LOCAL PLASTIC MECHANISMS IN THIN STEEL PLATES UNDER INPLANE COMPRESSION

Thin-walled steel plates subjected to in-plane compression develop two types of local plastic mechanism, namely the roof-shaped mechanism an d the so-called flip-disc mechanism, but the intriguing question of wh y two mechanisms should develop was not answered until recently. It wa s considered that the location of first yield point shifted from the c entre of the plate to the midpoint of the longitudinal edge depending on the b/t ratio, imperfection level, and yield stress of steel, which then decided the type of mechanism. This paper has verified this hypo thesis using analysis and laboratory experiments. An elastic analysis using Galerkin's method to solve Marguerre's equations was first used to determine the first yield point, based on which the local plastic m echanism/imperfection tolerance tables have been developed which give the type of mechanism as a function of bit ratio, imperfection level a nd yield stress of steel. Laboratory experiments of thin-walled column s verified the imperfection tolerance tables and thus indirectly the h ypothesis. Elastic and rigid-plastic curves were then used to predict the effect on the ultimate load due to the change of mechanism. A fini te element analysis of selected cases also confirmed the results from simple analyses and experiments. (C) 1997 Elsevier Science Ltd.