[TXnMA]

Here is a rude, crude little sketch based on what I see on page 4 of the NTSB PDF.

The deflections appear to me to be all in the same direction -- as if the deck and upper span beam had shifted somewhat to the east relative to the verticals.

OTOH, after re-examining the overhead view, I now think that the roadway curve was too far south to have imparted any live lateral thrust to the L10/U10 section...

At any rate, jeffers, your suggestion that downward vertical deflection in mid-river could have caused these gusset plate "bends" doesn't seem to fit: That would have put these particular edges in tension.

So far, the deflection looks lateral to me -- but don't ask me how it could have happened... ;-)

[brityank]

Thank you all for the pings and info and explanations; definitely enlightening. Something I noticed on the pic of the bridge in AA’s doc from the lock is some type of addition at the bottom of the Position 10 posts on both sides. Note that there are ladders on both sides going up to a catwalk beneath the roadway, and the same assembly is noted on the north side (Position 18?). There are visible (strain guages ?) ‘patches’ on members attached to those of the south end , and what may be a signal light on the lower chord member. Could that addition have added some weakness to the structure?

If the Piers have shifted from scour, could there be enough ‘drop’ on the chords to effectively ‘close’ the angle between the horizontal and diagonal upper struts making those bends?

I find it telling that, from what little my inexperienced eye can see, they had strain gauges attached at that specific area before the collapse; someone at MDOT knew.