Specific technical problems, shortcommings, etc. with the NIST/ASCE reports thread.

[Realityhack]

I thought we should have a thread specifically for discussing technical problems, shortcomings, questions, etc. about the NIST and ASCE reports.

PLEASE look over the report you are commenting on before posting something here.

Your personal feeling that something looked like CD or a nuke or whatever is NOT a specific technical question or criticism of the reports. Saying they where done by the government and therefore must be lies is also NOT a specific technical criticism.

Let's try to keep this on topic and civil.

I am interested in knowing what specific technical criticisms or questions exist with regard to the NIST and ASCE reports. I am sure they are not perfect. I know people who understand them don't want to come across as conspiracy nuts but lets discuss what specific problems etc. you see with them.

[katukov]

1. Excellent idea - technical input

I have read all the NIST reports on WTC 1 and 2 and have not read the WTC 7 report yet. I have some thoughts which I will share in due time.

[katukov]

2. An issue with methodology

I've been studying the NIST reports on WTC 1 and 2 since about January.

An issue of methodology -

NIST went into exhaustive detail to describe, with a detailed finite element computer model, the dynamic interaction of the planes, with all their parts and contents, impacting the buildings. From this they derived the likely damage to perimeter and core columns, floors, and other load-bearing members.

From the modeling they also developed models for the fires on each floor, together with available fuel, (jet fuel and office furnishings), damage to fireproofing, etc.

They took the heat generated from the fires and applied it to adjacent steel columns and floor joists, resulting in weakening and thermal movement. From all this they derive a mechanism for each of the buildings to initiate collapse.

However, with all these wonderful tools available to analyze the dynamic interaction of the falling mass with the static mass underneath, they just quit - no more analysis. They have caused a collapse to initiate in their computer model (and I am not even convinced of that part), yet they do nothing to evaluate the collapse.

NIST's contention is that the gravitational potential energy of the falling mass is so much greater than the ability of the structure underneath to absorb it, that there is no need for analysis.

Perhaps...If the upper part is falling as a monolithic mass.

But if the laws of physics apply here, as the falling section damages the static lower section, the impact also damages the upper section, symmetrically. So, with WTC 1, by the time the falling top 15 floors reach the 80th floor, they would have crushed 15 floors below(81 to 95) - - but also they would have been crushed and pulverized themselves. The videos show this action, with debris ejected, and a lot of dust from lightweight concrete and fireproofing. The perimeter columns and spandrels mostly sheared at bolted connections and fell outside the building footprint, so their entire mass is unavailable to crush the lower structure.

Instead of a monolithic 60,000 ton falling mass, we would instead have an amorphous cloud of debris, with particles and chunks of all sizes, and the impact more dispersed in space and time with each floor downward. Would this cause the kind of collapse seen?

I don't have an answer, and NIST doesn't either.

[Bolo Boffin]

3. Does mass stop being mass when it's no longer a recognizable structure? n/t

[petgoat]

15. It stops meeting the criteria necessary to characterize it as a piledriver.

A disorganized mass of debris will expend a lot of energy simply
bouncing itself around as it falls, and will lose the ability to
penetrate the robust, extensively cross-braced core of the WTC.

[LARED]

4. A few comments

Regarding mass.

The mass is the same if it is a monolithic form or if it is is particles. While you are correct in noting some of the debris is pushed away from the mass that causes the floors to progressively collapse, I would assume there is a significant mass available.

Why?

Because the perimeter wall did not just peel away without a force. Based on the videos there was a large quantity of materials trapped within the perimeter walls (I would guess ten to fifteen floors of materials). This material provides a concentrated mass to collapse floors below and once enough of the structure was destroyed the perimeter walls would push away.

Regarding WTC upper section.

Once the upper section starts to fall there is no underlying structure holding it together. Without the bottom of the structure intact the building just opens up and comes apart was it falls through the lower section. A simple description is that the upper section was pulled apart and the lower sections were crushed. It required far less energy to pull the upper section apart than it did to crush the lower section.

[katukov]

6. Comment on mass and on the upper section

RE: concentrated mass versus debris cloud: Certainly a large mass of debris falling at speed has enough energy to do a lot of damage, perhaps to crush the rest of the building. However, consider the following:

Envision a 50 lb rock versus gravel of the same mass - which would you rather have dropped on your head? (assume you are wearing a hardhat or some kind of minimal protective equipment)- odds are good that the rock would crack your hardhat and your head, while the gravel would likely just slide off, even if it rang your ears a bit.

Same principle is accepted with anti-tank weapons, a large (120 mm) solid projectile at high velocity will punch out a tank, while an equal weight of 0.50 cal machine gun rounds at the same velocity will do nothing to a heavily armored target. The structure can absorb the energy of the multiple smaller impacts much more easily, and may have time to elastically deform and recover before the next one hits.

Another point is that the broken-up mass is shedding pieces outside the building footprint as it falls, therefore reducing the total mass, and reducing the total energy by the amount associated with those pieces.

A paper from the demolition industry that attempts to debunk the WTC demolition theory offers the observation that 95 percent of the debris fell outside the building footprint. See www.implosionworld.com and click on the WTC report. They seem to have debunked their debunking with this, if true (and I don't know if it is) because it's unlikely for the remaining 5 percent of the mass of the top section to have crushed the lower section.

As you have correctly observed, the upper section will fall apart much more readily than the lower section. To the extent most of the literature deals with the collapse mechanism, it seems to assume the upper section remains relatively intact. Here's one article - note the reference to the huge falling mass: http://www.civil.usyd.edu.au/wtc.shtml The NIST report also refers to "...a top section above the impact and fire floors that was also a heavy, rigid box." However, the more detailed WTC 7 analysis (that I have only skimmed at this point), shows anything BUT a rigid box falling, in fact it shows the building coming apart into pieces.

That said, I don't claim to know exactly what happened to the WTC 1 and 2. It is clear NIST had the tools to examine the entire collapse, because they did it for WTC 7. They just didn't do it for WTC 1 and 2, leaving these questions.

[William Seger]

7. There was certainly a lot of debris falling over the side

... but I think the 95% number is the amount that ended up outside the footprint after all the debris hit the ground and flattened out, not the amount that poured over the side during the collapse. While the building was collapsing, debris could only escape over the sides, and the buildings were over 200 feet wide, so it doesn't seem likely that a large percentage of the debris could have gotten over the sides in the critical early stages.

Frank Greening has done WTC1 collapse calculations including loss over the sides (I don't recall the amount he assumed): His mathematical model still collapsed, with little difference in the total time required. That's apparently because the dominant factor was the increasing velocity, not the increasing mass, of the falling debris (since the kinetic energy increases with the square of the velocity). In his simplified model, the first floor collision (after collapse initiation and the top falling 4 m) would have reduced the velocity of the falling debris by about one-half. But then that was the starting velocity for the next 4 m drop, so the next collision had more energy but only needed about the same amount of energy to break through. The velocity kept increasing while loss in velocity in the subsequent floor collisions would have been a smaller and smaller percentage, until eventually the collisions were slowing the fall so little that it was "nearly freefall." (Greening's calculations showed that if the building collapsed at all, it would probably collapse in not much more than twice the freefall time, whereas the actual collapses were somewhat faster than that, again indicating more than enough energy.)

But, really, the visualization of a flat "collapse front" hitting squarely on the floor below and crushing the columns can't be accurate, since we know that very few exterior columns and only a small percentage of the core columns were buckled. The collapse was certainly much more chaotic than the simplified models, and it seems likely that the falling debris mostly destroyed floors first, which left the columns unbraced laterally, which made them much easier to push over to the side than to buckle. The exterior columns were mostly pushed outward and broken at their end connections, but that effort would have funneled a lot floor debris downward first. That also means that debris going over the side was taking unbuckled exterior columns with it, so its effect can't be completely ignored. There was probably something of a "spire" of core columns standing throughout the collapse as debris pushed past it, but then those unsupported columns couldn't stand against the chaotic lateral forces for more than a few floors before they broke at the relatively weak end-to-end connections. So, the building was essentially ripped apart in pieces by destroying structural integrity first, and that would have taken less energy than actually crushing the columns. What the simplified models tell us is that if there was enough energy to crush the columns, even with mass going over the side, then there was more than enough energy to simply push them aside once the floors were destroyed.

I think the probable reasons that NIST didn't model the tower collapses were A) that would be a very complicated, time-consuming, and expensive model, which wouldn't have yielded much insight, because B) structural engineers understand that commercial office buildings are simply not designed to withstand the impact forces of that kind of failure; and C) it wouldn't have satisfied conspiracy theorists, anyway, so why bother. (It seems odd to me that conspiracists accuse NIST of faking the initiation sim, but then claim NIST didn't model the whole collapse because they were afraid of what it would show. Why not just fake that, too?) By contrast, with WTC7, the cause of total collapse after a local failure was not nearly so clear, so they needed to study that before they could say they had a good understanding of what happened.

I don't think either of the NIST reports should be taken as "the truth" about the details in either building, because so little is known about what was happening inside the buildings. Any analysis must necessarily include a lot of assumptions, so I won't be surprised to see some technical challenges from qualified people who think that different assumptions should have been used (which doesn't necessarily mean they are right). I do, however, think that the NIST scientists did their best to arrive at the most probable explanations, given the evidence, and that their theories make a lot of sense.

[Realityhack]

9. A couple points.

To be fair I don't think we can look at WTC 7 as being in any way related to WTC 1&2 in terms of how the collapse progressed because the buildings construction was so different.

Looking at the video we do indeed see the upper section break apart during the collapse as it impacts the lower sections but it stays surprisingly contained in the upper section. That may be because the 'skin' of the building was such a strong component.

Once that mass starts moving we are talking about a LOT of weight (even if it is a small amount) falling with increasing speed. So even if a bunch falls off the sides I think it would still be more than enough force.

Also I do not think the 95% figure is for the upper section contacting the next few floors but for the entire building. You can see from the photos of ground zero that large sections of the exterior of the bottom of the building seemed to 'peel' or fall outwards.

Even say 25% of 3 floors falling 12 stories onto the top of the remaining floors I would expect to smash through quite easily despite being in chunks.

I have no idea if the computer models could even attempt to show what was happening as things broke up but I assume they could not. That becomes a very complex situation. Plus just about every piece of evidence is obscured by dust.

Anyway it is an interesting consideration.

[Realityhack]

8. That is an interesting criticism

I have seen a couple of people criticize the NIST report on WTC 1&2 for not doing the calculation to prove that once the collapse initiated that it would progress past one floor. IIRC someone did a paper proving it would.
IMO that would have been good for NIST to do.
Once it gets past that point though, despite a lot of debris flying outward each successive floor destroyed adds to the mass. Given what we know from demolitions etc. I don't see any reason to pursue the idea that once moving past one floor anything could stop this. It is also what we see clearly on the videos.

Another point here is that NIST is mostly looking at this from a standpoint of understanding what happened to improve building codes etc. Therefore once 15 floors are crashing down on the rest of the building I am not sure they care too much. They aren't going to recommend building such that that can be resisted.

It is an interesting idea to model the collapse more completely but I also wonder if the data is there with so much cloud obstruction.

[AZCat]

16. They didn't have much choice.

Continuing the FEA was impossible because the simulation failed to converge. This is not uncommon when modeling highly nonlinear events. Compare this to the simulation of WTC 7, where the progressive nature of the collapse allowed the FEA simulation to continue past collapse initiation for some time before the simulation failed to converge.

Your claim about the "laws of physics" is misapplied, because the upper block picks up a layer of debris from the lower block as it moves downward. This prevents symmetric damage from occurring because the debris acts as a buffer for the upper block.

[katukov]

17. Symmetric damage

While the damage may not have been exactly symmetric, it appears from the available videos that the upper section suffered considerable damage on the way down. Also there is considerable material being ejected to the sides.

The mechanism of all this happening in the collapse is what we don't know, since the finite element analysis was not continued.

As I understand it, they couldn't even get the model to actually initiate collapse, just to show significant weakening of some of the columns. With some tweaking and leaps of faith, then "The upper section of the building collapsed onto the floors below."

On the other hand, they did manage to do a very complex model of the collision of the planes with the buildings.

[AZCat]

18. The model failed to converge.

Do you understand what that means? It means the mathematical algorithms at the heart of FEA have an inherent weakness, and it was encountered in the simulations of the WTC towers. NIST was unable to produce a model of the collapses (even the initiation) because the simulation basically broke at the point of initiation.

[katukov]

5. WTC 7 reports downloaded now

There is quite a lot to digest, they seem to have put as much effort into it as the WTC 1 and 2 studies.

One important difference: In contrast to my comment above, the WTC 7 study DOES do a computer model of the actual collapse. I presume this is necessary to demonstrate how a structurally asymmetrical building, with asymmetrical damage, collapsed so quickly in a symmetrical manner.

I have no other comments yet, just a lot of stuff to read.

[Realityhack]

10. I don't know if this is true or not...

I have heard that NIST has not released the actual computer models for peer review. Is that correct? If so is their a reason why? It seems like a bit of a shortcoming if true.

[AZCat]

11. They released at least one of their models from the WTC towers investigation.

The SAP2000 model was released to the public. I don't know if they made any of the other models available to researchers.

[Realityhack]

12. That is for WTC 1&2 right?

IMO they should release all the models used in contribution to the report. Like releasing your full data tables.

Just my opinion. I have no reason to question them I just think it would be better.

[AZCat]

13. It wouldn't do most of us any good.

With the exception of NIST's Fire Dynamics Simulator (available here), all of the software used to analyze the models is quite expensive (at least for an individual).

[Realityhack]

14. I was thinking more for university study.

Having the data available would allow at least a handful of people to play with it.