This photo shows the construction site of a bridge being built using PBES components. The bridge is on U.S. Route 6, traversing Keg Creek in Iowa’s Pottawattamie County. A truck is carrying a prefabricated abutment with corrugated voids (or pile pockets), which are backfilled with self-consolidating concrete after the abutment is set.
[Credit: Iowa DOT]
The Federal Highway Administration (FHWA) Every Day Counts initiative aims to identify and deploy innovation that can shorten project delivery, enhance roadway safety, and protect the environment. Prefabricated bridge elements and systems (PBES), an accelerated bridge construction (ABC) strategy, have gained notable traction since the initiative began in October 2010.
So far, 40 States, the District of Columbia, Puerto Rico, and all 3 Federal Lands Highway Divisions have elected to implement PBES into their bridge design and construction programs. In nine bridge replacement projects across the United States, PBES used in tandem with strategic innovative contracting techniques saved $30 million, according to a FHWA cost study. Since the start of the EDC initiative, over 600 bridges have been designed or constructed using PBES.
“The EDC program has encouraged decisionmakers to realize the benefits of PBES, which has allowed bridge practitioners the opportunity to advance it and other innovations into the mainstream of the bridge industry,” said Louis Triandafilou, P.E., who leads the Bridge and Foundation Engineering Team in FHWA’s Office of Infrastructure, Research and Development.
PBES are structural components of a bridge that are built away from the final bridge alignment to reduce the time of onsite construction and mobility impact that affects the traveling public. Effective for small and large projects, PBES applications range from deck, superstructure and substructure replacement elements, to modular superstructure system replacements, to complete bridge replacements. PBES constructed bridges have the potential for a minimum of a 75-year service life.
Prefabricating deck, beam, pier, abutment and wall elements, as well as miscellaneous bridge elements such as approach slabs and parapets, offers many benefits, including a reduction in onsite construction time, traffic delays, environmental impacts, and life-cycle cost; and an improvement in work-zone safety, site constructability, material quality, and product durability.
“This kind of innovation is exactly what President Obama means when he asks us to be smarter in the way we do business,” U.S. Transportation Secretary Ray LaHood stated last year. “Getting these bridges up and open to traffic quickly saves money and keeps traffic moving.”
Typically, conventional bridge construction methods involve building the substructure, superstructure, deck, and other elements onsite in a linear manner, often alongside ongoing traffic. With PBES, components can be prefabricated concurrently and delivered as needed, saving time and reducing costs. Also, because prefabricated elements are usually constructed in a climate-controlled environment, weather delays are less frequent. Reduced construction time also means reduced hazards associated with dangerous settings and moving traffic. What’s more, as the amount of heavy equipment time needed onsite for bridge construction is reduced, so is the environmental impact.
Last year, FHWA released a comprehensive manual, Accelerated Bridge Construction: Experience in Design, Fabrication, and Erection of Prefabricated Bridge Elements and Systems (Pub. No. FHWA-HIF-12-013), to assist transportation agencies and contractors in implementing ABC-PBES practices. The manual discusses major components used in ABC deployment, including PBES applications, and offers guidance on project planning, construction, and inspection activities.
Over the past few years, FHWA’s Highways for LIFE program has completed five PBES showcases. The program works with the highway industry to promote innovations that improve safety during and after construction, reduce congestion caused by construction, and improve the quality of the highway infrastructure. The showcases have attracted more than 100 people, representing FHWA Headquarters, Division, and Resource Center offices; State DOTs; the contracting and materials industries; consultant engineering companies; and academia.
Last summer, over 10-weekends between June and August, the Massachusetts Department of Transportation replaced 14 bridges on I-93 in Medford using technologies promoted by the Highways for LIFE program, including PBES and other ABC solutions.
“These technologies help keep traffic moving, which lets people spend less time in their cars and have more time doing the things they enjoy,” FHWA Administrator Victor Mendez said after witnessing the rapid construction last summer. Replacing all 14 bridges using conventional bridge construction methods would have cost much more and taken 4 years or longer to complete the work, during which time drivers would have faced long-term lane closures.