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29 Structural & Civil Engineers Cite Evidence for Controlled Explosive Demolition
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Christopher7
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Thank you for your relevant argument.
The table you referenced uses the collapse of the girder between core column 79 and exterior column 44, which is the beginning of the 'cascading floor failures', as a starting point.
5.7.2 pg 263 [pdf 307]
"The first detectable indication of the WTC 7 east penthouse collapse was a downward movement of the eastern side of its roofline."
This is in conflict with the graphic 12-46 which shows a kink near the center of the east penthouse was the first detectable movement.
12.4.4 pg 572 [pdf 234]
"The collapse reference time of 0.0 s starts when a kink was observed in the roofline of the east penthouse." [near the center of the penthouse - Figure 12-46 pg 578 [pdf 240]
No big deal, the difference is negligible.
The problem has always been:
You all say the building is collapsing when any part is collapsing starting with the 'cascading floor failures'.
That is technically correct.
Other people say the building is collapsing when the entire building is falling. NIST calls this 'global collapse'
This is also technically correct.
What we have here is two different definitions and a failure to communicate.
Be advised: When I say "The building is falling" I am using the second definition. Most people use this definition. You may use the first definition if you like.
9-1 Vol.2 pg 588 [pdf 250]
"the entire building above the buckled-column region moved downward as a single unit, resulting in the global collapse of WTC 7."
[FONT="]This is the beginning of free fall acceleration. The 1.75s prior to this, me[/FONT]ntioned on pg 45 of 1A, is the kink developing near the center of the building.
Sarcasm preferable to childish insults.
NIST is using a different starting point in this section and ends when the building is out of sight. The time line I posted is from the data on pages 579-585 [pdf 241-247] check it out. You will see that my assembled time line is correct. It starts with the collapse of column 79 and ends when all the core columns had collapsed. [6.3s after the kink in east penthouse was first detectable]tfk said:
The table you referenced uses the collapse of the girder between core column 79 and exterior column 44, which is the beginning of the 'cascading floor failures', as a starting point.
5.7.2 pg 263 [pdf 307]
"The first detectable indication of the WTC 7 east penthouse collapse was a downward movement of the eastern side of its roofline."
This is in conflict with the graphic 12-46 which shows a kink near the center of the east penthouse was the first detectable movement.
12.4.4 pg 572 [pdf 234]
"The collapse reference time of 0.0 s starts when a kink was observed in the roofline of the east penthouse." [near the center of the penthouse - Figure 12-46 pg 578 [pdf 240]
No big deal, the difference is negligible.
The problem has always been:
You all say the building is collapsing when any part is collapsing starting with the 'cascading floor failures'.
That is technically correct.
Other people say the building is collapsing when the entire building is falling. NIST calls this 'global collapse'
This is also technically correct.
What we have here is two different definitions and a failure to communicate.
Be advised: When I say "The building is falling" I am using the second definition. Most people use this definition. You may use the first definition if you like.
9-1 Vol.2 pg 588 [pdf 250]
"the entire building above the buckled-column region moved downward as a single unit, resulting in the global collapse of WTC 7."
[FONT="]This is the beginning of free fall acceleration. The 1.75s prior to this, me[/FONT]ntioned on pg 45 of 1A, is the kink developing near the center of the building.
.That was admirably lucid, concise, and absolutely irrefutable.
It'll be ignored in a frenzy of panicky arm-waving, of course... but: I thought somebody ought to tell you so, nonetheless.
Thank you, verbiage lovers...
BTW, I would gladly pay you Teooos-day ....
tom
Christopher7
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Chris,
No, it did not.
It fell CLOSE TO free fall acceleration.
"AT free fall acceleration" is just as IMPOSSIBLE as "faster than Free fall acceleration".
Only non-engineers may think that this is an irrelevant hair split. I assure you that it is NOT.
Repeating a falsehood does not make it magically become true.
tom
You-all consider facts like "WTC 7 fell at free fall acceleration for about 100 feet" to be raving nonsense.
No, it did not.
It fell CLOSE TO free fall acceleration.
"AT free fall acceleration" is just as IMPOSSIBLE as "faster than Free fall acceleration".
Only non-engineers may think that this is an irrelevant hair split. I assure you that it is NOT.
Did I mention that WTC 7 fell at free fall acceleration for about 100 feet?
Repeating a falsehood does not make it magically become true.
tom
Christopher7
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Christopher7
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Chris,
I see exactly what you are doing. You are confused about how NIST is defining their collapse stages, and confuse about how they sequence, one after the other.
As a result, you are starting your clock about 4.7 seconds too late, and ending your clock about 0.3 seconds BEFORE the external wall BEGINS to fall.
Let's get one thing set right at the beginning: the index time for ALL timing is when the east penthouse BEGINS to descend. This is exactly the same time (0.00 seconds) that the kink BEGINS to form.
Second point: the timings that you are quoting are MODEL timings. Because none of these events (except the index event, the start of the descent of the east penthouse) are externally visible. The emerge from the computer sim.
NIST divides the collapse into four successive segments (see 12.6 Summary of Findings, pg 603 - 607 (pdf 265 - 269):
1. Local Failure (start: -7.9 sec, by model only) to start of collapse of col 79 (@ -1.3 sec)
2. Vertical Progression of collapse of col 79 (@ -1.3 sec) to start of collapse of col 81 (@0.0 sec)
3. Horizontal Progression (0.0 sec) to beginning of collapse of external north wall ("Global collapse") (6.9 sec)
4. Global Collapse (start of downward motion of east edge of north wall) (6.9 sec) to roof disappears from sight (13.5 sec.)
(See Table 5-3. NCSTAR1-9, Vol 1. pg 290 (pdf 334).
Note two things:
The timing of everything except 1) The index event (begin of descent of east penthouse) & 2) the beginning of "global collapse" (beginning of descent of north wall) are invisible from the outside, and are determined by simulation.
All of those 4 event segments are "artificial". Each event led to, and blends invisibly into, the next. So the only logical "starting event" is the original failure: the floor collapse at about -6 seconds to -7.9 seconds.
There are several events. All of them are approximate times derived from modeling. The initiating event is GUESTIMATED at between -6 seconds to -7.9 seconds.
There is no conflict here. The kink STARTS to form at the same time (0.00 sec) that the east penthouse begins to drop. But the kink doesn't become EVIDENT to a still diagram until about 0.2 seconds later.
There are a bunch of POSSIBLE terminologies. But there is only ONE reality. Someone can choose to use terminology that enhances clarity. Or one can choose terminology that enhances confusion. I'd recommend the former.
The essential question is "when did the single event occur that led inexorably to total collapse?" And that happened somewhere around -6 to -8 seconds.
You can talk about any subset of these events, and their timing. But the fact is that the complete collapse time was well into the 20 second time frame.
BTW, re: Fig 12-77 (Vol 2, pg 603, pdf 265): This figure divides up the "Global collapse" segment ONLY into three separate Stages. Note that even this segment does NOT fall as though its supports were all simultaneously cut.
For 2 reasons:
1. The collapse had been going on for 13 - 15 seconds prior to the start of fall of the north wall.
2. The north wall does NOT fall as if its supports were cut out from under it. The downward acceleration starts out SLOW (near zero ft/sec^2) and gradually grows to NEAR free fall acceleration at about 2 seconds, and stays NEAR free fall acceleration between 2.0 & 4.0 seconds.
Parts that have their supports cut from under them IMMEDIATELY start dropping at free fall acceleration. The North Wall does NOT fall as if it were in free fall. It DOES fall as if the lower portions of the support columns buckle.
Tom
I see exactly what you are doing. You are confused about how NIST is defining their collapse stages, and confuse about how they sequence, one after the other.
As a result, you are starting your clock about 4.7 seconds too late, and ending your clock about 0.3 seconds BEFORE the external wall BEGINS to fall.
Let's get one thing set right at the beginning: the index time for ALL timing is when the east penthouse BEGINS to descend. This is exactly the same time (0.00 seconds) that the kink BEGINS to form.
Second point: the timings that you are quoting are MODEL timings. Because none of these events (except the index event, the start of the descent of the east penthouse) are externally visible. The emerge from the computer sim.
NIST divides the collapse into four successive segments (see 12.6 Summary of Findings, pg 603 - 607 (pdf 265 - 269):
1. Local Failure (start: -7.9 sec, by model only) to start of collapse of col 79 (@ -1.3 sec)
2. Vertical Progression of collapse of col 79 (@ -1.3 sec) to start of collapse of col 81 (@0.0 sec)
3. Horizontal Progression (0.0 sec) to beginning of collapse of external north wall ("Global collapse") (6.9 sec)
4. Global Collapse (start of downward motion of east edge of north wall) (6.9 sec) to roof disappears from sight (13.5 sec.)
(See Table 5-3. NCSTAR1-9, Vol 1. pg 290 (pdf 334).
Note two things:
The timing of everything except 1) The index event (begin of descent of east penthouse) & 2) the beginning of "global collapse" (beginning of descent of north wall) are invisible from the outside, and are determined by simulation.
All of those 4 event segments are "artificial". Each event led to, and blends invisibly into, the next. So the only logical "starting event" is the original failure: the floor collapse at about -6 seconds to -7.9 seconds.
There are several events. All of them are approximate times derived from modeling. The initiating event is GUESTIMATED at between -6 seconds to -7.9 seconds.
There is no conflict here. The kink STARTS to form at the same time (0.00 sec) that the east penthouse begins to drop. But the kink doesn't become EVIDENT to a still diagram until about 0.2 seconds later.
There are a bunch of POSSIBLE terminologies. But there is only ONE reality. Someone can choose to use terminology that enhances clarity. Or one can choose terminology that enhances confusion. I'd recommend the former.
The essential question is "when did the single event occur that led inexorably to total collapse?" And that happened somewhere around -6 to -8 seconds.
You can talk about any subset of these events, and their timing. But the fact is that the complete collapse time was well into the 20 second time frame.
BTW, re: Fig 12-77 (Vol 2, pg 603, pdf 265): This figure divides up the "Global collapse" segment ONLY into three separate Stages. Note that even this segment does NOT fall as though its supports were all simultaneously cut.
For 2 reasons:
1. The collapse had been going on for 13 - 15 seconds prior to the start of fall of the north wall.
2. The north wall does NOT fall as if its supports were cut out from under it. The downward acceleration starts out SLOW (near zero ft/sec^2) and gradually grows to NEAR free fall acceleration at about 2 seconds, and stays NEAR free fall acceleration between 2.0 & 4.0 seconds.
Parts that have their supports cut from under them IMMEDIATELY start dropping at free fall acceleration. The North Wall does NOT fall as if it were in free fall. It DOES fall as if the lower portions of the support columns buckle.
Tom
Chris,
Chris, please. I'm a mechanical engineer w/ 35 years experience. I've taught engineering dynamics to college engineering students. I know what "free fall acceleration" means.
And this is wrong. Air resistance is negligible ONLY at low speeds. As the speed increases, then air resistance increases at a rate that is approximately proportional to the velocity squared. As the force of air resistance the acceleration decreases.
Finally, the object reaches terminal velocity, at which point the acceleration is ZERO.
In the case of WTC7, the important air resistance is NOT the aero drag as it falls. It is evacuating the ground floor's air as it crushes down. This provided a cushion of air on the bottom floor that had to be pushed out of that bottom floor. It is EXACTLY this high velocity air jet that dispersed the dust & debris cloud so widely.
I'll say it again, Chris. I'm an old fart, old school engineer. I know BETTER than the people who put together, for example, Fig, 12-77. There are a couple of blatant idiocies associated with this graph. Anyone who REALLY knows numbers & graphs can immediately see what those errors are.
Do YOU see them?
And I stand by what I said. The building fell NEAR free fall acceleration. It did NOT fall AT free fall acceleration.
I am NOT guessing, Chris.
Tom
Chris, please. I'm a mechanical engineer w/ 35 years experience. I've taught engineering dynamics to college engineering students. I know what "free fall acceleration" means.
And this is wrong. Air resistance is negligible ONLY at low speeds. As the speed increases, then air resistance increases at a rate that is approximately proportional to the velocity squared. As the force of air resistance the acceleration decreases.
Finally, the object reaches terminal velocity, at which point the acceleration is ZERO.
In the case of WTC7, the important air resistance is NOT the aero drag as it falls. It is evacuating the ground floor's air as it crushes down. This provided a cushion of air on the bottom floor that had to be pushed out of that bottom floor. It is EXACTLY this high velocity air jet that dispersed the dust & debris cloud so widely.
I'll say it again, Chris. I'm an old fart, old school engineer. I know BETTER than the people who put together, for example, Fig, 12-77. There are a couple of blatant idiocies associated with this graph. Anyone who REALLY knows numbers & graphs can immediately see what those errors are.
Do YOU see them?
And I stand by what I said. The building fell NEAR free fall acceleration. It did NOT fall AT free fall acceleration.
I am NOT guessing, Chris.
Tom
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Christopher7
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NO!
I'm quoting a different section that uses a different start and ending time. Did you read my post? Go read it again.
Yes it does.
The entire building falls at free fall acceleration!
Wrong! Cut the double talk.
It falls at free fall acceleration for 2.25 seconds - 105 feet.
All supports on 8 floors were removed in 2.25 seconds.
WTC 7 fell as fast as it would fall through air for 105 feet.
That's what David chandler proved and NIST verified!
Exactly. This is a good view of the structure we're talking about :
Chris says "so what?" about the fact that such a large, heavy structure collapsed inside the building several seconds before global collapse. And can't appreciate that naturally the underlying structure had to be crumbling even before that, with the damage propagating upwards and sideways.
"So what" says a lot about Chris's obsession.
Christopher7
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You are desperately trying to talk around the FACT that
WTC 7 fell at free fall acceleration for 105 feet!
Thar's what it says on page 45 of the NIST report.
funk de fino
Dreaming of unicorns
funk de fino
Dreaming of unicorns
Oops
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Christopher7
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He did not explain away the fact that
WTC 7 fell at free fall acceleration for 105 feet!
That's what it says on page 45!
Give it up.
[FONT="]On NIST 1A pg 45 it says:
"In Stage 2, the north face descended at gravitational acceleration"
This is another way of saying "free fall acceleration"
They continue:
"This free fall drop continued for approximately 8 stories or 32.0 m (105 ft)"
The entire building* fell at free fall [gravitational] acceleration for 105 feet.
*[/FONT][FONT="] 9-1 Vol.2 pg 588 [pdf 250][/FONT]
[FONT="]"the entire building above the buckled-column region moved downward as a single unit, resulting in the global collapse of WTC 7."[/FONT]
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You-all consider facts like "WTC 7 fell at free fall acceleration for about 100 feet" to be raving nonsense.
Quite the contrary, I reference facts in the NIST report that debunk the NIST report.
You don't know who I talk to.
Wrong.
Attempted subject shift noted.
You rave the same nonsense over and over, establishing that you know absolutely nothing about engineering. There is a reason why you fail to impress real engineers with your free-fall crapola.
There is nothing in the NIST Report that "debunks" the NIST Report. Certainly there is nothing that real engineers have noticed.
You talk to no real engineers. You wouldn't continue to babble such foolishness if you did.
The FACT that demolition professionals reject your myths about explosives is highly relevant to the subject at hand.
Yes, you mention your free-fall idiocy constantly. You have no idea of what you're trying to claim.
Tfk's posts demonstrate that he understands the collapse of WTC 7. You do not, and you refuse to disturb your delusions by making any attempt to learn.
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H'ethetheth
fishy rocket scientist
I have to say, I can't see why the penthouse would be a "heavy structure", but I don't think that matters.
So Cristopher, when the top of a building falls in, apparently the building is gutted. 200 m high walls don't stand by themselves. What fell at freefall was just the facade; an empty shell.
Newtons Bit
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Uh, no. Engineers have an ethical obligation to demand the removal of their name from a publication that they don't agree with. If they don't, than they don't have any serious disagreement with the conclusions/methods/results. They also have an obligation to show how it is wrong if they think so.
Please read the engineering code of ethics, you obviously have no clue how my profession works:
http://www.asce.org/inside/codeofethics.cfm
funk de fino
Dreaming of unicorns
I have bolded the relevants parts that C7 does not like to see or read. he cherrypicks and does not understand what is written on a page.
What is your qualification C7? Inept reading?