Postbuckling of Stiffened Panels Using Strut, Strip, and Finite Element Methods

Postbuckling results are presented for isotropic stiffened panels loaded in compression. Comparisons are made between single-bay and double-bay finite element (FE) models (where "bay" denotes a repeating portion, between supports, in the load/length direction) and a new strut model, following a Shanley-type approach, for single-bay and multibay panels. The strut model has been incorporated within the strip program VIPASA with CONstraints and OPTimization (VICONOPT) to design a multibay example panel with postbuckling reserve of strength in its skins, assuming linear elastic material properties. The panel has been shown by VICONOPT to have a stiffener buckling failure mode when an overall sinusoidal imperfection causing increased stiffener compression is present. The failure is confirmed by the double-bay FE model, which is shown to be an imperfect representation of the multibay case. Single-bay analysis using the strut model shows good agreement with the single-bay FE results. The VICONOPT code is able to design a metallic panel of realistic dimensions and loading using 50 strip elements (compared with the 9600 shell elements required by the finite element model) but cannot correctly account for material nonlinearity. The important phenomenological difference between postbuckling of single-, double-, and multibay panel models are indicated. [PUBLICATION ABSTRACT]