Simulation of flexural behaviour and design of cold-formed steel closed built-up beams composed of two sigma sections for local buckling

Abstract This study focused on the structural behaviour of cold-formed steel (CFS) closed Built-up beams composed of two sigma sections primarily fail due to local buckling under four-point bending about the major axis. It is aimed to establish accurate finite element models for CFS built-up I-beam subjected to a transverse load. The numerical model was developed by using Finite Element (FE) software ABAQUS 6.13. The numerical models were discretized with S4R element, end condition as simply supported and non-linear analysis which includes material, geometric, contact non-linearities and geometric imperfections. The numerical model is validated by means of comparison with the experimental results published in the literature in terms of moment capacities, moment versus deflection curve and failure mode of specimens. For different cross-section geometries and different thickness of the built-up closed beam, the numerical parametric study has been carried out by using the verified FE model, and the obtained flexural resistances were compared with those predicted by using current DSM and DSM proposed for built-up beams. The moment capacity decreases with increase in compression flange width to thickness ratio. In general, the moment of resistance of the section increases with decreasing the aspect ratio. There is no significant effect in flexural strength of the built-up closed beams due to the change in depth of web stiffener. Based on the comparison of results, suitable modifications are proposed herein for DSM, especially for the closed built-up beams made of two sigma sections normally failed by local buckling and also the performance of the current DSM, DSM proposed for built-up beams and the DSM proposed by this study are assessed by reliability analysis.