Source: Earthquake Commission – EQC
New technology to improve the resilience of bridges on New Zealand state highways is currently being developed with EQC funding by scientists of the Auckland University of Technology (AUT).
At present, any damage or loss of strength caused by slow deterioration or earthquakes on thousands of bridges over rivers, gullies or roads is extremely hard to see or monitor.
AUT structural engineering senior lecturer Dr Sherif Beskhyroun says the way each bridge vibrates can reveal the health of the bridge.
To keep an eye on these vibrations in bridges and buildings, Dr Beskhyroun is leading an EQC-funded project to make monitoring easily and cheaply available.
Up until now, big structures like bridges and buildings have generally been inspected by engineers on site as part of maintenance or after an earthquake, but they can’t see what is happening inside the concrete or steel.
Using vibration measurement is a way of keeping close tabs on a structure’s health, says Dr Beskhyroun.
“Every structure like a bridge or big building vibrates in its own certain way,” he says. “This is a normal effect of wind and traffic.
“When you can measure that vibration all the time, you see what the ‘healthy’ vibration for that structure is. And when something is out of that range, you know it might need some attention. “
Dr Beskhyroun and his team have developed low-cost wireless monitors that can be installed on bridges, giving constant readings to an automatic analysis system back at the lab that sends an alarm if anything of out the ordinary is detected.
To make sure the monitoring system was accurate, the team first used a model of a bridge on a shake table at AUT to test the measurement of both usual vibration and how that vibration would change in an earthquake.
With success established in the lab, they have now installed 20 sensors inside the cavity of the Newmarket Viaduct on Auckland’s Southern Motorway (SH1) for real-world, real-time testing. It’s one of the busiest sections of motorway in the country with an average 201,000 vehicles every day.
“We’re grateful to Waka Kotahi NZ Transport Agency for giving us the opportunity to trial the new technology on such an important part of Auckland’s infrastructure,” says Dr Beskhyroun.
Transport Agency Senior Manager, Operational Policy, Planning & Performance, Vanessa Browne welcomes the insights the new technology can provide.
“The Newmarket Viaduct is less than 10 years old and we expect it to last a hundred years or more, but the more we understand about the structure, the more confident we can feel about the capacity and durability of such a strategic asset.”
“On older bridges around the country, the technology will enhance our understanding of when and how fast bridges might be deteriorating and how we can strengthen or otherwise extend the life of critical structures.”
EQC’s Dr Jo Horrocks says bridges are critical to keeping New Zealand communities connected and is looking forward to a time when these sensors are commonly used on big buildings as well.
“One of our aims is to support resilient infrastructure for New Zealand. The new technology being developed by Dr Beskhyroun and his team will help ensure New Zealand can stay connected and will also be very useful for monitoring the health of other structures like big buildings.
“After a natural disaster like a large earthquake, we can only tell how damaged a structure is by sending people in to physically inspect it. This could be a much quicker, safer way to check on a structure’s health.”
Dr Beskhyroun says that although monitoring sensors exist now, analysis is not easy. “What we’re doing is putting the sensors, data, analysis and alerts into one system that is cheap, fast and easy to use.
“Constant monitoring of the vibrations makes it much easier to pick up problems, whether it’s the structure deteriorating slowly, or alerting an engineer to potentially significant problems after an earthquake,” he says.