Flexural-torsional buckling strength of thin-walled channel sections with warping restraint

This paper presents the details of an experimental and numerical study on the effect of warping on the flexural-torsional buckling (FTB) behaviour of axially loaded cold-formed steel lipped channel members. Eleven controlled experiments on two different lipped channel sections are conducted with simply-supported flexural end conditions. A unique scheme of compression loading is evolved, which allows the ends of the member to warp freely. Experimental investigations reveal that warping end conditions play a significant role in the compressive strength and failure modes. The results from the experiments are used to calibrate the numerical model developed using ABAQUS. Parametric studies are conducted on different cross-section sizes of the members to quantify the effect of warping restraint on the FTB strength under compression. Results are compared with the current AISI S100–16 specification using both the effective width method (EWM) and the direct strength method (DSM). The comparison of results reveals that for warping restrained condition, the present DSM framework based on the finite strip method (FSM) predicts FTB strength conservatively. A possible correction factors are identified for members with warping restrained ends, which can be applied over the traditional strength curve in DSM. A reliability study is also carried out on the modified design procedure for the FTB strength of CFS members.