Bridge collapses in Minnesota

[iron81]

BS, Civil Engineering

There have been a few people in this thread who know more about bridges than me, but my best guess is that the bridge deck was balanced on the piers. Once one span dropped, there would be enormous torque forces on the other span that would normally be balanced out by the first span almost like a counterweight. There are no fasteners strong enough to resist that kind of torque. The remaining span would simply slide off the pier.

Another guess is that when the center spans began to fall, they remained attached to the outer spans, pulling those sections apart. I'm not in Civil Engineering now, but hey, its the internet where everyone's an expert.

[suzzer99]

Right, that was my guess about the secondary spans as well. But do you have any theories as to why the main span would just shear off from the pillar like that? Do you think that could happen from some cause other than the pillar shifting or settling quickly (or slowly I guess)?

[JackCase]

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Why did they call off the search & rescue so early last night?

I think I'd be fairly pissed if I where a family member of a victim.

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I believe it was after midnight. They had already checked out everything on the surface, and were searching the cars that were under water at the time. By that time it was considered to be a recovery operation rather than a rescue operation.

[iron81]

The other guesses in this thread are as good as mine: fatigue in a joint, settling of a pier, rust, etc. The heat might also have something to do with it because heat causes bridges to expand, even new bridges. But bridges are designed to expand so since it wasn't that hot the heat could only be a contributing factor.

[revots33]

This is a horrible story and it reminds me of a (hopefully) useful PSA that relates to it:

I saw a safety expert on tv a while back who said that every car should have a window punch tool in it. I have one called ResQme that is on my keychain and also includes a blade for cutting seat belts. Amazon sells them for like 9 bucks.

Not to say they would necessarily help in a bridge collapse, but if trapped in a flash flood, or submerged, or if the car flips on its side and you can't get out the door - it could save your life.

[scotchnrocks]

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Right, that was my guess about the secondary spans as well. But do you have any theories as to why the main span would just shear off from the pillar like that? Do you think that could happen from some cause other than the pillar shifting or settling quickly (or slowly I guess)?

[/ QUOTE ]

I've got a BS and MS in structural engineering and work in a bridge design office in the southeast. From what I've read so far, fatigue is the most likely culprit. A summary of one of the inspection reports noted that the bridge had poor fatigue details. It's impossible to say for sure w/o being there and having access to the drawings and inspection reports, but fatigue seems most likely.

[icepick]

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Were there any notices to not talk on your cell phones?

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This was on WCCO about 6:30:



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So wait, if you are in Texas and are looking to call someone else in Texas on a cell phone number with a Twin Cities area code, that taxes their network up there? I don't know jack sh*t about this sort of thing but it doesn't make sense.

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It don't make sense, but that's the way it works. Calls have to touch base will the switches at the original area code. They'll then be routed to the actual area.

[JackCase]

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I've got a BS and MS in structural engineering and work in a bridge design office in the southeast. From what I've read so far, fatigue is the most likely culprit. A summary of one of the inspection reports noted that the bridge had poor fatigue details. It's impossible to say for sure w/o being there and having access to the drawings and inspection reports, but fatigue seems most likely.

[/ QUOTE ]

MNDOT had a news conference this afternoon. They said that the bridge was on the structurally deficient list because of fatigue cracks found in the late 1990's, but that recent inspections had found no enlargement or extension of those cracks. They said that the bridge was scheduled for a repair/replace decision in 2020.

For those who have not seen it, this is the best "before" picture of the bridge and its environment I have seen. If you scroll down on that picture, you will see the lock and dam just upstream from the bridge.

P.S. To all you good ol' boys down South, yes, that is what the Mississippi looks like way up here.

[HeroInBlack]

I'm a structural engineer, and a professor from my alma mater (Georgia Tech), Dr. Lawrence Kahn was just on with Sean Hannity (no I'm not a regular listener).

Dr. Kahn said that there was at least a chance that the construction being done on the bridge could have had something do with the failure this way: Even though the bridge was designed where the steel is supporting the concrete surface, if the steel had weakened enough over time, it could be that composite action between the steel and concrete had begun. So it's possible that the crew removed a hunk of concrete from the surface that was never intended to be structural, but was acting structurally. Imagine being that guy if this turns out to be the case.

Dr. Kahn also said that ASCE (American Society of Civil Engineers) had been telling Congress for years that a multitude of bridges needed attention.

[Quicksilvre]

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Dr. Kahn also said that ASCE (American Society of Civil Engineers) had been telling Congress for years that a multitude of bridges needed attention.

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I have heard that for a while myself, but I always took it for granted that something was getting done. OTOH, there are a lot of scary looking, rusted out bridges/overpasses around Albany, so I guess I really shouldn't be surprised nothing's getting done.