Elastic Bifurcation, Postbuckling Behavior, and Collapse of Thin-Walled Regular Polygonal Columns

This paper summarizes recent findings concerning the elastic bifurcation and postbuckling behaviors of thin-walled regular convex polygonal tubes subjected to uniform compression. Such cross sections exhibit rotational symmetry, a feature that is at the root of several behavioral peculiarities, which are demonstrated using a specialization of Generalized Beam Theory (GBT). In particular, it is shown that (1) duplicate bifurcation loads can occur both in linear stability analyses and postbuckling analyses; (2) local or distortional buckling can be critical, depending on the cross-section geometry; (3) the pure local postbuckling behavior is very similar to that of simply supported plates under uniaxial compression; (4) the pure distortional postbuckling behavior has no postcritical strength and is imperfection-sensitive; and (5) the unstable nature of distortional buckling generates an unstable local-distortional interaction even if the distortional critical load is well above the local one. For comparison and validation purposes, results obtained with finite strips and shell finite-element models are reported.