Numerical Studies of Collapse Behaviour of Multi-Span Beams with Cold Formed Sigma Sections

Multi-span cold-formed steel beams are widely used for roof purlin and cladding rails due to their high strength to weight ratio and ease of installation on site. There are a wide variety of cross-sectional shapes e.g. C, Z, top hat and sigma sections. A sigma section possesses several advantages such as high cross-sectional resistances and large torsional rigidities compared with standard Z or C sections. Traditional design methods for cold-formed multi-span steel beams have been based on elastic theory, such as the Effective Width Method (EWM) and the Direct Strength Method (DSM). Both methods ignore the effect of redistribution of moments on the ultimate failure load. A Pseudo-Plastic Design Method (PPDM) has been recently proposed for statically indeterminate structures in order to improve the efficiency of the methods. This method is analogical to conventional plastic design theory by introducing a pseudo-plastic moment resistance (PPMR) to allow for the benefit of redistribution of moments. The objective of this paper is to summarize the efforts in numerical validation of the PPDM method used in the continuous beams. A series of finite element models are described to examine the collapse behaviour of multi-span cold-formed beam systems. Parametric studies are carried out to investigate the influence of geometric dimensions on the collapse behaviours. Comparisons are made between different design methods and laboratory tests for determining the ultimate load, demonstrating that the PPDM method can lead to more economical result when compared with traditional design methods