An optimization strategy for wide stiffened plates subject to interaction of local and overall buckling

Abstract A strategy for minimum weight design of axially compressed stiffened panels is presented. It is first noted that the ‘naive’ criterion of simultaneous buckling in the local and overall modes, is not applicable in view of the severe imperfection-sensitivity of such designs. Imperfections are admitted and the required maximum capacity is viewed as the limit point of the nonlinear structure. The interaction of local and overall buckling—the central feature of the behavior of the panels—is accounted for by a well tested analytical model which incorporates amplitude modulation and the influence of secondary local mode(s). The optimization technique employed is based on Powell's algorithm (VMCON). A systematic approach has been developed for the selection of the trial section. This is based on appropriately ‘beefing up’ and separating the critical stresses of a preliminary section obtained using the ‘naive’ criterion. A reduced model is developed by utilizing the patterns of overall deformation and amplitude modulation obtained from the nonlinear analysis of the trial section. A potential energy expression is developed in terms of the geometric parameters and four degrees of freedom. The algorithm was found to be extremely efficient from the points of view of both computational ease and accuracy. It is found that the configuration of the optimum panel with blade-type stiffeners lies in a transition from ‘thin’ to ‘stocky’ stiffener range. The weight of the optimized panel is sensitivie to initial imperfections and can vary over a range of 20% due to moderate level of imperfections commonly assumed in the analyses. The weight of optimal panels with given values of the aspect ratios vary over a wide range and the careful selection of the width of the panel holds the key for successful optimal design.