A large simulated earthquake was strong enough to rock the foundations of the old Whirokino Trestle near Foxton
earlier this week as scientists put it under duress in search of valuable seismic data.
Cutting-edge research on the decommissioned Whirokino Bridge will give scientists and engineers around the world invaluable new insights into the strength of key infrastructure during seismic events.
Dr Lucas Hogan from the University of Auckland said it was an unprecedented opportunity to do "real life" testing of how a long bridge behaves in an earthquake.
"We have done a lot of bridge testing in the lab, and this is a unique opportunity to put a real bridge through its paces and even push it to failure," he said.
"You don't often get the chance to pull a bridge down and study it...it's surprisingly robust, given its age."
The huge piles were 10m deep in the ground and would be dug for examination after the earthquake tests were complete to see how they behaved.
They could move as much as 200-300mm when pushed and pulled under the pressure of hydraulic rams.
"A big focus will be on how the piles holding the bridge up behave in earthquake conditions. These kind of piles are used in around half of all bridges in New Zealand, and many internationally, so it's very practical science," he said.
"That first stage includes installing instruments on the bridge to find out how it moves dynamically."
"Because seismic waves travel at a finite speed, one end of a bridge will start shaking before the other. In a long bridge, this can potentially cause a whip-saw effect. While many computer models have shown this effect, there is very little physical testing to prove it.
"The Whirokino Bridge provides an opportunity to see how these long bridges behave, which is very important given that there are many such bridges over braided rivers in the South Island."
The research will take place over 10 weeks and will include removing sections to test at the University of Auckland, as well as testing the piles on site to simulate the stresses of earthquake shaking by pushing and pulling in a controlled manner.
"This will tell us a lot about how these bridges behave after 90 years in service. Having the whole bridge means we can also test potential fixes for making the columns and piles more robust which could be used on any similar bridges if needed," he said.
Hogan's research is the result of a ground-breaking partnership between a multitude of government, academic and corporate organisations.
The research, funded by the Earthquake Commission (EQC) and QuakeCoRE, is being carried out in cooperation with Waka Kotahi NZ Transport Agency, as the owner of the bridge, and demolition sub-contractors working alongside the lead contractor, Fletcher Construction, who are fine-tuning the deconstruction programme to fit with the scientific needs of the University of Auckland team.
Dr Jo Horrocks, head of strategic research and resilience at EQC, said it invests more than $17 million each year in research.
"We're really pleased to be part of the team on this project. That we have so many organisations involved shows the importance of ensuring New Zealand has resilient infrastructure."
Waka Kotahi senior manager project delivery Andrew Thackwray said there were more than 4500 bridges on New Zealand's roading networks.
"New Zealand's engineers have created a terrific network of bridges that have proven to be extremely robust despite all the natural hazards we are exposed to in this country. This research will let us continue that proud tradition and build even more resilient bridges."
The 90-year-old bridge on State Highway 1 south of Foxton officially opened in 1939 and was recently replaced by a wider $70m structure over the Manawatū River and Moutoa floodplain.