The Interaction Between Strength and Fatigue Reliability for a Minimum Structure in Shallow Water

Abstract

The relationship between strength and fatigue reliability of an offshore platform is an important aspect in the setting of appropriate structural inspection programs, as well as providing valuable information when considering the life extension of ageing offshore structures. This paper uses the example of a braced monopod to examine the interaction between strength and fatigue reliability for shallow-water platforms subjected to wave climates typical of the North West Shelf of Australia. The central role played by the local wave climate in both the strength and fatigue response of the structure is investigated. The probability of fatigue failure at the critical location was found to be approximately three orders of magnitude less than the overall probability of storm overload failure. This inequity between strength and fatigue reliability raises the possibility of redirecting inspection effort toward higher-risk threats such as accidental damage and corrosion. The potential for further optimizing the total life-cycle costs of new offshore structures is also briefly discussed.