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When the Iowa Department of Transportation announced in 2011 that it would replace a state-owned bridge near the rural town of Council Bluffs, residents braced for the projected six-month project and the 14-mile traffic detour that would accompany it. Yet a mere 14 days later, a new bridge had already been installed.
Though more than 90% faster than initially estimated, the project could have been even shorter, says Bala Sivakumar, the director of special bridge projects at infrastructure solutions firm HNTB Corporation.
“We could have compressed that down to a week, but the state left it to two weeks,” Sivakumar says. “They felt that the two weeks was easily manageable for the local community.”
Sivakumar effectively served as the mastermind behind not only the Council Bluffs bridge replacement, but also an ever-growing number of additional such projects across the United States. A professional engineer, Sivakumar came to the U.S. from India in 1980 with hopes of earning his PhD. He never ended up pursuing his doctorate, he says, instead starting his first job after completing a master’s degree program at Cornell University.
After a quarter-century working in civil engineering, Sivakumar joined HNTB in 2007. It was around that time, he says, that the company was poised to begin a major research project he would eventually help lead. “When I got to HNTB we had just been selected by the Transportation Research Board (TRB) for a major national project. We were asked to come up with innovative techniques for the rapid replacement of bridges, which is known popularly as ABC, or accelerated bridge construction,” Sivakumar says.
“What this project entailed was looking at previous ABC projects and trying to identify promising technologies and obstacles to find ways to essentially standardize ABC so that it could see more widespread use by state DOTs [Departments of Transportation] and other bridge owners,” he says. “Basically, the TRB and the Federal Highway Administration wanted to improve ABC so that bridges could be built quickly—overnight, over a weekend, or within a week—as opposed to shutting down a bridge for a whole season.”
Sivakumar has played a pivotal role in transforming that dream into a reality, overseeing a team of researchers that has collaborated on the development of a streamlined ABC protocol. Drawing on their research, Sivakumar and his colleagues created a master toolkit that, he says, illustrates how a wide array of bridge replacement projects can be completed significantly faster and for far less money through the use of ABC technologies.
Among the ABC methods HNTB researchers have pioneered is Prefabricated Bridge Elements and Systems, where bridge components and even entire bridges are built offsite before being transported to their final locations, where they are then rapidly installed. The HNTB toolkit, Sivakumar says, also contains a number of other ABC techniques, each of which is designed for a particular kind of bridge replacement project. “In terms of ABC technologies there are other key ones we use besides prefabricating,” he says.
“One that we used on the New York project last year is called a slide-in bridge replacement, where you build a new bridge on temporary supports next to the existing bridge. You then do a rapid, overnight demolition of the old bridge and slide in the new one. A third technology we use that’s similar to a slide in is known as a drive in replacement, where a bridge is completely built offsite. On the night of the replacement, it’s put on heavy trailers and driven to its final position before it’s placed on the supports that have already been built below the existing bridge.”
Although they can’t be utilized in every kind of bridge replacement scheme, ABC technologies nonetheless offer a cost-effective alternative to traditional replacements, which, Sivakumar says, routinely take more than six months to complete and are dangerous for both motorists and construction workers. They also exacerbate traffic, with the resulting lane closures contributing to increased vehicular congestion.
“There are several benefits to using ABC over traditional methods,” Sivakumar stresses. “One is obviously what we call the mobility impact and how we can reduce traffic and lane closures. The other thing is that by being able to build a bridge outside of traffic we can build a more durable structure and make sure that the bridges are built to last a lot longer. A third benefit is safety, because work zones are notoriously unsafe for workers and motorists.”
With one out of every nine bridges in the U.S. currently deemed structurally deficient by the American Society for Civil Engineers, state and local governments are increasingly scrambling to perform critical infrastructure upgrades. HNTB’s toolkit, Sivakumar says, provides civil engineers with a simple breakdown of ABC technologies and better equips them to confront the many challenges they’re facing as they work to implement badly needed fixes.
“The engineers of our era have very different challenges than the engineers who were around 60 years ago building the interstate highway system,” he points out. “The challenge of our time isn’t in designing and building bridges—we’ve been doing that for a century. The challenge of our time is how to do that at a lower cost while making them last for 100 years while minimizing the impact on traffic and on the environment. ABC gives us a great way of doing that.”