Pseudo-plastic moment resistance of continuous beams with cold-formed sigma sections at internal supports: A numerical study

Most thin-walled steel sections exhibit a softening moment–rotation characteristic under bending, and as a result, an elastic method of analysis and design is usually recommended for continuous beams with this type of section. A more economical design approach, the pseudo-plastic design method, has been proposed to allow for the development of moment redistribution in the system. One key to this design method is to determine the pseudo-plastic moment resistance (PPMR) at internal supports. This paper reports a numerical study on the pre-buckling, buckling, post-buckling and post-failure behaviours of continuous beams with cold-formed sigma sections near internal supports, based on which the PPMR was derived. Detailed information on input parameters required in the numerical modelling process, such as the choice of element type, element size, loading and boundary conditions, material properties, initial imperfections and the selection of solution scheme, are presented. The developed numerical model was validated by 20 laboratory tests. It was then applied to carry out parametric studies to investigate the influence of geometric dimensions (e.g., the depth and the thickness of the cross-section and the span) on the failure mode, the ultimate moment resistance and the PPMR of sigma beams at internal supports. Numerical results of ultimate moment resistance were compared with theoretical predictions obtained using two codified methods, i.e., the Effective Width Method (EWM) and the Direct Strength Method (DSM). The difference in predictions from numerical simulations and codified methods was studied, which was followed by suggestions for improvement in using codified methods. Finally, a semi-empirical approach has also been proposed to determine the PPMR of cold-formed steel Sigma beams at internal supports.

► A pseudo-plastic design method for continuous cold-formed steel sigma beams.
► FEA numerical model.
► Buckling, post-buckling and post-failure behaviour of continuous beams.
► Ultimate moment resistance of sigma beams under the concentrated load.
► Pseudo-plastic moment resistance of cold-formed steel beams at internal supports.