Contractors arrived Tuesday at the Hernando de Soto Bridge outside Memphis for a routine inspection. Within hours, they were on the phone with 911 dispatchers.

A crack had formed in one of the bridge’s steel support beams, and it was so large that the murky waters of the Mississippi River could almost be seen through the gap. No one was sure how long it had been there. Overhead, motorists crisscrossed the six-lane structure, unaware of the problem below.

Inspectors called in the emergency just before 2 p.m. “I am doing a bridge inspection here on the I-40 Mississippi River bridge. We just found a supercritical find,” an inspector told a dispatcher, according to audio posted by Fox13. "We need to get people off the bridge immediately.”

“We need to shut traffic down in both directions,” another inspector pleaded in a follow-up call a few minutes later. “We just need police cars out here.”

On Friday, after avoiding a potential catastrophe, transportation officials were beginning the complex work of figuring out what caused the massive crack and what it might take to make the bridge drivable again, if ever.

Traffic was blocked entirely and will remain that way indefinitely while crews investigate the crack, officials said, cutting off a major artery for trucking and commuter traffic. Mississippi River traffic under the bridge was halted for more than two days and reopened Friday morning with more than 1,000 barges in the queue, according to the U.S. Coast Guard. The bottleneck disrupted shipments of grain and other dry cargo, as well as “red flag” cargo such as fuel oil, officials said.

The nearly five-decade-old bridge, which straddles the Tennessee-Arkansas line, became the latest symbol in the tortured effort to fix the nation’s failing infrastructure, which was in the spotlight this week as President Biden met with congressional Republicans to try to negotiate a deal on his proposed $2.3 trillion infrastructure plan.

The discovery of the crack came just a couple of months after the American Society of Civil Engineers, the country’s leading engineering professional group, gave the United States a miserable C-minus on its quadrennial infrastructure report card. The group found that more than 40 percent of the nation’s roadways were in poor or mediocre condition, with some of them facing increased risk of catastrophic failure, a figure essentially unchanged from the previous report four years earlier.

Transportation Secretary Pete Buttigieg says repairing and modernizing America’s infrastructure is a “matter of economic competitiveness, as well as safety and well-being.” “We need first-rate infrastructure if we want to have a first-place economy.” (Washington Post Live)

Bridges were particularly high on the group’s list of concerns. Close to half of the country’s 617,000 bridges are more than 50 years old, according to the report card, and more than 46,000 are structurally deficient.

Biden’s infrastructure plan seeks to address some of those problems by steering $115 billion in extra money to help repair 20,000 miles of roads and 10,000 bridges nationwide. But Republicans have balked at some aspects of the legislation, such as climate-change initiatives that they say stretch the traditional definition of infrastructure, leaving the path forward unclear.

In a fact sheet supporting Biden’s infrastructure plan, the White House said Tennessee, like other states, “has suffered from a systemic lack of investment” in infrastructure. Nearly 900 of the state’s bridges were rated in poor condition, it said.

With a critical flaw exposed, the future of the Hernando de Soto Bridge is now up in the air. Engineers are assessing the structural integrity of the bridge, modeling the damage and working out a plan to fix it, said Nichole Lawrence, a spokesperson for the Tennessee Department of Transportation. The process could take months.

“There’s no way 100 percent we can tell you, ‘This is what happened and this is what caused it,’” Lawrence said in an interview. “Whether it’s a fatigue fracture or what, we don’t know. That may be something we don’t ever know. Our inspection teams are still on the ground running those inspections.”

Even to an untrained eye, the crack discovered this week would have looked alarming. It appeared in the center of one of the bridge’s 900-foot steel support beams, looking almost like someone had taken a buzz saw to the material.

The clean split was a telltale sign of a fatigue crack caused by continuous stress on the bridge’s weak spots, according to Adel Abdelnaby, a professor of civil engineering at the University of Memphis.

Abdelnaby, who helped install seismic sensors on the bridge in 2015, said the crack probably started as a small fracture inside the metal where it wasn’t visible — perhaps caused by a welding error — and got worse over time as traffic roared over it. He estimated that the full crack had been there for six weeks or more based on the dark coloration of the metal.

“A fatigue crack looks like a knife cut. When they’re fresh, they’re shiny,” he said in an interview. “This crack is not fresh, for sure. It has been there for a while because it takes time for the surface to corrode.”

A state engineer gave a similar assessment in an interview with CNN, saying the crack had probably been there a couple of weeks.

More than 40,000 vehicles cross the bridge every day, with 25 percent of that traffic coming from trucks, said Lawrence, the TDOT spokeswoman. It was last inspected in August 2020, she said, and the crack wasn’t reported at the time. She added that most of the state’s bridges, including the Hernando de Soto Bridge, get some sort of inspection every year.

Abdelnaby said the bridge, which opened in 1973, was never intended to bear such high traffic volumes. On top of that, he said, the bridge has a unique design that may have exacerbated the bending of the beam that cracked.

“That’s something that was overlooked when they did the original design,” he said, “because they didn’t have the advanced tools that we have now to show that type of behavior.”

People could have been killed had inspectors not found the crack in time, he said. “It could collapse. It could partially collapse. Something major and catastrophic would happen, that I can guarantee.”

The problem now, Abdelnaby said, is that engineers don’t know whether the flaw that caused the fracture is isolated to that particular beam. Other parts of the bridge are made of the same material, subject to the same loading and weather conditions, he said. Inspecting the rest of the structure will involve not only a visual inspection but other noninvasive tests.

“The best-case scenario is this is an isolated event for some reason we don’t know,” Abdelnaby said. “The worst case is that it will happen in other locations and that other beams are prone to fatigue and fractures. You’ll have to do a cost analysis to see if the repair scope is going to be too much and see if it’s cheaper to demolish the bridge.”

Until a solution is found, the bridge closure is bound to cause headaches for commuters and shipping disruptions in the Memphis area, which is home to the FedEx hub. The only other Mississippi River crossing in the region is the Interstate 55 bridge, about two miles south. The next detour across the river is about 80 miles away.

“It’s fortunate that routine inspection averted a potential disaster,” Rep. Steve Cohen (D-Tenn.), whose district encompasses Memphis, said in a statement after inspectors discovered the crack. “But the state of our crumbling infrastructure is deeply troubling and the closure of a major thruway will negatively affect us both here in Memphis and around the country.”

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