Report: Memphis Bridge Cracked From Faulty Weld Repair Before Installation

An analysis of the fracture on three sides of a box beam holding up the Interstate 40 bridge over the Mississippi River in Memphis, Tenn., has determined the crack likely developed in a weld repair before the bridge was built.

The cracking took place in a welded seam between two plates on a tie girder.

“In all likelihood the cracking in the weld occurred within hours of its completion but was not detected by any post-weld repair fabrication testing and remained unchanged for a number of years,” Wiss, Janney, Elstner Associates, a global engineering, architecture and material science consulting firm based in Northbrook, Ill., said in its 47-page report, parts of which were reprinted by the Arkansas Democrat-Gazette newspaper of Little Rock, Ark.

A contractor hired to inspect the bridge discovered the crack May 11 and immediately called for the bridge to be shut down. In addition to vehicles, river traffic was halted between Mile 736 and Mile 737. Traffic on the Lower Mississippi River under the bridge resumed after three days. During the river closure, 62 vessels and 1,058 barges had to queue before the Coast Guard lifted restrictions. The bridge remained closed to all cars and trucks until August 2 and did not fully reopen with all lanes until August 6, after the completion of emergency repairs.

The analysis also said it is likely other cracks won’t occur on the steel of the Hernando DeSoto bridge, which connects Memphis to West Memphis, Ark., and is one of only two bridges crossing the river in the Memphis area. Traffic was diverted to the other crossing, on I-55, until the repairs were carried out.

“Given the 48-year service life of this structure, the fact that the subject fracture occurred in three separate phases over several years, the recent inspection efforts to identify welding defects at the tie girder thickness transition welds and no evidence of observed fatigue crack growth during this study, it is highly unlikely that an additional major fracture of a similar tie girder thickness transition weld will occur,” the report determined.

However, the company suggested it would be prudent to conduct “arm’s-length” inspections of the bridge as well as periodic ultrasonic inspections, which can detect issues not otherwise visible.

A separate Arkansas Department of Transportation report, also cited by the newspaper, noted that weld repairs were more susceptible to cracking because of both the type of steel used and the welding method used in the fabrication of the tie girder in the 1970s.

“In all likelihood the cracking in the weld occurred within hours of its completion but was not detected by any post-weld repair fabrication testing and remained unchanged for a number of years,” the ArDOT report said.

An ultrasonic testing inspection performed in 1982 failed to detect the problem as well. Complicating the issue, the bridge is of an old design that lacks redundancies common in more modern bridges. That lack of redundancies meant the bridge was in danger of collapsing into the river if the girder fractured completely.

The ArDOT report added that the initial fracture would have taken place on the interior face of the box beam, which isn’t visible in conventional inspections.

“The second phase of crack propagation fractured through the remaining thickness and was later identified in the 2019 drone video,” the report said. “The third fracture event propagated up the remaining web, across the top flange, and arrested in the flange to web weld of the tie girder.”

ArDOT fired a bridge inspector after saying the inspector did not report the crack despite it being visible in the drone footage. ArDOT and the Tennessee Department of Transportation share responsibility for the bridge’s maintenance and annual inspections.

The ArDOT report said it’s “likely the existing weld cracks became unstable as a result of a unique combination of low temperatures, increasing tie girder stress, and the effects of live loads to which the bridge had not been previously subjected.”