- What are Prefabricated Bridge Elements and Systems (PBES)?
- What is the advantage of using PBES, rather than creating them onsite when they are needed?
- Which factors are most important in determining whether PBES should be used?
- Will shipping large bridge elements or complete systems require bridge or highway closures? What if closing is not possible or practical?
- Can PBES be used for smaller-scale needs, such as the repair or replacement of bridge parts?
- Is PBES a good option in environmentally sensitive regions?
- If bridge work needs to be done on a structure that is on or eligible for the National Register of Historic Places, can PBES be used?
- Are many bridge elements standardized?
- Is stockpiling of prefabricated components typical in bridge construction?
- Is it difficult to find contractors with PBES experience?
- Can prefabricated components be transported to the site over existing roads, railways, or waterways?
What are Prefabricated Bridge Elements and Systems (PBES)?
PBES are manufactured offsite, so they are ready for installation when they are brought to the construction site. Bridge elements are the basic building blocks of bridge construction, such as decks, deck panels, girders, pier caps, columns, pile cap footings, and foundations. Bridge substructure and superstructure systems are made from various combinations of the bridge elements.
What is the advantage of using PBES, rather than creating them onsite when they are needed?
Using PBES greatly reduces onsite construction time and costs, particularly when many similar components are required for a project. PBES also reduces the impact to travelers, and work zone safety is improved, since parts can be manufactured in a controlled environment. Weather has a smaller impact. Quality increases, since fabrication conditions are controlled.
Which factors are most important in determining whether PBES should be used?
If average daily traffic and/or average daily truck traffic in the work zone is high, PBES is recommended. If the bridge is essential as an evacuation route, or if the bridge replaces an existing essential structure, the speed of PBES makes it an obvious choice over traditional construction, which is slower. Where bridge construction poses unusual hazards to worker safety and/or traveler inconvenience, using PBES can alleviate those conditions. These elements can be evaluated through the use of a FHWA decision-making framework, or one developed specifically by a State.
Will shipping large bridge elements or complete systems require bridge or highway closures? What if closing is not possible or practical?
Replacing or rehabilitating a bridge is typically more efficient and economical if the bridge can be closed for the entire construction period, but lane and highway closures can be minimized. Deliveries of elements and systems can be planned for off-peak times, including weekends. For some deliveries, single-lane closures are sufficient.
Can PBES be used for smaller-scale needs, such as the repair or replacement of bridge parts?
Yes. Prefabrication allows faster partial or total repair of bridges and bridge parts. If standardized bridge elements are used, the use of PBES can offer costs savings in both small and large projects.
Is PBES a good option in environmentally sensitive regions?
Yes. Environmentally sensitive areas, such as wetlands or urban areas in which air and water quality and noise pollution are issues, can limit the amount of construction work that can be done onsite. They can also limit construction scheduling, as during seasons when wildlife and plant life are particularly vulnerable. Because PBES offers rapid onsite installation, the environmental impact of construction is reduced.
If bridge work needs to be done on a structure that is on or eligible for the National Register of Historic Places, can PBES be used?
Communications with the State Historic Preservation Officer are crucial during the preliminary planning stages. The prefabrication of bridge components should be consistent with historic bridge requirements. The owner will need to determine if appropriate pieces of the existing bridge can be incorporated into the new bridge. In some cases, monuments, parapets, stone work cladding, plaques, or other significant features can be salvaged and added on after the new bridge is in place.
Are many bridge elements standardized?
Prefabrication may involve standardized or unique components and systems. Using standardized components can shorten onsite construction time and increase cost savings. In some cases, using a State’s precast slab span standards or precast bent cap system at multiple locations in a bridge project will result in more economical construction. Further savings can be achieved through mass production and stockpiling standardized prefabricated components in regional locations.
Is stockpiling of prefabricated components typical in bridge construction?
So far, widespread stockpiling of prefabricated components has only occurred with temporary bridge truss members. Stockpiling a wider range of components for permanent bridges will require planning. The most appropriate entity to own and manage the stockpile must be determined. The owner will also need to determine which components are used commonly enough to make stockpiling economically sensible.
Is it difficult to find contractors with PBES experience?
Construction of prefabricated bridges is no more difficult than conventional construction. It does, however, require some different skills and areas of experience, particularly from the construction superintendent. Using contractors with the proper training, equipment, and experience offers the best guarantee of a successful outcome. If such contractors are not locally available, it may be necessary to advertise the project to a wider market to get enough qualified bids.
Can prefabricated components be transported to the site over existing roads, railways, or waterways?
Preliminary planning requires a site survey for impacted intersections, allowable haul times, permit regulations, utility relocations, second party easements (municipal, railroad, airport), and ease of movement throughout congested areas, including job site detours. Longer and heavier prefabricated components can require modification to conventional transportation and erection practices. For transportation over highways, the hauling systems must have axle numbers and spacing such that the loads are within permit limits. The transporter must find a route that has adequate turning radii to get longer components to the bridge site. In some cases, parts can be shipped by barges without requiring any re-handling on land.