Structural reliability analysis of a seafastening structure for sea transport of heavy objects

Abstract

This paper addresses the safety of marine operations related to a seafastening system for large-object transport. The aim is to present a structural reliability approach to accommodate the uncertainties affecting design checks. The probability of structural failure by use of design standards for assessing marine operations is studied using structural reliability analyses to shed light on the implicit reliability levels of such standards. A structural reliability model that includes the effect of uncertainty in weather forecasts is established. The reliability analyses show that the method to account for forecast uncertainty as defined in the standards compensates well for that uncertainty, and the failure probabilities in the case studies are between 10−4 and 10−3 per operation. A reliability model that includes the long-term statistical distribution of the environmental conditions is also established. This model is applicable for operations with a duration longer than three days and is used to study seasonal variations and the failure probability as a function of the duration of operations. The failure probability is calculated for execution in several months, showing the dependency on the time of the year and the duration of the operations. The failure probabilities are on the order of 10−4 per operation.