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

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am still a little unsure why the furthest right span failed.

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2 words for ya...


THERMITE PAINT

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Looking at the bridge I am still a little unsure why the furthest right span failed.

To me it looked like with the left pier out, the right span turned into a simple span supported on both sides (one side the remaining pier, and the other the approach).

My guess is the furthest right section of the bridge (where the bridge starts) was never meant to support that kind of shear load when the central span fell, but I do buildings and not bridges.

Any bridge structural guys out there that can help me out?

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you are right that it should have been a simple span supported on both sides but if you look at the video you will see when the left side falls it jerks the right side up and the connection on the right fails as it comes off, then its simply balancing and falls back down to the right side.

sorry if i didnt explain well. but it was simple failure of the connection to land on the right when other side of the bridge failed. watch the video a couple times and you will see it.

quote:

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Looking at the bridge I am still a little unsure why the furthest right span failed.

To me it looked like with the left pier out, the right span turned into a simple span supported on both sides (one side the remaining pier, and the other the approach).

My guess is the furthest right section of the bridge (where the bridge starts) was never meant to support that kind of shear load when the central span fell, but I do buildings and not bridges.

Any bridge structural guys out there that can help me out?

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First things first, I am not a degreed engineer but Uncle Sam spent a lot of time and money teaching me to produce dynamic bridge failures and to identify and exploit the vulnerabilities that can produce this using the least time, explosives, and manpower. In a nutshell, I was taught to break shite y'all build so basically failure modes is what I see when I look at a bridge.

When the continuous span fails left of the right bearing you are not left with a simple span to the right of the bearing. You are left with a component of a continuous span. If you watch the GIF the moment the lower chord fails on the left side of the right bearing that chord loses all its axial tension and the remaining portion of the span has nothing to hold it and it fails to the right side of the right bearing and just rotates on the bearing into the water.

The engineers could have used far more material and built the individual portions between bearings to function as simple spans but that costs a lot of money and would have been a completely different bridge design (arguably less aesthetic) with three sets of trusses that functioned independently. I have occasionally seen this approach used on rail bridges but they have different loading requirements.

BTW I know I am preaching to the choir so don't take anything as intentional condescension.