Aging spans: A national concern

  • Article by: KEVIN DIAZ and DAVID SHAFFER , Star Tribune
  • Updated: August 10, 2007 - 11:54 PM

Pittsburgh's rusty framework is one sign of the eroded state of bridges across the nation


In a city of vintage bridges, Kent Harries sees nothing remarkable in the streaks of rust and rotting concrete on much of the Rankin Bridge.

"That's telling a story," says Harries, a University of Pittsburgh bridge engineer who has investigated collapses, pointing his binoculars at a rusty beam under four lanes of rush-hour traffic. While Harries believes the rust signals a crack in the center of the road, he doesn't think the bridge has a structural problem, yet.

At the confluence of the Monongahela, Allegheny and Ohio rivers, Pittsburgh calls itself the City of Bridges, many of them built more than a half-century ago of steel made with Minnesota ore. Dozens of its bridges are showing evidence of the ravages of time.

The city and the rest of Pennsylvania are now an outsized piece of the mounting national bridge repair bill that is coming due. One in four major highway bridges in the state are rated structurally deficient, the highest rate in the nation.

While modest progress has been made in fixing the nation's bridges over the past decade, federal officials estimate that addressing all the problems will take more than $12 billion each year for 20 years.

The tab will increase each year that repairs are put off. As bridges age, Harries said, the deterioration tends to increase at an exponential rate. "So it is likely to get worse," he said.

About one in eight bridges in the United States -- a total of 59,000 -- were rated structurally deficient last year. Slightly more bridges are considered functionally obsolete, meaning they have been made inadequate by increased traffic or for other reasons.

Some states, especially in the Rust Belt and the agricultural heartland, have a disproportionate share of bridges in these categories. While not considered unsafe, many carry weight restrictions that force heavy trucks to detour. Low ratings also are a sign that a bridge may someday need major rehabilitation or replacement.

Bridge bubble from the past

Bridge construction in the United States peaked in the 1950s and 1960s.

Now, many of the bridges, like the baby-boom generation that grew up with them, are beginning to age.

In Pittsburgh, the Rankin Bridge, a steel truss design similar to the failed I-35W bridge in Minneapolis, is a costly illustration of the problem. Built in 1951, it has suffered the effects of traffic and weather, to the point where it is classified as structurally deficient and in need of a $45 million renovation, which is to start next year.

Allegheny County, which owns the bridge and 520 others in and around Pittsburgh, has completed two other major bridge rehabilitations and has six more projects in design stages. The work sometimes involves replacing structural steel members and decks.

"We found members where the original ... was meant to be an inch thick, and it was half an inch, " said Thomas Vena, chief bridge engineer for the county.

The deterioration on some bridges, such as the two-lane, steel-truss McArdle Roadway Viaduct No. 1 bridge, is so advanced that the city has resorted to twice-a-month inspections.

Big urban bridges are not the only ones that are deteriorating.

In Missouri, which has nearly 4,300 structurally deficient bridges, officials plan to award a single contract worth up to $600 million to rebuild or replace 800 smaller bridges over five years.

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