Old meets new - innovative technology on Grafton Bridge

Revolutionary: Carbon-fibre technology will allow Grafton bridge to handle more than three times its load capacity while retaining its original look

From City Scene, published on 14 June, 2009.

Revolutionary carbon-fibre technology is being used in the work on Grafton Bridge. This will allow the bridge to handle more than three times its load capacity while retaining its original look - an essential consideration, given the bridge's status as a category A heritage structure.

The detailed design for the strengthening of the historic bridge in 2004 confirmed it to be unsafe for heavy vehicles, and not compliant with modern earthquake-proofing standards.

This work will prepare the bridge for its 100th birthday next year, and for its inclusion as a key part of the Central Connector, a dedicated busway between Newmarket and the CBD that will allow for quicker, more efficient bus travel through the area.

The carbon-fibre strips will stop the bridge from cracking, increase stability and will increase its load capacity from about 13 tonnes to 40 tonnes. They will also make the bridge strong enough to stand a one-in-1000-year earthquake and will comfortably allow for up to 1200 buses to use the bridge each day.

The strips increase the strength of century-old concrete reinforced deck beams. The carbon-fibre material is very thin and light, but is also extremely strong. Specialised contractors are currently working on implementing the new technology, which is the biggest project of its type undertaken in this country.

"This process has been more akin to building an America's Cup boat than a bridge," says Councillor Ken Baguley, chairperson of the Transport Committee, referencing the pioneering use of carbon fibre that has revolutionised boats that enter in the competition. "It's great to see cutting-edge technology used on such a valuable and historic bridge - an innovative mixture of old and new engineering that will protect this marvellous structure for generations to come."

Ongoing work - including the carbon-fibre reinforcement - looks set to be finished on budget and ahead of schedule.

More information on the Grafton Bridge upgrade, Central Connector or other roading and maintenance projects the council is undertaking is available online.