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Spencer Guthrie
This bridge deck is undergoing treatment for structural damage. The sound of rain on a bridge determines its stability, according to a recently released BYU study.

Singing in the rain isn't just a human thing anymore, Brigham Young University engineering professors Brian Mazzeo and Spencer Guthrie say. Bridges sing in the rain, too, and the sound they make can provide tips about their safety.

Mazzeo and Guthrie studied the sound — or song — that rain or any water makes as it falls on a bridge and say they found a simpler and more efficient way to check the stability of these infrastructures.

The study, published in the October edition of “Non-Destructive Testing and Evaluation International,” outlines a new technique developed by the engineers — impact-echo testing. By recording, then listening to the sound water makes while dropped onto the deck of a bridge, the strength and well-being can be determined, as opposed to previously used methods.

“There is a difference between water hitting intact structures and water hitting flawed structures,” Mazzeo said in a BYU news release on the study. “We can detect things you can’t see with a visual inspection; things happening within the bridge itself.”

Every year the American Society of Civil Engineers produces a report card on the nation's infrastructures, and with its last release, bridges were given a C grade, Guthrie told the Deseret News. More than 10 percent of bridges in the U.S. are considered structurally deficient; the safety of bridges everywhere is a health issue that engineers are addressing.

Much of the structural damage and deficiency is "corrosion of reinforcing steel," Guthrie said. With much of the U.S. affected by freezing and thawing in the traditionally cold climates, it is necessary to put salt on bridges to melt ice. The problem is the corrosive nature of the salt on the structure.

"Engineers in charge of managing bridges need tools to properly assess the condition of bridges at any time, and then administer the proper treatment at the proper time," Guthrie said. Impact-echo testing "has a lot of potential for rapid assessment of bridges."

To use the technique, the researchers would most like to "be able to drive over a bridge at 25 or 30 mph, spray it with water while we’re driving and be able to detect all the structural flaws on the bridge,” Mazzeo said in the news release.

Guthrie got Mazzeo, an electrical engineer, involved with projects related to long-term bridge performance, specifically looking at non-destructive techniques to assess bridge stability, about two years ago. Current common practices for assessment include dragging chains behind a vehicle over the bridge, or hitting the material with hammers, but the projects centered on investigating the use of other types of solid matter to test bridge stability.

It was a late night in January and Mazzeo was working in the lab. He began exploring the sounds water poured from a beaker made on the bridge sample, and how the sample was impacted, and from there the study evolved into looking at how water could determine a bridge's state.

"It is an innovative approach for applying a simple concept to complex issue," Mazzeo said of their technique and its discovery.

Both undergraduate and graduate BYU students were heavily involved in the study, including Anjali Patil, a graduate student of Mazzeo's and co-author of the study.

"One of the wonderful things here at BYU is being able to allow undergrad and grad students to have an influence in the study," Mazzeo said, "to look in-depth at problems with infrastructure in the country."

The unique thing about the technique is how water is used to determine the health of a bridge, not the fact that water is used. Instead of a steady stream of water being poured onto a surface — which does not make a distinct sound — droplets make a pat-pat-pat sound, also known as the water-hammer effect, Mazzeo said.

"It's because you have the droplets you are actually able to excite a much greater force," he said. "That familiar water dripping out of a pipe has a lot of complicated physics associated with it, with its acoustic response ... it's very different from a stream of water."

The sound of droplets on deteriorated, less-secure concrete is a dull, hollow sound, as opposed to the higher-frequency sound made when droplets hit good quality and intact concrete, Guthrie said.

The method could be used to test materials prone to deteriorate — like wind turbines, power plants, even roofs that age due to water exposure.