Fire design of slender cold-formed lipped channel and sigma section members with uniform temperature under compression

Steel structural elements with cold-formed thin-walled sections are increasingly common in building structures due to their high strength-weight ratio. These elements can provide adequate resistance to different action efforts, such as bending, axial compression, or compression and bending. Lipped channel sections are the most commonly used sections because the application of sigma sections increase due to their lower slenderness walls. When designing these cold-formed steel profiles, local, distortional and global buckling are key failure modes that should be considered, as these instability phenomena are more susceptible to occur under fire conditions. After validating numerical models at elevated temperatures with experimental tests, this paper presents a parametric study of the lipped channel and sigma cross-section columns in the case of fire, considering different steel grades and cross-section slenderness values. Comparisons are made between the numerical results and analytical design rules from EN1993-1-2 using Annex E and its French National Annex, where a different constitutive law is recommended explicitly for cold-formed steel profiles. It is possible to conclude that Eurocode's simple calculation rules are too conservative and sometimes unsafe. Therefore, to increase the accuracy of existing design formulae, new adjustments to the current fire design rules were developed for these profiles.