Experimental Investigation of CFS Unequal Plain Angle Compression Members

Global buckling modes of cold-formed steel (CFS) unequal-leg plain angle (UPA) compression members are flexural-torsional buckling (FTB) modes due to their nonsymmetric cross section. Although the behavior of CFS equal plain angle (EPA) members under axial compression has been studied extensively, only limited studies in the literature have investigated CFS-UPA members. The results of an experimental study of CFS-UPA specimens under axial compression with fixed support conditions are presented in this paper. This is the first experimental investigation of CFS-UPA compression members in which the postbuckling strength in the FTB mode and global-global interaction between the first two FTB modes (denoted FT1-FT2 interaction) are demonstrated. The test specimens were grouped into three categories-Test A, Test B, and Test C-based on the elastic FTB load ratios of the first two modes (P-crft2/P-crft1), corresponding to low (P-crft2/P-crft1>50), medium (5<P-crft2/P-crft1<7), and high (P-crft2/P-crft1<5) FT1-FT2 interaction, respectively. The postbuckling strength of the FT1 mode decreases as P-crft2/P-crft1 decreases due to FT1-FT2 interaction. The design methods available in the literature were evaluated using the experimental results. The current effective width method and direct strength method are conservative, whereas a procedure proposed in the literature accurately estimates the strength of CFS-UPA members.