DSM-Based Design Proposal for CFS Columns Failing in Local-Distortional Interactive Modes

Cold-formed steel (CFS) members invariably display very slender thin-walled open cross-sections, a feature responsible for their high susceptibility to individual (local - L, distortional - D, global - G) or coupled (L-G, L-D, D-G, L-D-G) buckling phenomena. Nowadays, it is consensual amongst the technical/scientific community the need to have efficient design approaches to handle interactive failures, a goal that has long been achieved for L-G ones, in both cold-formed and hot-rolled steel members. Concerning interactive failures involving distortional buckling, virtually exclusive of CFS members, the situation is completely different and the development of adequate design approaches requires in-depth knowledge about the response of members affected by the coupling phenomenon considered. In CFS columns undergoing L-D interaction, such knowledge already exists, mainly due to the authors' efforts. Thus, it may be argued that only the development and codification of a design approach are lacking.

This work proposes an efficient design approach, based on the Direct Strength Method (DSM), for CFS columns failing in L-D interactive modes. The development, calibration and validation of this proposal, which is intended for codification, is based on available experimental and numerical failure load data concerning columns with several cross-section shapes (plain, web-stiffened and web-flange-stiffened lipped channels, hat, zed and rack-sections). Three types of L-D interactive failures are covered, namely those due to "true", "secondary-local bifurcation" and "secondary-distortional bifurcation" L-D interactions. The accuracy and reliability of the proposed DSM-based design approach are assessed and compared with those exhibited by the existing methodologies to design CFS columns against L-D interactive failures.

Learning Objectives:
Awareness and understanding of the relevance of interactive failures in the design of open-section cold-formed steel columns.

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