Inspectors called for an emergency shutdown May 11 of a major Mississippi River bridge in Memphis, Tennessee, after a crack was found on a steal beam.
“We just found a super-critical finding that needs traffic shut down in both directions on the I-40 Mississippi River bridge," an inspector is recorded saying in a 911 call.
“We have critical findings in one of the members that has split," he adds later. "We need to get people off the bridge immediately.”
With the bridge closed, the Tennessee and Arkansas departments of transportation are assessing the damage along with engineering firms to determine the needed repairs and when the I-40 Hernando de Soto Bridge could be reopened.
“This fracture had the potential of becoming a catastrophic event that was prevented by our staff’s diligent effort in managing our bridge inspection program,” said Arkansas DOT Director Lorie Tudor. The DOT's last inspection, in September 2020, "did not reveal any structural deficiencies," ARDOT says. The bridge was rated to be in fair condition. ARDOT says the bridge is inspected annually because it is deemed "fracture critical" because of its construction.
Steve Frisbee, ARDOT assistant chief engineer of operations, said, “The fracture is a result of wear-and-tear.”
On May 14, ARDOT revealed that a drone video during an inspection in 2019 showed damage to the same bridge section that is cracked. "ARDOT is now investigating to see if that damage was noted in a September 2019 inspection report and, if so, what actions were taken." {Related: Inspector Fired After Cracked Beam Led to Closed Mississippi River Bridge.}
Inspectors find a cracked beam May 11, 2021, on the DeSoto Bridge.Arkansas DOT
The Arkansas Trucking Association estimates the shutdown will cost the trucking industry $2.4 million a day. "The closure of the I-40 bridge creates bottlenecks and delays impacting all 26,500 trucks relying on this major freight corridor connecting east and west,” said Arkansas Trucking Association President Shannon Newton.
Newton said this would add to the overstrained supply chain. “Driver shortages, equipment shortages, fuel shortages and now a major roadblock through one of our country’s busiest trade corridors – an impact to consumers is inevitable.”
The fracture is just off the midpoint of the 900-foot-long mid-span on the unique steel-tied arch bridge. The entire structure is 3.3 miles long, with 164 spans, 160 piers and 10 abutments, according to TDOT. The channel spans consist of five steel-box girder spans and two steel-tied arch truss spans.
The crack was discovered within the elements of a steal box beam beneath the bridge deck. The arch truss is connected to box beams. The crack affects all of the box beam's outboard plate, all of its top plate and 20% of its bottom plate, according to TDOT.
"The bridge is undergoing intense analysis, including bridge modeling, to determine the extent of the damage," TDOT says. "As of May 14, 2021, there is no indication that the bridge is continuing to deteriorate. Additional modeling and analytical tools will be used to ensure quality control before making a final determination on structural stability. Design teams are working on short- and long-term solutions that would allow traffic to safely resume on the bridge."
TDOT has hired engineering firm Michael Baker International, which conducted the initial inspection for ARDOT and called 911, to reassess the bridge's load capacity to determine if it is safe for inspectors to return and for the bridge to reopen to barge traffic. A further analysis will be conducted to determine to what extent the bridge could be reopened while repairs take place or if the bridge will need to remain closed until repairs are completed.
Paul Degges, chief engineer for the Tennessee DOT, said the Federal Highway Administration and the U.S. Department of Transportation have granted emergency approval for a repair contract when it is ready.
The location of the fracture on the Hernando de Soto Bridge in Memphis is noted by the red arrow.Tennessee DOT
Under the states' agreement, ARDOT is in charge of inspecting the bridge, and TDOT is in charge of repairing and maintaining it. The two states split the costs. ARDOT has hired architectural firm HNTB to conduct a forensics analysis to determine what caused the crack.
Degges also speculated that fatigue could have been the cause due to the bridge's 48-year age and the amount of traffic it handles. He said he did not know when the bridge would reopen and couldn't speculate until the load calculations were completed.
"We can't let the public get on this bridge until we understand exactly how much it can carry," he said during a press conference May 12. He expected it to take a few days before the load calculations were done. Then the two DOTs and engineering firms would develop a repair plan.
Degges said there was some rust at the fracture, indicating it had been there at least a week, but the department did not know how long it had been there before inspectors spotted it. He did say that it was a significant crack and one that would be easily identified by inspectors.
The cracked beam on the De Soto Bridge.Arkansas DOT
The bridge underwent a $268.4 million seismic retrofitting between 2000 and 2015 to withstand earthquakes, but Degges doubted that contributed to the crack. He said that work mostly focused on the piers and the steel components on top of them, and the crack was away from the joints. No modifications were made to the section of the bridge where the crack was found, according to TDOT.
"It looks like it might be a fatigue-induced type failure," Degges said.
He said overall the bridge is a "robust structure."
The I-55 bridge where drivers will be detoured to is actually older than the de Soto Bridge. It was built in 1949. ARDOT, however, says it is in good shape and can handle the additional traffic load.
Degges said repairs to the de Soto Bridge would be done as soon as possible. The DOT wanted to ensure they were done properly and also prevent future such incidents.
"We want to be able to learn from this," Degges said. "...We want to make sure we don't see this type of fracture again."
The I-40 Hernando DeSoto Bridge between Tennessee and Arkansas.Trevor Birchett, CC BY-SA 4.0 via Wikimedia Commons. Link to license: https://creativecommons.org/licenses/by-sa/4.0. Link to credit: https://commons.wikimedia.org/wiki/File:HernandoDeSoto_Bridge_Pyramid.jpg
