Local-Plate and Distortional Postbuckling Behavior of Cold-Formed Steel Lipped Channel Columns with Intermediate Stiffeners

This paper reports a detailed investigation concerning the local-plate and distortional elastic postbuckling behaviors of coldformed steel lipped channel columns with web and flange intermediate stiffeners (the corresponding unstiffened lipped channel column postbuckling behaviors are often used as reference). This investigation relies on results obtained through geometrically nonlinear analyses based on a recently developed and numerically implemented generalized beam theory (GBT) formulation that incorporates (1) conventional (no shear deformation), (2) shear (nonlinear warping), and (3) transverse extension deformation modes. The numerical results shown provide the evolution, along a given local-plate or distortional postbuckling equilibrium path, of the column (1) deformed configuration and (2) relevant displacement profiles and/or stress distributions— mostly for validation purposes, some of them are compared with values yielded by shell finite element analyses performed by means of the code ABAQUS. In order to assess the influence of the member end support conditions, the paper also includes a comparison between the distortional postbuckling behaviors of columns with pinned / free-to-warp and fixed / warpingprevented end sections. Taking full advantage of the GBT unique modal features, all the above results are discussed in great detail and it becomes possible to unveil, explain, and/or shed some new light on several interesting and scarcely known behavioral aspects. In particular, one is able to provide illuminating and structurally (mechanically) meaningful explanations for the qualitative differences exhibited by the local-plate and distortional postbuckling behaviors of plain and stiffened (web and flanges) lipped channel columns.