Bridges

Weathering or weather resistant steel has been used on overseas bridges since the mid-twentieth century. There are only a limited number of weathering steel (WS) bridges in Australia and most of them are of a relatively new construction. It is envisaged that use of WS in Australian bridges will increase significantly in future due to its inherent characteristic of the formation of a protective patina on the atmospherically exposed surfaces in a suitable environment, enabling it to be used uncoated and, thus, avoiding the need for protective painting, consequently supporting sustainability and reducing maintenance costs. Due to a greater impetus on sustainability globally, WS is emerging as the preferred material for future steel bridges. However, as with any other material, WS also has limitations and unless these are considered in the early stage of project development, the material performance may be undermined due to non-formation of the protective patina, resulting in the need for protective paint application to mitigate the risk of corrosion. Failure of the protective patina formation has led to the underperformance of several WS bridges overseas and, at least in one instance, a complete collapse of the bridge has been reported. This could have been prevented by monitoring of patina formation and if need be, application of protective coating.

This paper describes the evolution of weathering steel, its corrosive behaviour, provisions in the design standards for corrosion allowance, the technical risk associated with its use and the management of technical risk by taking necessary mitigating actions. It is envisaged that the paper will provide guidance to the engineers, specifiers, designers and asset owners in developing a proper understanding of behaviour of this material enabling them to use it judiciously and successfully, thus managing the associated technical risk.