Prefabricated Bridge Elements and Systems Introduction
Prefabricating bridge elements and systems (PBES) offers major time savings, cost savings, safety advantages, and convenience for travelers. The use of PBES is also solving many constructability challenges while revolutionizing bridge construction in the US.
Prefabricating bridge elements and systems offers major time savings. With traditional bridge construction, foundations for piers and abutments must be built first. Pier columns and caps must be built before beams and decks are placed. With PBES, these components can be fabricated concurrently, and then shipped in as needed.
PBES also permits a more effective use of work time. Prefabricated elements are typically constructed in a climate-controlled environment, so weather only affects the portion of the work done onsite. As a result, weather delays are less frequent. Since there is less disruption of traffic, fewer workers need to be exposed to traffic control.
Reducing construction time reduces costs. According to an FHWA cost study, the combination of PBES and effective contracting strategies saved $30 million in just nine bridge replacement projects across the country.
With PBES, delivery trucks and other commercial vehicles encounter fewer delays, and individuals experience fewer road closures. Some PBES construction projects involved no delays at all during rush-hour traffic. Since traffic congestion costs billions of dollars in wasted gas and wasted person hours per year, PBES can play an important role in controlling these costs. As a result, PBES offers an extended effect on the local and national economy.
In traditional bridge construction, workers are often exposed to moving traffic. Particularly during peak hours, this can be a hazard. Drivers may ignore directional cones or fail to notice lane closures. With PBES, construction time is reduced, so exposure to these hazards is also reduced.
Hazards in bridge construction can also include working over water or near power lines. Because prefabrication allows many stages of bridge construction to occur in a safe, controlled environment, exposure to these dangerous settings is reduced. For over-water bridges, the use of prefabricated bent and pier caps reduces the amount of time that workers need to operate over water.
Many job sites impose difficult constraints on bridge construction. A bridge on an interstate highway may have heavy traffic. High elevations may present difficulties in constructing or rehabilitating bridge segments. Construction areas may be restricted due to adjacent stores or other facilities.
The use of PBES can solve many of these constructability challenges. With PBES, many time-consuming construction tasks no longer need to be accomplished in the work zone. Instead, prefabricated bridge elements and systems can be constructed offsite and brought to the project location, ready to erect. Formwork erection, formwork removal, steel reinforcement and concrete placement, and concrete curing can all be done offsite.
If necessary, suitable staging areas can allow PBES to be constructed adjacent to the project site but out of the way of traffic. This can be useful if transporting large elements or structures would be logistically impossible. The construction environment can still be controlled, and the PBES can be moved into position when they are needed.
Greater Convenience for Travelers. Using prefabricated elements and systems minimizes construction-related traffic disruptions for commuters and other travelers. Shorter construction time ensures that bridge and roadway closures are shorter in duration. Traffic patterns can quickly return to normal.
Even during construction, traffic delays are minimal. Fewer lanes need to be closed while construction is in progress. To minimize traveler inconvenience, transporting PBES is often scheduled during nonpeak times.
Added Benefits with PBES
PBES also reduces the environmental impact of construction. Much of the heavy equipment needed for bridge construction can be located in factories rather than on the construction site. In this way, sensitive ecosystems, such as wetlands, are not disrupted.
Reducing construction time also reduces the environmental footprint. Construction can be scheduled around crucial times for plant growth or animal life.
25percent of publicly-owned bridges in the United States are structurally deficient or functionally obsolete. As a result, approximately 150,000 bridges must be built or rehabilitated. FHWA supports the use of PBES as an economical way to address this problem while increasing quality, reducing costs, and supporting safety.