Onetai Bridge, about halfway between Paeroa and Kōpū on State Highway 26, might reach just 9m over a tiny stream, but its upcoming replacement marks a giant leap in bridge design for Waka Kotahi NZ Transport Agency.

It will be the first state highway bridge built from timber in 50 years, representing an exciting move towards using climate-friendly materials. 

It’s the timber elements of the new design that make the project more than just a run-of the-mill replacement, says Waka Kotahi Regional Manager Maintenance and Operations, Rob Campbell. 

“Road bridges in Aotearoa New Zealand are generally built with concrete or steel. Onetai will be the first to mark a return to more sustainable design, with timber beams and deck. 

“We’re hoping to make this the new norm, so while it might seem like a minor project, it marks a ground-breaking shift in design for bridge replacements on state highways.” 

It all comes down to the magic of layering – using an engineered timber product called glulam, which is made from layers (laminates) of wood glued together. As Mr Campbell explains, glulam has twice the strength per kilogram compared with steel, and is specially designed to be hard-wearing and durable. 

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