Iowa county’s GRS bridge construction technique to be studied for cost savings

Updated Nov 11, 2016
Photo credit: Still from KCRG TV footagePhoto credit: Still from KCRG TV footage

Engineers in Iowa’s Buchanan County used a new construction technique and new construction materials to replace the Catt Bridge on 215th Street, northeast of Independence, reports. Outside contributions helped pay for one-third of the $250,000 price tag on the 40-foot-wide bridge over Nash Creek.

Buchanan County engineer Brian Keierleber said they used wooden beams instead of the usual concrete on the bridge as an experiment. â€śIf you look at the beams there on the bridge, those are two by 12 sections of wood that are pressure treated and glued together, so pressure treating them keeps them from decaying,” Keierleber told the news agency.

Plus, the bridge abutments are made using a technique of mixing tough fabric with gravel in layers, called Geo-synthetically reinforced soil (GRS). Gluing and laminating the wooden beams together with GRS is a new technique and might even be unique to this bridge.

Travis Hosteng, a bridge research engineer at Iowa State University’s Bridge Engineering Center, told the news agency that the GRS technique could save counties money on smaller bridges by eliminating the need to hire specialized bridge contractors. â€śYou don’t need large equipment to set this material or build these bridges as the county engineer showed, you could do it with a county work force, and smaller numbers of less skilled labor,” he said.

The bridge office at Iowa State will be watching the bridge using cameras and built-in sensors to monitor the stress of daily traffic, and will have images and data available in real time. County engineers across the state will be watching to see if the wooden bridge holds up, and if all goes well, might decide to give it a try in their own counties.