Fatigue Reliability of Maintained Welded Joints in the Side Shell of Tankers

Abstract

A formulation is presented for the assessment of the reliability of a local ship hull structure regarding fatigue failure. The potential cracks are considered to occur in the side shell, in the connections between longitudinal stiffeners and transverse web frame. The analysis is performed for T-shaped stiffeners. The model accounts for the crack growth process applying linear elastic fracture mechanics. The long-term stress range acting on the elements is defined as a function of the local transverse pressure of internal cargo and outside water, combined with the stresses resulting from the longitudinal bending of the hull. The global hull loading is a combination of horizontal and vertical bending moments. The present paper analyzes the importance of including the transverse pressure loading for the process of the crack growth and also the distribution of the net section area of midship and location of stiffeners. The formulation has been applied to a tanker. The fatigue reliability is predicted by a time variant formulation and the effects of maintenance actions in updating the reliability assessment are shown.