It's in the hot seat, but accelerated bridge construction is increasingly used, contractors say, because it doesn't interrupt traffic or place workers in danger.
When a newly installed pedestrian bridge collapsed and killed six people at Florida International University in Miami in March, investigators including the National Safety Transportation Board and the Florida Department of Transportation began scrutinizing the project's construction process.
The investigation is ongoing, and so far there's been no conclusion yet that the method used — known as accelerated bridge construction, or ABC — is inherently flawed or even fit to blame in this particular instance.
So, while there are still many unknowns surrounding the FIU bridge failure, one question can be answered, and that is why the ABC method is being chosen in increasing numbers by bridge design teams, state transportation departments and infrastructure contractors.
What is ABC?
But first, what is ABC? The system of bridge building is still being studied and perfected and is still unfamiliar to many of those outside the infrastructure arena. FIU is actually home to its own Center for Accelerated Bridge Construction, which researches issues and technology related to ABC and serves as a basis of consultation to the transportation industry on the method.
Using language from the FIU's website, ABC is a "delivery solution method of building and repairing bridges with the capability to reduce the interruption to traffic and increase safety." The method, also known as rapid renewal, essentially boils down to being a process that allows teams to build a bridge in some location other than its future footprint and then install it on-site in as little as a day.
The method actually encompasses a range of individualized strategies. For example, Bala Sivakumar, professional engineer and resident ABC expert at engineering, construction and infrastructure planning firm HNTB, said that for span replacements of approximately 50 feet to 200 feet, a contractor might build a new bridge next to the one slated for replacement and then, using temporary towers of support, roll the old bridge out and the new one in. For longer spans, the bridge can be divided up into shorter segments and replaced the same way, using expansion joints to link the new sections together.
If there isn’t a time crunch, Sivakumar said, or if the terrain around the bridge does not allow for a lateral slide of spans, the bridge can be prefabricated in pieces, which are transported to the site, if necessary, and then lifted into place and connected after the old bridge is removed. “It’s almost like a Lego set,” he said.
In January, Oklahoma City residents were able to see the process unfold in person when the Oklahoma Department of Transportation trucked in prefabricated railroad bridge pieces to replace an old section of Interstate 235.