Stiffness recovery in steel bridge components repaired by wire arc additive manufacturing

Repairing existing steel structures rather than replacing them offers substantial environmental and economic benefits. Wire Arc Additive Manufacturing (WAAM) is a promising route for the on-site repair of damaged structural elements, with greater geometric flexibility than conventional techniques. This study investigates, at proof-of-concept level, the automated repair of part-through damage in steel components. Repairs were produced by depositing AM316L stainless steel wire onto C40 substrates by Cold Metal Transfer welding, following longitudinal and transverse deposition strategies. The elastic response was characterised by tensile tests with fullfield Digital Image Correlation (DIC) on a pilot series of four specimens, one milled reference and three repaired coupons. All repaired specimens recovered or exceeded the apparent elastic stiffness of the reference, with continuous strain fields across the repair interface. Finite element models calibrated against the DIC data supported these findings and enabled a parametric evaluation of damage depth on repair efficiency. On this basis, a conceptual WAAM repair methodology for fatigue-cracked steel bridge girders is proposed, targeting the restoration of static elastic stiffness after damage removal. Simulations of a representative composite bridge cross-section showed that the repair restored local stiffness and reduced principal stresses, closely approaching the behaviour of the undamaged structure. Within the elastic regime investigated, and with the trends from a four-specimen series regarded as indicative, these results establish a proof-of-concept for the automated WAAM repair of damaged steel bridge components and provide a calibrated numerical framework for extending it to full-scale details.