Innovations - Prefabricated Bridge Elements and Systems
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Offsite manufacture of bridges offers many onsite advantages
Prefabricated bridge elements and systems (PBES)—bridge components or entire bridges built offsite and transported to their final location for quick installation–offer a number of advantages over cast–in–place bridge construction.
- PBES components can be built offsite while earthwork and foundation construction is underway, shortening onsite construction time that impacts traffic from months to weeks, days, or just hours.
- Bridge components are manufactured in a controlled environment where the use of consistent materials and methods contributes to uniform quality in the end product.
- Flexible start times for manufacturing components ensures adequate time for proper concrete curing for good long–term performance.
- Less time in the work zone reduces safety risks, especially when working over water or near power lines or other hazardous site conditions.
- PBES construction minimizes site impact, a necessity when working over wetlands or other environmentally sensitive locations.
PBES have been used in new construction and in rehabilitation or replacement of existing bridges. Materials used for PBES are primarily concrete and steel. Lightweight and corrosion–resistant fiber–reinforced polymer has been used in applications such as full–depth deck panels.
Bridges installed using PBES with durable field connections can have a service life of 75 to 100 years. Prefabricated bridge elements include partial and full–depth deck panels, girders, pier caps, columns, footings, and foundations. Prefabricated bridge systems include complete superstructures, complete substructures, and entire bridges. Fabrication plants build most prefabricated elements and transport them directly to the bridge site for assembly or to an adjacent site for assembly of the larger prefabricated systems.
Although prefabricated elements, such as pretensioned concrete beams, have been used by most states for half a century or more, larger and more complete prefabricated systems are becoming more common, such as entire superstructures moved into position with self propelled modular transporters (SPMTs). The next step in the United States is multispan superstructure units and multispan bridges complete with substructures, moved into position with SPMTs as is now done in Europe.
A number of recent projects show the diversity of PBES. These projects range from deck replacements to superstructure replacements to complete bridge replacements, many with no impact on rush hour traffic.
- In 2002, the Virginia Department of Transportation (DOT) replaced the superstructure of its Interstate 95 James River Bridge in Richmond with prefabricated superstructure segments. More than 100 superstructure spans were replaced in nighttime closures using high–capacity cranes and conventional flatbed trailers, with all lanes remaining open to traffic from 6 a.m. to 7 p.m. The superstructure replacement was completed in just 137 nights over 17 months, versus 24 to 36 months using conventional methods. Project costs came in at 11 percent below the engineer's estimate.
- In 2004, the Washington State DOT replaced the deck of the Lewis and Clark Bridge on State Route 433 that crosses the Columbia River between Washington and Oregon during 124 nighttime closures plus three weekend closures, versus the 4 years it would have taken using conventional construction methods. This allowed the steel through–truss bridge to be kept open to traffic during rush hour, eliminating the need for a long detour. More than 100 36–foot–wide full–depth lightweight concrete deck panels, totaling 3,900 linear feet, were installed using a special frame mounted on SPMTs. Every night an existing deck segment was removed and a new panel installed. Installation costs were 38 percent below the engineer's estimate.
- Also in 2004, the New York City DOT replaced the Belt Parkway Bridge over Ocean Parkway in Brooklyn while completely reconfiguring the interchange and parkways, and did so without reducing traffic lanes during rush–hour traffic. Prefabricated components included the piles, T–walls, cap beams, superstructure, parapets, barriers, and approach slabs. Bridge assembly required only a few nights over several weeks. The entire project was constructed in 14 months, including a 3–month winter shutdown, rather than the 3 to 4 years conventional construction would have required. The project came in at 8 percent below the engineer's estimate.
- In October 2007, the Utah DOT replaced the four–span deteriorated 4500 South Bridge that crosses I–215 East near Salt Lake City with a one–span steel girder bridge in just one weekend. The old bridge was removed and the new bridge installed using SPMTs. The 4500 South Bridge was reopened to traffic in 10 days, and I–215 was detoured for just 2 days.
Various prefabricated bridge resources are available. Completed projects with contacts and some plan details and specifications are available on the FHWA prefabricated bridges Web site. A decisionmaking framework helps bridge owners determe whether PBES provide benefits for a specific project is also available there. A new publication, Manual on the Use of Self–Propelled Modular Transporters to Remove and Install Bridges, is available at www.fhwa.dot.gov/bridge/pubs/07022. A compilation of PBES connection details used across the country is at https://knowledge.fhwa.dot.gov/cops/ep.nsf/home.
- "Brooklyn Memorable Season: New bridge features 100–year life and will be completed in less than a year."
- Roads & Bridges, July 2004, Vol. 42, No. 7, pp. 19–23 and 64, http://roadsbridges.com/Brooklyns-Memorable-Season-article5329
- "Prefabricated Bridge Elements and Systems in Japan and Europe," FHWA–PL–05–003, Federal Highway Administration, March 2005,
- FHWA prefabricated bridges Web site, www.fhwa.dot.gov/bridge/prefab/
- "Framework for Prefabricated Bridge Elements and Systems (PBES) Decision–Making," www.fhwa.dot.gov/bridge/prefab/framework.cfm
Senior Bridge Engineer
Office of Infrastructure