Bridges

The most easily recognisable landmark in the northern NSW town of Grafton is the Grafton Bridge. Spanning the mighty Clarence River, it links the CBD with the southern suburbs. However, this 90-year-old icon needed to be duplicated to meet the current needs of the community.

As lifeline structures, bridges play an important role in any road network and are of great economic value to cities. The New Grafton Bridge is a key flood evacuation route for the city in the event of a flood within the river it crosses, something which was of concern to the people of Grafton. Reducing the community impacts during flooding was the key driver of the innovation on this project. The end user was at the heart of our decision-making process.

The new bridge is 525 m long in total but has a 475 m long continuous concrete box girder constructed using precast concrete match cast segments by the balanced cantilever methodology. Several innovations were adopted on the project including the use of 3m diameter bored cast in place piles to streamline the piers and reduce afflux during a flood event. Four integral piers across the river eliminated bearings at these locations, reducing future maintenance requirements at the most difficult to access locations. In addition, an unconventional approach of temporarily hanging two segments on each side of each pier cantilever prior to permanent stressing was adopted to accelerate the program for superstructure construction which was on the critical path for project completion.

This paper will present the design and construction methods adopted and make recommendations for future projects based on lessons learned.