A nearly century-old bridge is revealing secrets that will have worldwide significance for earthquake proofing.
Auckland University civil and environmental engineers Dr Lucas Hogan and Dr Max Stephens say it is exciting to be at the cutting-edge of research, the envy of engineers and scientists worldwide.
They are researching the decommissioned 90-year-old Whirokino bridge, which withstood decades of traffic crossing the bridge on SH1.
They say their research is a unique opportunity and will give invaluable information into the strength of key infrastructure during earthquakes.
It will also give insight into the structures of the many bridges that cross the South Island's braided rivers in the South Island.
"This is important internationally, as long bridges are almost identical in form and size."
Hogan said the Whirokino was built in the 1930s and the-then Ministry of Works kept good records.
"It is a long narrow bridge, over 1km long, and was built really well."
The Whirokino, south of Foxton, was replaced this year by Waka Kotahi with a wider $70m structure over the Manawatū River and Moutoa floodplain.
The concrete cover has worn away by the weather and wear from the sea air of the Tasman, exposing the steel structure.
Beneath the bridge, Hogan and Stephens are drilling to take samples of the concrete.
"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."
Hogan said the focuses on how the piles holding up the bridge behave in earthquakes.
"These types of piles are used in around half of all bridges in New Zealand, and many internationally."
There are more than 4500 bridges on New Zealand's roading networks.
The Whirokino research project has been planned for over two years, but put on hold until the Covid-19 lockdown was lowered to level 3.
Last week they installed 20 instruments on the bridge, which will pick up any movement.
"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 whipsaw effect.
"While many computer models have shown this effect, there is very little physical testing to prove it."
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," Hogan said.
The research is a partnership with Waka Kotahi, which owns the bridge, funded by Earthquake Commission and QuakeCore and corporate organisations.
Waka Kotahi senior manager project delivery Andrew Thackwray said New Zealand's engineers have created a terrific network of bridges.
"They have proven to be extremely robust despite all the natural hazards we are exposed to in this country."
Thackwray said the research means engineers will continue to build more resilient bridges in the country's roading network.