A New Approach to Bridge Inspection and Safety

Unmanned aerial vehicle – Digital image correlation (UAV-DIC) System

Forest Products Laboratory’s (FPL) researcher James Wacker with collaborators from the Department of Civil Environmental Engineering, South Dakota State University are working on a new approach to inspecting bridges that will allow inspections to one day be more cost-efficient, easier to conduct, more accessible, and safer for motorists and inspectors alike. The journal article, “New Bridge Inspection Approach with Joint UAV and DIC System,” was published in Structures Congress 2020.

Our nation’s bridges have been under an every-two-year mandated inspection for nearly 50 years. The current method of inspecting bridges is accomplished largely by visual assessment often using costly snooper trucks. Wacker describes this approach as “a passive approach that has provided subjective and unreliable data.”

James Wacker,
Research General Engineer

Basically, our bridges need better methods of inspection. And Wacker is developing ways to do just that—while discovering important research can also include a lot of play.

Wacker and his collaborators have been developing drone technology or unmanned aerial vehicles (UAV), that integrate with digital image correlation (DIC) in order to assess and inspect bridges for more efficient identification of critical damage. DIC “can measure displacements or strains by analyzing patterns of reference and deformed images.” Additionally, images attained from the UAV were analyzed using ImageJ software which can identify and quantify structural damage.

“Being able to learn how to fly a drone vehicle using only a tablet device was fun. It provides a unique perspective above and below the bridge that cannot be realized with land-based digital photography,” said Wacker.

There is a real need for the technology Wacker and his collaborators are developing. To keep our nation’s bridge infrastructure healthy, inspection techniques need to evolve. Bridges really require more quantitative inspection techniques that can capture the exterior as well as the interior of a bridge’s components in order to develop advanced active systems of maintenance and repairs.  

Wacker thinks drones will be the answer.

“In the case of structural health monitoring systems, continuous data collection can be performed by an autonomous system at the bridge site. Other complimentary inspection devices could be implemented by bridge owners (county or local governments) to provide key information between mandated inspections,” explained Wacker.

The researchers used a commercially available drone, DJI Matrice 210, and attached a DIC system to it using a 3D printed mounting plate.

DJI Matrice 210: (a) full package and (b) UAV and remote controller

They practiced their piloting and camera skills in South Dakota State University’s Structure Lab on a timber bridge girder before taking it out to inspect an existing timber slab bridge in Pipestone, Minnesota.

Bridge overview: (a) bridge road captured by digital camera and (b) bridge captured by the UAV

And although the team experienced some challenges, from non-forecasted wind conditions to a herd of cows unpredictably traveling beneath the bridge, Wacker sees real potential for this technology to positively change the landscape of bridge inspections in the future.

“Non-contact inspection methods like UAV systems can help to ensure the safety of bridges for the motoring public. UAV techniques also help to reduce hazards to the safety of inspectors and motorists, most prominently on those bridges where underside access is a challenge due to height over-water and/or depth and current of underlying streams,” Wacker explained.

Wacker and his collaborators are focused on cost-savings because it makes their research more accessible to tight county or local government budgets. That’s why they chose only commercially available technology for their research. And he sees the challenges they faced during the Pipestone bridge inspection as only a matter of time before they are resolved by the rapidly evolving field of drone technology.

To find out more about the amazing advancements our scientists are making, visit the Forest Products Laboratory at: https://www.fpl.fs.fed.us/