Post-Buckling Shear Strength of Thin Steel Plates

Thin walled steel members, such as cold-formed steel (CFS) members, are susceptible for local buckling at low loads. However, initiation of local buckling of elements does not necessarily mean the ultimate limit state of the member, and thin-walled plate elements can exhibit substantial post-buckling strength. International cold-formed steel design specifications recognize the post-buckling strength of uniformly compressed stiffened and unstiffened elements, and the post-buckling strength of stiffened and unstiffened webs in flexure. However, potential post-buckling shear strength of webs is not considered in CFS design specifications, though post-buckling shear strength of stiffened webs is considered in structural steel plate girder design. The objective of this study is to quantify the post-buckling shear strength of thin-walled cold-formed steel members. This numerical investigation is based on finite element method.This paper presents the finite element modelling details associated with the thick/thin plates representing the web of a cold-formed steel member. The study considered simply-supported rectangular plates subjected to in-plane shear loadings experiencing buckling, post-buckling, and yielding until failure. The plate was modelled using geometrically non-linear quadrilateral shell elements, and non-linear steel stress-strain relationship derived from experiments. Total Langrangian with large displacement/small strain formulation was used for such analyses. The model also considered the initial geometric imperfections. The first part of the investigation established the ultimate shear strength of plates having different parametric dimensions. The next part compared such results with the strength values based on the current code provisions. For slender plates, the current code uses the shear buckling load as the strength, whereas the analyses indicated significant post-buckling strength. The third part of this paper establishes the shear design equations incorporating the post-buckling strength of plates.