Consequence and uncertainty-informed fatigue life prediction of ships

Abstract

Currently, fatigue life prediction of steel welded joints in ships is carried out using class rules and guidance, e.g. DNV-CG-0129. Such methods use a lower bound of the S-N curve. A Design Fatigue Factor (DFF) is suggested in DNV-RP-C203 as a safety factor to the fatigue life for locations that require a higher reliability level. It does not include model and modelling uncertainties. Therefore, this paper provides a framework to select an effective fatigue (FAT) class based on a probabilistic approach at a reliability level appropriate to the uncertainty in design and consequence of failure of the detail. This is offered as a more transparent alternative to the application of a DFF. The designer can perform the fatigue analysis with limited additional effort, whilst obtaining a reliable fatigue life prediction that can ultimately result in improved designs and fewer premature repairs.