Checking in with Michigan 3DOBS project

By: Tim Bruns

A major motion picture is coming to theaters courtesy of the Michigan DOT (MDOT) and Michigan Tech Research Institute (MTRI).

Or … so one would think based on the fact that the two entities are engaged in a partnership to develop a system that captures high-quality images of concrete bridge decks for their inspection using a professional cinema-grade digital camera known as the RED 8K S35.

“The system is a movie camera that they use to make actual Hollywood movies,” Rick Dobson, research scientist for MTRI acting as principal investigator on the project, told Roads & Bridges. “And that’s mounted onto a vehicle mount that can fit into any standard trailer hitch on a truck or SUV.”

Over the past few years, MDOT and MTRI have collaborated to develop a new system that would allow bridge inspectors to scan the finer details of bridge decks at near-highway speeds without the need for lane closures or exposing workers to potential traffic hazards. The system, known as the 3-D optical bridge evaluation system (3DOBS), uses the aforementioned vehicle-mounted camera combined with an image analysis software as an additional method to traditional bridge inspections.

Phase 1 of the 3DOBS project began around 2012 for MTRI, with a home-built wooden mount that would fit in the bed of a truck, according to Dobson. At the time, the team was working with a 12-megapixel (MP) Nikon D5000, while only driving at a speed of 1 to 2 mph across a bridge. Since its partnership with MDOT, MTRI has further developed the system, which now uses the 35.5-MP camera, to drive up to speeds of 45 mph. The new camera has the capacity to capture high-quality video images and spatial orientation data at near-highway speeds under real-world conditions.

Under phase 2 of the project, the research team has driven the system across 11 structures for assessment of large bridge decks. One of the structures included the I-696 bridge over I-75 in the Detroit metro region. The high-resolution imagery collected from the system tests over these bridges allowed the team to locate cracking, spalling, and other structural conditions otherwise potentially missed.

One advantage noted by the research team was the speed and accuracy of collecting the data with the 3DOBS system. According to MDOT, the new camera was able to resolve cracks down to 1/64 in., and the typical data collection time for an average-sized bridge deck was 30 minutes or less.

“With traditional bridge inspections, you’re doing a visual inspection, typically from the shoulder,” Brandon T. Boatman, P.E., North & Superior Region bridge engineer for MDOT, told Roads & Bridges. “You might not get the hairline cracks. What this does is it actually puts you right overhead of that deficiency. And it’s going to give you an accurate boundary or quantity to quantify the deficiency.”

Once data is collected, the software can generate either a 2-D mosaic stitched together from many individual images or a 3-D model of the bridge deck. The imagery can be used to monitor deterioration over time.

With 75% of MDOT’s highway bridges at 40 or more years old, implementing asset management tools such as 3DOBS is critical to preserving the system. The 3DOBS technology could prove particularly effective for structures with larger deck areas. “These are high-investment structures where we need to focus our preservation efforts,” Boatman said. “So if we scan the deck and have a baseline, we can continue to track the deterioration over time. And then apply a preservation treatment at the ideal time.”