Baltimore’s Key Bridge Collapses After Container Ship Collision

Baltimore’s Francis Scott Key Bridge collapsed at 01:27 am EDT (05:27 am UTC) on March 26. The Singapore-flagged container ship “Dali” collided with one of the bridge’s pillars leading to a catastrophic collapse of the whole structure. At the time, there were workers on the bridge and the Baltimore City Fire Department stated that at least seven vehicles fell into the water. At the time of writing the number of casualties is unknown.

The bridge, named after the author of The Star Spangled Banner, connected the two banks of the Patapsco River and was the third longest continuous truss bridge in the world with a span of 366 meters (1,200 feet). Continuous truss bridges have been popular since the 19th century and like any bridge design have advantages and drawbacks.

Unlike cantilever bridges, which require a structure projecting horizontally from sturdy supports, a truss bridge is made of a superstructure of trusses – the usually triangular units that allow the distribution and spread of the tension, compression, and stresses a bridge is bound to experience. In the case of a continuous truss bridge, the truss superstructure extends without hinges over three or more supports.

Content Warning: A live stream from the port of Baltimore recorded the collapse of the bridge. Some viewers might find it distressing.

The support in this case was hit by an object carrying a lot of momentum, destroying it. Without the support, the whole structure became unbalanced – the superstructure was no longer able to hold the weight of the bridge.

“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 designer, told BBC News. “So, the bridge has collapsed simply as a result of this very large impact force.”

Continuous truss bridges are known to be statistically indeterminate – in structural mechanics that means that even knowing all the forces and moments acting on the bridge in equilibrium is not enough to determine the internal forces and reactions of that structure. Computers have been instrumental in making these bridges more common, as they can better calculate the stresses in the bridge.

This is a developing story. 

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