Strength evaluation of intersection between stiffeners and primary supporting members considering the effect of shear force on the primary member web

The intersection between stiffeners and primary supporting members is one of the most critical details in ship hull structures. Learning from the lessons of actual damages experienced in the past, many formulae to estimate stresses around the slot cut-out structures have been developed. However, good agreement with finite element analysis or experiments has not been achieved, and the formulae have been used with empirical correction coefficient, introduced using actual damage and no-damage records or calibration based on finite element analysis results. In this study, the authors develop a consistent theoretical formula taking account of all the structural components affecting the load share of each member, in combination with the combined load effect of direct force from the longitudinal stiffener and shear force on the primary supporting member. The derived formula was verified through comparison with the results of finite element analysis and past experiments, and good accuracy was confirmed. Then, using the proposed theoretical formula, various parametric studies are carried out, and effective countermeasures to enhance the strength of slot cut-out structures are discussed. Finally, critical review on IACS CSR formulae on the slot cut-out structures is conducted. Because the rules take account of only the direct load from the longitudinal stiffeners, and do not consider the effect of the shear force on the primary supporting member, it is probable that the rules give insufficient strength when the effect of the shear force on the primary supporting member superimposes the effect of the load from the longitudinal stiffener. On the other hand, the rules may be too conservative when they cancel each other. It is shown that rational evaluation of the strength of slot cut-out structure is possible using the proposed theoretical formula.