A study on the scantling formulae of a stiffener against lateral pressure under the simultaneous action of axial load

Stiffeners support lateral pressure and axial load and are one of the essential members of a ship structure composed of stiffened panels. Their scantling formulae are important to ensure adequate strength against lateral pressure and for the rapid and proper initial design of hull structures. However, the current rule scantling formulae are based on the elastic beam formulation, and the effect of the simultaneous axial stress is considered differently by the rule as a coefficient for reducing the allowable stress. In this study, based on the fully plastic moment under the action of axial stress, the stiffener bending strength corresponding to the plastic hinge formation criteria (initial hinge and plastic collapse) was determined using simple theoretical formulae considering the additional lateral force induced by the axial stress on the deflected stiffener. Subsequently, the structural behaviors were investigated comprehensively by theoretical parametric studies based on various stiffener scantlings and loading combinations, which were further compared with the results of finite element analysis (FEA) based on the residual deflection criterion, thereby verifying the validity of the theoretical proposals. Consequently, by combining the findings from the theoretical and numerical investigations, the effect of the axial stress on the stiffener bending strength was expressed as closed-form coefficients. These proposed axial stress coefficients were verified to govern the actual structural behaviors well and are expected to provide a rational basis and contribute to improving rule-scantling formulae.