Engineering Safer Bridge Inspections
May 18, 2016 / by Michele McDonald
George Mason University engineering professor David Lattanzi was inspecting a bridge several years ago in his hometown of Pittsburgh when a drunk driver sped past “lane closed ahead” signs and slammed into the final sign—a giant flashing, lighted arrow—the only barrier remaining between Lattanzi and the driver.
The driver walked away from the crash, but Lattanzi and his crew were left shaken.
“I’ve almost gotten killed on the job three times,” he says. “Inspecting bridges is really dangerous for humans, and we don’t get good results.”
He knew there had to be a better way.
It’s no secret that the nation’s infrastructure is crumbling. Inspecting bridges is hazardous, expensive, and well behind schedule. UAV inspections are more efficient— about 10 percent of the traditional cost—and offer more exact comparisons from inspection to inspection, Lattanzi says.
Last summer the U.S. Forest Service, which manages 7,500 bridges—more than any other organization in the United States—took Lattanzi’s idea on a large-scale test drive in Alaska. That test drive included a UAV, or drone, zipping around and snapping photographs of the 280-foot Placer River Bridge, the longest timber bridge in North America, on Alaska’s Kenai Peninsula.
Results from the photographic flyby went to Lattanzi’s Advanced Infrastructure Monitoring Lab at the Volgenau School of Engineering. There they were compiled into a sophisticated 3-D model, which takes about 500 hours of computational time.
“You can see the knots in the wood,” Lattanzi says of the footage they gathered. “You can see the grain. You can count the threads on the bolts.”
In fact, the 3-D model’s detail is so precise that the name of the bolt manufacturer is easy to read.
Lattanzi’s method is also more flexible; all the equipment can fit into a backpack, while traditional methods rely upon heavy equipment.
That’s of particular importance to the U.S. Forest Service because, like many of the bridges under its auspices, the Placer River Bridge is off the beaten path where large trucks can’t pass.
The bridge is the only way hikers can reach the Spencer Glacier. A school bus on train tracks brings visitors part of the way to the bridge. The rest of the trek is on foot.
Mason civil engineering doctoral student Ali Khaloo is one of seven students working in Lattanzi’s lab. This was his first trip to Alaska, and he found that overseeing the inspection came with some unusual guidelines, as well as moose and black bear sightings.
“We were told to always be in a group of two, no matter what,” says the Iranian native. “I was really surprised that the guide carried a rifle.”
Khaloo, who wants to follow in the footsteps of his uncle, a civil engineer, says the Alaska trip was a one-of-a-kind experience.
“It was one of the most beautiful places I’ve ever been to in my life,” Khaloo says. “Spencer Glacier was magnificent.”
Lattanzi says he expects more organizations will follow the lead of the U.S. Forest Service in the next few years, making sure bridges are safe for drivers and pedestrians.
He is also exploring, with the help of a National Science Foundation grant, the use of these 3-D modeling techniques in post-disaster situations, such as inspecting buildings after earthquakes.
“Fully realized, this technology will enable post-disaster inspectors to rapidly and accurately estimate structural damage using only a digital camera and portable computer,” says Lattanzi.