156 state bridges ‘deficient’

Twenty bridges that carry upward of 100,000 vehicles daily are among 156 Arkansas spans that inspectors consider structurally deficient and at risk of failing if one component of them fails, according to records in the federal National Bridge Inventory.

The bulk of Arkansas bridges considered deficient and “fracture critical” are on county roads and not heavily traveled, but eight are on more-traveled federal highways and 11 are on Arkansas roads that are maintained by the state. Still another bridge is on an interstate exit ramp in central Little Rock.

“Bridges now are designed with redundancy. Fracture-critical bridges do not have the amount of redundancy that today’s bridges have,” said Randy Ort, a spokesman for the Arkansas Highway and Transportation Department. “But just because it’s fracture critical, it doesn’t mean it’s unsafe.”

An Associated Press analysis of 607,380 bridges in the most recent federal National Bridge Inventory showed that 65,605 were classified “structurally deficient” and 20,808 were classified “fracture critical.” Of those, 7,795 were classified as both - a combination that experts say indicates significant disrepair and risk of collapse.

A bridge is “structurally deficient” when it is in need of rehabilitation or replacement because at least one major component of it has advanced deterioration or other problems that lead inspectors to deem its condition as “poor” or worse. A bridge is deemed “fracture critical” when it does not have redundant protections and is at risk of collapse if a single, vital component fails.

The number of bridges nationwide that are both structurally deficient and fracture critical has been fairly constant for several years, experts say. But bridges on the list change frequently, especially at the state level, because repairs can move one bridge off the deficient list, while dilapidation moves another bridge onto the list.

There are occasional data-entry errors regarding the inventory. And there is considerable lag time between state transportation officials’ reports to the federal government and the addition of the data to the National Bridge Inventory.

For example, Iowa, Nebraska, Missouri and Pennsylvania have all been listed recently on the national inventory as having more than 600 bridges that are structurally deficient and fracture critical, but lists kept by those individual states may show fewer problem bridges.

Pennsylvania has whittled its backlog of structurally deficient bridges, though it still has many more on the list. And every year, an estimated 300 bridges are added to its list because of lack of maintenance.

SPECIFIC SPANS

In Arkansas, the Highway Department is in charge of inspecting all of the state’s 12,500 bridges, and of rehabilitating or replacing any that fall under state authority. If a bridge is owned by a city or county, the Highway Department can recommend a number of remedies for it, including closure.

At Pocahontas, the northbound U.S. 67 bridge needs to be replaced in the next few years, Pocahontas Mayor Frank Bigger said. Until the 1950s, the bridge spun on an axis to let barge traffic through. It gave off a familiar clunk-a-clunk-a-clunk as drivers drove over its joints.

“It was almost a soothing sound,” Bigger said. “You knew you were back in town.”

Then it was modified to remain fixed.

U.S. 67 through downtown Pocahontas handles 25,000 cars daily. Southbound traffic crosses the Black River on the “new” U.S. 67 bridge that was built 30 years ago, Bigger said. Northbound traffic still uses the older bridge. The stretch of road is among the busiest in the state that has a bridge that is both structurally deficient and fracture critical.

Other busy stretches of highway in the state that have problem bridges include the Broadway Bridge in Little Rock, with 24,000 vehicles using it daily to cross the Arkansas River; and the U.S. 70 Roosevelt Road bridge, with 12,000 daily crossings over railroad tracks near the State Fairgrounds.

The Pocahontas and Broadway bridges are scheduled for replacement, as are the U.S. 63 bridge over the Black River at Black Rock - which carries 8,700 vehicles daily - and the Arkansas 7 bridge over the Buffalo River north of Jasper,with 2,400 vehicles a day.

Every bridge in Arkansas must be inspected every two years, Ort said. Those found to have some deficiencies are inspected yearly. Of the 156 bridges considered structurally deficient and fracture critical, all but one are inspected annually. The String Town Creek bridge on Sevier County Road 17 near its intersection with County Road 13 is inspected every eight months, but Ort said he wouldn’t call it the worst bridge in the state.

“We are not going to name a ‘worst bridge,’” Ort said. “They’re either safe or they’re not, and if they’re not, we’re going to shut them down.”

Also, as a safety measure, the state can impose weight limits on bridges.

Bigger hopes some way will be found to preserve the old U.S. 67 North bridge - one of the few still-in-use spans that once rotated from the middle - adding that it “represents an era.” When a railroad span nearby was torn down, he said, it upset some people in town.

TROUBLING BRIDGES

Across the nation, many fracture-critical bridges were built from the 1950s to 1970s as part of the interstate highway system. That’s because they were relatively cheap and easy to build. Now, though they have exceeded their designed life expectancy, they 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.

The Frederick Douglass Memorial Bridge in Washington, D.C., was designed to last 50 years. It’s now 13 years past that. It accommodates more than 70,000 vehicles a day.

The District of Columbia’s transportation department has inserted “catcher beams” under the bridge’s main horizontal beams as a precaution to keep the span from falling into the Anacostia River should a main component of it fail.

Cities and states would like to replace their aging and vulnerable bridges, but few have the money. Nationally,old bridges are a multibillion-dollar problem. Consequently, highway engineers are juggling repairs and retrofits in bids to stay ahead of the deterioration.

There are thousands of inspectors across the country “in the field every day to determine the safety of the nation’s bridges,” Victor Mendez, head of the Federal Highway Administration, said in a statement. “If a bridge is found to be unsafe, immediate action is taken.”

But, experts say, all that is needed to cause a fracture-critical bridge to collapse is a single, unanticipated 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.

Peter Vanderzee, CEO of Lifespan Technologies of Alpharetta, Ga., which uses special sensors to monitor bridges for stress, said steel fatigue is a problem in the older bridges.

“Bridges aren’t built to last forever,” he said. He compared steel bridges to a paper clip that’s opened and bent back and forth until it breaks.

“That’s a fatigue failure,” he said. “In a bridge system, it may take millions of cycles before it breaks. But many of these bridges have seen millions of cycles of loading and unloading.”

That fatigue is evident in a steel-truss bridge over Interstate 5 in Washington state - south of the similar steel truss that collapsed in May. The span that carries northbound drivers over the east fork of the Lewis River was built in 1936.

Because of age, corrosion and metal fatigue caused by vibration, the state has implemented weight restrictions on the bridge. Washington state’s Department of Transportation spokesman Heidi Sause said the span wasn’t built for the kind of wear - bigger loads and more traffic - that is now common.

“This is a bridge that we pay close attention to, and we monitor very carefully,” Sause said.

The biggest difference between the bridge over the Lewis River and the one over the Skagit River that collapsed May 23 is that the Lewis River span was classified as being in worse condition than the one that fell. State officials hope to replace it in the next 10 to 15 years.

The Skagit River span was not considered structurally deficient, but the Interstate 35 West bridge that collapsed in Minneapolis in 2007 had received that classification. That bridge fell during rush hour, killing 13 people and injuring more than 100. The National Transportation Safety Board concluded that the cause of the collapse was an error by the bridge’s designers, not the deficiencies found by inspectors. A gusset plate, a fracture-critical component of the bridge, was too thin, the agency said.

Information for this article was contributed by Troy Thibodeaux of The Associated Press.