Old bridge used for seismic study
Seismic research into the decommissioned Whirokino Trestle bridge will give insights into the strength of such structures to withstand earthquakes.
The 90-year-old bridge on State Highway 1 south of Foxton was recently replaced by a new structure.
Dr Lucas Hogan of the University of Auckland started examining the bridge two weeks ago and demolition began on Monday.
Hogan said the decommissioned bridge created an unprecedented opportunity to do ‘‘real life’’ testing into how a long bridge behaved in an earthquake. The bridge spans 1.1 kilometres.
‘‘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.
It would give engineers insights into how they could look after existing bridges and make sure the structures were as resilient as possible during an earthquake.
The research, funded by the Earthquake Commission and earthquake resilience research group Quakecore, is being carried out in co-operation with the New Zealand Transport Agency and has been in the works for two years.
‘‘A big focus will be on how the piles holding the bridge up behave in earthquake conditions. These types of piles are used in around half of all bridges in New Zealand, and many internationally,’’ Hogan said.
He said testing included installing instruments to find out how the bridge moved.
‘‘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 includes the removal of sections to test at the university, as well as on-site testing of the piles to simulate the stresses of quake shaking.
‘‘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.’’
Transport agency project delivery senior manager Andrew Thackwray said that with more than 4500 bridges on New Zealand’s roading networks, strong, safe bridges were vital to keep the country moving.
‘‘New Zealand’s engineers have created a terrific network of bridges that have proven to be extremely robust ... This research will let us continue that proud tradition.’’
The agency was working with Brian Perry Civil and Jurgens Demolition to support the scientists carrying out their research.