Distortional Buckling of CFS Stiffened Lipped Channel Compression Members

The direct strength method (DSM) simplified the design of cold-formed steel (CFS) beams and columns compared with the traditional effective width method (EWM). In this paper, DSM equations for the distortional buckling (DB) strength are evaluated using the results of the experimental study on channel compression members with edge and intermediate stiffeners as well as nonlinear finite-element analysis (FEA) of the stiffened lipped channel compression members with various configurations, which fail after only DB. A total of 14 fixed-ended stiffened lipped channel compression members with intermediate stiffeners in both the web and flanges were tested, which failed after only DB. Further, additional data on the DB behavior is generated based on a parametric study using the nonlinear FEA, which was initially calibrated with the test data. A study on effect of parameters, such as the type of cross section, the dimensions of the cross section, the lip depth to flange width ratio (d/b), the web height to the flange width ratio (h/b), the yield stress (fy), end boundary condition (EBC), and the failure modes, shows that the nondimensional ultimate strength, expressed as the ratio of the ultimate strength to yield strength under compression, Pu/Py, is adequately addressed through the nondimensional DB slenderness, d, alone as assumed in the DSM. The test and the analysis results show that the DSM equations generally evaluate the strength of stiffened lipped channel members under DB conservatively. Modifications to the DSM equations are suggested to evaluate the DB strength of stiffened lipped channel members more accurately.