Local–overall interactive buckling of welded stainless steel box section compression members

• Interactive buckling tests on eight welded stainless steel box section columns.
• Numerical modelling and systematic parametric studies were carried out.
• Assessment of existing design methods by the generated test and numerical results.
• Modifications to the current EN 1993-1-4 design curves and the DSM are proposed.

The interaction between local and overall buckling of welded stainless steel columns has been investigated experimentally and numerically in this study. Eight stainless steel box section compression members were fabricated from slender hot-rolled plates. The material properties and welding residual stress patterns in the test specimens had been obtained previously. Initial geometric imperfections, both local and global, were accurately measured prior to the tests. The test specimens were axially loaded between two pin-ended supports, and both local plate buckling and overall flexural buckling featured visibly in the observed failure modes. Finite element (FE) models were also set up using the ABAQUS software package to conduct numerical simulations, which were initially validated by means of comparison with the experimental data. Using the validated FE models, parametric studies were carried out to assess the influence of the key input parameters, such as the residual stresses, the material strain hardening exponent and non-dimensional proof stress, geometric imperfections and slenderness ratios. Existing design methods, including the design provisions of Eurocode 3 Part 1.4, the design proposal of Rasmussen and Rondal, the direct strength method (DSM) for cold-formed carbon steel and two revisions thereof, were all evaluated against the obtained test and numerical results. It was revealed that the EN 1993-1-4 buckling curves, which do not differ with grade, provide reasonable average strength predictions, but tend to slightly overpredict the local–overall buckling resistances of welded austenitic stainless steel members and slightly underestimate those of duplex stainless steel members. Furthermore, the three considered DSM design curves, all of which were developed on the basis of structural performance data from cold-formed sections, provide generally unconservative strength predictions for welded stainless steel sections. Based on the generated data points, modifications to the current EN 1993-1-4 provisions and the DSM have been proposed, which offer more accurate strength predictions for local–overall interactive buckling resistances of welded stainless steel box section columns.