables is developed in the (hyper-) polar co-ordinate space. This has distinct advantages for problems, such as involving offshore structures, for which the structural analysis for safety checking is complex (e.g., requiring a finite element analysis or dynamic analysis etc.).
Offshore structures are major structures and involve very significant capital expenses and operating costs. They also have significant potential for failure or malfunction as history has already amply demonstrated. It is appropriate, therefore, to address the issues of risk and reliability, the factors that govern them and procedures for their calculation. Attention will be restricted herein to risk of structural failure. An offshore platform is a base for potentially dangerous. operations in a hostile environment. The factors involved include loadings (wave, wind, ice, operational, temperature, live and dead); the resistance of the elements of the structure and their interaction effects (e.g, strength, fatigue strength, overall stability, foundation behaviour and strength); the workmanship, seamanship and operational competence of those involved in design, construction and operation. The information which is available about these matters is uncertain to various degrees, particularly in relation to loadings, and this must be properly taken into account in reliability analysis (c[Melchers, 1987, 1989a). Details of how this might be done are beyond the scope of this paper. Herein it will be assumed that probabilistic descriptions. are available or can be hypothesized (perhaps with the use of Bayes theorem). The approach will be probabilistic, considered by many the only rational choice for decision-making (e.g., Lindley, 1985).