What exactly does NIST say about collpase times

[ozeco41]

I can understand a concept such as the isolated example of a ball in an elevator.

OK - step 1 satisfied

But of course this is not the building or the real world where a single point on the face of the building (roof line?) is used to plot the motion.

Correct but at this stage we need to know what situation we are talking about or we end up with a false conflation of factors from different scenarios.

The assumption being the point represents an entire building moving as a block. We know this is clearly not an accurate statement.

Whose assumption?? Where is that assumption stated?? Are you imposing it?? You are at full liberty to propose your own scenario but it is not valid to impose limits of your scenario on different scenarios.

You have not defined such a scenario so at this stage we do not have a specific situation to discuss.

If you used a point on the roof where the IB is observed it would likely give a different plot that one on the west corner of the roof.

True but what building are you talking about and what claim are you addressing??

What I am saying here is a single plot is hardly descriptive of the motion acceleration or whatever of the ENTIRE collapsing building.

Correct ..but....

it is a plot for a single point of a structure which is twisting, as it collapses. it is not a block as it was in its static condition.

Possibly - it depends on the situation we are presumed to be discussing. And that is not defined explicitly in your statements.

The recent thread discussion is about "leveraging of over G".

The concept was proposed in the scenario of WTC7 collapse. It accepted the findings of femr2's measurements which confirmed the accelerations approximating G at one point of the building as claimed by NIST, Chandler and others. The extra precision of femr's measurements seem to confirm over G. Some persons questioned EITHER the possibilty of over G in any gravity fall situation and/or the reality of over G in the specific situation of that corner of the façade of WTC 7. Nowhere in those discussions was the claim made that the whole building fell either at G or with momentary over G. And this thread OP was about WTC1-2.

Ergo... time motion studies reveal false motion information or motion that CANNOT be ascribed to the entire structure.

Both true within the undefined context of your statement. HOWEVER it is a strawman and false dichotomy within the WTC7 scenario PLUS AFAICS unrelated to WTC1-2 other than as general musing.

And not relevant to the step one modelling exercise I posted.

 

[chrismohr]

JSanderO,
Check this thread out: http://www.internationalskeptics.com/forums/showthread.php?t=182833
It's an extensive analysis of femr's data re greater-than-freefall of Building 7. I'm convinced now that it happened, for a total of around 3/4 second, and even that was the aggregate time over multiple instants when one point atop the north perimeter wall went barely faster than freefall. I doubt it was an error in measurement.

 

[JSanderO]

JSanderO,
Check this thread out: http://www.internationalskeptics.com/forums/showthread.php?t=182833
It's an extensive analysis of femr's data re greater-than-freefall of Building 7. I'm convinced now that it happened, for a total of around 3/4 second, and even that was the aggregate time over multiple instants when one point atop the north perimeter wall went barely faster than freefall. I doubt it was an error in measurement.

Chris,
Thanks for the link... I'll review it. But this does not change the nature of my last post. femr2's data is for a single point and it can only reflect the local environment. If there was some sort of spring action at the frame in close proximity to the point in question it could impart additional downward force I suppose. I wouldn't extract this to the entire building however.

As I believe the frame behind the curtain wall was coming apart... pulled down by the collapse of the north core columns then it's not unreasonable to expect some sort of spring-like snapping motion to be imparted as the frame was pulled apart and from the perimeter columns and spandrels. I can't describe how this would happen.. but the breaking of the frame was more complex than it dropping as a *unit*. That's for sure.

I found this in the second page of the linked thread:


Quote:
It is correct to say that "for about 2 seconds (from 5 to 7 seconds, by this time index), the average acceleration of the wall was close to free fall."

femr writes:
Okay, though think it should be made clear in text that over-G is present, and that it refers to the NW corner, not the wall.

Quote:
But the claim that "the wall fell at FFA for 2.25 seconds" is not supported by this data.

femr writes:
Agreed, and such a simplistic conclusion could never be true anyway. It's clear that behaviour varies slightly depending upon what point along the roofline is selected.

 

[LSSBB]

Chris,
Thanks for the link... I'll review it. But this does not change the nature of my last post. femr2's data is for a single point and it can only reflect the local environment. If there was some sort of spring action at the frame in close proximity to the point in question it could impart additional downward force I suppose. I wouldn't extract this to the entire building however.

As I believe the frame behind the curtain wall was coming apart... pulled down by the collapse of the north core columns then it's not unreasonable to expect some sort of spring-like snapping motion to be imparted as the frame was pulled apart and from the perimeter columns and spandrels. I can't describe how this would happen.. but the breaking of the frame was more complex than it dropping as a *unit*. That's for sure.

Correct, in that it was complex and did not fall as a composite unit. The exterior was held together by the moment frame and gave the appearance of a fall as a unit. Also, the interior collapse was complex however a net pull would still be imparted on the exterior as the interior fell. No magic here. There is still a possibility due to measurement error of below g, however it is irrelevant. The pull of the interior can fully account for above g acceleration.

 

[JSanderO]

Correct, in that it was complex and did not fall as a composite unit. The exterior was held together by the moment frame and gave the appearance of a fall as a unit. Also, the interior collapse was complex however a net pull would still be imparted on the exterior as the interior fell. No magic here. There is still a possibility due to measurement error of below g, however it is irrelevant. The pull of the interior can fully account for above g acceleration.

The full height inward bowing puts a lie to the notion that what we see dropping (at about FF) was the entire 40 stories (we can't even see that many stories in the various camera angles. The IB is a clue that the frame had broken at the col 76-46/47 line... and the floors plates behind the north face had fractured on all floors behind that kink/IB and likely collapsed toward the col 76-46/47 line and core. It would be completely impossible for the floor plate to remain as composite with the frame, and beams connecting the north core columns to the north perimeter columns.

The asymmetry of the floors collapsing and the beams supporting and composite with them could impart moments which would have local influence (torque) the movement of the facade and the frame supporting it.

The IB means that part of the facade was moving laterally as well as vertically in the descent phase.

At one point femr2 mentions that he does not accept the notion that the floors were not attached to the perimeter frame. He'd have to explain how he reaches this conclusion in light of the explanation above. Admittedly there was a very small fraction of time between the inside collapse and the facade descent... but the disintegration process had mutliple mechanisms and forces in play. It was simply not *BOOM* (CD) and the tower dropped as a mass. The visuals put a lie to that conception.

 

[LSSBB]

The full height inward bowing puts a lie to the notion that what we see dropping (at about FF) was the entire 40 stories (we can't even see that many stories in the various camera angles. The IB is a clue that the frame had broken at the col 76-46/47 line... and the floors plates behind the north face had fractured on all floors behind that kink/IB and likely collapsed toward the col 76-46/47 line and core. It would be completely impossible for the floor plate to remain as composite with the frame, and beams connecting the north core columns to the north perimeter columns.

The asymmetry of the floors collapsing and the beams supporting and composite with them could impart moments which would have local influence (torque) the movement of the facade and the frame supporting it.

The IB means that part of the facade was moving laterally as well as vertically in the descent phase.

At one point femr2 mentions that he does not accept the notion that the floors were not attached to the perimeter frame. He'd have to explain how he reaches this conclusion in light of the explanation above. Admittedly there was a very small fraction of time between the inside collapse and the facade descent... but the disintegration process had mutliple mechanisms and forces in play. It was simply not *BOOM* (CD) and the tower dropped as a mass. The visuals put a lie to that conception.

We do not know exactly what went on inside and it was no doubt comes, however the explanation I give needs no CD, merely sufficient pull as the interior collapses. And their would have been pull. And at one point the perimeter breaks at the base, probably due to a combination of the force applied from above by the collapse, and the stress from debris striking from the bottom. Once the perimeter breaks, the exterior falls. The tenting at the top and emptiness behind the top windows show the interior collapsed first.

The only way this could have been a CD would have been them specifically targeting the area of column 79 and using hush-a-boom explosives. And super secret ninjas. Who wanted to blow up an empty building that everyone would forget about and no one would profit from it's demolition.

 

[pgimeno]

To the benefit of those who don't follow links, I'll post here the explanation I linked to in a previous message, that I believe develops the idea that LSSBB is trying to convey, and can help JSanderO with clarifying the misunderstandings.

Ok, it took a bit to make these diagrams but here they are finally, sorry for the delay. This is my view of what happened inside the building. The diagrams are 2D, so the E-W progressive collapse is not accounted for in them.

Bear with me if I tell you that this is WTC 7 The thicker vertical lines in the middle represent the core and the outer thinner ones represent the perimeter.

[qimg]http://www.formauri.es/personal/pgimeno/xfiles/11-s/wtc7fall1.png[/qimg]

Now, the core collapses and starts to fall. The beams and girders transmit force from the falling core to the perimeter. The perimeter was until that point just holding its own weight and that of the connected floors as normal.

[qimg]http://www.formauri.es/personal/pgimeno/xfiles/11-s/wtc7fall2.png[/qimg]

The core is now effectively pulling the perimeter downwards. Elastic tension accumulates. The perimeter can't bear its own weight plus that of the core and fails. There may be a certain dynamic overloading effect at this point, but it's probably mostly static overloading.

[qimg]http://www.formauri.es/personal/pgimeno/xfiles/11-s/wtc7fall3.png[/qimg]

Under that elasticity hypothesis, the core could have bounced if the perimeter and girders resisted, and go upwards. It's not a physical impossibility. Of course, in practice the unions would probably break before that happened, and many other things could be happening inside preventing that.

And here's where I said that there is a possibility (infinitely unlikely) that the force the core is exerting on the perimeter equals the resistance of the columns, and therefore the resultant force is its own weight, making it fall at exactly g, even if the buckling columns of the perimeter are opposing resistance (cancelled by the sum of the downward forces of the girders and beams).

​

 

[pgimeno]

To address JSanderO's questions in the context of the above explanation:

Don't buy that. Sounds like nonsense physics to me. Who told you that? Would this be a continuous greater than G?

No.

and increasing rate of acceleration or would be be momentary?

Momentary.

Why?

Because the core starts falling first and elastic tension accumulates, so when the perimeter falls it does at its own falling rate plus the pull downward, which overall exceeds g, and afterwards the acceleration decreases as said elastic tension relaxes and the curtain wall catches up with the core. Of course, by the reaction principle, the core would be have the same extra force that pulls from the perimeter downwards, pulling upwards on it, slowing it down, and the CoM would be at or below g.

What about some less than G acceleration? What caused that?

Less than g acceleration, under that hypothesis, would happen when the perimeter failed and not enough elastic tension accumulated in the first stages, and then again after the elastic tension relaxed and thus that extra force ceased being there.

In any plot I've seen the motion was not smooth... as in a perfect straight line... was this a measurement issue or was the rate changing slightly. If the latter why?

The rate was changing for the reasons explained.

 

[chrismohr]

JSanderO,
Most of us agree that Building 7's >g moments are for that one point that femr2 measured, not the whole building. However, since NIST stated that Building 7 collapsed as a single unit, as observed, 9/11 Truth people like Chris Sarns argued endlessly that NIST said it therefore I had to accept it and not limit my >g argument to the one point on the top of the perimeter that was actually measured. NIST also said there was a 2.25 second period at freefall, so when I brought femr2's data into it and used it as evidence of slightly greater than freefall AT THAT ONE POINT, once again Sarns posted dozens of posts against THAT assertion. All I ever said was that at this one point where the collapse speeds were measured, the evidence points to a few brief moments of greater than freefall. I believe than when NIST said "at freefall," or that Building 7 fell as one unit, these are reasonable approximations of what happened. As NIST people told me repeatedly, their careful study ended at collapse initiation/inevitability. Then, "gravity takes care of it." They also said that no computer model in the world could fully analyze the chaotic collapse. The old battles with Chris Sarns over all this inspired me to come up with the term "NIST-picking," which is what the whole argument was about. Ozeco41, when JSanderO wrote, "The assumption being the point represents an entire building moving as a block. We know this is clearly not an accurate statement."... you challenged him with "Whose assumption?" Well, it certainly was Chris Sarns's assumption, and NIST's less-than-100%-precise statements about this irrelevant detail gave people like Sarns endless ammunition to talk circles around the issue. JSsanderO is right that this assumption is out there, and that it is clearly not accurate!

 

[JSanderO]

To the benefit of those who don't follow links, I'll post here the explanation I linked to in a previous message, that I believe develops the idea that LSSBB is trying to convey, and can help JSanderO with clarifying the misunderstandings.

Ok, it took a bit to make these diagrams but here they are finally, sorry for the delay. This is my view of what happened inside the building. The diagrams are 2D, so the E-W progressive collapse is not accounted for in them.

Bear with me if I tell you that this is WTC 7 The thicker vertical lines in the middle represent the core and the outer thinner ones represent the perimeter.

...

Now, the core collapses and starts to fall. The beams and girders transmit force from the falling core to the perimeter. The perimeter was until that point just holding its own weight and that of the connected floors as normal.

....

The core is now effectively pulling the perimeter downwards. Elastic tension accumulates. The perimeter can't bear its own weight plus that of the core and fails. There may be a certain dynamic overloading effect at this point, but it's probably mostly static overloading.

....

Under that elasticity hypothesis, the core could have bounced if the perimeter and girders resisted, and go upwards. It's not a physical impossibility. Of course, in practice the unions would probably break before that happened, and many other things could be happening inside preventing that.

And here's where I said that there is a possibility (infinitely unlikely) that the force the core is exerting on the perimeter equals the resistance of the columns, and therefore the resultant force is its own weight, making it fall at exactly g, even if the buckling columns of the perimeter are opposing resistance (cancelled by the sum of the downward forces of the girders and beams).

​

Thanks for the cartoon. It's not related to real world but conceptually it has some currency. The structure was clearly much more complex and your cartoon fails to show the east west progression of failures which occurred along the column line at the north of the core. Note that there were interior columns which were not part of the core per se and such as 79, 80 and 81 but stood between the core and the east facade. The cartoon suggest core failure, when it was TTF which pulled the north core columns out of alignment with the columns above at floor 7.

My TTF may not be correct... and it's a guess because we can't see what happened inside. But I believe it is coherent and consistent with all visual observations of movement.

If you have some comments about it... please put them out.

You depiction suggests that the entire facade/curtain wall HAD to be pulled inward as the rectangular frame was distorted into a parallelograms. That's didn't happen. The dropping of the core line of columns more likely caused SEPARATION of the column to beam connections and I'll bet there steel beams will show bolt withdrawal at those connections. It's likely that the n-s beams separated at the MG27 and MG23 5/16" fillet welds to column connections at the core (just a guess).

Agreed it's rather hard to depict a 4D event with a 2D cartoon. But for what your cartoon describes there would be hundreds of beam and girders bizarre geometry in the debris. What we see in clean broken rectangular end conditions. This is the tell take sign of CONNECTION FAILURES and not frame distortion depicted. But I suspect the process of connection destruction likely yanked the perimeter frame downward.

Chris:

The rate of descent is a complete non issue as to the cause of the motion. Truthers are all wet about this and can't link any of their evidence claims to a coherent CD scheme which matches ALL the visuals. When they provide one we can review it.

 

[jaydeehess]

Pgimeno, so that I can understand your diagram;
You are positing that when the core failed and floors began to buckle downwards, the elasticity of the floors added downward force to the perimeter columns, the perimeter then fails but is already under greater than g downward force and thus experiences greater than g acelleration.

Basically they were slingshotted downwards.

Perhaps.

However, it strikes me that the burden of proof has been reversed, as often happens. The CT claims that g was achieved by CD and can only occur via CD. It is then incumbent upon the CT then to provide proof of this claim rather than handwaving arguments. To that end they would also have to explain the over g portion of the collapse. If there is a mechanism, rotation, leverage, elastic reaction, that can cause over g in a CD then its also very possible to occur in a collapse initiated by heat weakened steel structural members.

BTW, ozeco is correct, the thread originally was dealing with 1&2WTC

 

[ozeco41]

BTW, ozeco is correct, the thread originally was dealing with 1&2WTC

Correct.

Than it morphed into the issue of "leveraged over G" which is a specific to WTC7 issue. Since everyone seemed happy with the drifting topic I set out a four stage road map to explain how "over G" could be legitimate part of a plausible collapse mechanism. And detailed the first two steps.

The discussions have fallen into three distinct approaches to reasoning with my preferred step by step clarity approach not favoured by any.

At this point it is tempting to refer to "Alligators and Swamps". (Or forests and trees) And not a single troll in sight to take blame for the.....whatever

So:

 

[ozeco41]

However, it strikes me that the burden of proof has been reversed, as often happens. The CT claims that g was achieved by CD and can only occur via CD. It is then incumbent upon the CT then to provide proof of this claim rather than handwaving arguments. To that end they would also have to explain the over g portion of the collapse. If there is a mechanism, rotation, leverage, elastic reaction, that can cause over g in a CD then its also very possible to occur in a collapse initiated by heat weakened steel structural members.

 

[LSSBB]

Pgimeno, so that I can understand your diagram;
You are positing that when the core failed and floors began to buckle downwards, the elasticity of the floors added downward force to the perimeter columns, the perimeter then fails but is already under greater than g downward force and thus experiences greater than g acelleration.

Basically they were slingshotted downwards.

Perhaps.

However, it strikes me that the burden of proof has been reversed, as often happens. The CT claims that g was achieved by CD and can only occur via CD. It is then incumbent upon the CT then to provide proof of this claim rather than handwaving arguments. To that end they would also have to explain the over g portion of the collapse. If there is a mechanism, rotation, leverage, elastic reaction, that can cause over g in a CD then its also very possible to occur in a collapse initiated by heat weakened steel structural members.

BTW, ozeco is correct, the thread originally was dealing with 1&2WTC

Yes, it is reverse burden of proof, because Truthers don't understand that:

1: There was no constant free fall.
2: Free fall can be produced without CD.

Therefore they don't understand that what they think is evidence of CD, is not.

They persist in claiming CD because of free fall, and either are ignorant of alternate explanations, or hand waive them away. AE911 is fully aware of the alternate explanations, and refuse to acknowledge them. That can, in my opinion, only be due to an intention to mislead, because the alternate explanation to CD as a cause for free fall (and above) is basic physics. As for the rank-and-file Truther , they don't grasp basic physics and are just believing in their con-artist movement leaders.

ETA: In case you are wondering about my qualifications, I have a dual B.S. in Physics and Astrophysics and an M.S. in Mechanical Engineering. I also have 19 years of combined Engineering and Lean Six Sigma Black Belt experience.

 

[JSanderO]

I am not concerned with a burden of proof. I am more concerned with a coherent explanation which matches all the observations. I don't think NIST's does. I am not concerned about FF. I find the column 79 failure scenario not compelling to lead to ALL the observed movements. I have no interest in convincing truthers.

Does anyone aside from NIST accept the column 79 floor 13 scenario leading to the global collapse we witnessed?

 

[ozeco41]

Yes, it is reverse burden of proof, because Truthers don't understand that:

1: There was no constant free fall.
2: Free fall can be produced without CD.

Therefore they don't understand that what they think is evidence of CD, is not.

They persist in claiming CD because of free fall, and either are ignorant of alternate explanations, or hand waive them away. AE911 is fully aware of the alternate explanations, and refuse to acknowledge them. That can, in my opinion, only be due to an intention to mislead, because the alternate explanation to CD as a cause for free fall (and above) is basic physics. As for the rank-and-file Truther , they don't grasp basic physics and are just believing in their con-artist movement leaders.

A good summary IMO

...esp. the ethical divide between the leaders and the followers.

ETA: In case you are wondering about my qualifications,

Your comprehension of physics is evident in your posts.

 

[ozeco41]

I am not concerned with a burden of proof. I am more concerned with a coherent explanation which matches all the observations. I don't think NIST's does. I am not concerned about FF. I find the column 79 failure scenario not compelling to lead to ALL the observed movements. I have no interest in convincing truthers.

Does anyone aside from NIST accept the column 79 floor 13 scenario leading to the global collapse we witnessed?

my position on Col 79 published many times.
1) Column 79 must have failed; AND
2) Column 79 failure must be CAUSAL of EPH falling NOT consequential.

3a) NIST's hypothesis is plausible and backed by a lot of effort. I have no need to accept it or reject it. It exists. It is;
3b) Your thoughts also represent the basis for an alternate plausible hypothesis. Your hypothesis also is on my list of known hypotheses. (one of only two at present and I still have no need...etc ) AND
3c) There could well be more other plausible hypotheses. HOWEVER

4a) I doubt we will ever prove anything. Remember that is the reason the truth movement ran and runs with WTC7 - they want us disproving things and the evidence on WTC7 is more hidden than for WTC1/2; PLUS
4b)
(i)Why does it matter?
(ii) To whom does it matter?
(iii) Do those persons to whom it matters have sufficient political pull to require that Government should expend additional public funds researching further? If I was a US citizen I would vote against it.

And that is me contributing to a third derail of the topic....I'll have to stay in after school....

 

[JSanderO]

my position on Col 79 published many times.
1) Column 79 must have failed; AND
2) Column 79 failure must be CAUSAL of EPH falling NOT consequential.

3a) NIST's hypothesis is plausible and backed by a lot of effort. I have no need to accept it or reject it. It exists. It is;
3b) Your thoughts also represent the basis for an alternate plausible hypothesis. Your hypothesis also is on my list of known hypotheses. (one of only two at present and I still have no need...etc ) AND
3c) There could well be more other plausible hypotheses. HOWEVER

4a) I doubt we will ever prove anything. Remember that is the reason the truth movement ran and runs with WTC7 - they want us disproving things and the evidence on WTC7 is more hidden than for WTC1/2; PLUS
4b)
(i)Why does it matter?
(ii) To whom does it matter?
(iii) Do those persons to whom it matters have sufficient political pull to require that Government should expend additional public funds researching further? If I was a US citizen I would vote against it.

And that is me contributing to a third derail of the topic....I'll have to stay in after school....

Ozzie,
My problem with your logic is not that col 79 failure was contributory to the collapse of the EPH, but it wasn't the ONLY column supporting the EPH which would have had to have failed fore the ENTIRE EPH to drop.

And even if the three columns under the EPH (79, 80 & 81) failed... we need to determine how far down the failure occurred and the proximate cause.

I don't accept that the fires on 13 did in 79, 80 and 81. My proposal for consideration is that these three column were linked/connected to TT#1 and TT#2 down on floors 5-7 and the failures of 79, 80 and 81 were a CONSEQUENCE of the transfer truss failure.

This is like a multi car pile up. Car A rear end car B which rear ends car C which rear ends car D. Car D damage was caused by car C.... but the entire accident was caused by Gage driving car A while listening to a talking book of David Ray Griffin and rear end car B.

Actually I think we could go back in the chain of causes... the progression as it were and right back to the AA11 hitting 1WTC which cause shorts and electrical gear to explode in Con Ed starting the fires at about 9am in the AM. But I am more concerned with the first STRUCTURAL failure which cause building MOVEMENTS. And that I believe was NOT column 79 but a failure in the transfer truss region.

Column 79's failure did NOT cause the WPH to drop following the drop of the EPH. No? Or if it did... please explain.


(i)Why does it matter?

It may have a bearing on several things such as:

a - Not building towers of main power sub stations
b - Not using massive trusses to support multiple columns (reducing the columns coupled to the foundations by almost 40%)
c - Perhaps not siting diesel storage tanks in close proximity to high voltage electrical equipment
It may make those responsible for a,b,& c legally negligent for damages

(ii) To whom does it matter?

a - it might to the company who paid the insurance claim
b - it might to future developers and tenants
c - engineers and code enforcement agencies

(iii) Do those persons to whom it matters have sufficient political pull to require that Government should expend additional public funds researching further?

Who knows? Probably not.

 

[chrismohr]

JSanderO, The Council on Tall Buildings and Urban Habitat more or less agrees with the NIST interpretation, but also asserts that NIST did not take into account thermal shrinking after thermal expansion. In other words, the long-span trusses expand and then start bending downwards as they push against the perimeter columns as NIST said. Then, as the fires burnh out and move to other parts of the building, we see those now-frozen bent spans shrink and create even more strain on the structure. What CTBUH said about COlumn 79 specifically I am not sure.

 

[JSanderO]

JSanderO, The Council on Tall Buildings and Urban Habitat more or less agrees with the NIST interpretation, but also asserts that NIST did not take into account thermal shrinking after thermal expansion. In other words, the long-span trusses expand and then start bending downwards as they push against the perimeter columns as NIST said. Then, as the fires burnh out and move to other parts of the building, we see those now-frozen bent spans shrink and create even more strain on the structure. What CTBUH said about COlumn 79 specifically I am not sure.

Chris,

I know the thread was about the twins and morphed into 7WTC. I also don't agree with NIST as to the proximate cause of the twin towers collapse as related to the bar truss supporting the OOS. I agree that heat was the straw that broke the camel's back but the proximate cause was MORE than likely a core failure... not sagging trusses.

I'd score 0 for 2 for NIST on their explanations for the initiation of the collapses.