Abercorn Bridge – An Innovative Approach to Bridge Remediation

Abercorn Bridge was built in 1932. It is located in Newtownstewart, Northern Ireland and is a ‘Hennebique Ferro’ integral reinforced concrete 4 span viaduct. The structure, being of the order of 84 years old, was showing... [ view full abstract ]

Abercorn Bridge was built in 1932. It is located in Newtownstewart, Northern Ireland and is a ‘Hennebique Ferro’ integral reinforced concrete 4 span viaduct. The structure, being of the order of 84 years old, was showing signs of significant deterioration, so much so that one span was recommended for demolition due to its particularly poor condition. However, an alternative solution was proposed which offered to: retain all four spans; retain the overall aesthetics of the bridge; restore additional load capacity; preserve the bridge for at least a further 25 years; and reduce refurbishment costs. The alternative solution was adopted. Detailed inspection and testing of the bridge provided an accurate view of the bridge’s condition thus allowing a concrete repair scheme, incorporating cathodic protection, to be designed. A finite element analysis (FEA) model was created to allow the bridge to be more rigorously analysed, particularly comparing its as-built, deteriorated state and refurbished conditions. Importantly, the FEA model indicated that the repair scheme on its own was not sufficient to restore the required load capacity and an innovative, lightweight, structural over-slab was incorporated. This “bespoke” over-slab was among the first such projects to use a combination of basalt reinforcement and lightweight aggregate concrete to create a strong yet lightweight slab. To increase the confidence of the alternative, innovative solution, Fibre Bragg Grating (FBG) sensors were used to: monitor the bridge during repairs; ensure the structural behaviour was consistent with the FEA model; and confirm that the over-slab was working integrally with the bridge deck beneath. A final load test was undertaken on completion of the Works to ensure that the required load capacity had been achieved. This paper describes in more detail the remediation process.