Bridge collapses, although rare, have raised concerns in certain quarters that bridges are not being optimally monitored. Therefore, researchers of KTH Royal Institute of Technology in Stockholm, Sweden, have taken a hi-tech approach to monitor the aging infrastructure by equipping the country’s bridges with multiple sensors which would enable early detection of wear and tear. The bridges could tweet throughout the day.
Engineer Raid Karoumi, a professor at KTH’s Structural Engineering & Bridges division who is leading the project, believes that internet connections, though not an alternative to visual inspections, provide valuable information on the impact of various factors such as traffic, wind and temperature fluctuations on the bridges.
Karoumi said, “Just as a doctor places a stethoscope and heart-rate sensors on your chest, we put our sensors where we want to monitor the condition of the bridge.” He added that like a heart monitor, sensors on the bridge could pick up deviations that indicated any change.
He also claimed that real-time detection could extend the life of existing bridges. Providing the example of the old bridge connecting Stockholm City to Lidingö (an island on the east of the archipelago), he said that the bridge was scheduled to be replaced in 2020. “But the sensors, which will be installed soon, will provide detailed information about the bridge’s state which may be allowed to stand for another 10 years,” Karoumi said.
Bridges erode slowly, and with the sensors on the bridge delivering a stream of data (in some instances 400 readings per second from a single bridge), engineers continuously look for clues to deduce the causes of wear and tear. Karoumi said the technology enabled engineers to detect cracks which were not even visible to the naked eye.
“Of course you still drive out and look,” he added, “But this technology will help determine when and where an inspection is required. It will also provide valuable information to those who perform the inspections. Since it is costly to block traffic, it is better if inspections are carried out only when necessary.”
Aging bridges are not the only ones getting connected.
For instance, 72 sensors were installed on the bridge connecting Sweden and Norway over the Svinesund sound when it was completed in 2005. This has provided researchers at KTH with 10 years of data regarding the uniquely-designed bridge that is supported by a single concrete arch.
Karoumi maintained that researchers were interested in the behavior of newly constructed bridges to confirm that the calculation models used for dimensioning were correct.
“We dimension our bridges for 120 years of life, and want to use the measurements as a footprint to compare with later,” he said.
The idea of micro-blogging bridges was also conceived, but was abandoned after transport authorities decided it was a potential security risk. For instance, the Årsta Bridge, which connects one of Stockholm’s two major islands to the mainland, was equipped with wireless sensors that could transmit information 50 times per second to a cloud-based internet service. The sensors provided information such as how much the bridge oscillated when trains passed over it, and the results were continuously presented to an app.
Nevertheless, Sweden’s bridges are on their way towards the internet of things (IoT) as KTH researchers continue developing cloud connectivity and artificial intelligence for the sensor system.
“There is a lot of development remaining before we get there,” Karoumi said, “but our goal is to develop the technology to extend the life of our bridges.”
More information can be found at: KTH Royal Institute of Technology.