Why 3D scanning could be wave of future for bridge inspection

As the backlog of bridges needing inspection or repair across the U.S. reaches a critical point, technological improvements have never been more important.

ASCE’s 2021 Report Card for America’s Infrastructure found that 42% of the country’s 617,000 bridges are at least 50 years old – with an average age of 44 – and more than 46,000 are structurally deficient. According to the report card, “a recent estimate for the nation’s backlog of bridge repair needs is $125 billion.” (The 2025 report card will be released this month.)

Inspections usually focus on the steel beams that support the bridge deck. Bridge inspectors “use ultrasound to measure the thickness of the beam,” said Sergey Sukhovey, co-founder of Artec 3D, a developer of advanced 3D scanning hardware and software. “And by making an analysis of these measurements, they calculate the residual load capacity of the beam itself and then the overall load capacity of the bridge.”

But ultrasound may be too slow and imprecise to tackle the backlog of bridge inspections. “If you hold the mic at the wrong angle or slightly off, or you have too much ultrasonic gel on it or not enough, you can get different readings,” said Matt Weidele, P.E., a bridge load rating and overload engineer at the Massachusetts Department of Transportation. “The same inspector could put that mic up to the beam web and get three different readings on three consecutive touches to the beam based on how he’s holding the probe.”

Ultrasound sensors also must touch the bridge beams, meaning inspectors find themselves in all sorts of challenging positions, often hanging from a bucket.

Meanwhile, countless steel bridges are slowly deteriorating, due in large part to corrosion, which weakens a bridge’s load capacity over time. Corrosion is a “very nonuniform phenomenon,” says Simos Gerasimidis, an associate professor of civil and environmental engineering at the University of Massachusetts Amherst and a visiting associate professor at Massachusetts Institute of Technology.

“So the first line of attack of the problem was to take out some of the real bridges from the field and bring them to our lab for testing,” Gerasimidis said. His research team at UMass obtained beams – courtesy of MassDOT – from bridges slated for demolition. “We tested the bridges mechanically to find their remaining capacity, but in the process we also documented corrosion using ultrasound sensors (conventional method) and laser scanning (the new method).

“This comparison led to finding that laser scanning can be a game changer.”

The research team developed new guidelines to better predict load capacities but realized that it was “challenging for inspectors to be able to document this problem adequately,” Gerasimidis added

The team needed technology more precise than ultrasound.

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