Local buckling of stainless steel stub columns with novel octagonal hollow sections

Octagonal hollow section, a novel type of polygonal hollow sections, combines the advantages of traditional circular and rectangular hollow sections while mitigating their limitations, with higher load-carrying capacities over rectangular hollow sections due to smaller plate element widths and better constructability over circular hollow sections owing to multiple flat faces providing operation platforms for welded and bolted connections. The present paper reports experimental and numerical studies on the local buckling behaviour of stainless steel octagonal hollow sections under axial compression. The testing programme included axial compression tests on fifteen stainless steel octagonal hollow section stub column specimens with five different outer cross-section dimensions and three different wall thicknesses, as well as tensile coupon tests and initial local geometric imperfection measurements. In parallel with the testing programme, a numerical modelling programme was carried out, with finite element models developed and validated against the test results and afterwards adopted to carry out parametric studies. The test and numerical data were used to evaluate the applicability of relevant design rules, as specified in the European code, American specification and ASCE standard, to stainless steel octagonal hollow sections. The evaluation results generally revealed that (i) the three sets of codified slenderness limits were unsafe when used for cross-section classification of stainless steel hexagonal hollow sections, (ii) the European code and American specification resulted in overall accurate and consistent cross-section compression resistance predictions for stainless steel octagonal hollow sections, but still with some overly conservative predictions for non-slender cross-sections and slightly unsafe predictions for those at the boundary of non-slender and slender cross-sections, and (iii) the ASCE standard provided overall scattered and inaccurate cross-section compression resistance predictions. Finally, improved slenderness limits for the three considered design codes and a revised ASCE design approach for predicting cross-section compression resistances were proposed.