How the Baltimore Key Bridge collapsed: experts breakdown the perfect storm of errors
The Dali set out from the Port of Baltimore around 1am on Tuesday, a local pilot manoeuvring the container ship towards open waters after two days in the harbour in preparation for its next sail to Sri Lanka. The 948-foot vessel edged closer to Francis Scott Key Bridge and its four lanes of I-695 over the Patapsco River; early-morning traffic was relatively light as construction crews fixed potholes on the major thoroughfare that’s served the region since 1977.
The bridge was in fair condition, according to records from its last 2021 inspection viewed by the Wall Street Journal; the construction was essentially cosmetic and the workers, presumably, immersed in routine. Then the lights of the Dali went off, on, and off again; it wasn’t long before the ship issued a mayday call and officers rushed to stop additional traffic from crossing Key bridge. The Dali, having lost propulsion and power, crashed into a bridge support buttress just before 1.30am; less than a minute later, the majority of the structure vanished beneath the surface of the Pataspco.
The collapse sounded like a crash to nearby residents; others thought it was an earthquake. But as speechless locals surveyed a scene now devoid of its landmark bridge, authorities launched a frantic recovery effort to save construction workers and motorists who’d been caught up in the accident.
And everyone began asking questions about how this could have happened.
“It was a time and place: Everything that could have went wrong did go wrong, and the place, unfortunately, was right by the bridge,” Kevin Calnan, a maritime transportation professor at Cal Maritime, tells The Independent. “As far as engine failures and situations like this, it is rare. And then it’s exceptionally more rare for this to be in a port area.”
Despite the rarity of such an event, however, contributing factors may have been at play from both the bridge engineering and shipping sides, according to experts. Construction began on Key Bridge in 1972 and continued after its 1977 opening, but the size of particularly container ships has changed drastically in the intervening decades.
Calling the incident “a true tragedy,” Jerome Hajjar – professor of civil and environmental engineering at Northeastern University – said the collapse could have resulted from “a mismatch between the size of the load” on the Dali and “the expected loads at the time of the bridge design.”
The bridge supports would most likely have been designed “to be able to withstand some amount of sideways or lateral load like this,” he told Northeastern Global News.
“And therefore I would also assume that this load was significantly higher than typical design loads.”
Older bridges like this one, then, may not have sufficient pier protection cells to act as buffers, essentially stopping any colliding forces from directly making impact with support structures, which are not built to withstand such tonnage, experts say.
“Regardless of what type of bridge you have, if a cargo ship hits one of the supports, and if the bridge is a multi-span, if one of the supports are gone, that bridge is going to collapse,” Atorod Azizinamini, professor of civil engineering at Florida International University, tells The Independent.
“When we design a bridge, there is a very specific requirement that you have to protect the supports of the bridge against the ship colliding [with] supports,” says Azizinamini, who is also director of FIU’s Accelerated Bridge Construction University Transportation Center. “So you’ve got to remember that the cargo ships … the impact force could be in the millions of pounds. So there’s very specific requirements … you have protection cells or you build some massive structures around the bridge so that the ship doesn’t hit the support of the bridge but hits those protection cells or the massive structure.
“From what I have seen, it seems like those protection cells that were around the support were minimal,” Azizinamini says. “It doesn’t appear to be up to current codes. But it’s very early to say.”
A multitude of agencies were investigating on Tuesday, with Secretary of Transportation Pete Buttiegieg, Federal Highway Administrator Shailen Bhatt and the NTSB on site offering federal support and assistance, the FHWA told The Independent in a statement.
