Calculated and prescribed stress concentration factors of ship side longitudinal connections

Stress concentration factors (SCFs) of typical details of the connection of the side shell longitudinals and the web frame stiffeners are among the most important issues of ship fatigue analysis. Classification societies propose pre-defined values of SCFs, obtained by experimental analysis and a limited number of finite element (FE) calculations on similar details. In this paper, SCFs are calculated by the FE method, using shell elements and are then compared with their prescribed values according to the rules of classification societies. FE analysis is performed for various configurations of the detail that may appear in practice. A simplified procedure for calculating fatigue life is employed and discrepancies in calculated fatigue life caused by differences in SCFs are assessed. The methodology of calculating SCFs is verified based on the FE analysis of details with derived target hot spot stress and corrected SCFs are thus obtained. Influence of the correction of SCFs on the fatigue life is discussed. Different procedures for extrapolating stresses to the weld toe are considered and the resulting SCFs are compared with the values proposed by rules of classification societies. The results of the study may be used in the harmonization process of ship structural rules and within fatigue reliability analyses. Another obvious motivation for this paper is that nowadays a detailed FEA can be carried out in most design offices and the presented results may help to enhance such applications.