Hybrid steel tubular T-joints featuring 3D printed components: optimisation and experimental verification

Wire-arc directed energy deposition (DED-Arc) is well suited to the fabrication of optimised structural connections that often feature intricate geometries with more efficient material distribution for load transfer. In this study, hybrid tubular T-joints featuring DED-Arc components are, for the first time, optimised, manufactured and tested. Topology optimisation was applied to the brace-to-chord junction, with continuous conventional chords retained and DED-Arc-specific fabrication constraints addressed. The optimised designs were initially assessed through nonlinear finite element (FE) analysis, after which seven hybrid and four conventionally welded square hollow section (SHS) T-joints were fabricated and tested under brace compression. The hybrid joints achieved significantly improved structural performance and material efficiency over their benchmark counterparts, driven by two key mechanisms: (1) redistribution of load toward the SHS chord sidewalls, and (2) extension of the effective loading length along the chord, enabled by the optimised DED-Arc components. The greatest gains occurred in joints whose benchmarks exhibited chord face failure and high chord cross-sectional slenderness, with stiffness increases of up to around 2000% and capacity increases of up to almost 500%. These results demonstrate the feasibility and advantages of the hybrid DED-Arc concept integrated with the proposed optimisation workflow and its potential for scalable deployment in efficient and sustainable steel structures.