Numerical investigation of the flexural-torsional behaviour of built-up cold-formed steel beams

• A technique for the accurate finite element modelling of built-up cold-formed steel beams is presented. The technique considers the modelling of discrete fasteners and contact between component sections. • A comprehensive parametric study is presented of built-up cold-formed steel beams of different cross-sections, including open and closed, and lengths. A range of fastener stiffnesses and spacings are included in the study to determine the influence of these parameters on the strength and failure mode(s) of the beams. • The parametric study provides a database of ultimate strengths covering a wide range of cross-section types and failure modes, including in-plane bending, flexural-torsional buckling, local buckling, distortional buckling and combinations of these modes. The database can be used to derive design strength equations for built-up cold-formed steel beams. This study examines the structural behaviour of built-up cold-formed steel (CFS) beams with and without lateral bracings, failing under four-point bending due to various buckling modes. The numerical models are developed using the Finite Element (FE) software ABAQUS 6.13. The models are discretised with S4R elements, end conditions are modelled as simply supported, and non-linear analyses are conducted which include material, geometric and contact non-linearities as well as geometric imperfections. The numerical models are validated by means of comparisons with published experimental results in terms of moment capacities, moment versus deflection curves and failure modes. Subsequently, using the verified FE models, a parametric study is carried out for different cross-section geometries and different thicknesses by varying the fastener spacings and fastener shear stiffness. The paper draws conclusions about the effectiveness of varying the fastener parameters for different built-up cross-sections, and presents a comprehensive database of ultimate strengths towards deriving design strength curves.