When planning for the replacement of the old timber Supply Mill Bridge over the Supply River at Robigana in Northern Tasmania, West Tamar Council saw an opportunity to apply best practice. Opened in November 2004, the bridge is an example of a single span bridge casting the longest prestressed super Troff beams and the first arched super Troff beams in Australia.
West Tamar has been progressively replacing its old timber bridges with long life concrete structures as part of its asset management program.
Council’s Manager Technical Services, Ray Wright, said the new bridge is a reflection of the communities’ needs.
“The previous bridge, built in 1908, had reached the end of its useful life,” he said. “The new bridge maintains access and is a testimony to leading practice in consultation, engineering design, project management and bridge construction.”
The bridge comprises a cast in place concrete deck supported by six massive prestressed concrete Troff beams. Each beam weighs 66 tonnes and is 38 metres long, hence the process of launching the beams required specialist planning and engineering.
The beams were too large to be lifted into place by any mobile crane available in Tasmania, so Council implemented the use of steel launching trusses. Moving the beams to the site was also a challenge. Vehicle adjustments were required to create specific manoeuvrability at tight corners. This meant that one truck had to be reversed for the last two kilometres to the site.
During the planning stage, Council held a number of consultation meetings with the local community to discuss and determine preferences for the alignment of the bridge, its appearance and a timetable for works and traffic management. As a result, works were undertaken outside of the major tourism period, and a single lane detour bridge was built across the river to prevent major disruption to traffic.
Council funded the entire development of the bridge at a cost of $1.5 million, which is a third of its Capital Works Budget.
The Supply Mill Bridge has recently been awarded an Engineering Excellence Award by the Tasmania Division of Engineers Australia. It also won the Transport Engineering category of the National Awards for Local Government, which recognise innovation and excellence by Local Authorities.
For further information contact Ray Wright on 0418 133 577.
