Fragile bridge ‘had no chance’
BALTIMORE: “Be advised, the entire bridge, the entire Key Bridge, is in the harbour.”
This was the urgent radio message Baltimore’s 911 operator delivered to the city’s emergency vehicles just after 1.30 on a freezing Tuesday morning as the Patapsco River churned with the remnants of the Francis Scott Key Bridge after it was hit by a cargo ship.
While locals were woken by what they thought was an earthquake, questions were already being asked about whether design flaws, structural problems, inadequate maintenance or the age of the bridge may have contributed.
Investigators will need to work out how the Dali cargo ship came to veer off course and strike the bridge, but in engineering terms, a “continuous truss” bridge of that kind was never likely to survive a direct hit to one of its piers from such a large vessel, experts say.
Robert Benaim, a bridge designer and fellow of the Royal Academy of Engineering, said a key question was why the bridge’s slender piers were not surrounded by comprehensive protective barriers when it spanned such a busy shipping lane. Another is whether a bridge built in 1977 was still suitable for a port that has welcomed increasingly large ships and handled 52.3 million tonnes of foreign cargo last year.
“Major bridges over shipping lanes must have substantial protection for piers or columns,” Mr Benaim said. “These protections are either in the form of structural protections like ‘sacrificial dolphins’, which are made of steel and embedded in the sea bed to stop or divert a ship. They can also be in the form of artificial islands: these are for very large ships and mean the ship will never reach the bridge pier itself. Clearly the protection of the piers in this instance was inadequate.”
The section of the bridge struck by the ship was made from “a single long steel truss over the three main spans”, with no hinges or joints, said civil engineer Andrew Barr.
“The collision of a vessel as large as the Dali will have far exceeded the design loads for the slender concrete piers that support the truss structure.” The London Times