In marine structures, fatigue is typically the dominant limit state. The fatigue resistance of welded joints in steel marine structures is a critical aspect of ensuring the structural integrity and safety of the components. To determine the structural response, finite element method is necessary to evaluate structural stress. For thin-wall structures, shell element model is usually preferred to solid element model, because the former can save time in calculations. In order to study the effect of weld modeling in shell model, the structural stress levels of the shell model in both the as-welded and unwelded cases are investigated respectively, using the solid element model results for reference purposes. The first chapter is the introduction and the second chapter is literature survey of state-of-the-art research. Chapter 3 and chapter 4 focus on the structural stress estimation with respect to frame-stiffener structure and stiffener-plate structure. The traction forces based procedure is clarified and applied to evaluate HS structural stress. In consequence, the preliminary conclusion on the influence of weld modeling on the structural stress of the shell model is obtained.

Apart from that, fatigue resistance data for arc-welded joints are typically derived from small-scale specimens. However, structural aspects can affect fatigue resistance characteristics. Therefore, to validate whether the fatigue resistance observed in small-scale specimens accurately represents that of full-scale structure, similarity research is necessary. In Chapter 5, the effective notch stress of large-scale specimens is evaluated. Fatigue failure criteria are discussed to derive the appropriate lifetime. Finally, the LSS fatigue resistance data evaluated by the effective notch concept are substituted into SSS fatigue resistance scatter band, to validate the similarity between SSS and LSS.