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Materials list for I-40 span heavy on steel

Plates, brackets being made, shed light on repair timeline by Noel Oman | June 5, 2021 at 4:44 a.m.
The I-40 Hernando de Soto Bridge crossing the Mississippi River connecting Arkansas and Tennessee on Tuesday, May 18, 2021. The bridge has been closed since inspectors found a fracture in the bridge. (Arkansas Democrat-Gazette/Thomas Metthe)

A review of the parts on order to repair the Interstate 40 bridge over the Mississippi River makes it easy to understand why it will take the balance of a month for them to arrive on site.

The parts include two steel plates weighing a total of 53 tons, 3,000 bolts and 1,400 feet of 3-inch diameter, high-strength steel rods that will be placed under 3 million pounds of tension, all items unavailable at the local hardware store or even to Amazon Prime members.

The steel plates will be 150 feet long and 32 inches wide once they are fabricated, said Nichole Lawrence, a spokeswoman for the Tennessee Department of Transportation, which hired contractor Kiewit Infrastructure Group of Omaha, Neb. to repair the bridge.

The 48-year-old bridge connecting West Memphis and Memphis was abruptly closed to traffic May 11.

Other parts on order include four brackets weighing 20,000 pounds each, according to a daily update provided by the Tennessee agency. The brackets are each 8 feet long and 4 feet wide, Lawrence said. They also will be post-tensioned.

[What do you want to know about the I-40 bridge closure? Ask your questions here » arkansasonline.com/bridgequestions]

Referred to as PT for short, post-tensioning is "similar to pulling on your shoelaces to tighten your shoes," said Gary Prinz, an associate professor and civil engineer at the University of Arkansas, Fayetteville.

Prinz conducts specialized research in fatigue and fractures of metals, particularly steel, and has served as an adviser to the Arkansas Department of Transportation on the I-40 bridge.

"The PT rods will likely bridge the member fracture and then be tensioned (pulled on) ... to re-establish the member load path before installing the final retrofit plates," Prinz said in an email Friday.

The bridge was closed more than three weeks ago after a private contractor conducting a specialized inspection of the bridge's arch and cables, and working for the Arkansas agency spotted a "significant" fracture on a 900-foot-long steel load-bearing beam helping support one of the bridge spans.

The leader of an inspection team employed by the Arkansas Department of Transportation was fired after top agency officials confirmed that the fracture had existed since at least May 2019, but the team missed it twice -- in September 2019 and September 2020 -- because their inspections were conducted improperly.

The traffic has been shifted to the Interstate 55 bridge, which also crosses the Mississippi between West Memphis and Memphis.

The Arkansas transportation agency asked its Tennessee counterpart to oversee the inspection of the I-55 bridge, which is older than the I-40 span.

"A thorough inspection of the I-55 bridge is complete, and TDOT finds that all previous inspection work done by ArDOT accurately reflects the bridge's condition," Friday's update said. "It is safe and can carry the current load."

It will have to carry that load -- about 67,000 vehicles daily and up from the 40,000 it carried before the I-40 bridge was closed -- through at least July and, according to Tennessee transportation officials, likely into August.

Another wild card that could push that reopening even further out is the in-depth inspection the bridge is undergoing now. Bridges are typically inspected visually by trained personnel, but the in-depth inspection is using ultrasonic testing that can detect cracks invisible to the naked eye, a process that can take weeks.

"If any issues are found during the repairs, it could affect the opening date of the bridge," according to the update. "The safety of the workers and the public is our number one priority."

Kiewit has completed the first phase of the repairs, which was to brace the bridge enough to allow personnel on the span to make permanent repairs and complete a full re-inspection of the bridge. It is now doing preparatory work while awaiting the repair materials, which will be fabricated at two separate facilities, according to the Tennessee Department of Transportation.

Tennessee Transportation Department officials say they continue to collect data and study ways to alleviate congestion and advance flow on the I-55 bridge. It can take as long as an hour to cross the bridge, and drivers of trucks, which make up about a third of the traffic, have been adjusting schedules to cross the bridge at night or avoiding the bridge altogether.

Gov. Asa Hutchinson used his weekly radio address to point out how the bridge closing underscores the importance of infrastructure investment, highlighted by voter approval of Issue 1 in November. Issue 1 makes permanent a half-percent statewide sales tax devoted to road and bridge construction and maintenance.

"The closure has caused delays that are costing the trucking industry $2.4 million a day," Hutchinson said. "That's just one of the costs when we have to shut down a piece of the infrastructure that connects our nation.

"This near disaster illustrates how interdependent we are. It also illustrates the urgency for states to be proactive in maintaining infrastructure. That is why Issue 1 was so important. Our investment in highways provides Arkansas the resources to inspect roads and bridges, and to keep them in good repair, and to respond quickly to emergencies."

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