The Rakaia Gorge bridge deck replacement and seismic strengthening

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 deteriorating timber deck required replacement. Some innovative solutions were required to resolve the numerous challenges presented by this unusual structure related to load capacity, heritage effects, operational safety, seismic resilience, constructability and traffic management. The project 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 heritage significance and successfully preserving the exceptional landmark appearance of the bridge.