Engineers working on safety, stability of I-40 bridge
Engineers are conducting studies to determine if the Interstate 40 bridge over the Mississippi River from Memphis, Tenn., to Arkansas is stable enough for boat traffic to resume on the river.
“I’m hoping to be able in the next day or two to be able to give an answer to the Coast Guard but right now I don’t know,” said Paul Degges, chief engineer for the Tennessee Department of Transportation. “As far as opening the Interstate, that’s at least out 6-8 weeks, minimum.
The bridge was closed to highway traffic Tuesday after a fracture in one of the bridge’s tension members was discovered during an inspection. The fracture also raised concerns from the U.S. Coast Guard about its stability. The Coast Guard closed the river to all traffic.
As of about 1 p.m. Thursday, the Coast Guard indicated 44 vessels and 709 barges were blocked on the river waiting to move.
“We are shut down; it’s a catastrophic closure for us,” Golding Barge Line President Austin Golding said. “We have a number of barges on either side of it. We have barges that need to go north and need to go south. We’re stuck above and below it.”
He said several agencies were working on a game plan.
“This is a very unique bridge with a very unique failure and there’s a lot of people meeting on this trying to find a solution because it’s a one-of-a-kind situation; they really have to put some thought in it,” Golding said.
Degges said engineers are running a series of models on the bridge to ensure it will not fail.
“This is a bridge designed and built in the 60s, and so we ‘ve got a couple of steps we’ve got to go through,” he said. “The Coast Guard, to be able to make a decision whether to be able to reopen the river traffic, wants assurances from us that the bridge is stable; there’s not continued fracturing of steel or anything.”
Bridge observations, Degges said, indicate the bridge is stable; there’s no active movement.
“A bridge has to hold its own weight, known as dead load, and hold the weight of traffic crossing it, the live load. The live load is maybe 25-30 percent of the total load on the bridge,” he said. “The weight of the bridge holding itself up is the major structural issue.”
To further determine the bridge’s stability, Degges said, engineers are building a mathematical model of the bridge in 3-D. They will run the model without the traffic and introduce the fracture into the model.
“We have done some initial work doing that and initially, things look good; the bridge is in a stable condition,” he said. “We still have to run some quality control. We don’t want just one person’s calculations. We’re trying to make sure it’s in good shape.”
Once the engineers are able to verify the bridge is stable, Degges said, “We’ll be able to get with the Coast Guard and make some recommendations. It’s ultimately the Coast Guard’s decision, but based on the information we provide them they will be able to make a decision to open the river back to river traffic.”
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