A Shorter Span
Accelerated Bridge Construction Projects Can Help Sponsors and Motorists
Bridge construction projects are a commuting nightmare. There's no easy detour around the interminable lane closures and traffic jams they trigger. But as U.S. state transportation departments embrace accelerated bridge construction (ABC) practices, this type of disruption could become less common.
“ABC projects are a lot more efficient, but they require very careful project planning.”
—Fernando Quiroga, Quiroga Pfeiffer Engineering Corp., Albuquerque, New Mexico, USA
ABC can dramatically compress construction phases. Bridges are closed entirely, and prefabricated elements built off-site are assembled on-site to speed assembly. This method reduces traffic headaches and environmental impacts; less gridlock means fewer auto emissions. And by enabling projects to be completed within traditional construction seasons, ABC practices reduce the risk of potential weather-related delays.
“You get the structure up much faster, which makes the public and project owners a lot happier,” says Joe Carrara, president of J.P. Carrara and Sons, a concrete production company located in Middlebury, Vermont, USA.
As of 2016, ABC projects have been completed or are underway in 44 of 50 U.S. states. Governments have been slow to adopt the approach; they had to be assured bridges delivered via ABC practices would meet durability and seismic requirements. Now ABC is becoming a standard practice for bridge projects across the United States, which needs to invest US$20.5 billion annually to eliminate the nation's deficient bridge backlog by 2028, according to the U.S. Federal Highway Administration.
Most ABC projects cut construction schedules from months to weeks, says Mr. Carrara. When his company recently completed an ABC project in Waitsfield, Vermont, USA, the bridge was erected in just four weeks, with a few additional weeks needed to finish and pave connecting roads. Without ABC, the project could have extended much longer, he says.
But all the time savings don't come out of nowhere, says Fernando Quiroga, president, Quiroga Pfeiffer Engineering Corp., Albuquerque, New Mexico, USA: “ABC projects are a lot more efficient, but they require very careful project planning.”
During the design phase, precasters and engineers need to work closely with project owners. The team must ensure the design is achievable and that the precast pieces can be shipped to the site and assembled without requiring specialty cranes or massive storage sites. These early conversations are important, because transportation departments might not be aware of shipping and assembly limitations, Mr. Quiroga says. “If the pieces are too tall or too wide, it can create real complications later on.”
U.S. bridge projects have been putting the “accelerated” into ABC.
Location: Interstate 95, near Christiana, Delaware
Budget: US$4.7 million
Achievement: Working 24 hours a day, project teams turned what would've been a six-month project into one that lasted six weeks.
Location: Interstate 10 Tex Wash Bridge, California
Budget: US$5 million
Achievement: When parts of the bridge collapsed during a storm, the state turned to ABC methods to replace the structure in two months. Otherwise it could have taken almost 10 times as long.
Location: Bessemer Avenue Bridge, East Pittsburgh, Pennsylvania
Budget: US$2.3 million
Achievement: A 20-person crew replaced an 86-year-old bridge in just 57 hours—avoiding a big headache for those in the 22,000 vehicles that traverse it every day.
Project teams also need to collaborate with local transportation departments and law enforcement to plan a delivery strategy. Precast bridge beams can weigh 80 tons or more and often require road closures, police escorts and special routes to ship them to the project site, Mr. Carrara says. For every project, his team is required to submit a shipping plan to the transportation departments of every state they will travel through. Plans include analysis of axle load impacts on roads and bridges, timing and requests for escorts. “All of this needs to be considered as part of the project plan and factored into the budget and schedule,” he says.
Meanwhile, because bridge pieces are cast off-site rather than in the field, a team can work on-site to build footings for the new bridge while the old bridge is still operating. When the footings are completed and new pieces have arrived at the site, the old structure is demolished. Its replacement can be assembled in a matter of days. Mr. Carrara's teams use a fleet of remote-controlled steerable dollies to transport the massive components to the project site.
Because bridge elements are precast, there are fewer workers required on site. That can make management of an ABC project site easier than a traditional project site. “The key is making sure everyone on the site understands their role for getting the project completed,” Mr. Carrara says. A critical path schedule submitted to the department of transportation prior to the start of construction helps ensure this. Project leaders should also set expectations for rapid response times and stick to them. “If we need to discuss a problem or get drawings approved, they need to be available,” Mr. Carrara says. “Collaboration among all the teams is important.”
The bottom line: ABC construction methods require more careful planning than conventional projects, Mr. Quiroga says. That's because of the compressed schedule and greater site constraints due to the existing bridge remaining in service until the new bridge is ready for quick installation. But, he says, “the quality and time savings make it worth it.” —Sarah Fister Gale