Proposal of a design curve for the overall resistance of cold formed RHS and SHS members

Possible inaccuracies and conservatism in the design against the local and local+global buckling of slender square (SHS) and rectangular (RHS) hollow‐sections is currently hindering the construction sector from a wider application of high‐strength steel (HSS) and slender hollow sections. Eurocode and other design provisions define class 4 at a cross‐section slenderness > 42ε (compression only) with ε2=235/fy. Thus, a significant number of SHS and RHS with fy ≥ 690 MPa – both cold formed and hot‐finished – are considered to be slender and consequently penalized. Besides that, the classification approach itself presents discontinuities in the estimation of the buckling reduction factor, whereas a design curve ranging from the plastic to the slender range would be more efficient and cost‐effective both for steel producers and designers. This paper discusses the results of an extensive numerical campaign, showing that the Eurocode 3 classification is too conservative in the case of SHS and RHS. The local buckling and local+global buckling behaviour will be analysed through an extensive parametric FEM‐model study. The gathered data are collated, and the resulting design curve is a proposal for the determination of an overall buckling reduction factor for the determination of the member resistance. The study represents one of the steps of the RFCS research project “HOLLOSSTAB”, during which new design rules for HSS hollow sections are developed on the basis of an “Overall Interaction Concept” (OIC). The paper discusses the effectiveness of this approach in the general framework of buckling design checks for hollow sections, discusses existing rules and their implications, shows the numerical campaign results and introduces overall design formulas based on the overall buckling resistance approach