Transportation
4:13 am
Tue October 29, 2013

With Fixing The Greenfield Bridge, Funding's Not The Biggest Problem

City of Bridges: The following report is the second is a three-part series examining the status of Pittsburgh bridges as the Pennsylvania Legislature considers funding for transportation infrastructure.

Hundreds of bridges in Allegheny County alone are overdue for repairs or upgrades, and whatever happens in the final weeks of the legislative session, it’s unlikely lawmakers will approve funding for all of them.

But sometimes funding isn’t the biggest issue. Take, for example, the 300-foot Greenfield Bridge over the Parkway East. It's due for demolition and reconstruction late next year, and funding for the $17 million project is already in hand. Pittsburgh is set to pick up 5 percent of the tab, with the state contributing another 15 percent and the federal government paying the rest.

While that’s no small chunk of change, the biggest impact may come with the work itself. It’s expected to close the Parkway for about a week, and cut off a major conduit linking Oakland with Greenfield and Squirrel Hill for at least a year.

Unlike many structurally deficient bridges in the area, there's no danger — real or theoretical — of a structural failure that would affect its users.

"There’s not a public safety risk," said bridge designer Patrick Miner, "other than falling chunks of concrete."

Miner, a civil engineer with a local firm, referred to a series of mishaps in the 1980s and ‘90s that prompted officials to wrap the bridge in a protective mesh, and later to build an entirely separate structure underneath it.

That subdeck is there for the sole purpose of shielding the Parkway from errant bits of masonry, like the 10-inch piece of debris that allegedly injured a driver in 2003. Though there’s nothing structurally wrong with the bridge, the concrete it’s built from inevitably cracks, letting in moisture that corrodes the steel reinforcements within.

"It’s kind of like the Hulk when he gets angry and his clothes rip off," Army Corps engineer Katie Bates said. "The rebar is getting corroded and rusting, and it expands. And just like the Hulk throwing off his clothes, the rebar is casting off its concrete."

Over the years that aging concrete has become the Greenfield Bridge’s greatest liability. But back in 1923, when concrete was first coming into its own as a modern building material, it was a major architectural showpiece for Pittsburgh.

"At the time it was built it was the largest single span concrete bridge in the U.S.," Bates said.

It wasn’t always this ugly, either. In fact, it’s a prominent example of the early 20th-century City Beautiful  movement in public architecture — an offshoot of the era’s progressive politics, which sought to to instill civic virtue in the populace through aesthetically ambitious projects. You can see the movement’s influence all over town, in structures like the 1903 Penn Station building on Liberty Avenue.

The coming redesign will honor that architectural legacy by replicating the bridge’s original form-factor, upgraded to steel construction, and retaining or re-creating some of the original ornamental elements. It will also add bike lanes and a wider pedestrian walkway.

"This will be a beautiful design when it’s all said and done," Miner said.

But that’s looking ahead more than two years. First, the old bridge will have to come down, in late 2014.

"Get your popcorn," Bates said. "They’re going to close the freeway for a week and put 10 feet of dirt on top of it. Then they’re going to implode the bridge, and the bridge will collapse on said pillow of dirt, so you’ll see not only the explosion but a really cool ‘poof’ when the rubble hits the freeway."

After the mess is cleaned up, PennDOT says the Parkway should be reopened in early 2015. But it will take another year before the new bridge is ready for use. During that time, residents in surrounding neighborhoods can look forward to heavier and more widespread congestion, as Oakland commuters headed for the outbound Parkway East seek out detours from a short list of possible alternatives, none them very good.

Those kinds of impacts are real, if harder to measure in dollars and cents. But according to PennDOT’s estimates, a less disruptive rehab of the existing bridge would cost just as much, and would buy only a few more decades of use.

Funding for the project itself is not at issue in this case. But the Greenfield Bridge can serve as a cautionary tale: It’s a glimpse into the possible future of any number of perfectly good spans that are wearing out faster than they otherwise might, for lack of consistent maintenance and repairs.

"Frequently you’ll see infrastructure outliving its designed lifespan, and it becomes more expensive when that happens, especially if you’ve been deferring maintenance for other reasons," Bates said. "You can find that it’s a lot more expensive, it takes a lot more time than it would have if you’d done the maintenance 10 or 20 or 30 years ago."