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Aging spans: A national concern

  • Article by: Kevin Diaz and David Shaffer
  • Star Tribune
  • August 10, 2007 - 11:54 PM

PITTSBURGH

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.

The successful contractor must raise money for the work, rebuild the bridges and maintain them for 25 years, during which the state makes annual payments under the contract.

"We are going to get a lot of them done -- fast," said Jeff Bridges, spokesman for the Missouri Department of Transportation.

Oklahoma and Iowa lead the nation in structurally deficient bridges. These states are criss-crossed by section-line roads, many of which have old bridges needing repair. "We have 1920s and 1930s bridges -- they were built for Model T's," said Walt Peters, Oklahoma's assistant bridge engineer for operations.

Last year, the Oklahoma Legislature approved an extra $100 million to repair or replace 137 bridges over six years. Even for a small bridge, a typical rehabilitation can cost $2 million.

Iowa, whose covered wooden bridges were made famous in the book and movie "The Bridges of Madison County," has more than 600 bridges of all types more than 100 years old, according to federal bridge data.

Most states, including Iowa, have done better maintaining bridges on major highways, where less than one in 12 is structurally deficient.

Yet many of the spans built during the bridge-building boom of the 1950s and 1960s soon will be reaching the end of their useful lifespans, even with repairs.

"They might be OK now, " said Gary Novey, Iowa's assistant bridge engineer. But what happens in 10 or 20 years? "That is what we have to be concerned about," he added. "If we get those coming at the same time, I don't know how we are going to deal with them."

No postcard bridges

Pittsburgh has long prided itself on its blue-collar ethos, and its bridges are no exception. Suspension bridges, truss bridges, arch bridges, they're all here, but none of them is the stuff of postcards. "There's no signature bridge in Pittsburgh," Harries said. "They're all just built for a purpose."

Virtually every major road goes over one of the city's 446 bridges, and the problems are in plain sight, like the Rankin Bridge's rusting rails and crumbling sidewalk. Underneath, Harries points to exposed, rusty reinforcing bars. Nearby, a disconnected downspout deposits water and debris at the foot of the bridge.

Two years ago, Pennsylvania had its first major bridge mishap in eight decades. A concrete beam broke and dropped off a bridge over Interstate 70 near Washington, Pa., narrowly missing vehicles passing beneath. One driver suffered a broken leg. The bridge's long exposure to corrosive road salt was partly to blame. Harries was PennDOT's principal investigator in that case.

Pennsylvania has a $1 billion statewide backlog of highway and bridge improvements. The planned solution, which still faces political hurdles, is to transform its portion of I-80, one of the busiest coast-to-coast highways, into a toll road and use the revenue to for needed repairs.

Until money becomes available for repairs, however, engineers have to resort to half measures like the "diaper" net that hangs beneath the Greenfield Road bridge over I-376 to catch falling concrete.

"We know what needs to be done, and we know how to do it," Harries said. "The problem is getting the resources to do it."

kdiaz@startribune.com • 202-408-2753 dshaffer@startribune.com • 612-673-7090

Computer-assisted reporting editor Glenn Howatt contributed to this report.

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