Behaviour and design of stainless steel SHS and RHS beam-columns

Abstract

Previous studies on stainless steel tubular section beam-columns have revealed shortcomings in established codified design methods. These shortcomings stem principally from inaccurate predictions of the bending and column buckling end points of the design interaction curves, where the bending moment end points are tied to the elastic or plastic moment capacities without considering strain hardening, while the column buckling end points are often over-predicted. Inaccuracies also arise due to the adopted interaction factors, which do not fully capture the structural response of the stainless steel members under combined loading. These observations prompted the present research, which is aimed at developing more efficient design rules for stainless steel tubular section beam-columns. In the presented design proposals, the deformation-based continuous strength method (CSM), allowing for strain hardening, was used to determine the bending moment capacities (i.e. the bending end points), while the column buckling strengths (i.e. the column end points) were calculated according to recently proposed buckling curves. Based on these more accurate end points, new interaction factors were derived following a comprehensive numerical simulation programme. The accuracy of the new proposals was assessed through comparisons against over 3000 experimental and numerical results. Compared to the current design standards, the new proposal yields a higher level of accuracy and consistency in the prediction of stainless steel square and rectangular hollow section (SHS and RHS) beam-column strengths. Use of the proposed interaction factors but with the Eurocode bending moment capacities and revised column buckling strengths as the end points was also assessed and shown to result in more accurate and less scattered strength predictions than the current Eurocode provisions. The reliability of the proposals has been confirmed by means of statistical analyses according to EN 1990, demonstrating its suitability for incorporation into future revisions of international design codes for stainless steel structures.