U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
The aging highway bridge infrastructure in the United States is being subjected to increasing traffic volumes and must be continuously renewed while accommodating traffic flow. The traveling public demands that this rehabilitation and replacement be done more quickly to reduce congestion and improve safety. Conventional bridge reconstruction is typically on the critical path because of the sequential, labor-intensive processes of completing the foundation, substructure, superstructure components (girders and decks), railings, and other accessories. New bridge systems are needed that will allow components to be fabricated offsite and moved into place for quick assembly while maintaining traffic flow. Depending on the specific site conditions, the use of prefabricated bridge systems can minimize traffic disruption, improve work zone safety, minimize impact to the environment, improve constructibility, increase quality, and lower life-cycle costs. This technology is applicable and needed for both existing and new bridge construction. The focus of this initiative is on conventional, routine bridges that make up the majority of the bridges in the United States.
To obtain information about technologies being used in other industrialized countries, a scanning study of five countries was conducted in April 2004. The overall objectives of the scanning study were to identify international uses of prefabricated bridge elements and systems, and to identify decision processes, design methodologies, construction techniques, costs, and maintenance and inspection issues associated with use of the technology. The scanning team, therefore, was interested in all aspects of design, construction, and maintenance of bridge systems composed of multiple elements fabricated and assembled offsite. The elements consisted of foundations, piers or columns, abutments, pier caps, beams or girders, and decks. Bridges with span lengths in the range of 6 to 40 meters (m) (20 to 140 feet (ft) were the major focus, although longer spans were of interest if a large amount of innovative prefabrication was used.
The focus areas of the study were prefabricated bridge systems that provide the following:
The scanning study was sponsored by the Federal Highway Administration (FHWA) and the American Association of State Highway and Transportation Officials (AASHTO). The 11- member team included three representatives from FHWA, four representatives from State departments of transportation (DOT), one representative from the National Association of County Engineers, one university representative, and two industry representatives. The team visited Belgium, France, Germany, Japan, and the Netherlands, and held meetings and site visits with representatives of government agencies and private sector organizations. The countries were selected because of their known use of prefabricated systems. Visiting Japan was particularly important because of the country's seismic design requirements.
After completing the scanning study, the team had identified 33 bridge technologies that, in one or more aspects, were different from current practices in the United States. Not all of these related to the primary objectives of the scanning study. Using the six focus areas as selection criteria, the team identified 10 overall technologies that it recommends for further consideration and possible implementation in the United States. A brief description of each of the 10 technologies is given in the following sections.
During the study, many different methods that can be used to remove partial or complete existing bridges and move bridge components or complete bridges into place were observed. These methods allow a new bridge to be built at one location near or adjacent to the existing structure and then moved to its final location in a few hours. Construction, therefore, can take place in an environment where construction operations are completely separated from the traveling public. These methods reduce traffic disruption times from months to days or hours, restore the use of existing highways in significantly less time, improve work zone safety, minimize environmental impact, improve constructibility, and lower life-cycle costs. The controlled environment off the critical path also facilitates improved quality of components. This concept of building bridges offline and then moving them into place needs to be developed for use in the United States.
In Europe, it was observed that large bridge components or even complete bridges weighing several thousand metric tons have been built at one location and then lifted and transported to their final location using a series of vehicles known as self-propelled modular transporters (SPMTs). These multiaxle computer-controlled vehicles have the capability of moving in any horizontal direction with equal axle loads while maintaining a horizontal load with undeformed or undistorted geometry.
In addition to using SPMT and conventional land or barge-mounted cranes to erect large structures, other methods of moving bridge components observed by the team included the following:
These systems can be used to minimize the time an existing bridge is out of service while it is replaced, in many cases within 3 to 48 hours.
The typical sequence of erecting bridge superstructures in the United States is to erect the concrete or steel beams, place either temporary formwork or stay-in-place formwork such as steel or concrete panels, place deck reinforcement, cast deck concrete, and remove formwork, if necessary. Eliminating the need to place and remove deck formwork after the beams are erected can accelerate onsite construction and improve safety. Three systems to accomplish this were identified during the study.
One method to eliminate formwork and provide a working surface is the Poutre Dalle system developed in France. In this system, shallow, inverted tee-beams are placed adjacent to each other and then made composite with cast-in-place concrete placed between the webs of the tees and over the tops of the stems to form a solid member.
One system in Germany involved the casting of partial-depth concrete decks on steel or concrete beams before erection of the beams. After the beams are erected, the edges of each deck unit abut the adjacent member, eliminating the need to place additional formwork for the cast-in-place concrete. This process speeds construction and reduces the potential danger of equipment falling onto the roadway below, because a safe working surface is available immediately after beam erection.
U-Shaped Segments with Transverse Ribs
To reduce the weight of precast concrete segments, the Japanese use a segment in which the traditional top slab is replaced with a transverse prestressed concrete rib. After erection of the segments, precast, prestressed concrete panels are placed longitudinally between the transverse ribs. A topping is then cast on top of the panels and the deck is post-tensioned transversely.
Four innovations for bridge deck systems were identified and are recommended for implementation in the United States.
The use of full-depth prefabricated concrete decks in Japan and France reduces construction time by eliminating the need to erect deck formwork and provide cast-in-place concrete. The deck panels are connected to steel beams through the use of studs located in pockets in the concrete deck slab. The use of full-depth prefabricated concrete decks on steel and concrete beams provides a means to accelerate bridge construction using a factory-produced product.
Prefabricated deck systems require that longitudinal and transverse joints be provided to make the deck continuous for live load distribution and seismic resistance. This is accomplished by using special loop bar reinforcement details in the joints. Various joint details observed during the scanning study should be evaluated for use in the United States to facilitate the use of prefabricated full-depth deck systems.
Hybrid Steel-Concrete Deck Systems
The Japanese have developed hybrid steel-concrete systems for bridge decks. The steel component of the system consists of bottom and side stay-in-place formwork and transverse beams. The transverse beams span over the longitudinal beams and cantilever beyond the fascia beam for the slab overhang. The bottom flanges of the transverse beams support steel formwork for the bottom of the slab while the top flanges support the longitudinal deck reinforcement. When filled with cast-in-place concrete, the system acts as a composite deck system. The system allows rapid placement of a lightweight deck stay-in-place formwork system complete with reinforcement using a small-capacity crane.
In Japan, Germany, and France, concrete bridge decks are covered with a multiple-level corrosion protection system to prevent the ingress of water and deicing chemicals. The systems generally involve providing adequate concrete cover to the reinforcement, a concrete sealer, waterproof membrane, and two layers of asphalt. This type of corrosion protection system may be beneficial with prefabricated systems as a means of protecting the joint regions from potential corrosion damage, thereby ensuring a longer service life. The system may also be used to extend the service life of existing bridges.
Limited use of prefabricated substructures was observed during the scanning study, although such systems could provide significant benefits in minimizing traffic disruption. One substructure system is recommended for implementation in the United States.
The SPER system (Sumitomo Precast form for resisting Earthquakes and for Rapid construction) is a Japanese method of rapid construction of bridge piers using stay-in-place, precast concrete panels as both structural elements and formwork for cast-in-place concrete. Short, solid piers have panels for outer formwork, and tall, hollow piers have panels for both the inner and outer formwork. Segments are stacked on top of each other using epoxy joints and filled with cast-in-place concrete to form a composite section. Experimental research in Japan has demonstrated that these piers have similar seismic performance to conventional cast-in-place reinforced concrete piers. The system has the advantage of reduced construction time and results in a high-quality, durable external finish.
In 2004 and 2005, the scanning team plans numerous written papers and technical presentations at national and local meetings and conferences to describe the overall results of the scanning study and details on specific technologies. The scanning team has also prepared a scanning technology implementation plan for each of the 10 technologies described above.
In general, the strategies involve obtaining more information about the technologies from the host countries, making this information available on FHWA's or other Web sites, seeking demonstration or pilot projects, and holding workshops in association with the pilot projects.
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