U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
At the completion of 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 of minimizing traffic disruption, improving work zone safety, minimizing environmental impact, improving constructibility, increasing quality, and lowering life-cycle costs as selection criteria, the team identified 10 overall technologies that it recommends for possible, immediate implementation in the United States. Although it is expected that all technologies can be beneficial in most focus areas, the particular benefits will depend on the circumstances of each project and may not always be applicable. The reduced construction time that can be achieved with these technologies could result in a substantial savings in traffic control costs and inconvenience costs to the traveling public.
Brief descriptions of the 10 technologies are given in the following sections, together with the team's assessment of the benefits of each technology and an implementation strategy. In general, the strategies involve obtaining more information about the technologies from the host countries, making the information available on Web sites, seeking demonstration or pilot projects, and holding workshops in association with the pilot projects. In addition, the scanning team has planned numerous papers and presentations at national and local meetings and conferences in 2004 and 2005. The purpose of the papers and presentations is to describe the overall results of the scanning study and details of specific technologies for participants to consider implementing in their States.
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 next 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 and lane closures 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. The 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. These multiaxle computer-controlled vehicles are capable of moving in any horizontal direction with equal axle loads while maintaining a horizontal load with undeformed or undistorted geometry.
The scanning team was impressed by the opportunity this technology offers to minimize traffic disruption, improve work zone safety, improve constructibility, improve quality, and lower life- cycle costs. The technology is employed frequently by highway and railway owners to reduce construction impact to days or hours from the months required by traditional construction methods. The usual approach is to construct the superstructure offsite and then move it into place using SPMTs. The same equipment can also be used to remove existing bridges in a very short time rather than demolishing the bridge above existing traffic. Although use of this equipment may be perceived as increasing initial construction costs, the offsetting benefits are a substantial reduction in traffic control costs and inconvenience costs to the traveling public, resulting in lower life-cycle costs.
For implementation, a project-planning guide for bridge owners will be developed. This will emphasize the necessity for early project planning, right-of-way needs for construction, and contract provisions, such as maximum lane closure times, to support and encourage the use of SPMTs. Draft specifications will be developed for DOTs to consider for their projects. The intent is to detail the required qualifications for lifting contractors and appropriate tolerances for placement and distortions of the structure being moved. Information on the technology will be made available to all interested States. Pilot projects will be solicited and workshops held in association with the projects.
In addition to using SPMTs and conventional land or barge-mounted cranes to erect large structures, other methods of moving bridge components include the following:
These systems can be used to minimize the time an existing bridge is out of service while it is replaced, many within 3 to 48 hours. A limited amount of transverse and longitudinal launching has been done in the United States. Some bridges have been floated into place. In Europe and Japan, these methods are more commonplace and accepted by bridge designers and contractors. The scanning team believes that the variety of methods observed can be applied more frequently in the United States, especially to remove and replace bridges in urban areas, minimize traffic disruptions and environmental impact, improve work zone safety, and improve constructibility.
For implementation, the information on a variety of bridge projects observed during the study will be posted on Web sites to stimulate consideration of creative alternatives to conventional construction methods. Pilot projects will be solicited and workshops held in association with the projects.
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 formwork for the deck above traffic after the beams are erected can accelerate onsite construction, reduce lane closures, and improve safety. The following systems to accomplish this were identified during the study.
One method to eliminate formwork and provide a safe working surface is provided by the French Poutre Dalle system. In this system, shallow, inverted tee-beams are placed next 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. A typical Poutre Dalle bridge can be erected in a day. A similar inverted tee-beam has been used on a few bridges in the United States, but the scanning team believes that the Poutre Dalle system offers a faster, more reliable, and more durable system. Adjacent box beams are used in the United States with limited continuity between adjacent units. As a result, deterioration occurs along the longitudinal joint. The loop joint detail used to join adjacent members in the Poutre Dalle system is expected to provide better continuity than details now used in the United States. As a result, reflective cracking along the joint will be less and durability will be enhanced.
For implementation, sample drawings, specifications, and photographs of construction details and completed bridges will be obtained and posted on a Web site. Research will be proposed to validate the loop joint detail and States will be solicited for demonstration projects.
One system in Germany involved the casting of partial-depth concrete decks on steel or concrete beams before erection of the beams. The use on prestressed concrete beams is similar to a deck bulb-tee beam except the deck is not full depth. 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, immediately provides a safe working surface, and reduces the potential danger of equipment falling onto the roadway below.
For implementation, sample drawings and photographs of construction details and completed bridges will be obtained and posted on a Web site as resource material for bridge designers. One demonstration project with steel girders and one with concrete girders will be sought. If appropriate, workshops for FHWA and DOT engineers, contractors, and consultants will be held.
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 slab is then cast on top of the panels and the deck post-tensioned transversely. In addition to reducing the shipping weight, the U-shaped segment allows for longer segments and, therefore, fewer segments per span. The lighter weight allows the capacity of the erection equipment to be reduced. The use of precast panels spanning longitudinally between the transverse ribs eliminates the need for deck formwork and means that the CIP concrete slab can be removed if it needs to be replaced.
For implementation, sample drawings and photographs of construction and completed bridges will be obtained and posted on a Web site as resource material for bridge designers. Available information will be disseminated to the American Segmental Bridge Institute.
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 by 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, eliminates placing and removing formwork above traffic, and reduces lane closures. Although similar systems have been used in the United States, the Japanese system has proved to be low maintenance and durable. One reason for the success may be the use of a multiple-level corrosion protection system. The transverse joint between panels is made with CIP concrete placed over overlapping loops of reinforcement with additional reinforcement threaded through the loops. The Japanese no longer use longitudinal post-tensioning because of previous corrosion problems. They now prefer to use the joint detail.
For implementation, the design basis, test reports, and sample drawings and specifications for both steel and concrete girder bridges will be obtained and posted on a Web site. Research will be proposed to validate the loop joint details and states will be solicited for pilot projects.
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 study should be evaluated for use in the United States to facilitate the use of prefabricated full-depth deck systems. The CIP deck joint may provide better continuity between adjacent precast elements compared to details now used in the United States. It is expected that the joint details will provide better control of cracking along the joint and result in a more durable and longer-lasting structure.
For implementation, the design basis, test reports, and sample drawings and specifications will be obtained and posted on a Web site. A literature search and research, as necessary, will be conducted to validate and enhance standard connection details. The research will address longitudinal joint details for the Poutre Dalle system and transverse joint details for the full-depth prefabricated decks. The work will be coordinated with ongoing activities of NCHRP, State DOTs, and the Precast/Prestressed Concrete Institute. Critical issues to be addressed are concrete cover, loop bar bend radius, type of reinforcement, properties of concrete used for the closure placement, sealing of the interface between the precast and CIP concrete, and the need for a protective overlay. States will be solicited for pilot projects.
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 beams 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. The system eliminates the need to erect formwork over traffic. The scanning team noted that this system was more versatile than conventional stay-in-place steel formwork because the system included the internal beam support system to form the slab overhang. It also allowed the reinforcement to be placed offsite, which reduces onsite construction time.
For implementation, sample drawings and specifications together with photographs of systems will be obtained and posted on a Web site. Details will be evaluated and potential suppliers contacted through the National Steel Bridge Alliance. If suppliers are available, States to build pilot projects will be sought.
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 and ensuring a longer service life. The system may also be used to extend the service life of existing bridges. In Germany, these systems have been used since the mid 1980s and are expected to provide a 100-year service life. Maintenance of the system requires that the riding surface of the asphalt be replaced periodically. Use of these systems, however, will increase the design dead loads for bridges not currently designed for these loads. The other disadvantage of these systems is that they prevent visual inspection of the deck surface. Nevertheless, the scanning team concluded that the systems should be compared with systems now being used in the United States, since these systems are used throughout Japan, Germany, and France. One difference may be the quality of workmanship and attention to detail in these countries, which appeared to be higher than in the United States.
For implementation, a translation of the German specifications will be posted on a Web site as resource material for bridge maintenance, construction, and design engineers. Demonstration projects will be sought from States that now use waterproof membrane systems.
Limited use of prefabricated substructures was observed during the study, although such systems could provide significant benefits in minimizing traffic disruption during bridge construction. One substructure system is recommended for implementation in the United States.
The Japanese SPER system is a 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.
For implementation, sample drawings together with photographs of construction and completed bridges will be posted on a Web site as resource material for bridge engineers. Demonstration projects will be sought and workshops conducted for FHWA and DOT engineers, contractors, and consultants.
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