The rehabilitation of short span masonry arch highway bridges using near-surface reinforcement

Near-surface reinforcement has been developed as a minimum intervention, minimum disruption repair or strengthening technique for masonry arch bridges and similar structures. It involves installing small diameter stainless steel reinforcing bars, typically 6mm to 12mm in diameter, into pre-cut grooves or pre-drilled holes in the near-surface zones of the bridge that are likely to be subject to tensile stress. The principal aims of adding reinforcement are to improve flexural crack control, increase flexural and shear strength and to increase robustness and ductility. Typically the reinforcement is installed in the readily accessible surfaces, i.e. the intrados (or soffit) of the arch barrel and the exposed faces of the piers, abutments, spandrels, parapets and wingwalls. This paper summarises the results of a series of tests carried out on 2.95m span clay brick arches in the laboratory. The results of the research were used when designing the strengthening works for a single span arch bridge constructed in the late 18th century to span the Kennet and Avon Canal at Hungerford in Southern England. An innovative feature of this project, which is also briefly described in the paper, is that the longitudinal steel reinforcement was installed in holes that were pre-drilled into the soffit of the arch barrel to follow the line of the arch using a directed drilling technique. The strengthening scheme was given an Historic Bridge and Infrastructure Award by the Institution of Civil Engineers.