Bridges

In September 2020 a 128 km/hr gust of wind caused a truck travelling over the Auckland Harbour Bridge to tip over damaging a diagonal member of the central truss bridge at the middle of the main span. This incident took the central four lanes of State Highway 1 out of action and led to significant disruption of the Auckland motorway network with long delays for the travelling public. Early media reports suggested a minimum of six weeks until the remedial works could be completed - however two and a half weeks later the bridge was fully re-opened to traffic.

This paper will describe how the AHB bridge engineers worked through the damage assessment, analysis of load effects on the structure, design of the remedial solution, and coordination of fabrication and installation of repair works with the bridge maintenance team. Assessment of the structure showed that internal forces were redistributed around secondary load paths when the connection of the diagonal member failed.

This led to unexpected displacements of critical structural elements resulting in limitations in the load-carrying capacity of the bridge. Repair works to replace the damaged member included detailed planning and monitoring of installation methods, including reinstating dead load forces in the diagonal member to recover the displacements caused by the impact. The design, fabrication, jacking, monitoring and physical load testing of the repair works were coordinated in a collaborative Alliance team and completed in eighteen days when the full load-carrying capacity of the structure was re-instated. Close collaboration and communication between the designers Beca, the Auckland System Management Maintenance Alliance, construction partners and client Waka Kotahi NZ Transport Agency was critical to achieve effective and safe repairs during a rapid design and construction programme.