Time-variant Reliability Analysis Of Maintained Ship Hull Girder Subjected To Corrosion And Fatigue

A time-variant reliability formulation is presented in this paper to account for the effects of fatigue, corrosion and maintenance actions on the first yield reliability of midship section modulus. A probabilistic model for long-term distribution of wave-induced fatigue stress range is established. For the purpose of obtaining the performance of structure that stands random fatigue load, the concept of stress parameter and equivalent stress range are introduced. The propagation of fatigue crack is predicted by applying the Paris-Erdogan equation. The effects of corrosion can be evaluated quantitatively by introducing an appropriate simple probabilistic model for the generation and progress of corrosion. The Ferry-Borges load combination method is applied to combine the stochastic processes of stillwater and wave bending moments, and the failure of ship hull girder occurs when the combined value of stillwater and wave bending moments exceeds the first yield bending moment. The formulation has been applied to a bulk carrier which sails in the North Atlantic Ocean. Furthermore, the effects of maintenance actions in increasing the reliability level of ship hull girder are analyzed. It shows that the degradation effects of fatigue and corrosion have important influence on the safety of ship structure, especially after the ship has put into service for 10 years. And the detailed inspection should be done at this time to maintain the reliability level of ship hull girder.The purpose of this analysis is to provide some valuable suggestion for risk assessment of ship hull and the plan for maintenance actions.