Structural failure of compact tubes in bending

This paper presents a plastic mechanism analysis for compact circular hollow section (CHS) tubes deforming in a kink collapse mode under large deformation pure bending. The fold formation process was such that the shell curvature flattened on the compression side transforming into two large flat triangles attached to each other. The collapse proceeded progressively by folding about the base and sides of these two triangles. An expression for the plastic collapse moment was obtained by equating the total energy absorbed in bending and flattening to the external work carried out during deformation of the tube. Comparisons of the predicted post-buckling moments and slopes of the collapse curves with those obtained from experiments carried out by the author on cold-formed circular hollow sections show very good agreement. Existing analytical models are assessed using the newly derived theory.