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Wood v Concrete Bridge Decision Looms

11 June 2024

Using wood instead of concrete for Kakanui’s new bridge could save the Waitaki District Council hundreds of thousands of dollars.

On April 23, councillors will decide which design will be built, with estimated prices ranging from $8.59 million to $9.97m

If the council’s funding application to Waka Kotahi NZ Transport Agency(NZTA) is successful, 57% of that will be subsidised.

Council major transport projects manager Mike Harrison said the lifetime cost of maintaining the current bridge was much higher than building a new one.

The bridge would be built just upstream of the current one and would be about 2m taller, to protect against flooding.

The main differences between the options were the width of the bridge and whether it was made of wood or concrete, he said.

Pre-stressed concrete is considered the standard solution. It is considered low maintenance and has a proven track record, but has a large carbon footprint, requires more intensive machinery to build and is much heavier.

The alternative is a glulam bridge, made from timber and ply and designed to be lightweight.

Glulam bridges are uncommon in New Zealand, but are more prevalent in other countries.

The design is one quarter the weight of the concrete bridge, leading to smaller foundations and seismic loads, which means it fares better in an earthquake.

Click here to read more.

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