Design and Engineering

The Liffey Viaduct was constructed between 1872 and 1877 for the Great Southern and Western Railways. The bridge has seven spans, with three approach masonry arches on each side and a central span of lattice girders which carries two railway lines.

The abutments are 7.5m in height from the top of the foundation to the springing of the side arches. The soffit of the central lattice girder is at a height of the top of the voussoirs in the crown of the side spans. The side spans are 5m in width and have semi-circular arches. The central span measures 34m and both the abutments and smaller side piers are provided with cutwaters.

From the original drawing it is not clear what type of foundations have been used though they seem to have been founded on rock without piles. The main girders are of wrought iron riveted construction. At either end of the span the lattice girders are resting on cast iron bearings on a flat masonry surface. There is no bracing across the line between the top of the lattice girders which would help prevent sway and vibration. A longitudinal camber is visible in the bridge which is most unusual for a truss girder bridge. The abutments would appear to have been built in a cofferdam as, on the south side, timber sheet piles are visible around it.