CFS Columns Under Buckling Interaction: Direct Strength Method Generalised Approach

AbstractCold‐Formed Steel (CFS) members are highly susceptible to several structural instability phenomena, involving either individual (Local – L, Distortional – D and Global – G) or interaction (LD, LG, DG, and LDG) buckling modes. The buckling mode interaction of CFS columns and beams may lead to strength erosion compared to isolated modes and must be considered in structural design. The North American, Australian/New Zealand and Brazilian standards incorporated the Direct Strength Method (DSM) that provides accurate design approach for columns and beams affected by L, D, G, and LG buckling modes. Moreover, the coupled LD, DG, and LDG buckling modes are not currently considered in the DSM and many research projects have been focused on these topics. The procedure adopted by DSM estimates the CFS member strength through experimentally calibrated design strength curves, considering the relationship between the member elastic stability and the steel yielding property. In this context, the present paper presents the main results of the investigation, based on both experimental and finite element method numerical results, that conducted to calibrated Winter‐type strength curves for CFS columns covering LD, DG, and LDG buckling modes. To take into account the effect of the buckling modes interaction, the proposed procedure for design purposes incorporates the slenderness factors ratio RλDL = λD/λL and λG/ λmaxLD, with λmaxLD = max {λL, λD} and λL, λD, λG as the local, distortional and global slenderness factors, respectively.