Is building a prefabricated structure the best choice for your bridge project? Will prefabrication be achievable and effective for a specific bridge location in your state? These questions and more are covered in the Federal Highway Administration’s (FHWA) new Framework for Prefabricated Bridge Elements and Systems Decision-Making. As states such as Connecticut, New Jersey, New York, Texas, Utah and Washington have demonstrated, the use of prefabricated bridge elements and systems offers significant advantages over on-site cast-in-place construction, including faster and safer construction and better quality. Depending on the specific project, construction costs also can be comparable to or lower than conventional construction. Costs can particularly be reduced where repetitive components and systems are needed for long water crossings and in high-traffic corridors where traffic control and maintenance needs can be minimized using accelerated construction schedules. Costs also can be lower as a result of reduced contractors’ overhead.
Prefabricated bridge systems are manufactured off site at a prefabrication plant or adjacent to the project site by the contractor, under controlled conditions and with improved quality, and brought to the bridge location ready to install. Building in a controlled environment provides the advantages of reducing weather-related delays and enhancing constructibility, while reducing traffic congestion and improving work-zone safety.
Careful planning, design and implementation will help transportation departments realize the significant advantages of prefabricated bridge construction. The FHWA’s new framework provides a quick and useful tool for making a decision on using prefabrication. It is offered in three formats for users: a one-page flow chart, a one-page matrix and a more detailed question-and-discussion format. The flow chart guides the user through a series of questions about different elements of the bridge project, such as “high traffic volumes,” “emergency replacement” and “environmentally sensitive site.” The matrix provides more detail on these and other questions, while the question-and-discussion format presents an in-depth evaluation of the use of prefabrication. The three different formats are designed to accommodate the different responsibilities of users, who might range from a state bridge engineer to a bridge design engineer or project manager.
The Utah Department of Transportation (UDOT) is using a “Decision Tree” adapted from the FHWA’s new framework to make decisions on when to use prefabricated bridge systems. UDOT has used prefabricated bridge technology on a rapid deck replacement project on I-80 near Coalville and for a project on I-215 in Salt Lake City. The I-215 project involved a deck replacement on one bridge and the whole bridge replacement of another structure. The use of prefabricated elements allowed both projects to be completed faster, with improved quality and less disruption to traffic. Among the lessons learned on the projects to date is the need to familiarize contractors and other industry personnel with the process; involve contractors and prefabricators in the design process; and consider construction issues such as staging areas needed, work hours required and contingency plans.
The Connecticut Department of Transportation, meanwhile, saved at least $1.1 million by using a prefabricated truss center span when constructing a new bridge over the New Haven Interlocking and Rail Yard. The 320-ft-long, 850-ton truss center span was constructed over several months next to the rail lines and then lifted into place on a single morning, using a mobile, high-capacity crane.
A joint project by the Oregon and Washington state departments of transportation to widen and replace the deteriorating deck on the historic 1929 Lewis and Clark Bridge also was completed more rapidly by using prefabricated bridge elements. The use of prefabricated concrete deck panels and prefabricated widening sections supported on floor beams and steel girders allowed the work to be accomplished in 124 nighttime road closures, in addition to three weekend closures. The project also came in under budget. If the prefabricated elements had not been used, replacing the bridge deck lane by lane would have taken four years.
To obtain a copy of the decision-making framework or to learn more about prefabricated bridge technology, visit the FHWA’s prefabricated bridge elements and systems website at www.fhwa.dot.gov/bridge/prefab/index.htm. The website includes information on best practices, video clips of bridge projects and details on how prefabricated bridge elements and systems are being used around the country and in Japan and Europe. The FHWA also can bring in a team of experts upon request to assist transportation departments in evaluating or scoping out projects using prefabricated bridges for accelerated construction.
