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Engineers blame $3m structural 'flaw' for Baltimore's Francis Scott Key bridge collapsing - and tens of thousands of bridges across US could also have fault
Engineers have blamed the deadly collapse of Baltimore's Francis Scott Key bridge on a design flaw that is present in tens of thousands of US bridges.
Several experts told DailyMail.com that the Maryland bridge was missing critical protection systems that would have stopped the the nearly 105,000 ton container ship from smashing into the bridge's support.
The Francis Scott Key Bridge was built in 1977 and anti-collision devices like fenders or protection cells were not introduced until the 1980s.
Experts said installing fenders would cost at least $3 million, but the collapse means a $15 million per day loss in economic activity and $1.5 million daily in state and local taxes - and that doesn't include the six men who are presumed dead.
Video of the 1.6-mile-long Francis Scott Key bridge collapsing into the Patapsco River after a cargo ship struck one of its piers at low speed created a surreal scene as the entire bridge appeared to crumble in one fell swoop.
The Francis Scott Key Bridge was a continuous truss bridge, which can fail if it loses one support pillar. Multiple high-profile failures of such bridges have occurred, and thousands remain across waterways throughout the US.
The ship, called Dali, was only traveling around nine miles per hour when it collided with the bridge at 1:28am ET, but the boat's massive weight meant it had a near-unstoppable momentum.
The ship took down a pair of bridge piers, which left the roadway totally unsupported, so the bridge appeared to crumble instantly.
Anti-collision devices like fenders or protection cells only became the norm in the 1980s, after a freighter slammed into the Skyway Bridge in Florida, collapsing a portion of it.
More than half of the US's 621,581 bridges were built before 1980, though, according to the National Bridge Inventory.
The Northern Boulevard Bridge across the Flushing River in New York City has such fenders, as do many smaller bridges spanning waterways, like the Route 3 Bridge over the Piankatank River in Virginia, seen below.
The Francis Scott Key Bridge rests partially collapsed after a cargo ship ran into it in Baltimore
And the Delaware memorial Bridge received protection cells in 2023 at a cost of $93 million. These devices are meant to deflect a boat, taking the damage for a bridge.
Even with protective structures, though, whether a bridge is safe from a boat strike depends on the size of the boat, and experts said that a large enough boat - like today's massive cargo ships - could take out bridges like the Brooklyn Bridge or the Golden Gate Bridge.
'I believe that there should have been a protection system,' Sherif El-Tawil, professor of civil and environmental engineering at the University of Michigan, told DailyMail.com.
Nonetheless, he explained that not all protection systems will be up to the task of stopping a more than 100,000-ton ship like the Dali, and sometimes these accidents will simply happen due to human error - or as early reports indicated in this case, power failure.
FENDERS: These structures can deflect ships away from bridge piers. This bridge spans the Piankatank River in Virginia. It has pier fenders, but if it were struck by a cargo ship it would be no match.
PROTECTION CELLS: These structures are meant to deflect ships away from bridge piers. If damaged, they are much cheaper to fix or replace than a bridge.
The Maryland Transit Authority owns and operates the Francis Scott Key Bridge.
DailyMail.com has reached out about why there were not sufficient protective structures built around it.
To build a bridge with piers are strong enough to withstand a blow from such a vessel, 'you'll end up just building a castle in the middle of the river,' Bilal Ayyub, former chair of the American Society of Civil Engineers' Infrastructure Resilience Division, told DailyMail.com.
When one major piece failed in Tuesday's crash, the weight of the bridge had nothing else to support it and nowhere else to go but down.
Based on the videos, it appears that the boat leaned against one of the A-frame pillars holding up the bridge, Sherif El-Tawil, professor of civil and environmental engineering at the University of Michigan, told DailyMail.com.
Then the weight of the bridge collapsed the remaining pillar.
'And without that support, the bridge's span becomes very large,' El-Tawil said. 'And it was never designed for that.'
In other words, a long expanse of roadway was left with nothing to hold it up.
El-Tawil and the other engineers said that the Francis Scott Key Bridge seemed to lack the necessary structures that would have protected against such a strike - piers in the water, seafloor piled up to make a ship run aground before it struck the pillar, or concrete structures that could divert the boat away from the bridge.
According to Ayyub, there are features that can be built into waterways to divert a runaway boat from hitting the crucial structures of a bridge.
'You cannot design a bridge to withstand the energy that comes with a moving object as large as a barge,' he said.
Instead, engineers can develop ways to keep ships from hitting bridges.
Bridge fenders can protect the piers of a bridge from being struck by large ships, but they were not required back when the Francis Scott Key Bridge was built.
One way, Ayyub said, is to define a navigation channel to divert ships from hitting the crucial piers, whose failure would collapse the bridge.
Other options include steel protection cells or fender systems surrounding the bridge piers, as well as seafloor dredging that will pile up material around the pier and make a ship run aground before it collides with the bridge.
'Basically, they what they will do is they will make the ground [underwater] elevate higher so that a ship will be grounded,' he explained. 'It was designed to basically alert the operator that you know you're approaching an object.'
None of these appeared to be in place around the Francis Scott Key Bridge, Ayyub and other civil engineering experts told DailyMail.com.
Unfortunately such protective structures are not required, even if they would be logical.
'I believe that there should have been a protection system,' El-Tawil said.
'And the protection system could be like you mentioned, it could be where there's a gradual rise in the level around the pier to prevent vehicles from running into it. But you could also have fender systems, you could have pile systems that essentially redirect these vessels.'
Atorod Azizinamini, professor of structural and bridge engineering at Florida International University, agreed, saying that such structures can 'prevent the ship from coming anywhere close to the supports.'
None of these systems appeared to be in place, said the experts.
'I think that protection systems should have been considered for a situation like this, especially for a critical system like this,' El-Tawil said.
The Francis Scott Key Bridge carried over 11 million vehicles across it each year, and its collapse will cause major problems for the people living nearby, experts said.
Initial reports indicate that at least a dozen cars hit the 47 degree water in addition to a 20 or so construction workers who were working on the bridge at the time
Aside from the lack of protective structures, another reason for its collapse was a lack of redundancy - when a pair of piers were destroyed, there was nothing there to bear the weight they had held up.
Redundant piers may have helped, but engineers rarely design redundancy of that type into their construction.
Because bridges like the Frances Scott Key can be built without extra support columns, they usually are, Ayyub said.
'If we can do without that pier then the design will be done without that pier,' he said. 'I mean, they really try to minimize the number of piers.'
Unfortunately that means that the design of the bridge was 'fracture critical,' meaning one break took it down.
And this design feature is not unique in the US, where aging transportation infrastructure has not kept apace with the design and absolutely massive size of modern shipping vessels.
It is theoretically possible to build redundancy into a bridge like the Francis Scott Key, but since ships need to pass under to enter the busy Port of Baltimore, extra piers would clog up their way.
Besides, the simple fact is that if a bridge can be built without extra pieces,
'With longer spans, there is no redundancy in losing a pier,' Ayyub said.
In some cases, a disproportionally small issue can lead to a catastrophe, as in the case of the 2013 I-5 Skagit River Bridge in Washington that completely collapsed after an oversized truck knocked out a single truss.
In other cases, as in the 2007 collapse of the I-35W Mississippi River Bridge in Minnesota, support plates that weaken over time can suddenly give out - in that instance killing 13 and injuring 145.
The Francis Scott Key Bridge collapse was unique, but the bridge itself shared a design feature with these others: It was what's known as a continuous truss bridge.
A continuous truss bridge is designed to spread the weight of its occupants out over a continuous series of trusses - as the name implies.
These trusses, a network of crisscrossing beams, are held up by a series of support pillars.
Crucially, a continuous truss bridge has some disadvantages, including the fact that over time their joints can weaken and their actual capacity may go down.
And though that does not seem to be what happened with the Francis Key Bridge, there are tens of thousands of continuous truss bridges around the country, Ayyub said.
But more important than the construction of the bridges themselves, experts agreed, was protections to keep ships from hitting them.
And no such protections were there when the Francis Scott Key Bridge needed them.