Novel hybrid sleeve connections between 3D printed and conventional tubular steel elements

Metal additive manufacturing, or metal 3D printing, is an emerging technology within the construction sector that is suitable for hybrid use with conventional manufacturing methods to maximise its benefits. In this context, a novel sleeve connection between metal 3D printed parts and conventionally produced circular hollow section (CHS) members for use in hybrid tubular structures is proposed and experimentally verified in the present study. Hot-finished S355 steel CHS profiles were adopted, while the 3D printed parts were produced by cold metal transfer (CMT)-based wire arc additive manufacturing (WAAM) using ER70S feedstock material. The geometric features of the WAAM specimens were analysed based on 3D laser scan data. Tensile tests on two as-built coupon specimens were carried out to examine the mechanical properties of the printed material. A total of nine hybrid sleeve connection specimens with a variety of bolt layouts were then examined. Initial free rotations in the connections were firstly measured, and their structural performances under axial tension were determined through tensile testing. Digital image correlation (DIC) was employed in both the material and connection tests for full-field measurements of strain and displacement. The examined hybrid sleeve connection specimens exhibited different failure modes (i.e. shear-out and net section fracture in the WAAM parts) and in general, excellent tensile load-carrying and deformation capacities. Compared with the obtained test results, the EC3 resistance predictions were shown to be overly conservative for shear-out failure, but can be optimistic in the cases of net section fracture. Future research is needed to improve the EC3 design rules for hybrid sleeve connections.