Large‐scale experimental investigation of a novel Fe‐SMA‐UHPFRC strengthening system for bridges

This paper proposes a new prestressed method for flexural strengthening of reinforced concrete bridges, which consists of casting a layer of ultra‐high performance fibre reinforced concrete with embedded iron‐based shape memory alloy (Fe‐SMA) bars over an existing reinforced concrete bridge deck. The system makes use of smart alloys’ ability to generate internal stresses, therefore actively unloading the parent structure upon installation. To evaluate the feasibility and performance of the new system, experiments were conducted on large‐scale 2.5 m cantilever slabs involving sequential testing stages, in which the slabs were first loaded to service levels to induce a cracked state prior to strengthening. The performance of the novel system was compared to non‐prestressed alternatives. Distributed fibre optical sensors were installed along the reinforcing steel bars, and digital image correlation was used, for strain and crack monitoring, respectively. While all strengthening methods more than doubled the load‐bearing capacity of the slabs, the prestressed method also significantly improved their performance under service loads. Following the activation of the Fe‐SMA bars, which were heated up to 200°C using resistive heating, the preloading deflections fully recovered, with existing cracks closing by more than 50 %, and the stresses in the internal steel were substantially reduced.