Estimation of ultimate strength of ring-stiffened cylindrical shells under external pressure with local shell buckling or torsional buckling of stiffeners

This study discusses the ultimate strength and collapse behavior of ring-stiffened cylindrical shells under external pressure with local shell buckling or torsional buckling of stiffeners. In past studies, the effect of initial deflection shape on the ultimate strength has not been completely elucidated. Additionally, a clarification of the collapse behavior and theoretical formulation based on it has not yet been reached. Therefore, in this study, the influence of the initial deflection shape is investigated using eigenmodes obtained from the elastic buckling eigenvalue analysis and the hungry-horse mode described by a simple equation. Then, the ultimate strength analyses of 432 models of ring-stiffened cylindrical shells with various dimensions are carried out using the nonlinear finite element method. From the analysis, the collapse modes are classified into five categories, namely, the shell buckling (SB) collapse (localized mode SB-1 and uniform deformation mode SB-2), the torsional buckling (TB) collapse (localized mode TB-1 and uniform deformation mode TB-2), and the combined shell-torsional buckling collapse. A new slenderness ratio is proposed using the formula for strength when the circumferential stress reaches yield stress, and the formula for the elastic buckling strength developed previously by the authors. Then, theoretical formulas for the ultimate strength are developed using the slenderness ratio, which can rationally estimate the strength.