Flexural buckling performance and capacity of recycled 6061-T6 aluminium alloy square hollow section columns

Aluminium alloys have been increasingly used in civil engineering, due to their high strength-to-weight ratio, excellent corrosion resistance and full recyclability. With the growing number of aluminium alloy structures approaching the end of their service life, reprocessing the resulting aluminium alloy scrap into recycled aluminium alloys provides a promising pathway towards sustainable and circular construction practices. This paper experimentally and numerically investigates the flexural buckling behaviour and resistances of recycled 6061-T6 aluminium alloy square hollow section (SHS) columns. Twelve column specimens with different recycled content ratios (30%, 50% and 80%) and member non-dimensional slendernesses (ranging from 0.51 to 1.15) were prepared and tested under pin-ended boundary conditions. Afterwards, finite element models were developed to replicate the experimental observations. Through parametric studies, additional numerical data were generated, and the influences of the recycled content ratios were analysed. The results showed that (i) the recycled content ratios affected the flexural buckling behaviour of recycled 6061-T6 aluminium alloy SHS columns, mainly owing to the differences in material properties, (ii) the influence of the recycled content ratios on the flexural buckling resistances was found to be more pronounced at shorter effective member lengths, and (iii) the mid-height lateral deflections at the failure loads decreased with the recycled content ratios, with this trend generally remaining consistent across different effective member lengths. Design analyses were then performed, where the applicability of the relevant design rules for primary 6061-T6 aluminium alloy SHS columns, as specified in the European code, Aluminium Design Manual and Australian/New Zealand standard, was evaluated based on the obtained test and numerical data. It was revealed from the evaluation results that the three design codes generally resulted in accurate and consistent flexural buckling resistance predictions for recycled 6061-T6 aluminium alloy SHS columns, though many resistances were overestimated by the Australian/New Zealand standard.