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Why did the WTC columns pull in?

Exactly how does molten metal, even if it existed, support a CD theory?
 
realcddeal:

That all depends on the time-temperature-load profile for the column of interest and that varied from column to column.
 
Apollo20 said:
realcddeal:

That all depends on the time-temperature-load profile for the column of interest and that varied from column to column.
Click to expand...

Oh, I HATE when people whom I wish didn't but nevertheless DO know what they are talking about raise interesting points!
 
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twinstead said:
Exactly how does molten metal, even if it existed, support a CD theory?
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Let's not derail here, guys.
Don't let the twoofers off the hook that easily. They've run up agin' it real hard, here, and are attempting to hijack the thread.

There are lots of "Molten Metal" threads to play in. Let's leave this one to the bowing.
 
twinstead said:
Usmani et al. I think I had that sushi last night with a nice Asahi lager.
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Make it a Sapporo and you're on!

Apollo20 said:
realcddeal:

That all depends on the time-temperature-load profile for the column of interest and that varied from column to column.
Click to expand...


I was just going to ask if the Usmani paper had a time plot. I will be the first to admit that I am not a structural engineer, and have had to go back to my husband's metallurgy books for some of these discussions, but it seems to me that the length of time between the impact and the collapse should make it easier to rule out (or in) what is plausible.
 
rwguinn said:
Let's not derail here, guys.
Don't let the twoofers off the hook that easily. They've run up agin' it real hard, here, and are attempting to hijack the thread.

There are lots of "Molten Metal" threads to play in. Let's leave this one to the bowing.
Click to expand...

Yes. I agree. Molten Metal most certainly does not ROCK!

The cameras pointed on the WTC for hours prior to the collapse are the key. Sadly for truthers, their conspiracy was observed in detail and shown to be crap.
 
realcddeal said:
How much shortening through creep would you estimate for the core columns?
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Not an easy thing to estimate, and I don't feel remotely qualified to throw a WAG at it. It depends on load and temperature, and that depends on impact damage, fireproofing damage, combustible fuel distribution, oxygen availability, and time.

NIST estimated creep on the order of 8 inches in the core of WTC 1 at t+100 minutes, as seen in Figure 8-18 in NCSTAR1-6, and 12 inches in WTC 2 at t+43 minutes, in Figure 8-37. WTC 1 preferentially creeps in the center with little effect at corners and perimeter, while WTC 2 creeps throughout and leaning slightly.
 
Apollo20 said:
realcddeal:

That all depends on the time-temperature-load profile for the column of interest and that varied from column to column.
Click to expand...

Time-temperature may have varied, but the unit stress was the same for each column at a specific floor. This was done to eliminate warpage between the core and perimeter due to differential deflections. Of course, that would have changed slightly, due to the aircraft damage, and the extra load would probably not have been distributed in a perfectly uniform way, but it wouldn't be way off either.

I have looked at this and for the 98th floor, with 20% of its core columns incapacitated, the unit stress would go from approximately 10,800 psi to 13,500 psi on the 36,000 psi yield strength A36 steel.

With these unit stresses it is hard to imagine very much creep occurring due to office fire temperatures, especially not at the relatively low temperatures which the actual core columns, which NIST did testing on, saw.

It would have been very nice if all the steel from the fire affected areas was saved. Unfortunately, it is hard to see any innocent reasons for why it wasn't.
 
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This is an awesome thread. Thank you NB. You've cleared a lot of things up for me in your simple anaylsis.

Mackey: Doesn't his model also demonstrate that core column cutting due to therm?te (assuming proper therm?te cutting devices exist) theoretically could have been the culprit too? I'm pretty sure firgure 3 and 4 support the notion that cut core columns alone, could result in perimeter bowing.
 
Sizzler said:
This is an awesome thread. Thank you NB. You've cleared a lot of things up for me in your simple anaylsis.

Mackey: Doesn't his model also demonstrate that core column cutting due to therm?te (assuming proper therm?te cutting devices exist) theoretically could have been the culprit too? I'm pretty sure firgure 3 and 4 support the notion that cut core columns alone, could result in perimeter bowing.
Click to expand...


Did you understand the difference between Calculation 1 and Calculation 2?
 
Hokulele said:
Did you understand the difference between Calculation 1 and Calculation 2?
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Yes I do.

Calculation1= no fire=slight bowing=no collapse

Calculation2=fire=increased bowing=collapse

(simply put)

But in both calculations, bowing occurs.
 
Sizzler said:
This is an awesome thread. Thank you NB. You've cleared a lot of things up for me in your simple anaylsis.

Mackey: Doesn't his model also demonstrate that core column cutting due to therm?te (assuming proper therm?te cutting devices exist) theoretically could have been the culprit too? I'm pretty sure firgure 3 and 4 support the notion that cut core columns alone, could result in perimeter bowing.
Click to expand...

I'm glad I could help.

Not impossible, but exceedingly improbable. For the CD theory to work here, the columns would have to be severed by whatever fantastical therm*te charges, then have kicker chargers on them that would push a piece away from the column so that the top just doesn't rest on the bottom. The exterior columns would still need to be at about 600c, and therm*te ain't going to work there. Most of the length of column needs to be heated to near 600c. Just a small piece of it heated up, such as in Max Photon's fantasy isn't going to cause the inwards bowing. However there's still problems with this scenario: the kicker charges would be heard, the fire still needs to be HOT and there needs to be severe damage to the floor slab (by heat or collision).

edit: My figures are not to scale. An inward bowing of 1 inch at that scale wouldn't be noticeable, thus they are exaggerated. With just the core column losses, the inwards bowing of the perimeter would not be noticeable.
 
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Newtons Bit said:
edit: My figures are not to scale. An inward bowing of 1 inch at that scale wouldn't be noticeable, thus they are exaggerated. With just the core column losses, the inwards bowing of the perimeter would not be noticeable.
Click to expand...


And you just gave away the punchline. I was hoping Sizzler would figure out the actual values for the bowing on his own. :(
 
Nb wrote:
With just the core column losses, the inwards bowing of the perimeter would not be noticeable.
Click to expand...

And if more core columns were cut then expected due to impact and fire?

Would that not increase bowing?
 
Newtons Bit said:
I'm glad I could help.

Not impossible, but exceedingly improbable. For the CD theory to work here, the columns would have to be severed by whatever fantastical therm*te charges, then have kicker chargers on them that would push a piece away from the column so that the top just doesn't rest on the bottom. The exterior columns would still need to be at about 600c, and therm*te ain't going to work there. Most of the length of column needs to be heated to near 600c. Just a small piece of it heated up, such as in Max Photon's fantasy isn't going to cause the inwards bowing. However there's still problems with this scenario: the kicker charges would be heard, the fire still needs to be HOT and there needs to be severe damage to the floor slab (by heat or collision).

edit: My figures are not to scale. An inward bowing of 1 inch at that scale wouldn't be noticeable, thus they are exaggerated. With just the core column losses, the inwards bowing of the perimeter would not be noticeable.
Click to expand...

I understand what you are saying and I agree that it is improbable for collapse initiation to be caused by the above model, but using therm?te as the culprit instead of fire+collapse damage.

Assuming a different model caused collapse initiation and assuming cutting core columns (via therm?te) was part of that model, would a large amount of cut core columns not result in observed bowing?
 
realcddeal said:
Time-temperature may have varied, but the unit stress was the same for each column at a specific floor. This was done to eliminate warpage between the core and perimeter due to differential deflections. Of course, that would have changed slightly, due to the aircraft damage, and the extra load would probably not have been distributed in a perfectly uniform way, but it wouldn't be way off either.

I have looked at this and for the 98th floor, with 20% of its core columns incapacitated, the unit stress would go from approximately 10,800 psi to 13,500 psi on the 36,000 psi yield strength A36 steel.

With these unit stresses it is hard to imagine very much creep occurring due to office fire temperatures, especially not at the relatively low temperatures which the actual core columns, which NIST did testing on, saw.

It would have been very nice if all the steel from the fire affected areas was saved. Unfortunately, it is hard to see any innocent reasons for why it wasn't.
Click to expand...

And what exactly would those temperatures be? Over 1000 deg C?
 
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