Analysis to determine flexural buckling of cold-formed steel built-up back-to-back section columns

In the current AISI standard, the modified slenderness method (MSM) is proposed for the design of cold-formed steel (CFS) built-up columns. According to the available literature, such a method has been extensively adopted in hot-rolled steel research, and usually generates very conservative strength estimates. Nonetheless, there are few corresponding theoretical studies into CFS built-up columns. In this situation, this paper presents a new analytical approach to establish a computing method for the flexural buckling bearing capacity of the CFS built-up back-to-back section column. To achieve this goal, a new flexural buckling model is proposed to establish the kinematic relationship of single profiles. In addition, shear panels are employed at the location of screws to consider the discrete shear deformation restraint effect. The shear rigidity of the shear panels is determined using the cross-sectional shear stress transfer path. Then, based on the energy method, a computing method is derived. Further, simplifications are made to the formula to allow easier use in practical engineering situations. To verify the derived formula a finite-element model (FEM) is developed and validated using the available test results. Then, based on the developed FEM, parametric studies are conducted to verify the derived formula. In addition, the performance of the derived formula is further verified by comparing the corresponding ultimate strength based on the direct strength method (DSM) expressions using available test results and FEM parametric studies. The comparison and validation results show the following: (i) the derived formula can predict the critical flexural buckling load as well as the corresponding budding strength based on the DSM expression, and (ii) with an increase in screw spacing, the MSM will result in very conservative strength estimates for CFS built-up back-to-back section columns. (C) 2019 Elsevier Ltd. All rights reserved.