A semi-analytical procedure for global postbuckling analysis of stiffened panels under longitudinal compressive load is derived. Based on the observations from nonlinear finite element solutions, deflections for plate, stiffener webs and flanges are assumed. The deflections are coupled such that the displacement continuity is ensured. All energy formulations are derived analytically. A reduced stiffness distribution for stiffener-plate combination is assumed to take into account the effect of stiffener inelastic behavior. A set of equations from the Ritz method is solved numerically. The stresses in certain critical points on plate are checked using the von Mises yield criterion, and the onset of yielding is taken as an estimate of the ultimate strength for design purpose. Various computations are performed using the proposed model, and comparisons with nonlinear finite element methods demonstrate that the results are accurate.
Because of their simplicity in fabrication and excellent strength to weight ratio, steel stiffened panels find wide applications in ships and offshore structures. The structural design criteria to prevent the ultimate limit state of stiffened panels are based mainly on inelastic buckling. Due to difficulties in the experimental investigation of inelastic buckling, there is not much experimental data regarding the ultimate strength of stiffened panels. The preferred tool for evaluating the ultimate strength of stiffened panels is now nonlinear finite element (FE) analysis. The work presented in this paper is to develop improved numerical methods for overall collapse mode of stiffened panels based on FE investigations. The observations from FE investigations lead to the hypothesis that for a stiffened panel subjected to longitudinal compression, collapse very often involves a combination of overall collapse and beam-column (stiffener-induced) collapse. In regard to deformed shape, the collapse mode is still overall collapse.