Simplified semi-analytical model for elastic distortional buckling prediction of cold-formed steel flexural members

The expressions for elastic distortional buckling stress predictions available in literature are used with reasonable accuracy, but are either iterative or involve increased calculation effort for design. It is an accepted fact among researchers that these expressions are not evaluated enough for the distortional stress prediction of sections with complex lip stiffeners. In this paper, a candidate model for distortional buckling stress predictions is presented which is semi analytical in nature and is simple to incorporate in the direct strength method (DSM) of cold-formed steel design. The proposed expression incorporates the effect of complex lip stiffeners on the elastic distortional buckling capacities of cold formed steel flexural members. In the proposed model, the (i) translational stiffness at lip-flange junction and (ii) rotational stiffness at the flange-web junction, are derived from regression analysis of wide range of cross sectional dimensions. The proposed method is calibrated with semi-analytical finite strip method presented in the literature and this formulation has been demonstrated to be good in comparison with recently published numerical based distortional buckling predictions.