The newly completed US 6 bridge over Keg Creek, built in just 16 days using prefabricated elements | Wikimedia Commons
6 bridge over Keg Creek in Pottawattamie County in 2011 closed the road for 16 days instead of the roughly six months that were estimated by Iowa DOT, which would have been required with conventional construction. The accelerated bridge construction project that replaced the U.S. The bridge was completely prefabricated off-site, which made the project a demonstration of accelerated bridge construction techniques that were developed through the federal Strategic Highway Research Program. It was the first project of its kind in Iowa and was described by the Federal Highway Administration as a first in the United States for completely prefabricating the new bridge system off-site and installing it at the crossing.
The bridge itself was a three-span steel and precast modular structure that measured about 210 feet long and 47 feet wide. The prefabricated bridge cost more to construct, but the shorter closure reduced vehicle operating and delay costs to a level that was enough to produce an overall advantage of about $440,000, according to FHWA’s 2013 account of the project. Because its three-span configuration was common in Iowa and other states, and engineers wanted the demonstration to help figure out certain construction methods that could be applied to similar bridges elsewhere, the Iowa DOT says that the bridge was chosen.
Researchers studied the prefabricated components and the ultra-high-performance concrete connections that were used in the bridge, and testing examined the performance of the joints under laboratory and field conditions.
The approach meant that a lot of the work could be completed before the main road closure began, and Iowa DOT selected the Keg Creek site as part of a national research effort that examined ways to replace bridges faster while maintaining structural performance.
