Fatigue assessment of welded trapezoidal joints of a very fast ferry subjected to combined load

This work deals with the fatigue assessment of a very fast ferry, describing several steps of the calculation. Considering the analysis of wave and cargo induced loads, the ship’s hull structure is evaluated on both global and local levels. The local structure is represented by a longitudinal stiffener with a trapezoidal transverse section. The critical point of concern is located at the middle of the span between two transverse frames where the longitudinal trapezoidal stiffener is connected by a backing strip plate. A detailed finite element analysis determines the critical hotspots and the stress distributions. The stiffener is considered to be subjected to axial forces due to the ship’s hull girder vertical bending moments and by additional transverse force due to the presence of a truck load. Finally the fatigue damage assessment of the considered hotspot is analyzed accounting for the combination of low- and high-frequency induced loading.