3D printing in construction: Wire Arc Additive Manufacturing for steel structural engineering applications

Digitalisation and automation are driving adoption of Additive Manufacturing in the construction sector. Among metal AM technologies, Wire Arc Additive Manufacturing (WAAM) offers high deposition rates and geometric flexibility, enabling the production of large-scale, structurally efficient elements. However, process-induced geometric irregularities affect the mechanical response of WAAM elements and must be characterised to ensure reliable structural design. This research investigates WAAM for tubular and lattice structural elements through a structural design for WAAM approach developed for structural engineering applications. The research establishes a concept-to-certification workflow for WAAM, defining a structured path from design conception to certification of both the process and the structural elements. Within this framework, the structural design for WAAM approach integrates process constraints, geometric irregularities, and material behaviour into the design phase and is implemented for both layer-by-layer and dot-by-dot WAAM deposition strategies. A novel tubular section for steel structural elements produced using layer-by-layer WAAM, the Tubular Sandwich Section (TSS), is then designed. Its geometric freedom enhances structural performance, with potential for higher buckling resistance under radial compression compared with an equivalent-area Circular Hollow Section. An experimental campaign addresses geometric, defect, and mechanical characterisation, supported by finite element analyses assessing sensitivity to geometric imperfections. Manufacturability is demonstrated through the fabrication of prototypes using ER70S-6 wire, and environmental performance is evaluated. The structural design for WAAM approach is further applied to dot-by-dot deposition to optimise steel lattice-based geometries, developing novel Diamond lattice structural elements. The influence of process parameters on the geometric and mechanical characterisation of single rods, and the influence of nodal intersections on mechanical behaviour, are assessed for specimens manufactured using ER70S-6 wire. Correction factors are calibrated from parametric finite element analyses to guide the structural design. Experimental testing of unit cells is compared with numerical predictions, highlighting the role of geometric imperfections in post-yield behaviour.