Why did Francis Scott Key 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

FRANCIS SCOTT KEY BRIDGE
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Completed 1977, three years before collapse of Sunshine Skyway Bridge across Tampa Bay, Florida which led to new regulations

Last inspected May 2021, given “fair” rating by Federal Highway Administration

SOUTH
NORTH
Collapsed section
Truss bridge distributes load along entire length of structure  – designed to span longer distances with less material, but lacks redundancy – if one span fails, all three collapse

Main span 366m: world’s third longest continuous truss bridge
Navigation channel
Span
Impact zone
PATAPSCO RIVER

Interstate 695
Bridge debris blocking narrow shipping lane
Main span 366m: world’s third longest continuous truss bridge

Navigation channel
Span
Impact zone
PATAPSCO RIVER

SUNSHINE SKYWAY BRIDGE
Artificial island: Built around piers – sand core protected against wave and current erosion by armoured slope protection
 
Increased “dolphin” protection

Dolphin: Circular barrier filled with concrete or sand designed to divert ship, absorb  energy of impact

Sparsely situated dolphins may have been insufficient 

Fender: Crushable concrete box wrapped around pier to protect it from impact
Not designed for weight of modern cargo ships

At 8 knots, ship could have generated 1.2 million joules of energy

MV DALI
Singapore-flagged container ship
Gross tonnage 95,128
Length 300m



Source: Federal Highway Administration
Picture: Newscom
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