Hybrid tubular joints featuring topology-optimised DED-Arc nodes

• Hybrid X-joints with conventional CHS tubes and optimised DED-Arc nodes have been proposed. • A design-to-manufacture framework, encompassing topology optimisation and reengineering for manufacturability, has been developed. • Conventional and hybrid joint specimens have been tested under different chord-brace load combinations. • Hybrid joints with 3D-printed components showed disproportionate increases in capacity and stiffness over conventionally-welded joints. Relative to conventional formative or subtractive manufacturing techniques, additive manufacturing (AM) offers increased geometric freedom, and the potential for enhanced structural efficiency and greater automation. Hybrid construction, which combines conventionally produced structural components with AM parts, is considered the most practical way to deploy metal AM in construction. This study aims to develop an optimisation methodology for hybrid tubular joints, incorporating topology optimisation and printability considerations. The studied tubular joints have an X-shaped configuration, comprising conventionally produced circular hollow section (CHS) members and wire-arc directed energy deposited (DED-Arc) nodes. The DED-Arc nodes were topology optimised, with performance and printability enhanced by imposing stress and overhang constraints, preventing the formation of overly slender elements and excessive overhang angles. The printability was further improved by manual adjustments to satisfy manufacturing requirements. The structural performance of the hybrid joints, including the initial stiffness, ultimate load-bearing capacity, ductility and material efficiency, was assessed through geometrically and materially nonlinear numerical analyses and physical experiments on nine printed joints; five conventional X-joints were also fabricated and tested to provide benchmark results. Overall, the hybrid joints exhibited up to about 80 % higher initial stiffness, 20 % higher load-bearing capacity and 100 % higher capacity-to-mass ratios under biaxial compression compared with the conventionally produced joints, indicating markedly enhanced structural efficiency.