Bridges

Over the past 25 years, the use of weathering steel as the primary structural steel element, in both road and rail bridges, has increased in Australasia. This period saw advancement in locally fabricated bridges, from New Zealandís first weathering steel bridge, State Highway 1 Mercer to Longswamp offramp (opened in 2005) utilising 130 tonnes for this 87m long 3-span structure, to the 1500 tonne, 305m long 7 span Eco Bridge on the Manawatu Tararua Highway that is currently under construction. Whilst in Australia, examples include the 800 tonnes of trough girders fabricated with BlueScope supplied REDCORE® weathering steel used for 2 composite bridges on the Berry to Bomaderry stretch upgrade of the Princes Highway on the NSW South Coast, to the iconic landmark Bidgee Bidgee Bridge, a 1425 tonne 64m long weathering steel single span arch bridge built for the Parramatta Light Rail across Janes Ruse Drive in NSW.

Not to be outdone, rail bridges have also seen an increase in the use of weathering steel, with New Zealand's KiwiRail erecting more than 13 bridges over the past ten years, mainly through-deck girder types, including ballast trays.

This paper collates a number of case studies, highlighting the benefits of utilising weathering steel in each case, challenges relating to their fabrication and erection, as well as lessons learnt, especially in relation to optimal durability detailing, and an overview of their performance since erection.

The paper also outlines a summary of the latest revision of the HERA Weathering Steel Design Guide for Bridges in Australia commissioned by BlueScope, which captures the above lessons. As well as a discussion on comparing the costs between different types of welds, it also includes a comparison between the embodied carbon of weathering steel versus concrete and timber bridges over a 100-year design life and beyond.