re: Francis Scott Key Bridge in Baltimore has collapsed - container ship wrecked into it

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I just rewatched the GIF a little more closely and while I think it would have failed because of the loss of tension on the bottom chord I now think the failure occurred before that could happen. If you watch right before the upper and lower chords fail to the left of the right piling the upper chord actually goes into tension and the lower chord goes into compression (opposite of their designed states) and this shift lifts the portion of the span right of the piling up. Depending on the type of bearing used where the right portion of the truss span meets the concrete road bridge it either lifted off or stayed attached but either way excessive lateral torsional buckling in the lower chord and tensile failure in the upper chord would occur.

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