Bending Stiffness Requirement for Closed-Section Longitudinal Stiffeners of Isotropic Material Plates under Uniaxial Compression

Longitudinally stiffened plates with closed-section ribs are supposed to be an effective system for axially compressed members. However, current design specifications on closed-section ribs, particularly for the minimum required stiffness, are not sufficient, and thus, excessive designs are quite common because of the absence of suitable design guides. In this paper, simple closed-form formulas for the minimum required stiffness of compressively loaded isotropic plates braced by U-shaped longitudinal stiffeners (U-ribs) are derived. The effects of the sectional stiffness of U-ribs on the buckling modes and strengths of stiffened plates are examined by numerical analyses. Three-dimensional finite-element models of U-rib stiffened plates were obtained, and a series of eigenvalue analyses was conducted. By parametric study, thresholds of the sectional stiffness of U-ribs that may be adopted as the minimum requirement were collected, and these were used for regression analysis to obtain a simple and practical design equation for determining a suitable sectional stiffness after conducting a comparative study using a theoretically derived formula. The findings of this study would contribute to improving the optimum design of U-rib-stiffened plates.