NASA Scientist Ryan Mackey Answers ATS Questions

Griff ~

Here is yours.


Quote from Ryan Mackey:
If the complaint is about the failure modes observed during collapse, it is quite possible -- the perimeter columns essentially buckled inwards, whereas the core, being the heaviest part of the structure and the most compromised in the moments leading up to failure, would have been leading the collapse.

Griffs response:

A few points here. I was under the impression that the perimeter columns were pulled inward and that was what caused collapse? He is saying that the core was what caused collapse? Which goes along with my theory but is a contradiction with NIST I believe.

BTW, how was the core structure "the most comprimised"? Especially in WTC 2 where the plane practically missed the core?

But, the work of Bazant and Zhou included many assumptions that have not been proven or disproven.


Mr. Mackey's response:

Sorry if I'm confusing you -- the buckling of the perimeter columns was the last straw so to speak, but at the moment of collapse, the perimeter was already supporting the core. It stands to reason that the core started moving downward a fraction of a second before the perimeter. An academic detail. This is consistent with NIST, who computes the remaining capacity of perimeter and core in NCSTAR1-6D for different moments in time and describes how the core weakened (and shortened) first.

The core was the most compromised because that is where the fire was hottest. There is the least heat loss to the outside, the greatest stack effect due to the elevator shafts (all in the core!), and the fact that at impact most of the furnishings were pushed up against the core.
WTC 2's core was damaged MORE than WTC 1, not less. The plane didn't practially miss the core at all -- only the starboard wing did, the fuselage and port wing hit it directly. More importantly, WTC 2 was hit at a flatter angle, so the core took more of the impact than WTC 1, where the floor system took more of the blow. WTC 2 was also hit at higher speed. This not only destroyed more columns, but also sawed off the corner of WTC 2's core, whereas WTC 1 was hit pretty much dead center.

Bazant & Zhou's work uses simplifications, but it is fairly insensitive to most of their assumptions. You are welcome to try to disprove their paper. Nobody has done so, nor has anyone offered a different (valid) model with a different outcome.

MORE from Griff:

He basically said what I was saying. Depending on the source wind load is considered live load or not. Could you ask him about the conversion of the moment caused by the wind load into a concentric load for me? I'd like to hear his explaination. Thanks.

The equation is:

P(eff) = P + M(ux)m + M(uy)mu

P(eff) is the equivalent axial load
P is the total factored concentric load (dead and live loads)
M(ux) is the moment due to the total factored bending load (wind load in this case) in the x direction
M(uy) is the moment due to the total factored bending load in the y direction
m and u are factors coinciding with the column properties.

That is how a column that is subjected to bending and axial compression is designed.

Mr. Mackey:

The perimeter of the WTC is often described as a "Vierendeel Truss," i.e. a truss without diagonal members, one that relies on the connections to provide resistive moment. Resisting the wind means designing the structure to handle the overturning moment of the wind.
Computing the overturning moment is not practical. There are a lot of factors that are hard to model. Interference between the two towers, as well as that from surrounding buildings, is a huge correction. So the original designers used a wind tunnel model and empirical results. NIST replicated the experiment and got slightly different answers.
In any case, you work out the maximum design overturning moment and apply this as a body force to the structure. In the side facing the wind, this creates tension, and in the opposite face, it creates compression. Steel handles both with reasonable ease provided you join the members correctly. Tension opposes weight, but compression adds to it, so stress is higher on the compression side. You size the perimeter columns for the compression load. This load also decreases with height (think of drag over the whole face of the structure), so the most tension and compression is felt near the bottom.
To first order, simply divide the total force (at any given height) by the number of columns. The structure isn't really a homogeneous solid, but it's such a large structure that this is close enough. The largeness of the structure also allows you to ignore moment for any individual member and simply think in terms of axial stress. That gives you the design wind load for an individual column.

Bsbray11 ~

Here is your's.

From Bsbray11:

What physical tests did NIST do that corroborated their critical hypothesis (specifically that heated trusses could cause the required deflections in outer columns to initiate a failure), and how specifically was their hypothesis corroborated? Basically, I want to know where the meat is. I want to see a truss heated and subsequently pull a perimeter column out of place.

Mr. Mackey:

Actually, NIST doesn't need to provide this at all. The deflections in outer columns are determined by photographic evidence, not simulation. This is an input, not a result.
The actual force to pull the perimeter columns inward ("out of place" is a red herring) is small. The majority of the force is provided by the vertical load, not the floor trusses. A small side force leads to eccentric loading, and that reduces the perimeter column's ability to withstand buckling under load. Had the perimeter columns not been loaded, it would have taken much, much more force to pull the columns as seen.
The amount of force needed, as estimated by NIST, is not terribly high -- under 5,000 pounds per column, ten to twenty columns per floor. That's a total of perhaps 100,000 pounds or 50 tons on a given face of the structure. An individual floor can exert this with ease through mass alone. It can also apply thermal contraction forces (having sagged and then begun to cool late in the event).
NIST did this in simulation. The sag of floors was computed using their fire and thermal response model. This sag, by the way, is also seen in photographs. NIST also estimated whether the forces required (~ 5,000 pounds) were within the capabilities of the connections between floors and columns, and though the actual strength of these connections is imprecisely known, found that it was quite plausible.
But, again, this is not essential for their collapse model. Their collapse model takes the perimeter bowing as an input. It doesn't predict it, nor does it have to. NIST was satisfied to show that the bowing seen could be explained by the floor sagging mechanism.
Arup goes further and actually predicts the floors sagging and inward pull. In this respect, their model is superior, and independently verifies NIST's "critical hypothesis."

From Bsbray11:

Emphasis mine. What temperatures are you anticipating in the steel in these fires, and where is the experimental data to support your figure?

If you look up the tests done on steel frame structures in Cardington in the UK, by the University of Edinburgh and a few other institutions, you'll see high-powered fires (intentionally created to generate high amounts of power directly upon the steel itself for extended periods of time -- whereas NIST states that the fires tended to flare up and die down in different parts of the buildings, among other differences) uniformly heat steel only to a max of between 600 and 650 C or so, hot enough to glow in broad daylight. Again, NIST found no evidence of this kind of heating in the WTC Towers, but U of E et. al. did this intentionally to study the effects on the structure.

It was found in the final study (here's a link: www.studyof911.com... ) that failures in steel frame structures occur primarily from stresses between the members caused by thermal expansion. This is the primary cause of warping, sagging, buckling, etc. in fires heating steel to ~600 C and below.

Mr. Mackey:

If you'd read my whitepaper -- the subject of this discussion -- you'd note that I cite and use the Cardington experiments. I know all about them. I also cite Dr. Usmani's results.
The Cardington results demonstrate something quite different from what you claim, however. The Cardington full-scale test found beam temperatures of up to 800 Celsius, not "a max of between 600 and 650 C or so." The raw data is available online if you'd like to check. Please keep this in mind.
There were also reports from the NYPD aviation unit of structural members visibly glowing in broad daylight -- in the interior, of course, so there are no pictures, but nonetheless we have every reason to believe that a significant quantity of the structural steel exceeded 600 C.
Your claim that "NIST found no evidence" of this is wrong. The *recovered steel* may not have reached this temperature, but they were not looking for steel that exeperienced high temperatures. Quite the opposite. They only recovered steel that survived intact enough to (a) bear identifying marks, and (b) provide an unambiguous account of its failure mode. Steel that exceeded 650 C would be highly unlikely to yield either result, and as such was passed over. NIST's evidence for higher temperatures includes the NYPD report as above, but also its own full-scale fire test and its modeling effort, which predicts steel temperatures in some locations much higher than this.

The Cardington study, claiming that failures occur primarily due to thermal expansion, was based on a study of traditional column and beam structures. The WTC design does not fit this criterion. As I stated in my paper, I also feel that NIST underestimated the effect of thermal expansion, but it is simply incorrect to claim that the Cardington experiment is a good fit to the WTC. Different design entirely.
Also, the Cardington experiment was not a "high powered" fire, but rather a realistic one. Its fuel loading was in no way exceptional. The gas temperatures, steel temperatures, and structural damage were intended to synthesize an actual office fire, not -- as you claimed -- intentionally run for extended periods of time.

Regarding creep, the primary issue with creep is in the core shortening. This is where the steel was hottest and loaded the most. Over a period of an hour or so, at temperatures of 600C+, supporting a mass of 20,000 tons at minimum, creep is going to be a factor. This led to unloading of the core load through the hat truss to the perimeter, and partly explains why the structure failed in the manner that it did.

---

Hope this thread has been helpful to those that are not only posting questions, but are reading the Q & A's written by others.

Mr. Macky ended his e-mail with this:

These questions are increasingly tangential to my whitepaper. This is fine, but I would like to point out that, if there are no objections to the whitepaper itself, we should all agree that Dr. Griffin's opinions are dead wrong, as I claim therein.

Thanks,
Ryan Mackey

Please keep this in mind for future questions. As I stated before, Mr. Mackey isn't interested in debunking CT's. I have only forwarded questions that are relevant to his white paper and NIST questions. Holograms, nano nukes, etc... these questions will not be forwarded.

Thanks once again for your great questions!

C.O.

Captain O you should be commended for your effort in this thread and special thanks to Mr. Macky for his willingness to answer some well thought out questions and answer them accordingly.

Mr. Macky has proivded a very detailed explantion about what took place leading upto and during the initial collapse.

Thank you both for your efforts.

reply to post by ferretman2


Thanks Ferretman. I have been very impressed with Mr. Mackey's quick responses, and the detail he provides is incredible.

Originally posted by CaptainObvious

Actually, NIST doesn't need to provide this at all. The deflections in outer columns are determined by photographic evidence, not simulation. This is an input, not a result.

Then you don't have a case for what caused the deflections. I said proof that heated trusses deflect outer columns.

I don't think thermite caused the deflections, but let's say that I did. Would it be logical for me to say, "Well, you see the deflections, so therefore it was thermite, no more proof needed."?

The actual force to pull the perimeter columns inward ("out of place" is a red herring) is small. The majority of the force is provided by the vertical load, not the floor trusses. A small side force leads to eccentric loading,

Have you not considered that this relatively small force "pulling" the outer columns inward is only going to result in actual displacement proportional to the sum of all the forces holding the column "in place" when it starts to move?

So what kind of forces are we talking about, compared to the forces provided by the spandrel groups? Can you say? NOT theoretical values, because I've seen some horrible modeling done by supposedly credible people, ie Frank Greening in his more naive attempts at modeling a pancake collapse with 1-dimensional analysis, and I want to see someone lay out a truss assembly and heat it, and deflect a column. I don't want assumptions and I don't want pointing at the collapse and essentially feedbacking the whole point of the investigation in the first place: finding out what CAUSED the building to collapse.

The amount of force needed, as estimated by NIST, is not terribly high

May we see the calculations?

NIST did this in simulation. The sag of floors was computed using their fire and thermal response model. This sag, by the way, is also seen in photographs. NIST also estimated whether the forces required (~ 5,000 pounds) were within the capabilities of the connections between floors and columns, and though the actual strength of these connections is imprecisely known, found that it was quite plausible.

And that doesn't strike you as a big fudge? They estimated forces, then estimated connection strengths (! -- HOW could they be imprecisely known if they have the structural documentation?!) and found the whole scenario they've imagined, that they've all had in mind since damned near day 1, to be -- "plausible."

But, again, this is not essential for their collapse model. Their collapse model takes the perimeter bowing as an input. It doesn't predict it, nor does it have to.

It has to, to debunk us conspiracy theorists. There's no firm science behind not testing the major hypothesis. It's assertion, because you assume failure mechanisms.

There were also reports from the NYPD aviation unit of structural members visibly glowing in broad daylight

At Cardington? Don't assume what glowing structural members would mean at Ground Zero, where an open-atmosphere, uncontrolled fire feeding off of random materials burned sporadically for less than 2 hours against enormous steel columns. I don't buy it.

Beams heated to 800 C may have been the case, but only in the Cardington tests because they were intentionally ramping power levels up and the steel was generally smaller anyway. NIST did the same thing in their modeling (ramping up power from realistic levels). The real fires depended on the real amount of flammable material per area, which obviously varied, and NIST also assumed an enormous amount of energy release from combustibles before the towers fell.

Your claim that "NIST found no evidence" of this is wrong. The *recovered steel* may not have reached this temperature

And that's all I'm considering. I don't count their computer models, or their cherry-picking of testimonies. There are plenty of testimonies; let's consider them all simultaneously.

it is simply incorrect to claim that the Cardington experiment is a good fit to the WTC. Different design entirely.

The point was that additional internal stresses from heat tend to stay relatively localized, and do not cause global instantaneous failures.

Also, the Cardington experiment was not a "high powered" fire, but rather a realistic one. Its fuel loading was in no way exceptional. The gas temperatures, steel temperatures, and structural damage were intended to synthesize an actual office fire, not -- as you claimed -- intentionally run for extended periods of time.

You cannot tell me as an engineer that they didn't bias the test conservative and make sure heat could be efficiently transferred, etc. for their test results. You wouldn't, as an engineer, test a steel frame structure against fire by putting a weak or merely average fire against it, would you?

reply to post by bsbray11



Thanks Bsbray. I e-mailed him your response. I will post any reply's

This load also decreases with height (think of drag over the whole face of the structure), so the most tension and compression is felt near the bottom.

This is a point I want to stress from Mr. Mackey's own words. The most tension and compression is felt near the bottom.

Now, the exterior columns were the same in dimension (which relates to strength by F(y)=P/A...which is force over area) from the 10th floor up. The exterior columns at the 85th floor (which are the same dimensional strength as the 10th floor columns) could handle a significant amount of extra load obviously because they didn't have to handle as much dead, live and wind load as the 10th floor columns had to endure but had the same strength as the 10th floor columns. So, NIST is saying that the bowing of floors was enough to buckle columns that had the same strength as the bottom of the towers. How is that possible?

I'm starting to think the 2000% is not as far off as Mr. Mackey would like us to believe.

[edit on 10/25/2007 by Griff]

[edit on 10/25/2007 by Griff]

[edit on 10/25/2007 by Griff]

The following is Mr. Mackey's response to Bsbray. It is rather detailed so it will take up a couple posts.

Mr. Mackey's response in bold.

Bsbray11:

Then you don't have a case for what caused the deflections. I said proof that heated trusses deflect outer columns.

I don't think thermite caused the deflections, but let's say that I did. Would it be logical for me to say, "Well, you see the deflections, so therefore it was thermite, no more proof needed."?

That's not how the argument works.
We KNOW that the perimeter columns slowly deflected inwards, because we have photographs of them doing so.
We KNOW that the floors sagged dramatically, increasing over time, but remained attached to the columns. We have photographs of this, too.
We KNOW that sagging truss structures that remain attached to columns exert a pull on those same columns. See below.
As a result, this mechanism is entirely predicted. We do indeed have a cause. We only have a problem if the force exerted is unrealistic, and modeling by NIST, Arup, and Dr. Usmani all independently concluded that the force is not unrealistic.

It wouldn't be logical to say "thermite did it." Are you suggesting that thermite is capable of gradually exerting an inward pull on perimeter columns, gradually increasing over tens of minutes? If you're merely describing a heat-based weakening affect, how would this be distinguishable from the fires on those same floors, for those same time periods?
This hypothesis is not falsifiable, thus it is rubbish.
I've described above how to falsify the floor pulling mechanism. It is not rubbish, and to date has not been falsified.

Bsbray11:

Have you not considered that this relatively small force "pulling" the outer columns inward is only going to result in actual displacement proportional to the sum of all the forces holding the column "in place" when it starts to move?

I wouldn't say that, because it isn't true. To get a certain lateral deflection in the columns, you can either apply a small pulling force to the side, or you can apply a much larger compression force axially. You can't just add these two forces, not even in quadrature.
Let me give you an extremely simple example. Stand on an empty soda can. If you balance carefully, the can will support your weight. Then have a confederate dent the side of the can ever so slightly -- and you'll come crashing down. The side force, by increasing the eccentricity of the axial load, has a disproportionate effect on the column's buckling behavior. This is, roughly speaking, why the modest pulling forces were such a critical factor in the perimeter columns.

Bsbray11:

So what kind of forces are we talking about, compared to the forces provided by the spandrel groups? Can you say? NOT theoretical values, because I've seen some horrible modeling done by supposedly credible people, ie Frank Greening in his more naive attempts at modeling a pancake collapse with 1-dimensional analysis, and I want to see someone lay out a truss assembly and heat it, and deflect a column. I don't want assumptions and I don't want pointing at the collapse and essentially feedbacking the whole point of the investigation in the first place: finding out what CAUSED the building to collapse.

I gravely doubt you understand Dr. Greening's work, let alone have refuted it.
The spandrels have little relevance to this situation. They're flat, thin panels that provide shear support in a totally different direction. Also, since multiple columns are pulled at once, only two spandrels -- the ones at the edge of the pulled-in area -- are stressed.

I reject your request for me to build you a truss, heat it, and photograph the deflecting columns. You may as well ask me to prove that gravity pulls things down. The concept is remarkably simple, as I will explain.
At the start of the experiment, we have two columns, with a truss structure resting on top of them. Whether or not the truss is pinned at both columns, at rest it exerts only a downward force on the columns. This is because the truss experiences internal forces -- compression along the top chord, and tension along the bottom chord -- that transfer its weight to the edges.
If for whatever reason the truss weakens, causing it to sag, the situation changes. Sagging results when the top chord loses its resistance to compression, and/or the bottom chord stretches in response to tension. (In the case of a steel truss with slender members, the top chord is likely to fail first as it does so through elastic buckling, while tension leads to plasticity and necking, which occur at higher stress levels.) As a result, the truss bows.
If the truss is not pinned to the columns, it will fold in between them and fall at this time. This did not happen in the WTC case, so we instead consider what happens when it is pinned.
If it is pinned, the compressive force that can no longer be counteracted by the top chord instead is transmitted to the columns, resulting in a net pull on both of them.
In the unlikely scenario that the bottom chord fails first, at the moment of failure the top chord will transition from being in compression to being in tension, and we have essentially the same situation as above. We always wind up with tension on both of the columns.

The above scenario is true *no matter what* causes the truss to weaken.

If we are talking about heating, there is the additional component of thermal expansion and contraction. In the early stages of heating, the truss instead (if pinned) will exert an *outward* pressure on the columns. However, this is only true until the truss begins to anneal and weaken, as it always will in the presence of heat. Unless the truss is much stronger than the columns -- not true in the WTC case, and not generally true -- the elasticity in the columns will push back on the truss and force it into a caternary shape before the truss becomes plastic. As the truss weakens further, thermal expansion or not, it will wind up applying tension to the columns before it fails.

This is absolutely elementary engineering knowledge, the kind of thing taught in a first-year statics course. No experimental proof is required. You should be able to demonstrate this yourself if you demand empirical verification.
This effect is also demonstrated by NIST, Arup, and Dr. Usmani, independently. You have not even attempted to refute any of these results.

The amount of force needed, as estimated by NIST, is not terribly high

Bsbray11:

May we see the calculations?

They have been available for some time. Turn in particular to Chapter 2.5 and Appendix A of NIST NCSTAR1-6D, and the reasoning leading up to Figures A-48 through A-51.

Bsbray11:

And that doesn't strike you as a big fudge? They estimated forces, then estimated connection strengths (! -- HOW could they be imprecisely known if they have the structural documentation?!) and found the whole scenario they've imagined, that they've all had in mind since damned near day 1, to be -- "plausible."

The strength of the floor connections is NOT a big fudge. The forces they need are only about 5,000 pounds. It doesn't matter that we don't know if those connections could handle 8,000 or 20,000 or 100,000 pounds -- we don't care. As long as they're strong enough to handle the forces we predict, we have a viable mechanism.
This complaint is simply argumentative.

Bsbray11:

It has to, to debunk us conspiracy theorists. There's no firm science behind not testing the major hypothesis. It's assertion, because you assume failure mechanisms.

Nonsense. You simply throw out the tests, for your own poorly considered reasons. That's not science, and consequently, I don't care.

Bsbray11:

At Cardington? Don't assume what glowing structural members would mean at Ground Zero, where an open-atmosphere, uncontrolled fire feeding off of random materials burned sporadically for less than 2 hours against enormous steel columns. I don't buy it.

No, at the WTC. Self-glowing structural members do so because of their temperature. The NYPD helicopter crews saw it. This is further evidence that some of the structural steel reached elevated temperatures, at or above 650 C. You can't explain this away.

Bsbray11:

Beams heated to 800 C may have been the case, but only in the Cardington tests because they were intentionally ramping power levels up and the steel was generally smaller anyway. NIST did the same thing in their modeling (ramping up power from realistic levels). The real fires depended on the real amount of flammable material per area, which obviously varied, and NIST also assumed an enormous amount of energy release from combustibles before the towers fell.

False on all three counts. (1) The Cardington tests did not "intentionally ramp power levels up." Their full-scale office fire test used a realistic combustible load. I already told you this once. (2) The Cardington test similarly used typical steel -- I have no idea where you pulled this "generally smaller" thing from. Compared to the diameter of truss members in the WTC, the floor beams in the Cardington test were fairly large in cross-section. (3) NIST's modeling also did not "ramp up power." If anything, they underestimated it. Dr. Quintiere, who has been misinterpreted by many in the Truth Movement, has argued that the NIST fire models assumed a combustible loading a factor of three too LOW.
You made up all of those claims. I also see you retracting your earlier statement that in Cardington, steel didn't reach temperatures above 650 C. I caught you there -- what made you think I wouldn't catch you here?

Your claim that "NIST found no evidence" of this is wrong. The *recovered steel* may not have reached this temperature

From Bsbray11:

And that's all I'm considering. I don't count their computer models, or their cherry-picking of testimonies. There are plenty of testimonies; let's consider them all simultaneously.

You cannot reject out of hand the NIST models, and simultaneously assume (despite being warned explicitly not to) that the temperatures in the recovered steel (none of it from the heart of the fire) are indicative of steel that was in the heart of the fire. The one cherry-picking is you.

it is simply incorrect to claim that the Cardington experiment is a good fit to the WTC. Different design entirely.

From Bsbray11:

The point was that additional internal stresses from heat tend to stay relatively localized, and do not cause global instantaneous failures.

As I've already explained to you, this conclusion only applies to traditional post-and-beam style construction. The WTC Towers, with perimeter and core columns bridged by long-span lightweight trusses, is a diffferent structure entirely and has different vulnerabilities. See Dr. Usmani and Arup.

From bsbray11:

You cannot tell me as an engineer that they didn't bias the test conservative and make sure heat could be efficiently transferred, etc. for their test results. You wouldn't, as an engineer, test a steel frame structure against fire by putting a weak or merely average fire against it, would you?

As an engineer, I take them at their word when they described their experiment -- even providing pictures -- as having a fire load of 40 kg per square meter. This is a pretty average fuel load. I'm baffled by your insistence that it was "high powered." (NIST assumed 20 kg / sq. m in three of four cases and 25 kg / sq. m in the fourth, which again, Dr. Quintiere thinks is conservative by a factor of 3. NIST is, therefore, also not "high powered.")
The Cardington experiment was a BASELINE, used among other things to validate computational models. Biasing it upward in power would have defeated the purpose entirely. I can only assume that, besides your other errors, you didn't understand the purpose of the experiment.

This is twice I've had to correct you on the Cardington experiment. Your other questions belie a general unfamiliarity with structural engineering principles. Nothing you've stated casts the least bit of doubt on anything contained in my whitepaper, if indeed you have even read it. I strongly recommend you review the Cardington experiment as well as NIST NCSTAR1-5 and NCSTAR1-6 before attempting to challenge me again.

Thanks,
Ryan Mackey

Originally posted by CaptainObvious
That's not how the argument works.
We KNOW that the perimeter columns slowly deflected inwards, because we have photographs of them doing so.

So what? Do you get what I just asked for? Proof of what caused it? Just acknowledge that you understand what I'm pointing out, that there is a difference between seeing it and explaining it, and that explaining it scientifically requires reproduction of the observed phenomena. There is no already-proven theory that describes WTC collapses; that's why NIST was contracted.

We KNOW that sagging truss structures that remain attached to columns exert a pull on those same columns.

I know, but can you get enough force with the given truss assemblies and perimeter column grid? That's what we want to see!

As a result, this mechanism is entirely predicted.

No, no, no. An electrolytic capacitor installed with the polarities reversed may explode. But it is NOT LOGICAL to therefore predict that it's going to explode when you put 5mA through it backwards when it has a power rating of 250W.

Give us numbers, models, based on experimental data. Just because something theoretically can happen doesn't mean that therefore, it will. I've done labs. I've had to do reports, predict figures, and it isn't as simple as saying what could happen by plugging the right numbers into the right formulas! That has NEVER been acceptable research by what I was taught, and I've NEVER known engineers to fudge important numbers (what was that about figures for the connections being "imprecise" earlier?).

The side force, by increasing the eccentricity of the axial load, has a disproportionate effect on the column's buckling behavior.

I know this, but my point was that you don't just "put a dent" into a grid of some 200+ columns arranged in staggered grids, where only about 1/3rd of the columns terminate on any given floor, and you also have the spandrel plates "holding" the columns outside. It must take significant force to sufficiently deflect all of these columns, enough of them to overcome the safety factor and start bringing columns between yield and ultimate strengths. Think of the size and number of these columns, and as Griff pointed out, the minute difference in the physical size between the bottom-most perimeter columns, and the upper-story perimeter columns, when the bottom-most columns were obviously well able to take much, much heavier loads than the higher perimeter columns would have been expected to.

[edit on 25-10-2007 by bsbray11]

Originally posted by CaptainObvious
I gravely doubt you understand Dr. Greening's work, let alone have refuted it.

I understand it completely. He took an initial falling mass (single floor), and just dropped it into a free-fall until it hit the next floor, at which point it simply gains mass in his model and continues rolling along gaining floor by floor of mass until it slams the ground with a tremendous amount of energy. Very generalized, countless assumptions are made of the behaviors of this system, etc.

There is nothing to refute. No one would disagree with me if I pointed out all of the differences between Greening's model and the actual collapses, such as the fact that a minority of the mass of either tower was actually left in its footprint, and it was never established in the first place that this kind of model would be an accurate representation of the physical behavior of a Twin Tower structure collapsing around a small group of floors. It's just "plug and chug," where Greening plugs arbitrary numbers into formulas and asserts that they mean something factual.

The spandrels have little relevance to this situation. They're flat, thin panels that provide shear support in a totally different direction.

They connect column-to-column on the outside of the building laterally, like steel bands wrapped around the building exteriors. They are most definitely going to offer resistance if you tried to push or pull the perimeter columns inward towards the core.

Also, since multiple columns are pulled at once, only two spandrels -- the ones at the edge of the pulled-in area -- are stressed.

Sounds like a localized failure, considering how many trusses and how many perimeter columns there are on a given floor, right? Unless they all happened to be deflected/heated equivalently at about the exact same time.

I reject your request for me to build you a truss, heat it, and photograph the deflecting columns.

I don't expect you to; NIST should have done it but they failed to. If you want to convince me that some given amount of force is going to cause significant deflections in the system that I understand to be the structure of the WTC Towers, then I want to see quantities and their justification before anyone starts throwing numbers into formulas. I want to see lab verification.

The above scenario is true *no matter what* causes the truss to weaken.

Yes, yes; see above. I'm not contesting that you can deform structures with heat, or that deflections don't cause load increases. If everything were as simple as you make this out, then we wouldn't need numbers at all. The reality of the situation is that we don't have numbers in this specific case and there are a lot of people, such as yourself, who don't think there is a problem simply because they realize that you can manipulate the numbers in such a way and get reasonable results. But you don't know that the numbers you use (whatever they may be) are accurate, and I don't know that.

This is absolutely elementary engineering knowledge, the kind of thing taught in a first-year statics course. No experimental proof is required.

HA! Statics courses actually use numbers! The formulas themselves aren't in error.

You can have negative figures, when that column turns out to really be in compression and not tension, or... conflicting figures when that connection would happen to fail well before being able to exert enough force to sufficiently deflect an outer column to it's required share of load increase. You get the point.

They have been available for some time. Turn in particular to Chapter 2.5 and Appendix A of NIST NCSTAR1-6D, and the reasoning leading up to Figures A-48 through A-51.

And where is the information on the tension the connections could take before failure, and all the other structural documentation relevant to the exterior structure? Where is ANY of the actual structural documents?

[edit on 25-10-2007 by bsbray11]

Quote from Ryan Mackey:
If the complaint is about the failure modes observed during collapse, it is quite possible --

so far, i havent heard a single CT that isn't.

and so far, i havent seen any single theory proven.

reply to post by bsbray11


Response Sent to Ryan Mackey.
Thank you.

I found the following quote from mr Mackey, extremely over-simplifying and in fact dangerously close to snake-oil selling, and in my opinion intended to appeal to the non-scientifically schooled readers amassed here, and it seems to me he uses especially this kind of reasoning as his main point to explain the initiation of the WTC collapses, and their following global collapses :

Bsbray11 : Have you not considered that this relatively small force "pulling" the outer columns inward is only going to result in actual displacement proportional to the sum of all the forces holding the column "in place" when it starts to move?

mr Mackey : I wouldn't say that, because it isn't true. To get a certain lateral deflection in the columns, you can either apply a small pulling force to the side, or you can apply a much larger compression force axially. You can't just add these two forces, not even in quadrature.
Let me give you an extremely simple example. Stand on an empty soda can. If you balance carefully, the can will support your weight. Then have a confederate dent the side of the can ever so slightly -- and you'll come crashing down. The side force, by increasing the eccentricity of the axial load, has a disproportionate effect on the column's buckling behavior. This is, roughly speaking, why the modest pulling forces were such a critical factor in the perimeter columns.

This example appeals at first sight as convincing, and when you, the average reader, first read it, would probably have given you that well known AHA! feeling, at last seeing some comprehensible logic and reason amidst all this scientific "mumbo-jumbo" language you can't understand at all.

At last something everyone ever has tried out in their lifetime.
Thus you thought : yes, this must be true.
And if you hadn't tried it before, and were the investigating kind, you at last tried it out, and yes, it pretty well worked out as predicted.
So why read any further with a critical mind, since this capped it off in the very first stages of the argumentation.


Nothing however, is further away from the engineering truth as this soda can thought experiment, and I think mr. Mackey totally well understood that, but still choose to use this faulty reasoning to get the masses on his side of the argument.


Just look at the weight differences between the average person and a soda can.
It's somewhere in the range of about 70 kg, so 70,000 gram, to 10 grams, so 7000 to 1.

If you extrapolate these figures to both WTC towers, you are talking about putting first a weight on top of the towers in the range of 7000 more weight than the towers total weights itself, and then observe initiating of the buckling.

That's a whole different story then mr Mackey's soda can comparison.

What happened in fact, was the top one tenth of the towers rested as usual on the lower nine tenth part of them, and got partly heated to a certain degree, which we will never know exactly.

And the top weight was enough to overcome the rest of the huge inertia of the structures, started by a partial buckling around the whole periphery of the towers at one floor level, because of some heat, combined with initial impact damage ???
And then the whole tower collapsed smoothly, without any interruptions caused by increasing resistance by totally undamaged lower parts of the towers.

Again, that's a whole different story then mr Mackey's soda can comparison.

We now are supposed to try to imagine, roughly spoken, that the top tenth part of the soda can could have such a devastating effect on the underlaying outer shell of the can, when we heat a small band around the can, that the whole nine tenth part of the can will collapse in its footprint, solely by the weight of the upper "collapsing" one tenth of the can.
Remember, there's no one standing on top of the can, that's a ridiculous comparison to begin with.

In fact, we must imagine a reinforced soda can, with some pretty sturdy vertical pins in the middle, resembling the core columns, which are netted together, and are connected to the outer wall with 100 circular plates (floors), which all of them together add a tremendous extra strength to the resistance of the outer wall against buckling.

As we all know by now, since we at last realize what is wrong with this comparison, this kind of collapsing like a dented soda can, will never happen, and has not happened.

Nice catch Labtop. I must have skimmed through that part. I'd like to know, how much eccentricity is accomplished from the bowing floors. I've been looking into things and will have a few figures soon.

When you think about how the floor trusses were connected to the exterior columns (angle clips with bolts), it becomes clear that the columns were designed for vertical shearing force at the connections which is an eccentrical load itself since it is not acting down the centroid of the column but rather on one face.

The maximum horizontal force would occur when the angle clip deforms to a 45 degree angle because any more would just start returning the forces in the vertical direction. Remember there is no added force at this particular time. Unless you count the plane itself. Which I'd probably have to consider also. So, going by this, the maximum horizontal force would be the vertical load (dead and live load) divided by the tangent of 45 degrees (which is 1). So, the maximum horizontal force would be equal to the vertical forces.

Now, remember that Mr. Mackey has claimed that the wind load (horizontal force) exceeded the dead and live loads (vertical force). And remember what I said about the 85th floor columns having the same strength as the 10th floor columns. So, those columns were designed to withstand the wind load and then some, but NIST wants us to believe that the horizontal forces (equaling the dead and live load) were enough to overcome the designed strength that exceeds the wind load by several factors of safety?

Hope that makes sense?

reply to post by LaBTop


LabTop, forst of all he CLEARLY states a "simple example"...

Secondly, if you are going to claim to be able to show Mr. Mackey that he is wrong, please feel free to set forth some issues you have with his white paper. To date, he has yet been shown anything that shows he is in error. He appears not to have a problem discussing the NIST report either.

I think I am following this as well as one can with no knowledge of structural engineering.

Griff, Labtop, shouldn't you take into account the mass of the top 1/10 and the fact that it had built a certain amount of momentum and force as it fell from whatever distance it was from floor to floor? It would be like dropping something on the pop can from a predetermined distance. If the floor below is not built to hold that much weight it would in turn fall and add its weight to the mass of the top 1/10 and so on. If this was initiated by the core leading the collapse wouldn't it pull the exoskeleton inward causing the building to fall in it's own footprint?