Professor’s computer program simulates damage of I-40 bridge

Updated: May. 31, 2021 at 10:33 PM CDT
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MEMPHIS, Tenn. (WMC) - The specific design of the I-40 bridge at Memphis contributed to the fracture, and could cause more problems in the future, according to a University of Memphis engineering professor.

Dr. Adel Abdelnaby created a new computer program to simulate the wear and tear on the I-40 bridge. He says the very reason Memphians love the bridge, the iconic M-shape, is what makes it so vulnerable.

The movements of his simulation, which he showed to WMC Action News 5, are exaggerated for better visualization of what happens during cyclic loading as trucks and cars cross the bridge. His model shows the load path, the transfer of weight throughout the structure.

“This type of truss system with cables hanging to support the bridge deck is not idea,” he said of the new bridge and its arches

The length of the I-40 bridge, which stretches more than three miles, is also a problem.

“That span is too long to do that type of truss with cables,” he said. “It’s ok for half the span. That’s good.”

The result, he said, is stiff cables on the sides and flexible cables in the middle, creating uneven weight distribution and pressure near the bottom of the center portion of the M-shape where the fracture occurred.

Using a short, thin piece of metal, Abdelnaby explained how hinging happens and the impact hinging had on the steel beam that fractured.

“It’s bending more on the top side,” he said. “Bending more this way, bending like this. So, that’s why the crack happened at the top, not at the bottom. The crack started on the top where there’s higher tension, then the compression on the bottom.”

Abdelnaby says the key for engineers repairing the bridge is to make sure the weight doesn’t transfer to other weak points.

“Because that happens a lot,” Abdelnaby said. “You go strengthen one section and the load path finds the weakest link to break. So, it’s going to find somewhere else weaker to break. Make sure that’s not going to happen and then it’s an easy fix.”

Tennessee Department of Transportation officials say they may release a timeline this week on when the bridge will reopen. Phase two of repairs has yet to start. U.S. Transportation Secretary Pete Buttigieg will visit Memphis Thursday, June 3 to get an update on the I-40 bridge, which has been closed to traffic since May 11.

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