Bridges

Steel in bridge construction in Australia has declined significantly over the last 40 years from around 25% of bridges to as low as 5% of bridges in recent years. The main reasons for this have been the proliferation of precast prestressed concrete girders systems with the development of the Super-T girder in the early 1990s being the most notable, the high demand and cost of steel around the world and the higher ongoing maintenance cost of steel bridges to maintain the corrosion protection coatings. Steel bridges are typically only used now on road and rail bridges where site constraints on the handling of precast girders prohibit their use.

Bluescope Steel has recently commenced production of weathering steel in larger plate sizes and is investigating its manufacturing capability has the ability to manufacture welded I-beams in the weathering steel for a small additional cost compared to the conventional steel welded girders they produce and a net saving when the cost of coating the steel is taken into account. The cost of steel is also reducing with the increase in production and reduction in demand for steel from China. The removal of the need to recoat the steelwork with the use of weathering steel and the lowering of the cost of steel production warrants a relook at the use of steel in our bridges.

Jacobs have recently designed two bridges in weathering steel for the replacement of timber rail overbridges on the Country Rail Network in NSW. With careful detailing of the weathering steel and innovative use of precast concrete decking with the steel, modular steel composite bridge systems should again be a viable option for bridge designers, constructors and owners. Particularly for regional bridge replacement in the 15 to 50 metre span range. The paper will outline the requirements adopted for the design of the weathering steel bridges and highlight the key detailing measures adopted.