Sensors monitor various components on the bridge, such as the bearings where this sensor is located.
In 2008, Mehdi Kalantari, assistant research scientist in the electrical and computer engineering department of the University of Maryland, founded Resensys LLC. The company developed wireless sensor technology that could monitor the structural health of bridges. These devices have now become commercially available for use on new and existing bridges.
How It Began
“My background is in sensor networking and wireless communication,” explained Kalantari. “I was researching what applications I could use low-power wireless technology in and I felt that bridges were in need of more technology to monitor their health.”
Kalantari began the project in 2005. His goal was to make the sensors affordable to install in both new and existing bridges. During the course of his research, Kalantari and the rest of the country watched the aftermath of the I-35W Mississippi River Bridge collapse in Minneapolis.
“When I heard the news, I felt regretful. The collapse could have been prevented with the use of technology and real time monitoring of the bridge,” Kalantari said.
In 1990, and again in 2005, the U.S. Department of Transportation’s National Bridge Inventory gave the bridge a rating of “structurally deficient,” citing problems with corroded bearings and stress cracking. Though measures were taken to improve the bridge, I-35W continued to rank near the bottom of federal inspection ratings nationwide.
With the Resensys bridge health monitoring system, future collapses can be prevented by providing constant real-time data that measures strain, acceleration, moisture and humidity, crack activity and growth, tilt and inclination, and temperature at critical points of the bridge, according to the company.
The Resensys products include SenSpot, SeniMax and SenScope.
SenSpot is an ultra low-power sensor that uses RF and ambient light to function (a battery-powered version is available for areas where there is no light.) The installation is fast and easy, with little to no intrusion to the structure. It is guaranteed to run for 20 years, although Kalantari said that 30 years is typical. It is approximately 2 by 2 in. (5 by 5 cm) in size and has a free space communication range of .8 mi. (1.3 km.)
The SenSpot transmits real time information to the SeniMax. This solar-powered device can collect data from up to 1,000 SenSpot sensors. SeniMax uses cellular data services to transmit data of SenSpot sensors to a server, where it is stored and archived.
SenScope is a software program designed to retrieve data from the server and analyze it for detecting structural issues. It offers real time visualization and structural diagnostics. The software also has customizable alert levels and can perform a severity assessment of structural integrity issues. SenScope is able to simultaneously monitor multiple structures and offers data archiving for visualization of historical data of each structure.
Resensys in Action
The Resensys system was put into play about 14 months ago on the I-495 Capital Beltway NW Branch Bridge. By the end of 2011, Kalantari estimates that three to four bridges in Maryland will be equipped with the new sensor technology.
“The sensor system is very cost-effective for both new and existing bridges because there is no difference in the installation process,” explained Kalantari.
A typical bridge that measures 656 to 984 ft. (200 to 300 m) would use 30 to 40 sensors. With the SeniMax data box and the SenScope software, the system would cost approximately $10,000. The number of sensors is very bridge specific and depends on the number of components that need to be monitored.
Kalantari has not yet approached any states other than Maryland with his new technology, but has presented the information to Federal Highway Administration for future recommendation.
“There is no limit to what we could achieve in bridge safety and preservation on bridges worldwide.”
For more information, visit www.resensys.com. CEG