GRAPHIC: Why did Baltimore bridge collapse?
The Francis Scott Key Bridge, which collapsed after being hit by the container ship MV Dali as it left the Port of Baltimore, was built before the latest standards on bridge protection were put in place.
With the world’s third longest continuous truss bridge span, at 366m, the bridge was designed to distribute its load along its entire length, to span longer distances with less material, creating a more efficient structure than if the three spans were all independent of one another.
However, this fracture critical design lacks redundancy, meaning that if one span failed, all of them would collapse.
The bridge was completed in 1977, three years before the 1980 collapse of the Sunshine Skyway Bridge which crossed Tampa Bay in Florida, and which led to new regulations for protection of all new bridges, including artificial islands around the piers, “dolphins” - circular barriers filled with concrete or sand to divert ships and absorb the energy of an impact - and fenders, crushable concrete boxes wrapped around the pier to protect it from impact.
These were not applied to existing bridges however, and while some of them were implemented to a limited degree in Baltimore, they may have been insufficient and would have been unable to deal with a head-on collision from a modern cargo ship like the Dali, which, travelling at just eight knots, could have imparted 1.2 million joules of energy.
Graphic News