Bridges

The aim of this paper is to share the experience in managing the risks facing the Old Sheahan Bridge (48-year-old), which is a major bridge on the Hume Highway at Gundagai, New South Wales. It was built in 1977 and has twenty-seven spans of steel box girders (overall length 1,134 m) with two lanes of traffic.

This paper covers some aspects of the original design, the strengthening design installed in 1996 to cater for T44 loadings, and the risk management undertaken by Transport for NSW (TfNSW) after the discovery of critical defects. This paper also discusses some long-term sustainable and cost-effective solutions to manage this bridge in the medium and long term.

In 2021, a Level 3 inspection identified cracks that required urgent assessment and intervention including structural analyses, more frequent inspections, speed restrictions, non-destructive tests, load tests, structural health monitoring, and fatigue life assessment.

The load tests determined that the strengthening was performing adequately. However, cracks had appeared in some of the welds outside of the strengthened parts. Follow-up investigations determined that the cracks were due to defects in the original welds.
The development of a comprehensive short-term and long-term risk management strategy is underway to ensure the continued safe operation of the Old Sheahan Bridge.

The findings and methodologies outlined in this paper provide insights and a framework for managing similar steel bridges with inherent defects while maintaining structural integrity and minimising disruptions to freight / traffic movement.