More than 40,000 vehicles crossed the Interstate 40 bridge over the Mississippi River every day until it closed for emergency repairs nearly three weeks ago. The high traffic volume and the way the bridge is designed means the Arkansas Department of Transportation classifies it as "fracture critical."
It was not considered a "structurally deficient" bridge until inspectors found a crack in a steel support beam during a routine inspection May 11. The bridge has been closed since then.
There are 98 bridges throughout the state that are classified as both fracture critical and structurally deficient, according to Arkansas Department of Transportation data obtained and analyzed by the Arkansas Democrat-Gazette. These bridges are not necessarily unsafe even though the terms used to describe them might sound dire, said Gary Prinz, a University of Arkansas associate professor of civil engineering.
"Fracture critical bridges are just as safe as the other bridges," Prinz said. "They just have more processes in place to control safety."
Local, state and federal road departments place higher maintenance and inspection standards on fracture critical bridges, which the American Association of State Highway and Transportation defines as having "fracture critical members ... items defined as steel primary members, or portions thereof, subject to tension whose failure would probably cause a portion of or the entire bridge to collapse."
The Federal Highway Administration defines structural deficiency as the deck, substructure or superstructure being in poor or worse condition, based on rankings from zero to nine. Only one of the three components has to receive a rank of four or lower in order for the bridge to be classified structurally deficient.
Eleven bridges throughout Arkansas have poor decks and superstructures, according to Transportation Department data. Eighteen more have poor decks and 49 have poor superstructures. The Transportation Department did not include substructure information in its data, but process of elimination shows 20 of the 98 bridges in the data provided have poor substructures, since their decks and superstructures scores are both five or higher.
As of 2017, the Federal Highway Administration uses the term "poor" rather than structurally deficient.
Regular and thorough inspections are the primary means of ensuring that these bridges are safe to use.
Monty Frazier, a statewide bridge inspector at the Arkansas Department of Transportation, oversaw inspections for nine fracture critical bridges, including the I-40 Hernando de Soto Bridge into Memphis. He and his crew failed to notice the developing fracture in the bridge during consecutive annual inspections in September 2019 and September 2020.
The department fired Frazier on May 17 citing dereliction of duty, on the recommendation of Michael Hill, the department's heavy bridge maintenance engineer. Hill and Prinz said proper inspection techniques would have caught the crack before it became dangerous enough to close the bridge.
Of the other eight fracture critical bridges Frazier was responsible for, the only one that is also structurally deficient is the Newport Memorial Bridge on Arkansas 367 over the White River in Newport, according to Transportation Department data.
The department said it was reviewing all eight of the other structures that Frazier's team inspected.
SPAN REDUNDANCY
Bridges can have three types of redundancy built into them. Redundancy in bridge design and construction, industry experts say, refers to the capability of the bridge to carry a load after damage to or failure of one of its systems. If one redundant member fails, the rest of the bridge will not fail, according to a 2012 Federal Highway Administration memo.
Redundancy does not prevent a bridge from becoming structurally deficient, and load path redundancy is the only one of the three types that prevents a bridge from being labeled fracture critical. The Federal Highway Administration bases load path redundancy on "the number of main supporting members between points of support, usually parallel, such as girders or trusses," according to the memo.
Engineers can also use structural and internal member redundancies to stabilize bridges, but load path redundancy is unique in that if one member fails, the bridge's load will transfer seamlessly to the other parts of the structure.
More than 24,000 vehicles cross the Broadway Bridge over the Arkansas River in Little Rock every day, and it was built with internal member redundancy, Hill said.
"Until [federal authorities] change the code, I can't look at it as anything but fracture critical," he said. "I'm not worried about the Broadway Bridge. It's going to be there a long time."
Structural damage to the U.S. 63 bridge over the Spring River east of Ravenden in Lawrence County led the state Transportation Department to close the span briefly Tuesday. A routine inspection found a broken pin and a nearly broken hanger, but the bridge has four beams and load path redundancy so it is not fracture critical, Transportation Department spokesman Dave Parker said at the time.
The bridge fully reopened to traffic Wednesday, and it is not labeled structurally deficient in Transportation Department data.
If the bridge had only two beams, the damage would have been significantly more dangerous, Hill said, but the department closed the bridge anyway as a "precautionary measure."
One way to think about the safe construction of bridges is to compare them to aircraft, Prinz said.
"The fuselage isn't one piece of metal," he said. "It's multiple sheets riveted together. That's by design. If a crack forms in one of those panels on the aircraft, it can't just [continue] into the other panels because they're separate panels."
COST, REPAIR OPTIONS
Polk County has the highest number of bridges that are both fracture critical and structurally deficient, with a total of 13. Madison County has six, and all other counties have five or fewer.
The mountainous terrain and numerous waterways make bridges a necessary and common piece of infrastructure in Polk County, said County Judge Brandon Ellison. The county has taken one bridge per year off the structurally deficient list for the past 10 years, he said.
"We are aware of where we're at," he said. "Probably every county is better off than they were 10 years ago."
Rural counties have limited funding and manpower in their road departments, so they often seek to contract out their larger bridge projects, but it's difficult to find qualified, interested contractors that will charge an affordable price, Ellison said.
"When we put a bridge out for bid, sometimes we get zero bids," he said.
The Arkansas Department of Transportation's Salvaged Bridge Material Program could alleviate the cost issue, Hill said. When the department replaces a bridge, steel beams from the old bridge that are in good shape can be reused to build new bridges in any county that needs them.
"If the steel's free, you can put these beams really close together and you don't have to spend much on your slabs," Hill said.
The Silver Bridge in Mulberry crosses the Mulberry River at the border between Crawford and Franklin counties. Franklin County is responsible for maintaining it, but both counties will pay to replace the bridge, since it is not safe for larger vehicles to use, Crawford County's County Judge Dennis Gilstrap said.
It's one of eight bridges in Crawford and Franklin counties that are both fracture critical and structurally deficient, according to the data.
The bridge is open to normal traffic, but school buses and emergency response vehicles have not used it on their routes in decades, although some trucks still try to cross the bridge despite the height barriers and posted weight limits, Gilstrap said.
Neither county could afford to replace the bridge on its own, so they will combine some of their allocated funds from the State Aid County Road Program, run by the Arkansas Department of Transportation.
"It's mostly for safety reasons, but it's an economical benefit for people who are just on the Franklin County side, [so] they can come into Crawford [County] safely to shop," Gilstrap said.