Numerical investigation of cold-formed steel top-hat purlins

This paper considers the use of cold-formed steel top-hat sections for purlins as an alternative to conventional zed-sections. The use of such top-hat sections may be viable for use in cold-formed steel portal framing systems, where both the frame spacing and purlin span may be smaller than in conventional hot-rolled steel portal frames. Furthermore, such sections are torsionally stiffer than zed- sections, and so have a greater resistance to lateral-torsional buckling. They also do not require the installation of anti-sag rods. The paper describes non-linear elasto plastic finite element analyses conducted on top-hat sections. The results of twenty-seven tests on four different top-hat sections are presented. Good agreement between experimental and finite element results is shown. The finite element model is then used for a parametric study to investigate the effect of different thicknesses and steel grades. Design recommendations are provided in the form of charts that can be used to assist designers when deciding which geometry of top-hat section to consider for further development. The use of the finite element method in this way exploits modern computational techniques for an otherwise difficult structural design problem and reduces the need for an expensive and time consuming full laboratory study, whilst maintaining realistic and safe coverage of the important structural design issues.