Parametric study on cold-formed steel built-up columns using direct strength method

Abstract

The use of built-up cold-formed channels in the metal lightweight industry increases for higher strengths offers in comparison with a single-channel section. However, their unavailability of design guidelines determining the axial strength had made most researchers seeking to formulate new designs rules for different built-up sections. This research aims to convey parametric study on built-up columns using a proposed Approach based on the direct strength method for further knowledge and to understand the behavior of cold-formed steel built-up columns. For that a nonlinear finite element was developed to perform a parametric study, a total of 93 finite elements models were analyzed to study the effects of the cross-section, the gap between the two channels, the spacing between battens, the addition of web stiffener, the angle variation in C-sections simple lip edge stiffener, different lengths of the profiles and the ratio (d/D), on the stability of built-up columns. An approach based on the direct strength method (DSM) was proposed, where elastic, local, distortional or global elastic buckling solutions are determined from finite element or finite strip procedures. The obtained results were compared with the current design standard the North American specifications and the Australia/New Zealand codes, the AISI specifications, and European code EC3. The results of the parametric study were compared with the values found by AISI, EC3 and proposed DSM approaches, it stated that, the design specification noted in the AISI are generally conservative for overall buckling mode and slightly conservative for local buckling mode columns. For EC3 specifications, there is a difference between open and closed sections. For open sections, the results are conservative for local buckling mode and slightly conservative for global buckling mode. For the proposed DSM approaches, the results are slightly conservative for global buckling columns and non-conservative for local buckling mode columns.