The fault was found during a routine inspection of the Interstate 40 steel tied arch bridge – also known as the Hernando DeSoto Bridge – that connects Arkansas with Memphis in the USA.

Arkansas Department of Transportation director Lorie Tudor said that the fault had “the potential of becoming a catastrophic event” had it not been caught.

The cause of the damage is under investigation, but Tudor said stress caused by wear and tear on the 50-year-old bridge was likely a factor.

After examining images of the damage, independent bridge consultant Simon Bourne told NCE that the location of the break appeared unusual.

“Unusually, the failure is not at the joint or within the bolted splice area, suggesting that it is not a fatigue issue, even though the bridge is around 50 years old,” Bourne said.

“There is also no sign of any corrosion or other deterioration, although the failed surface looks quite old, suggesting that it might have been like this for a while.”

He added that the fractured longitudinal member is “absolutely fundamental to the strength of the whole bridge”.

Bourne suspects that the crack has developed over a number of decades due to the vertical movements in the deck.

He added that a project to retrofit the bridge in recent years could have “exacerbated” the issue.

He added: “It’s very serious, there are no signs of corrosion, but most likely it’s a fatigue crack that has developed over 50 years due to the vertical movements of the deck, causing a complete shear failure of this main tie/tension member.

“It’s a wonder that the whole bridge hasn’t fallen down.”

Bourne added that bracing elements added during a retrofit of the bridge could have exaggerated the damage which was likely caused by vertical movements of the older deck and vertical girders.

“The more recent seismic retro-fitting may well have exacerbated the issue,” Bourne said. “The location of additional bracing is very close to the site of the crack so it is highly likely that is would have had some impact and one would assume that it has been detrimental.”

The retrofit was carried out to both the I-40 and 1-55 Mississippi River bridges from 2000 to 2015 to provide a “post-earthquake” lifeline link for emergency vehicles and the general public. TRC (formerly Imbsen & Associates) provided engineering services for all phases of the $268.4M (£191M) project, including seismic analysis, retrofit design and retrofit construction.

A project report by TRC reveals that extensive strengthening or complete replacement was carried out to numerous components of the bridge.

The retrofit strategy consisted of the following work:

• Bent cap retrofit / widening
• Column strengthening
• Webwall retrofit
• Footing retrofit / enlarged cap with additional piles superstructure
• Diaphragm / cross frame replacement
• Bottom lateral retrofit
• Bearing replacement – 112 bearings
• Expansion joint R=replacement

The 5.3km I-40 bridge was first opened to traffic in 1973 and is comprised of 164 spans, 160 piers, and 10 abutments.

Arkansas and Tennessee share responsibility for maintaining the bridge. Arkansas DOT deputy director Rex Vines said that the fault was not noted on the bridge’s last inspection, which was carried out in September 2020.

The bridge has now been closed indefinitely. TRC has been approached for comment.

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