Rapid Bridge-Building Toolkit Nears Final Field Tests
State transportation departments wishing to replace bridges faster using accelerated bridge construction, or ABC, techniques will soon have a standardized design tool kit as a reference.
Developed as part of the second Strategic Highway Research Program(SHRP 2) and administered by the Transportation Research Board (TRB), the tool kit contains standardized plans for modular components, erection concepts, construction specs and other data that can be applied to a wide range of projects.
Monica Starnes, TRB senior program officer, says the goal is to help make ABC a common tactic for rapidly replacing bridges. The tool kit captures ABC concepts that have been used successfully to date, adds co-principal investigator Bala Sivakumar of HNTB Corp.
The entire tool kit will undergo beta testing this summer in Vermont as the state's Agency of Transportation plans to apply a variety of ABC techniques to replace 17 bridges damaged last September by the remnants of Hurricane Irene.
While the initial version of the ABC tool kit will be published by the end of this year, Starnes expects refinements to continue even after SHRP 2 ends in 2015.
With consultants Structural Engineering Associates Inc., San Antonio, and Genesis Structures Inc., Kansas City, Mo., HNTB developed erection concepts, while Iowa State University tested ultra-high-performance concrete used for joining the prefabricated elements.
The tool kit's sample plans for modular superstructures cover span lengths of up to 130 ft that use concrete-on-steel beams, concrete-bulb tees with precast decks and concrete double-T systems. The tool kit also addresses piers, abutments, wing walls and approach slabs.
"A designer can customize these standards for a specific bridge at a specific site," says Sivakumar.
The first full field demonstration of the tool kit took place last fall with the replacement of the U.S. Route 6 Keg Creek Bridge in Pottawattamie County, Iowa. Ahmad Abu-Hawash, Iowa Dept. of Transportation chief structural engineer, says the original, conventional plan for replacing the 180-ft-long bridge would have required a detour 22 miles away during an anticipated six months of construction. ABC required only a two-week shutdown.
Because the new three-span, 205-ft- long steel modular bridge is wider, shafts were drilled and poured before demolition work began in October. On adjacent land, Godbersen-Smith Construction Co., Ida Grove, Iowa, fabricated the components and lifted them into place. The new bridge was opened by Nov. 1.