Design and Engineering
A toll bridge, providing a direct link between East Wall Road and Ringsend, would take up to two miles off some journeys and relieve heavily congested areas in the city. Designed by Mc Carthy & Partners, Consultant Engineers (with Dorman Long Bridge and Engineering) and built by Irishenco Ltd with Thomsons of Carlow, construction began in May 1983.
The bridge consists of four precast prestressed approach spans of 26m each with a central single leaf steel bascule type opening span of 45m and hydraulically operated. The fixed spans bear on reinforced concrete piers bearing on steel circular or H-piles. The bridge width is 10m and an approach road of 1150m was also included. The opening span would continue to allow cargo ships and liners berthage close to the city centre.
The river had to be navigable at all times during construction. The design chosen is a combination of concrete and steel with precasting and prefabrication in use for economy and ease of construction. An important consideration was the location of the shipping channel which is off centre of the river. For this reason a single leaf bascule opening span was chosen with a main central pier to give a symmetrical appearance.
For the approach spans precast prestressed beams were chosen, however, these limited the length of span possible, which meant that three piers were required. The foundation conditions were found to be good with sandy silt overlying thick layers of stiff boulder clay which overlayed dense sand and gravel above the limestone bedrock. A single line of five circular concrete filled steel piles was used for the intermediate piers. The pier heads to carry the deck beams were then concreted on the top of the piles.
The main pier is located at the southern end of the cantilever bascule and contains the hydraulic control and lifting apparatus. The pier is a concrete box, supported on driven steel H-piles, which was constructed within a sheet piled cofferdam. A deep central shaft in the box accommodates the counterweight as it rotates. The system is able to lift the 500 ton section through its 80 degrees in under one minute.
The south abutment and wing walls were constructed within a sheet pile cofferdam due to their levels. The north abutment, in order to preserve the existing masonry quay wall, was located behind the quay wall. Both abutments were constructed on steel H-piles.
Six protective dolphins for the opening span are provided, with the design using greenheart timber piles driven deep into the boulder clay. The concrete superstructure for the fixed approach spans consist of precast prestressed beams with an in-situ concrete deck slab.
The opening span is a single leaf bascule structure with an integral counterweight and spans 45m. The bridge was fabricated in eleven sections at Thomson’s steelworks in Carlow, from where it was transported to the Alexandra Basin in Dublin Port. There the units were aligned on support trestles and welded in sequence. The opening span was carried out by a floating 400 tonne Sheerleg crane and placed directly into position. This operation took less than four hours.
The bridge was opened on the 21st of October 1984.