The senseFly albris UAV flies under a bridge deck in Minnesota.
Phase 1: Four bridges
While technologies and capabilities differ for the numerous UAVs available on the market, most have a number of features in common: they are powered by rechargeable batteries, controlled either autonomously or with a remote control device, contain four to eight rotors, have the ability to use GPS to track location, contain fail-safes such as return to home technology, and include cameras with both video and still image capabilities.
In phase one of the project to establish the effectiveness of drones for bridge inspection, the team used an Aeryon SkyRanger UAV to inspect four Minnesota bridges of varying sizes and types.
These four bridges were flown following the preparation of a detailed field-work plan. This addressed safety, Federal Aviation Administration (FAA) rules and inspection methods. Several imaging devices were also tested, including still image, video and infrared cameras. Various types of data were collected in the field, including still images, video, infrared images, site maps and 3-D models of bridge elements.
The SkyRanger proved to be a very robust and capable unit, and offered several advantages for the study: its all-weather capabilities allowed researchers to work in the rain, and it also has the ability to change payloads, meaning the team could use a standard camera, an optical zoom camera, and an infrared camera.
On the downside, however, the SkyRanger did not have the ability to look directly upwards, making it necessary to install a 360° video camera on top. Because of Wi-Fi signal interference, this did not perform correctly. In addition, the SkyRanger did not have the ability to fly under bridge decks because the loss of GPS signal would cause the drone to fly vertically and return to the launch point—obviously problematic with a bridge deck overhead.
Phase 2: Looking up
For phase two, at present the team is working with another UAV, the senseFly albris (previously called eXom). This is designed specifically for high-detail inspection work. Researchers chose this system to again inspect different types of bridges, including bridges featuring very confined spaces, such as culverts and box girders, and to conduct deck delamination assessments using the albris’ thermal camera.
The albris has the ability to look directly up and operate without GPS, so it can fly under bridge decks. It also offers infrared thermography and includes ultrasonic proximity sensors to help the operator avoid contact with the structure.
The results confirmed thus far have shown that UAVs are capable of effectively replicating the inspection detail learned through the use of snoopers and other traditional access equipment, without traffic-control requirements, and at significantly lower costs in terms of equipment and traffic control needs. Drones can provide both infrared and 3-D modeling detail of bridges, effectively identify concrete delamination, gather topographic mapping detail and efficiently map riverbank conditions, upstream and downstream, from the bridge site.
At a cost level, based on traditional methods of inspection, the second largest bridge in Minnesota would typically require three snooper inspection vehicles and a total of eight inspection days. This equates to a minimum cost of approximately $59,000, excluding equipment mobilization and travel expenses.
In contrast, the cost of a UAV contract to inspect the exact same approach spans of the project’s sample bridge would be around $20,000 with only five days onsite as per a consultant-obtained quote—a potential cost saving of 66%. This is a substantial saving and suggests that inspection via drone will have a significant impact on the outgoing costs of a transportation department.
