Fatigue assessment of bulb stiffener joints according to local approaches

This paper deals with the fatigue strength assessment of attachments of bulb plate stiffeners (Holland profile), typical of ship structures, applying local approaches proposed by the International Institute of Welding (IIW) and in open literature. The application of these methods in the captioned cases is not always straightforward nor sometimes possible, neither effective. Difficulties in following the suggestions of IIW for the finite element (FE) modelling of relatively complex geometries are shown. Basically, the bulb itself is a three-dimensional component interacting with two-dimensional shells surrounding it: the three-dimensional versus two-dimensional mismatch is the main source of complexity. Since a reference thickness of the bulb cannot be identified, even the identification of stress points in post-processing of FE analyses is difficult, often being a cause of scatter and/or disagreement among different approaches. Comparisons among approaches and with available experimental data of tests carried out in the Ship Structures Laboratory of the University of Genova and in the Institute of Ship Structural Design and Analysis of the Hamburg University of Technology provide a general view of this topic and offer a critical review of the application of local approaches in rather challenging test cases, evaluating, as far as possible, effects of weld geometry on fatigue strength.