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How Small, Cheap, Solar-Powered Sensors Could Change the Game for Bridge Inspections

 
  A Martlet wireless sensing node developed by Wang and Jacobs' team. Users can fit this base unit with a variety of different circuit boards that connect to various sensors. (Photo Courtesy of Yang Wang.)

It often takes a basket lift, hammers and chisels, and lots of safety equipment when a work crew inspects one of the nation’s 600,000 bridges.

The federal government requires such analyses every two years for each of those spans, a costly and time-consuming endeavor.

But what if we could install sensors that would deliver data wirelessly on a bridge’s condition, allowing transportation engineers to monitor its health all the time?

A group of researchers in the School of Civil and Environmental Engineering (CEE) has developed such a system. And they’re preparing to test it on a U.S. Highway 78 bridge with support from the School’s National Center for Transportation Systems Productivity and Management and transportation departments in Georgia and Alabama.

The technology has the potential to be a game-changer in nondestructive evaluation (NDE) techniques, according to the U.S. Department of Transportation’s Office of Research and Technology.

“In this country, the average age of our bridges is 42 years old. They’re getting older and older, and there’s no budget to fix them all,” said Yang Wang, a CEE associate professor who’s leading the project.

The American Society of Civil Engineers (ASCE) estimates it will take more than $20 billion a year for 15 years to eliminate the nation’s backlog of deficient bridges. In its 2013 infrastructure report card, ASCE also noted governments are currently spending just $13 billion.

The wireless sensing devices Wang has been developing could help those governments make decisions about the most critical needs.

“The idea is to have low-cost systems that can be instrumented on the bridge and monitor the bridge’s condition so that we can use the limited resources [we have] on the most dangerous situations,” Wang said.

Wang has been working with CEE professor Laurence Jacobs on the project, along with collaborators from the George W. Woodruff School of Mechanical Engineering at Georgia Tech and the University of Alabama at Birmingham.

Wireless sensing nodes in the BWIM/NDE system are placed on the bridge. They transmit data to a local gateway, which sends the data to researchers or transportation engineers via a cell-phone network. (Illustration Courtesy of Yang Wang.)

The sensing nodes cost just a few hundred dollars each, and they eliminate an expensive spider web of cabling and data processing for traditional sensor systems. The wireless nodes instead transmit their data to a small local gateway nearby that sends the data directly to researchers or engineers over cellular networks.

Those legacy systems are most often used now for significant “landmark” structures, Wang said. But his cheaper wireless technology could mean wider deployment.

“It would be impossible to instrument less-significant structures, everyday structures [right now]. That’s the motivation for our research, to develop those low-cost wireless sensing devices so that more and more bridges can be instrumented,” he said.

 
Researchers use a detailed model of the bridge and data from new wireless sensors to calculate gross vehicle weights and axle loading in real time. (Image Courtesy of Yang Wang.)
 
 

The project gets at the infrastructure-health problem another way, too, actually weighing the vehicles that traverse the bridge. Their data about the structure’s real-time response to traffic feeds a sophisticated computer model of the bridge, allowing for the calculation of gross vehicle weights and axle loading.

These data are called Bridge Weigh-in-Motion (BWIM), and they allow authorities to track—and police—overweight trucks.

That could help save money for local governments, allowing for fewer of the weigh stations common alongside highways and reducing wear and tear on roads and bridges in the first place.

Even with all the savings, however, Wang’s sensor systems probably won’t eliminate the need for trained eyes judging how the nation’s bridges are faring. They’ll just inform the process—and make it cheaper.

“We’re not trying to say we’re going to replace human evaluation,” Wang said. “I think there’s a certain value to human eyes, [which can see problems] that may be difficult for sensor to detect. But this can provide information so that there’s more data available for us to evaluate the bridge’s health.”