It's a well-known fact that America's infrastructure of roads, bridges, rail lines and electrical grids have been given a C-minus or D-plus rating by monitoring agencies. In light of that, a pair of assistant professors in Tennessee Tech University's College of Engineering are working on technology that could provide a partial solution to this crisis.
Matthew Yarnold is a newly-hired assistant professor in TTU civil and environmental engineering department; his resume' includes journal papers that deal with bridge evaluation and monitoring, as well as field experience with Philadelphia-based companies Ammann & Whitney and Intelligent Infrastructure Systems.
"The Federal Government mandates that any bridge in the national inventory be visually inspected every two years," said Yarnold. "There's a sliding scale where older bridges are inspected every year, but obviously there's a lot that can happen in the course of two years, or even a year. What's more, there are a lot of potential problems that a visual inspection is not going to recognize."
It's vitally important to come up with a more comprehensive system to monitor bridge performance, and for several years now researchers have been developing sensors that can stay in place on a bridge to track deformation, displacement, rotation and metal fatigue. That data can be used to reassess load ratings and restrictions for bridges, and should be especially useful in a time when federal dollars are scarce and state Department of Transportation budgets are running dry.
"Often it comes to a point where a state or federal body would rather just keep repairing and patching a 1930s-era bridge instead of condemning it and building a replacement," said Yarnold. "Taking a bridge out of service and replacing it is a huge, difficult undertaking that can drag out for years, for political, logistical and budgetary reasons."
One of the main problems with measuring bridge behavior using various sensors is supplying power to the system. Some larger bridges have electric power for lighting, but hard-wiring the sensing system to this source can be difficult and costly. Providing an energy independent system solves one of the largest logistical challenges for bridge field testing.
This is where mechanical engineering assistant professor Steven Anton comes in. Before coming to TTU, much of Anton's research at Virginia Tech and Los Alamos National Laboratory was focused on energy harvesting for low-power devices such as sensors. This work has applications in biotechnology, automotive, civil, aerospace and military fields, among others.
"If you're not using energy harvesting, your devices have to have a battery or capacitor, or hook into an existing electric source," said Anton. "Energy harvesting technology can use ambient thermal energy, sunlight or vibration as energy sources to run a small device. It's a pretty logical connection to use energy harvesting to power structural health monitoring sensors on bridges, because if there's one thing a bridge is always subject to, it's ambient energy like vibration and sunlight."
These harvesters typically aren't capable of converting or storing enough energy for industrial uses, such as powering laptops or cell phones, but they can still power small electronic sensors that can record and transmit data on bridge health. From strategic points along a structure, they can continuously send real-time information to a computer, which could conceivably be linked to an app on an engineer's or technician's smartphone.
"A sensor can pick up acoustic events, such as a crack or loose bolt," said Anton. "It's the kind of thing that the human ear certainly couldn't pick up, but a sensor could. Of course, one infinitesimal crack or loose bolt doesn't mean a bridge is going to come down – you drive a '98 model car and it's got plenty of loose or worn parts, yet you're still safe driving it – but keeping track of many of these kinds of events gives a much more accurate picture of the health and safety of a structure."
At TTU, our stated goal is to help develop Renaissance Engineers, who are defined as "an adaptive professional who is inquisitive and creative, and makes significant contributions for the betterment of humanity." In light of the huge challenges posed by a degraded infrastructure in America, it's hard to think of anything that represents a better embodiment of these principles.