Bridges

The New Bridgewater Bridge Project is the largest transport infrastructure project in Tasmania's history. It involves construction of a new bridge over the River Derwent and other associated road infrastructure. The New Bridgewater Bridge (NBB) is approximately 1.28 km long spanning the River Derwent connecting the Brooker Highway to the Midland Highway.

The precast yard for the construction of the 1,082 concrete bridge segments was located on the northern side of the River Derwent, therefore requiring the delivery of approximately 400 precast segments weighing between 50 and 90 tonnes to the southern work front. To deliver these segments required travel either across the old Bridgewater Bridge, or via a 1.5-hour journey via the Bowen Bridge and through Hobart’s outer suburbs. The alternative route presented significant delays for the Hobart travelling public. The use of the existing Bridgewater Bridge was much shorter and therefore resulted in much lower impact to road users.

There were concerns about the use of the existing bridge for transporting segments as it is a critical link on the National Highway and is approximately 80 years old, was originally designed for much lower loads, and has had defects that have required repair and maintenance over many decades including the need for emergency repairs.

A robust approach was therefore required for the assessment and management of the existing bridge for segment deliveries. The approach included desktop assessment, regular inspections and the installation of strain gauges and accelerometers. It also included the development of a Trigger Action Response Plan to monitor the bridge and outline required steps if the overload occurred. This paper outlines the process undertaken as well as discussing findings from the assessment and monitoring and lessons learned for future projects.