The collapsed Baltimore bridge didn’t stand a chance against such a huge cargo ship, engineers say

Julia Nikhinson/Reuters

Engineering experts sought to explain how the Francis Scott Key Bridge in Baltimore collapsed.They centered on one factor: the sheer size of the cargo ship that hit it.Faced with such momentum, a total collapse was inevitable, they said.

The Francis Scott Key Bridge in Baltimore stood no chance against the huge impact from a cargo ship Tuesday morning, engineering experts told Business Insider.

The bridge was destroyed in the early hours of Tuesday, collapsing in a violent fashion after a large cargo ship, the Dali, hit one of its support pillars.

This video shows the impact:

The physics of the impact are “pretty clear,” said Leroy Gardner, a professor of structural engineering at Imperial College London.

“There’s a heavy impact from a cargo ship into one of the piers,” he said in a call with BI. “Once that collapsed, then the rest of the bridge followed soon after.”

Experts told BI it was unlikely that any defects in the bridge’s structure were relevant to the collapse, given the scale of the impact.

Engineers would probably have been unable to protect against such a huge impact. The Dali is a substantial vessel, 300 meters long and weighing some 95,000 tons, according to the website vesselfinder.com.

It’s of comparable size and weight to a Nimitz-class aircraft carrier in the US Navy. The Dali was almost as tall as the bridge it was trying to pass under.

“All bridge piers will be designed to resist impact from a vessel. And I think this will be unquestionably no exception to that,” Gardner said.

“I think it’s the magnitude of the force in this case, which is extremely unusual, which has caused the problem for this bridge,” he said.

The Francis Scott Key Bridge opened in 1977. Its design is a steel truss bridge. The bridge was resting on concrete piers before the impact, experts said based on footage shared online.

“The support is a very, relatively, flimsy structure when you look at it — it’s a kind of trestle structure with individual legs,” Ian Firth, a structural engineer and bridge consultant in the UK, told the BBC. “So, the bridge has collapsed simply as a result of this very large impact force.”

The impact from the Dali seemed to knock out one of the concrete piers, a “critical, significant part of the bridge,” Gardner told BI.

“Structures generally are typically designed to have a certain amount of robustness. So if there’s damage to a small part of it, the rest of the structure can remain intact,” Gardner said.

“I think losing such an important element, I would expect the entire bridge to collapse, which is what happens,” he said.

It wasn’t clear from the footage how quickly the Dali was moving, experts said. It had only recently left the port.

Barbara Rossi, an associate professor of engineering science at the University of Oxford, told BI in an email that the impacting force “must have been immense to lead to these massive (concrete) structures to collapse, leaving the superstructure without one of its support.”

Later Tuesday morning it remained unclear why the ship struck the bridge.