Start Date  2018
Completion Date  2018
Cost   $1.2 million 
Client   New Zealand Transport Agency
Partners  Downers, Evolution Forest Products 
Recognition  ACENZ Awards for Excellence 2019


The Rakaia Gorge No. 1 Bridge on SH77 is a Category 1 Historic Place constructed circa 1882. The 55m span ‘Bollman-like’ truss is recognised as unique in the world and is also one of the oldest wrought iron bridges in New Zealand.

To ensure that this important structure continued to provide a safe and resilient transport route, the New Zealand Transport Agency commissioned WSP Opus to design the deck replacement. The ordinarily difficult access site conditions became an opportunity to undertake seismic strengthening works in parallel with the deck replacement. This took advantage of the scaffold required for both, leading to cost and time efficiencies for the client.

During design there were numerous complexities to be considered associated with the load capacity, heritage significance, safety, seismic resilience and traffic management. One of the innovations on this project was the use of NiuDeck (with steel transoms) as an alternative to traditional hardwood transoms and deck planks. Whilst this technology is used throughout Australia, this bridge is the first to use this product on a State Highway in NZ.

WSP Opus sensitively balanced the conflicting objectives of state highway operations and heritage preservation – refurbishing the deck and providing seismic resilience to this strategically important structure, whilst respecting the high significance of the heritage fabric and following conservation best-practice principles. Innovative techniques and materials were employed, successfully preserving the exceptional landmark appearance of the bridge.

Construction was completed in 2018 by Downer.