Saturday, December 7, 2013
By Joan Lowy and Mike Baker / Associated Press
WASHINGTON — Motorists coming off the Frederick Douglass Memorial Bridge into Washington are treated to a postcard-perfect view of the U.S. Capitol. The bridge however, is about as ugly as it gets: The steel underpinnings have thinned since the structure was built in 1950, and the span is pocked with rust and crumbling concrete.
A pickup truck drives on a bridge over Sagamore Creek in Portsmouth, N.H. on Sept. 4. According to federal records from 2012, the bridge is one of several in New Hampshire that are considered both "structurally deficient" and "fracture critical."
District of Columbia officials were so worried about a catastrophic failure that they shored up the horizontal beams to prevent the bridge from falling into the Anacostia River.
And safety concerns about the Douglass bridge, which is used by more than 70,000 vehicles daily, are far from unique.
An AP analysis of 607,380 bridges in the most recent federal National Bridge Inventory showed that 65,605 were classified as “structurally deficient” and 20,808 as “fracture critical.” Of those, 7,795 were both — a combination that experts say indicate significant disrepair and similar risk of collapse.
A bridge is deemed fracture critical when it doesn’t have redundant protections and is at risk of collapse if a single, vital component fails. A bridge is structurally deficient when it is in need of rehabilitation or replacement because at least one major component of the span has advanced deterioration or other problems that lead inspectors to deem its condition poor or worse.
Engineers say the bridges are safe. And despite the ominous classifications, officials say that even bridges that are structurally deficient and fracture critical are not about to collapse.
The AP zeroed in on the Douglass bridge and others that fit both criteria — structurally deficient and fracture critical. Together, they carry more than 29 million drivers a day, and many were built more than 60 years ago. Those are located in all 50 states, plus Puerto Rico and the District of Columbia.
The number of bridges nationwide that are both structurally deficient and fracture critical has been fairly constant for a number of years, experts say. But both lists fluctuate frequently, especially at the state level, since repairs can move a bridge out of the deficient categories while spans that grow more dilapidated can be put on the lists. There are occasional data-entry errors. There also is considerable lag time between when state transportation officials report data to the federal government and when updates are made to the National Bridge Inventory.
Many fracture critical bridges were erected in the 1950s to 1970s during construction of the interstate highway system because they were relatively cheap and easy to build. Now they have exceeded their designed life expectancy but are still carrying traffic — often more cars and trucks than they were originally expected to handle. The Interstate 5 bridge in Washington state that collapsed in May was fracture critical.
At the same time, all that is required to cause a fracture critical bridge to collapse is a single event that damages a critical portion of the structure.
“It’s kind of like trying to predict where an earthquake is going to hit or where a tornado is going to touch down,” said Kelley Rehm, bridges program manager for the American Association of State Highway and Transportation Officials.
Signs of age are clear. The Douglass bridge, also known as the South Capitol Street Bridge, was designed to last 50 years. It’s now 13 years past that. The district’s transportation department has inserted so-called catcher beams underneath the bridge’s main horizontal beams to keep the bridge from falling into the river, should a main component fail.
Alesia Tisdall, who drove over the bridge every day for 15 years but now crosses it only occasionally, said she found its “bounce” unnerving.
“You’d look at the person sitting next to you like, ‘Did you feel that bounce?’ And they’d be looking back at you like they were thinking the same thing,” said Tisdall, a computer systems specialist at the Justice Department.
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