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Client: Railway Procurement Agency
Contractor: Graham Project
Value: €11m

The William Dargan Bridge carries LUAS Line B (Green Line) across the very busy Taney Junction in Dundrum, south Dublin. The junction has been significantly enlarged since the original bridge, carrying the old Harcourt Line, was removed in the nineteen sixties.

Roughan & O'Donovan were appointed by the light Rail Project Office (now the Railway Procurement Agency, RPA) to carry out a Feasibility Study, Preliminary & Detailed Design and construction supervision of a cable-stayed junction crossing this busy junction. This bridge has won several awards including the ACEI 2003 President’s Award for Excellence and the Irish Concrete Society Award 2002.

Design Features: The slim, elegantly curved concrete deck is only 1.325 metres deep and was constructed using match-cast concrete shell segments glued and stressed together. Once the precast concrete shells have been erected they were filled with insitu concrete and further prestress is applied using grouted internal strand tendons. The deck is supported from the 50 metres high insitu concrete pylon by 13 pairs of high tensile steel cables. Each cable consists of between 16 and 37 No. 15.7mm diameter 7-wire strands.

Innovations & Challenges: No piers could be located within the junction and only a few weekend road closures were available for construction. The solution adopted is an asymmetrical cable-stayed bridge with spans of 21.5, 108.5 (main span), 18.0 and 14.0 metres. The concrete pylon is located off the junction and the main span was constructed by cantilevering out over the junction.