Optimisation and testing of wire arc additively manufactured steel stub columns

Wire arc additive manufacturing (WAAM), a method of directed energy deposition (DED) for metal 3D printing, is capable of producing intricate parts at a relatively high rate and low cost. Despite the great potential of WAAM for applications in construction, knowledge of the performance of WAAM structural elements is still lacking, and the geometric freedom is yet to be fully harnessed. This study is therefore aimed at investigating the local buckling behaviour of carbon steel WAAM elements and exploring the opportunity for improved structural efficiency through optimisation. An optimisation study was initially conducted to derive optimal stiffener layouts for square hollow sections (SHS) under compression. A total of six plain SHS with a broad range of width-to-thickness ratios, along with two SHS strengthened with optimised stiffeners, were manufactured via WAAM and tested. The six benchmark WAAM SHS profiles were examined to allow direct comparisons with conventionally-produced SHS. 3D laser-scanning was carried out to capture the geometric features of the WAAM specimens, and digital image correlation (DIC) was adopted for the full-field measurement of their structural responses during testing. The WAAM SHS stub columns were shown to have comparable load-carrying capacities to conventionally-produced SHS in the stocky range, but exhibited inferior local buckling behaviour in the slender range. Comparisons with the Eurocode 3 (EC3) resistance predictions showed that the existing Class 3 slenderness limit and effective width method specified in EC3 for plated structures may be overly optimistic for WAAM steel elements owing to their typically larger geometric imperfections. Finally, the SHS strengthened with optimised stiffeners were shown to exhibit significantly improved structural efficiency over both the WAAM and conventionally-manufactured plain SHS, bringing disproportionate increases in load-carrying and deformation capacity relative to the increases in mass.