Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns

ergo said:
Does that thread answer anywhere the question of how the truss-to-column connections can be so robust that the floor trusses, while sagging something like 40" (a feat in itself, without breaking) can pull in 14" steel box columns, causing them to break, but simultaneously be so flimsy as to then be unable to prevent rapid progressive floor collapse? Just curious.
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You already know the answer. Why should anyone waste their time answering question you claim you knew the answer to anyway. Or what?

You can answer that yourself. Right, you already know all the answers. You have shown with ease how things work.
http://www.internationalskeptics.com/forums/showpost.php?p=6263596&postcount=621

I'm not sure even a moon-sized field or mountain of rubble, dropped from a height of 12 feet would entirely crush the WTC. No. If you had it coming down from a higher height, in a steady stream over a long period of time, we would certainly see some major damage. Total collapse? I'm not sure.
- ergo
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There you have it. Apply your standard model to this topic, and please give your answer first. Show your work. What is the answer?
 
beachnut said:
ergo said:
Does that thread answer anywhere the question of how the truss-to-column connections can be so robust that the floor trusses, while sagging something like 40" (a feat in itself, without breaking) can pull in 14" steel box columns, causing them to break, but simultaneously be so flimsy as to then be unable to prevent rapid progressive floor collapse? Just curious.
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You already know the answer. Why should anyone waste their time answering question you claim you knew the answer to anyway. Or what?
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No, I don't know the answer. And it appears that none of you do, either.
 
ergo said:
No, I don't know the answer. And it appears that none of you do, either.
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Well then I suppose we have to go with the only theory that has been worked on at all and assume that until someone comes up with a better one that is explained in as great, or better, a detail as the one we have.

Until continue JAQing off as usual
 
ergo said:
Does that thread answer anywhere the question of how the truss-to-column connections can be so robust that the floor trusses, while sagging something like 40" (a feat in itself, without breaking) can pull in 14" steel box columns, causing them to break, but simultaneously be so flimsy as to then be unable to prevent rapid progressive floor collapse? Just curious.
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Yes.
 
ergo said:
Does that thread answer anywhere the question of how the truss-to-column connections can be so robust that the floor trusses, while sagging something like 40" (a feat in itself, without breaking) can pull in 14" steel box columns, causing them to break, but simultaneously be so flimsy as to then be unable to prevent rapid progressive floor collapse? Just curious.
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Not sure if that thread answers it, but that answer is obvious. Pulling is basically a static event, while the fall of a floor is basically a dynamic event. We know well that you don't understand the difference, though, as highlighted by beachnut above.
 
OTOH in the other thread ( http://www.internationalskeptics.com/forums/showthread.php?t=242773&page=23)there is some discussion of the paper by Usmani et al in which their FEA shows that the floors exerted outward push as they expanded to the tune of pushing the perimeter columns out by approx 15 mm, until the floor membrane itself failed under this compressive load, the columns rebound and without the floor membrane/trusses in play they no longer have any lateral support on the inward side and would preferentially buckle in that direction due to (now non-axial) vertical loading.

Perhaps you (ergo) find that a better explanation.
 
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pgimeno said:
Not sure if that thread answers it, but that answer is obvious. Pulling is basically a static event, while the fall of a floor is basically a dynamic event. We know well that you don't understand the difference, though, as highlighted by beachnut above.
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The pull-in force was less than 6kips per column. Two 5/8" diameter bolts have more than enough capacity to handle that force when heated.

The answer is simple: the pull-in force was small. But that force combined with heated columns and large axial forces in the columns produced a failure mode through p-delta.
 
Newtons Bit said:
The answer is simple: the pull-in force was small. But that force combined with heated columns and large axial forces in the columns produced a failure mode through p-delta.
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If the pull-in force was small, why did NIST contrive a 40" deflection?


Regarding heated columns, don't Usmani et al. say:
Usmani et al. said:
Therefore one must conclude that even if there were areas of high temperature inside the building, it is quite likely that the columns did not heat significantly (even if they had lost fire protection).
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?
 
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Newtons Bit said:
The answer is in the math. Go read the thread I linked and stop wasting my time.
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No, I doubt that it is, Newton's Bit. If you can't explain it in plain language, it's clear you don't have an answer.
 
ergo said:
No, I doubt that it is, Newton's Bit. If you can't explain it in plain language, it's clear you don't have an answer.
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Second-order moment magnification doesn't translate well to "layperson": differential equations aren't something I can hold your hand through when you refuse to even look at the math at hand.

Stay ignorant, little truther, the world will always be a big scary place full of evil men in dark shadows for you as long as you continue to avoid answers.
 
ergo said:
If you can't explain it in plain language, it's clear you don't have an answer.
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That's nearly up there with Christopher7's "you can't find something if you don't look for it." When discussing diffy q, if someone can't use plain language it means there is no answer?
 
ergo said:
No, I doubt that it is, Newton's Bit. If you can't explain it in plain language, it's clear you don't have an answer.
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I'm not an engineer, ergo, and I understood what he was saying. You need to try harder and stop letting your confirmation bias get in the way. As a helpful hint, try understanding how the magnitude of the deflection and the force exerted on the connections are not necessarily directly correlated. (For the pedantic, yes, there is a correlation, but there is another variable in play and I want to see if ergo can figure it out.)
 
NB, who doesn't use his real name, has been trounced numerous times here and elsewhere for his technical "prowess". Other engineers who he has tried to engage no longer bother with him.

I notice he didn't want to answer my question about Usmani et al's opinions about heated columns or creep buckling, which contradict the discussion in the thread he cites, nor my question about the 40" deflection NIST needed for the trusses. So if he doesn't want to explain it to me, or even his non-engineer colleagues here, no skin off my nose. He can continue to glow in his self-imposed internet obscurity.
 
ergo said:
NB, who doesn't use his real name, has been trounced numerous times here and elsewhere for his technical "prowess". Other engineers who he has tried to engage no longer bother with him.
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[Citation Required]

I notice he didn't want to answer my question about Usmani et al's opinions about heated columns or creep buckling, which contradict the discussion in the thread he cites, nor my question about the 40" deflection NIST needed for the trusses. So if he doesn't want to explain it to me, or even his non-engineer colleagues here, no skin off my nose. He can continue to glow in his self-imposed internet obscurity.
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Why don't you read the post I linked that answered the OP's challenge first, and then we'll see about answering your questions. Because as is, they're very ignorant and most would be answered just by reading aforementioned post.
 
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ergo said:
NB, who doesn't use his real name, has been trounced numerous times here and elsewhere for his technical "prowess". Other engineers who he has tried to engage no longer bother with him.
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That's rich, coming from you, Captain "moon-sized field of rubble". :rolleyes:
 
ergo said:
No, I doubt that it is, Newton's Bit. If you can't explain it in plain language, it's clear you don't have an answer.
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If the pull in from sagging floor truss starts the column bending - once it gets started to bend the column will continue to bend under the axial force of its normal load.

And once started that bending will continue to increase until that specific column can no longer carry all the axial load on it which then has to transfer to other columns. So it stops bending because there isn't enough load.

That is the "one column" version. It is more complicated in the multi column setup but the basic principles are the same.

To understand the "balance" between how much initial pull in is needed and how much bending comes from axial force you need the maths. But the principle remains simple.
 
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