Wireless Sensor System for Continuous Monitoring of Bridge Deformation

The displacement potentiometer is a small, robust, lightweight device that mounts to the girder of the bridge. It measures displacement, or movement of the girder, as the bridge temporarily deforms when vehicles pass along it. Changes in this pattern of deformation can be an early indicator of structural problems.

Because the system draws power from a solar cell and a backup battery, multiple potentiometers can be mounted on the bridge without wiring. The system can accommodate a number of different sensors that monitor bridge movements, such as acceleration, tilt and displacement, among other. Integrating multiple types of sensors into the system could provide a fuller picture of bridge health.

“The major advantage of this system is removing hundreds, and sometimes thousands, of feet of cables that are expensive, can be damaged, require care during installation and increase the overall cost of the sensing system,” Bartoli said. “The other advantage is that with one wireless platform, we could simultaneously read many different types of sensors, not just displacements but also accelerometers, tiltmeters and strain gages.”

A team of electrical engineers in Drexel’s Department of Electrical and Computer Engineering designed the power supply for the system and optimized it for endurance and durability in all climates. It includes a 21.8 by 35-centimeter, 10-watt photovoltaic cell and a large-capacity 14.8-volt lithium-ion battery to store and disburse the energy it collects. They tested it in a lab and outside in the middle of winter in Pennsylvania, to ensure it could continue to provide power during the most challenging weather conditions.

“We want to ensure that the sensors can continually take measurements and transmit data throughout the entire day, so we used a large-capacity battery so that it can power the system overnight or if it is cloudy for long periods of time,” said Wang, who led the development of the power system. “This configuration is expected to provide uninterrupted power for years and the battery can provide power on its own for three weeks if it’s cloudy or the solar cell has been disabled.”

The team hopes that proving an affordable, easy-to-install sensor array is rugged enough to withstand the elements with little or no maintenance for years will enable continuous monitoring of many bridges, not just those in poor condition. This level of data collection will help to determine what the “normal” structural behavior is for each bridge and raise an alert when that behavior unexpectedly changes.

“The goal is for the sensor to last indefinitely with minimal to no need for maintenance,” Bartoli said. “Reliable, continuous monitoring ensures these structures are operating as intended. It allows us to capture data about overloads and the structural deformation caused by large loads on a bridge. It also allows us to see how the structure deforms due to environmental factors, such as wind and temperature changes, so we can ensure that all of these deformations are within the expected range.

While the system is currently ready for deployment, the team plans to continue testing and refining it in the lab by adding additional types of sensors and pushing to determine the full lifespan of the power supply.