Bridges

The brittle fracture of the steel girders in the Kings Bridge in Melbourne in 1962 led to a Royal Commission into the failure. At the time of the Kings Bridge failure, the 256 m long steel girder bridge over the Barron River at Kuranda was under construction. The subsequent investigations at Kuranda also identified brittle steel in the girders. In 1962 the risk of brittle fracture of the Kuranda girders was managed through extensive non-destructive testing, repairs to remove flaws and the addition of external post-tensioning to the bottom flange. A similar retrofit was also applied to the Kings Bridge. Both bridges remain in-service. The Kuranda bridge was opened to traffic in 1963.

The Kuranda bridge was designed for H20S16 loads (33 t trucks) and carried 50.5 t truck and dogs on a two-lane highway 20 m above a lake with main spans of 45.7 m (150 feet). An engineering review of the bridge identified 1,000 locations vulnerable to fatigue. Theoretical calculations indicated fatigue cracking was possible. A careful visual inspection of the vulnerable locations identified potential fatigue cracks. The fatigue cracking was confirmed with extensive non-destructive testing at these and other locations after the thick, red lead-based protective coating was safely removed.

This paper discusses the investigations leading to the discovery of the cracking, the risk management responses, post-cracking investigations, and repairs. It details how brittle fracture assessments, risk assessments, instrumentation, and crack repairs were applied to keep this bridge safely in-service along with the practical aspects of working safely on a high bridge, under traffic, with steel protected by a red lead-based paint system.

The paper highlights the challenges and lessons associated with risk management, access management, teamwork, and the interactions with the public. The design implications for bespoke bridges will also be discussed.