AASHTO Journal, 09 October 2015
Minnesota Department of Transportation researchers who are testing the use of unmanned aerial vehicles, or drones, to inspect bridges expect to launch a second phase of their work this fall, after an earlier demonstration showed how one drone type can aid inspectors.
This past summer, MnDOT began researching how to employ UAVs to help inspect the state’s many bridges. “Our initial project was an encouraging first step,” said Jennifer Zink, MnDOT bridge inspection engineer. “Phase 2 of the project will better provide details as to methods, criteria and cost effectiveness for how to apply drone technology best to bridge inspection.”
The research team tested drones while inspecting four Minnesota bridges – in Chisago County, Olmsted County, Morrison County and near Stillwater – that were specifically selected for the study after an extensive evaluation and FAA approval.
Zink and her colleagues wanted to see if drones could help MnDOT curb rising costs of bridge inspections and collect more detailed information.
In addition, they believed drones could minimize risks for bridge inspectors, who traditionally use rope systems to hang off the sides of high bridges to inspect the structures, or special inspection trucks using mechanical baskets to carry inspectors to view hard-to-reach areas.
By contrast, using a drone to gather detailed images would allow inspectors to stay out of harm’s way and keep those inspection trucks out of active traffic lanes.
“The goal of the project was to study the effectiveness and possibilities of using UAVs to aid in bridge inspection work, typically in gathering images without the use of an under-bridge inspection vehicle and in areas where access is difficult or not safe for an inspector,” Zink said.
“There is no substantive guidance in existence for this application of this evolving technology. This initial effort was to gain a better understanding of potential capabilities, processes and planning best practices.”
Before simply launching drones and collecting bridge data, the research team reviewed FAA rules and received the necessary exemptions. While the team sought FAA exemptions to use several drone models, the FAA granted approval only for the use of an Aeryon Skyranger drone.
The team included personnel from Collins Engineers and Unmanned Experts, who worked closely with the MnDOT Office of Aeronautics to plan the project.
MnDOT said the drone “suitably performed a variety of inspection functions that didn’t require a hands-on physical inspection.” Researchers tested the remote-controlled flying device’s ability to gather high-quality still images, video footage and data from infrared cameras.
The drone also provided the ability to capture data needed to construct maps of bridge areas and three-dimensional models of bridge elements.
“The images, including infrared images to detect deck trouble spots, obtained from the drone correlate to the findings in the bridge inspection reports for specific bridge elements,” Zink said.
However, one aspect missing from the research were images of the underside of bridges. The drone model used in the study wasn’t able to shoot images upward from beneath a bridge.
Inspectors said being able to shoot images from beneath a bridge is a key feature, along with the ability to operate a UAV without a signal from global positioning satellites.
“The drone we used in this project was not completely ideal for an entire gathering of imagery for all bridge inspection elements as it was limited to GPS signal capability,” Zink said.
“However, it did give us an idea of what a drone could provide, what the limitations were, and what features we would like to see on newly available UAV models. Unfortunately, our hands were tied with obtaining FAA exemptions only for the particular model used in this project within the funding time frame.”
Still, the initial phase report concluded that drones can be used safely during bridge inspections, and that their risk to both the inspectors and public is minimal.
“Due to the successful outcome of the initial project, we have a better understanding of the drone capabilities we would like to use during an actual scheduled bridge inspection,” Zink said.
“The drone that will be used in Phase 2 is specifically designed for inspection of structures. Several goals exist for the Phase 2 research project, and if we can accomplish them, they will decrease MnDOT’s costs and increase bridge inspection abilities. It could improve inspection data collection for local agencies as well.”
The following video shows MnDOT researchers using the Skyranger UAV.
