Weld Root Fatigue Assessment of Fillet-Welded Structures Based on Structural Stresses

The problem of fatigue cracking is particularly significant for large welded plate structures being typical for ships and floating offshore structures. Here, fillet welding is applied to a large extent to join structural components. This leads to non-fused root faces, which can behave like initial cracks. In several cases the situation is even worse, when welding can be performed from one side only, resulting in a highly-stressed weld root on the other side. Although refined approaches exist for a fatigue assessment of such weld roots, for instance the crack propagation and the notch stress approaches, more practical approaches requiring less effort are demanded to handle typical problems occurring in practice. These problems are associated with locally increased load transfer, e.g. at crossing support structures and at fillet welded ends of attachments with additional stress concentrations. Also, pronounced bending can occur in fillet welds due to lateral loading of the attachment and/or the eccentricity of one-sided welds. In the paper, practical approaches for such problems are presented which have been developed in the recent past in different research projects and which are based on a structural stress or a local nominal stress in the weld. Their application is demonstrated by several examples taken from ship and offshore structures using relatively coarse finite element meshes for the stress analyses.