Author Topic: Florida Bridge collapse  (Read 7078 times)

Brad Johnson

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Re: Florida Bridge collapse
« Reply #50 on: March 20, 2018, 01:49:12 PM »
Just watched video of crews pulling out what was left of a full size Chevy pickup. Compacted to a mere fraction of its original height. Poor bastards inside never stood a chance. If there is any kind of positive to be gleaned, at least they didn't suffer.

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just Warren

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Re: Florida Bridge collapse
« Reply #51 on: March 20, 2018, 01:54:40 PM »
Member in Good Standing of the Spontaneous Order of the Invisible Hand.

Hawkmoon

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Re: Florida Bridge collapse
« Reply #52 on: March 20, 2018, 07:25:04 PM »
A rant on the diversity angle.

Ah, yes -- DIVERSITY!

A decade ago I was working as an assistant building official in a small town that had seen its building inspection department suddenly grow from one person to four because of the workload created by a huge golf course condominium project being built in town by an out-of-state developer. I don't speak fluent Spanish, but my late wife was from Sudamerica so I was trying to learn, so I could converse with her family when we went there for visits. The boss kept complaining about the workers placing the reinforcing steel for the foundations, because they kept getting it wrong and they didn't speak English, so he couldn't get them to do it right.

So one morning, on the day before a foundation pour, the boss dragged me away from the plans I was reviewing and we went out to the site. Sure enough, the rebar was being set to close to the forms, so there wouldn't have been enough concrete to protect the rebar from water in the ground. And, just as the boss had said, when he tried to get it fixed, they just looked at him and gave him the "No hablo ingles" routine.

So the boss looked at me, and I looked at the workers, and I just said "Escuchame, muchachos, necesitan mas espacio entre el acero y la madura."

Oh, my! They just looked at each other ... and the look was clearly, "Oh, *expletive deleted*it -- he speaks Spanish. We're fooked."

The spacing got fixed, and the boss never had another problem. But "diversity" is a problem, because the "diverse" elements don't think like Americans. There used to be a saying that there were three ways to do anything: "the right way, the wrong way, and the Army way." Today that has become: "The right way, the wrong way, and the way we do it back home where we came from and you Anglos probably shouldn't ever set foot." Anyone who presumes to tell them that we do it this way in the United States is racist.
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230RN

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Re: Florida Bridge collapse
« Reply #53 on: March 20, 2018, 07:56:48 PM »








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WHATEVER YOUR DEFINITION OF "INFRINGE " IS, YOU SHOULDN'T BE DOING IT.

Angel Eyes

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Re: Florida Bridge collapse
« Reply #54 on: March 21, 2018, 05:54:07 PM »
"End of quote.  Repeat the line."
  - Joe 'Ron Burgundy' Biden

K Frame

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Re: Florida Bridge collapse
« Reply #55 on: March 22, 2018, 07:08:08 AM »
I think I saw him on the local news talking about road conditions yesterday.
Carbon Monoxide, sucking the life out of idiots, 'tards, and fools since man tamed fire.

Angel Eyes

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Re: Florida Bridge collapse
« Reply #56 on: March 23, 2018, 06:10:09 PM »
Why the Miami bridge collapsed:  https://www.youtube.com/watch?v=JvmvFQKTrMY
"End of quote.  Repeat the line."
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Hawkmoon

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Re: Florida Bridge collapse
« Reply #57 on: March 23, 2018, 08:20:08 PM »
Why the Miami bridge collapsed:  https://www.youtube.com/watch?v=JvmvFQKTrMY


There are some rather fundamental errors in his explanation of how post-tensioned concrete works, and he's VERY wrong about where and how long it has been used, but his theory of a strand having been over-stressed by the incorrect placement of one of the lifting carriages makes sense.

I went to graduate school in Pennsylvania and early in my career I worked in Connecticut and New England. There were plenty of post-tensioned concrete structures around both areas, even in the early 1970s. I suppose that's "recent" compared to the first uses of concrete in the time of the Roman Empire, but in any conversational context I don't think 40+ years is exactly what most people think of as "recent."
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230RN

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Re: Florida Bridge collapse
« Reply #58 on: March 23, 2018, 08:41:17 PM »
I had a little trouble following how that one compression bar got loose.
« Last Edit: March 23, 2018, 10:40:08 PM by 230RN »
WHATEVER YOUR DEFINITION OF "INFRINGE " IS, YOU SHOULDN'T BE DOING IT.

Hawkmoon

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Re: Florida Bridge collapse
« Reply #59 on: March 24, 2018, 10:07:01 AM »
I had a little trouble following how that one compression bar got loose.


Tension strand, not compression bar. I think his thesis is that it was stressed beyond its yield point so it physically stretched. Then, when they attempted to tighten it, they stretched it farther ... until it failed.

The catch is that in a truss, half those diagonal web members are in compression and half are in tension. It's not intuitive which are which. 45 years ago I knew how to analyze a truss graphically and figure that out -- but I haven't done it since my thesis, and today I don't have even a fuzzy recollection of how to begin. He may be correct, but his explanation is terrible.
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230RN

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Re: Florida Bridge collapse
« Reply #60 on: March 24, 2018, 11:27:43 AM »
Thanks for nomenclature correction.  "Compression bar," to me, because that's what puts the "diagonal web members" (and presumably, the long horizontal members) in compression.

Glad to hear that it ain't an easy analysis.  I feel less dumb now.

TNX, Terry





WHATEVER YOUR DEFINITION OF "INFRINGE " IS, YOU SHOULDN'T BE DOING IT.

KD5NRH

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Re: Florida Bridge collapse
« Reply #61 on: March 24, 2018, 11:31:52 AM »
The catch is that in a truss, half those diagonal web members are in compression and half are in tension. It's not intuitive which are which. 45 years ago I knew how to analyze a truss graphically and figure that out -- but I haven't done it since my thesis, and today I don't have even a fuzzy recollection of how to begin. He may be correct, but his explanation is terrible.

Used to be a couple of freeware apps for simple (simple being a relative term when you're talking about FEA) modeling, and I think a web-based tool too.  I'll dig a bit if I remember when I get back from the laundromat.

But yeah, once steel stretches noticeably, pulling on it harder isn't going to fix the problem for long.

EDIT: https://trusstool.com/
And an online 2D modeler: http://engsci.stevenhe.com/trusssolver
« Last Edit: March 24, 2018, 12:24:51 PM by KD5NRH »