Bridge to be first built from timber in five decades

Onetai Bridge 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, the organisation said.
The bridge, located about halfway between Paeroa and Kōpū on State Highway 26, will be constructed using an engineered timber product called glulam, which is made from layers [laminates] of wood glued together.
It has twice the strength per kilogram compared with steel, and is specially designed to be hard-wearing and durable, Waka Kotahi regional manager maintenance and operations Rob Campbell said.
“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,” he said.
The new Onetai Bridge is designed to last at least 100 years, linking the greater Waikato region with the Coromandel Peninsula. Its replacement will add to the resilience and safety of this route, as the new design will be stronger and wider than the old bridge, Mr Campbell said.
The new design will be the same length as the old one, but will be 3m wider, and will boast extra safety features. These include a new type of side barrier which can be fitted right to the outside edge of the bridge, and therefore gives drivers more lane space, helping reduce the risk of head-on crashes.
The bridge will have simple concrete foundations, and new scour protection both upstream and downstream. Scour, which happens when water flows change or rivers flood, is a leading cause of bridge failure.
In the meantime, Onetai Stream Bridge remains safe to use, Mr Campbell said.