Bridges

The New Bridgewater Bridge (NBB) Project is Tasmania’s largest ever transport infrastructure project.

The project is a critical link in Tasmania’s transport network and forms part of the Australian Government’s National Land Transport Network. The NBB project involves construction of a four-lane, 1.28 kilometre long bridge over the River Derwent with new interchanges at Granton and Bridgewater, a shared path for cyclists and pedestrians, and a navigation clearance consistent with the Bowen Bridge, all aimed at improving traffic flow and connectivity. The NBB replaces the existing steel-truss vertical lift bridge, which was completed in 1946.

The bridge consists of a twin box girder supported on twin piers and monopiles. The bridge deck was precast off-site in segments and erected by a balanced cantilever method using internal post-tensioning with span continuity provided by external tendons.

The structural design was developed to maximise construction efficiency by limiting the number of very long piles to be constructed by using a monopile system, developing an innovative method of constructing the joint between the piers and piles, limiting precast segment weights to reduce the size of cranes needed for their handling and optimising the reinforcement in both segments and piles to minimise assembly times.

This construction driven design required a high degree of collaboration between designer, contractor, proof engineer and independent verification engineer in order that any potential construction difficulties could be eliminated by design and that approval of the designs could be obtained and construction could proceed in a timely fashion.