Bridge inspection with drones

SPECIAL REPORT: BRIDGE INSPECTIONS UNMANNED SYSTEMS GO OVER, ON AND UNDER BRIDGES TO MAKE INSPECTIONS CHEAPER AND FASTER America has a lot of bridges, more than 600,000. Many of them are in disrepair or are reaching the end of their planned lives.

According to the 2017 Infrastructure Report Card from the American Society of Civil Engineers, 9.1 percent of the country’s bridges were structurally deficient in 2016, meaning that drivers made an average of 188 million trips across a deficient bridge every day.

Inspecting bridges, then, is a critical activity for many states. Several states are looking at bolstering that activity by using drones, including Minnesota, which has been studying their use for years and is planning to make them a standard part of its bridge inspection toolkit.

Minnesota isn’t among the states with the highest number or percentage of deficient bridges, but it cited the increasing costs of bridge inspection as a reason for kicking off its study of drones for that use.

“We think it is really a good tool for bridge inspections,” says Barritt Lovelace of Collins Engineers, the principal investigator for the company, which headed up Minnesota’s study.

“It does a lot of things that really are advantageous if there are bridges with things that are difficult to access.”

Minnesota did its initial study in 2015, leading up to a report issued in July of that year. The state used an Aeryon SkyRanger to help inspect four bridges.

That report concluded that “UAVs can be used in the field during bridge inspections safely. Based on the UAVs size, weight, controllability and built-in fail safes, the risk to inspection personnel and public is very low.”

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by Brett Davis

It said “the use of UAVs to aid bridge inspection should be considered as a tool to a qualified team leader when a hands-on inspection is not required,” and that they could be used not just for large bridges but for smaller ones and culverts too.

However, the 2015 study also said that the then-current FAA restrictions, requiring a Section 333 waiver and a certificate of authorization, were “onerous,” and that more studies would be good.

So, more studies were done. Minnesota’s Department of Transportation, working with Collins Engineers, conducted a much longer study and is finishing a report on that work.

The SkyRanger, as it turned out, wasn’t suitable for some bridge inspection work, as it couldn’t look straight up and needed GPS to navigate. For the second round of tests, Collins used a senseFly Albris, a quadrotor that senseFly says was designed specifically for live inspection of buildings and structures. It doesn’t need GPS to fly, can look straight up and down and has an ultrasonic system to keep it from bumping into barriers.

As in the first study, the second looked at four bridges, of different types: a large steel arch, a steel truss, a culvert and a steel truss bridge with deck delaminations.

“We wanted to pick ones we thought would take advantage of the technology,” Lovelace says.

One of the largest bridges in the study was the John A. Blatnik Bridge located between Duluth, Minnesota, and Superior,

Wisconsin, and which carries I-535 and U.S. 53 over the St. Louis River.

MnDOT did a cost analysis comparing the use of the Albris to the traditional methods, which, for a bridge like the Blatnik, would involve four “snooper” inspection vehicles, an 80-foot lift and require eight total inspection days, for a minimum cost of $59,000, not including travel expenses and equipment mobilization.

With the Albris, “the cost of a UAS contract to inspect all of these same approach spans of this sample bridge would be around $20,000 with only five days onsite per consultant-obtained quote,” for a potential cost savings of 66 percent, a summary of the pending report says.

Phase III of the project is now slated to begin, which will include the inspection of many more bridges, according to Jennifer Wells, a state bridge inspection engineer with MnDOT. “Each phase became more successful than the previous one,” she says. “For each phase we learned more about different drone types that were also becoming available on the market at the time. We’ve been able to try different ones that meet our needs.”

The agency hopes to get a better estimate for cost and time savings, beyond what was calculated for the Blatnik bridge, Wells says.

“In phase three, we plan to get a better estimate, because we’ll be doing around 20 bridges this time, so we’ll be doing an average then between all of them to come up with a more definitive number.”

Using drones, ground robots and even amphibious drones that can fly and swim can be an effective tool for bridge inspections, saving time and money. The overall payoff could be huge: Extending the life of bridges is worth billions of dollars to the economy.

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For the third phase of the study, MnDOT and Collins Engineers will also analyze a new vehicle: Elios, the “collision-tolerant” drone from the Swiss company Flyability.

Elios is basically a small drone flying inside a cage, which means it can bump into things without harm, just the thing for enclosed spaces.

“The Albris isn’t going to fly inside of a box girder or really tight truss, so this kind of solves that issue of getting really close to things that we need to,” says Lovelace.

Wells and Lovelace kicked off the MnDOTfunded studies based on mutual interest in the technology, and agree that drones probably have a bright future for bridge inspections. Lovelace, who has his UAS airman certificate from the FAA, says using drones for bridge inspection makes sense.

“I think it does speed up the time, and it improves the access,” he says. “In a lot of ways, it improves the safety also.”

Interest in such inspections is growing, as was evidenced at AUVSI’s Xponential conference and exhibition in Dallas, where Intel built a mock bridge to demonstrate the inspection abilities of its Falcon 8+ drone and related software.

Collins Engineering does bridge inspections all over the country, well beyond its home base in Minnesota, and Lovelace says interest is growing everywhere the company goes.

“There’s a huge amount of interest from lots of different clients,” he says. “I think we’ve given 30 presentations last year at different professional organizations and clients.”

Wells has also been fielding calls from other agencies within MnDOT interested in the technology, as well as cities and counties in the state.

“Everybody has an interest in using these for tools, so I think it’s going to start out slowly here, but as rules get … less stringent, I think more people are going to be using them,” she says.

On the deck Inspecting bridges isn’t just something that can be done from the air. The Federal Highway Administration Long-Term Bridge Performance program, working with Rutgers University, created RABIT, or the Robotic Assisted Bridge Inspection Tool.

RABIT packs a panoramic camera, a high-definition imaging system, electrical probes to study the corrosion level of concrete, impact echo and ultrasonic surface waves to monitor concrete deck strength, ground-penetrating radar and GPS into its relatively compact chassis, which moves on four omnidirectional wheels.

Nenad Gucunski, chair of Rutgers’ Department of Civil and Environmental Engineering and director of the Infrastructure Condition Monitoring Program within the Center for Advanced Infrastructure and Transportation, says RABIT is now inspecting 20-25 bridges a year as part of the FHWA bridge performance program, and could do more.

“Certainly the capacity is much higher,” he says. “It could test many more bridges, but at the moment this is simply being controlled by the demand for the Federal Highway Administration’s Long Term Bridge Performance Program.”

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SubUAS' Naviator prepares to fly under the Delaware Memorial Bridge. Photo: SubUAS

That program is collecting data on bridge conditions in the Mid-Atlantic region, including West Virginia, Virginia, D.C., Maryland and New Jersey, focusing on bridges that are of similar ages and subjected to similar weather and traffic conditions.

RABIT, so far, is proving to be cheaper and faster than traditional methods.

“There is financial saving because you are so much faster at data collection with a smaller number of people,” he says. “Traffic control is a significant expense, so by reducing our time on the bridge, we are reducing the time for traffic control.”

RABIT can collect the same amount of data as a sixperson team and do so three times faster, he says.

For instance, he estimates that its examination of Washington, D.C.’s Memorial Bridge — which it has inspected twice — took about 30 to 40 hours, where a human team would require 100-120 hours.

RABIT can scan about 4,000 square feet per hour, versus about 1,500 square feet at best for a traditional team. It could get even faster — right now RABIT has to stop and apply some of its sensors directly to a bridge surface, which slows it down.

Gucunski says he’d like to move to air-coupled sensors that don’t require contact, which could make RABIT as speed as its namesake, up to five to 10 times faster.

A sign warns of Minnesota bridge inspection via drone. Collins Engineers

Over and under A Rutgers spin-off company is also working on a new drone that could help inspect bridges both from the air and beneath the water.

Javier Diez, a professor in the university’s Department of Mechanical and Aerospace Engineering, is heading up the concept for Naviator, and has created a small side company, SubUAS, to market it commercially.

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To see Naviator demonstrating its ability to fly into and out of water, scan this code with your smart device.

Using the system for bridges does away with the need to have a boat in the water, not to mention divers, says Contarino, “which is our advantage.”

Lovelace, of Collins Engineers, says he thinks that drones will become a standard tool in the bridge inspection toolbox, for spans large and small.

Although that inspection and in-water demonstration was done for the benefit of the U.S. military, the Delaware River and Bay Authority is no stranger to drone inspection of the memorial bridge.

In 2016, it conducted its first drone inspections, using two systems to make images of hard-to-reach spots.

“I think the endgame is that an inspector will have one in their trunk, and when they are out doing a bridge inspection and it’s useful, they will pull it out and use it,” he says.

Likewise, Rutgers’ Gucunski sees a bright future for ground robots like RABIT. Extending the life of bridges in the country by even a few years could save billions, he says.

The authority said anything that makes bridge inspection cheaper and more efficient is a good idea, as annual bridge inspection costs can top $500,000 a year.

The Office of Naval Research is funding the work at the moment. The Naviator was able to go below the water and fly out again repeatedly, which impressed ONR enough to award it the sole source for the second phase of a contract to develop amphibious systems that could be used to combat underwater explosives.

“We were in and out of the water with the small prototype,” Diez says. “That got us to phase two.”

Naviator uses a tether to communicate with the surface, although Diez says he’s working on adding more autonomy to the system so it can carry out missions on its own. It has four sets of double rotors with large blades, which spin slowly underwater to propel the craft.

“I see that this is the future, and we have to go in this direction,” he says.

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Mark Contarino, who has worked on UAS airspace integration for years, joined SubUAS as vice president of technology to help turn Naviator into a commercial product. He says the design can be made in a variety of sizes depending on need.

“There’s no reason this couldn’t be a gigantic, autonomous, flying submarine,” says Contarino, who is also president of AUVSI’s Liberty Chapter in Pennsylvania.

While the system could have a variety of commercial uses, from search and rescue to oil spill monitoring, SubUAS recently showcased its utility for bridge inspection.

Naviator flew under the Delaware Memorial Bridge, which links Delaware with New Jersey, and then also demonstrated its ability to drop into the water and surface to fly again.

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