REDMOND BRIDGE REPLACEMENT – WATERFORD

A specific requirement was that two traffic lanes and one footway were to remain open to the public throughout the construction work. To comply with this it was necessary to arrange for two lanes of the new bridge to be completed before demolition of the existing structure commenced.

The bridge is founded on 711 mm dia. tubular piles. The cofferdams for the trunnion pier and south abutments were designed in-house and were approximately 21 m x 13.5m and 19m x 13m in plan, respectively. The cofferdam in which the trunnion pier was constructed was subject to a 16.5m differential head and was formed using 33m long high yield Larsen 6 sheet piles with a 1 metre concrete plug at formation level.

The configuration of the approach spans was determined in the usual manner by a consideration of the balance between superstructure and foundation costs. Precast prestressed concrete beams were selected on the grounds of economy and durability. The south span was designed in in-situ concrete because of the "bell-mouth" shape required to connect into the approach road on the adjacent quay. The decks were arranged to be continuous (for live load) from the opening span to the river bank on either side to minimise the number of joints in the carriageway and improve the riding quality.

The opening span was a single-leaf trunnion bascule bridge with a concealed counterweight, constructed in two independent halves. Plate girder construction together with an orthotropic deck was adopted for the steel leaf. Each half-leaf was designed to permit shipment to the site in one 40 metre long piece weighing about 130 tonnes and to be lifted from the river on to its trunnion bearings by a floating crane.