UMaine student develops affordable option for shoring up Maine’s aging bridges
space the cost out over time, it’s almost like self-financing.”
Loring has been working with her adviser Bill Davids on the MaineDOT- and Federal Highway Administration-funded project since June 2011 after earning her bachelor’s degree in civil and environmental engineering in May 2011. Davids, the John C. Bridge Professor and chair of the Civil and Environmental Engineering Department, approached Loring with the research opportunity after working with former graduate student Timothy Poulin, who now works for global engineering firm T.Y. Lin International Group in Falmouth, Maine, to develop software that allows existing flat-slab concrete bridges to be analyzed more accurately.
Loring says calculations are used to determine the strength of a bridge and whether it needs to be replaced, but current calculations can be overconservative, calling for more replacements than what might be necessary. The software Davids and Poulin developed was designed specifically to assess the load rating of flat-slab bridges to determine which bridges can be repaired instead of replaced.
For the bridges that can last a few more years with reinforcing instead of replacing, a retrofitting system such as the one Loring engineered, could be applied to increase the bridge’s strength and weight limits.
Loring’s retrofitting system includes composite strips of high-tensile-strength, lightweight carbon fibers sandwiched between glass fibers. The strips are about 4 inches wide and 0.20 inches thick and can be as long as the bridge allows.
“The strips have strength comparable to steel but are light enough to be handled by a single person, which is not something you could do with a piece of steel of the same dimensions,” Loring says.
The composite strips are applied to bridges by drilling holes in the bridge’s concrete and placing threaded rods into an epoxy adhesive, which Loring also tested for durability.
The concrete on the underside of a bridge is weak in tension and is not responsible for supporting the bridge, but rather holding the internal reinforcing steel in place. The reinforcing steel is strong in tension and is the main component in keeping a bridge sturdy.
Bridges that are more deteriorated may not be able to withstand the drilling and would have to be replaced or use a more extensive rehabilitation system, Loring says.
While developing this technology, Loring tested four different composite material systems. She tested two all-glass systems, one with a core fiber orientation at plus or minus 45 degrees and one at 90 degrees, and two glass-carbon hybrid systems with
