Fatigue evaluation of ship structures considering change in mean stress condition

Conventionally, the effects of mean stress on fatigue strength of welded structure are regarded to be small. However, based on fatigue damage experience occurring in ship structures, it is obvious that the effect of mean stress on fatigue strength should be large. This relates to the large change of mean stress condition associated with the change in loading conditions during ship operations. In this study, fatigue damage experienced in the end connections of side longitudinal stiffeners of single-hull very large crude oil carriers (SHVLCC) were investigated to understand the effects of mean stress on fatigue strength. The fatigue evaluation method which considers the effect of mean stress was also examined. This method was verified by the evaluation of existing data on fatigue tests and residual stress measurements. This method was confirmed to be effective in understanding the occurrence tendency of fatigue damage in ship structures by its evaluation. This method was applied to the example of actual fatigue damage in the end connections of side longitudinal stiffeners of midsize double-hull tanker to demonstrate the effectiveness of the method.