Fatigue Failure Risk Assessment for a Maintained Stiffener-Frame Welded Structure with Multiple Site Cracks

Abstract

A probabilistic approach is proposed here for the failure risk assessment of a welded ship structure with respect to fatigue damage caused by multiple site cracks. The initiation and propagation of fatigue cracks often occurs at weld toes while a welded structure is subjected to alternating loading. To account for the interaction of multiple fatigue cracks and inherent uncertainties in fatigue crack growth process, a probabilistic model for fatigue crack growth is developed based on the Paris law. The probabilities of fatigue failure of multiple cracks in the welded structure are estimated by using the reliability analysis. Then, the failure risk assessment for the welded structure with multiple site cracks is performed based on the fatigue reliability estimation. As the service life of ship structures is usually very long, in-service maintenance activities for the locations of critical fatigue damage in ship structures are actually necessary to ensure the integrity of structures. The failure risk associated with fatigue crack growth can be updated through inspections and repairs based on the probabilistic model of damage detection. The effects of in-service inspection quality and frequency are investigated with respect to the risk assessment of structural fatigue failure.