Extra Lane to Ease Bridge Crawl

The strength of steel is being used to add an extra lane to Sydney's Western Distributor. BlueScope Steel specifically developed a series of long, heavy steel plates to make the project a reality.

A limited construction site, busy city streets and an ageing concrete structure were just some of the obstacles to widening the road leading onto Sydney's most famous bridge.

The city side of the Sydney Harbour Bridge will get an extra lane under the widening of the Western Distributor project commissioned by the NSW Roads and Traffic Authority (RTA) to ease traffic congestion. The partly raised western side of the Western Distributor will incorporate an additional southbound lane to complement the existing three southbound and two northbound lanes. Transfield has been appointed by the RTA as project contractor for phase two of the project, which involves widening the road between Kent Street and Sussex Street. It is due for completion in October 2003.

More than 600 tonnes of high strength steel - mainly Grade 350 and higher - will be used to extend the ageing concrete structure, providing a lightweight, easy-to-install solution. The extra lane will be supported by transverse steel girders projecting from the side of the existing roadway, and longitudinal steel girders running parallel to the existing structure. These steel supports will be placed on the existing concrete columns.

To meet these exacting demands, BlueScope Steel specifically produced a series of long, heavy plates in a bid to ensure economical fabrication of the complex beams. The design, which involved individual plates 80mm thick, more than 16 metres in length and weighing in excess of 11 tonnes each, reduced the number of welds per span.

Phase two of the four part project involves running this steel base along eight pairs of columns, or for nearly 300 metres. The steel is being fabricated off-site by Transfield sub-contractor Adua Engineering at Riverstone.

Transfield's project manager, John Ilott, said there were several major operational and functional issues that made steel the most suitable option for this project.

"The logistics of the site made the project very tricky," he said. "There is very little room on the site, it is surrounded by busy city streets, and there are a number of major construction zones in the area. Structural steel was by far the best option because it can be pre-fabricated off-site and then quickly and easily delivered ondemand - causing minimal disruption to the city drivers."

The RTA's Warren Stalder said steel was specified because of its light weight and its suitability to the tight construction zone.

"We found that by using steel we could match the form of the concrete structure, but with a much lighter weight," he said. "Also, the ability to deliver ready-to-install sections on-site was important because of the limited space we had to work in."