PhD Physicist Crockett Grabbe was recently published in the peer-reviewed Journal of Engineering Mechanics, disputing the the pile-driver or crush-down theory in which the tops of the Towers act as giant sledgehammers put forward by engineer Zdenek Bazant. One reason I bring this up, is to express my agreement with debunkers that his claim that the South Tower's "top segment... initially collapses at an acceleration rate more than four as large as that of gravity," is untenable. That said, Grabbe's stated goals in his paper includes three other solid points. Outlining his goals, Grabbe writes: First is their assertion about implications of their collapse model for the South Tower. Second is the very inadequate amount of energy expended in their gravitational collapse model, including the claimed ease of breaking through and demolishing each floor that they assert in explaining the smooth collapse, in contrast to independent calculations of the total energy expended in the observed collapses. Third is an underlying 1-dimensional (1D) assumption in the equations used to model the collapse in this paper and in previous papers it references. Shortcomings of this 1D model seriously challenge its validity, and thus that of the "crush-down, crush-up" model of gravitational collapse for the calculations they present. Fourth is a challenge to their broad claim that all objections have been shown invalid.Before getting into his other three points, I think it important to note that "debunkers" who bashed the Bentham journal for bad peer-review, should be doing the same here if they don't want to be hypocritical. In doing so, however, does that not put the peer-review of Bazant's papers in question as well? As Jim Hoffman at the website 911research.wtc7.net pointed out, "Bazant must be a super-genius to understand how two skyscrapers could crush themselves to rubble, a newly observed behaviour for steel structures, and write a paper about it in just two days." This paper was also published, and apparently reviewed, in the Journal of Engineering Mechanics during those 48 hours. Juxtapose this with the fact that Bazant's theory has been challenged, not once, twice, but three times, and likely a fourth time, with a paper coming from mechanical engineer Tony Szamboti, in that same journal and you have a good a priori case that Bazant is wrong, but we won't rely on that, just saying.
While addressing his second stated goal in the paper, Grabbe writes:
...Independent calculations of the energy expended in the collapses of the Towers have produced estimates of that expenditure to be at least 25MgH or more.[Hoffman, 1983] This implies that the "crush-up, crush-down" model cannot begin to account for the energy expended in the WTC collapses -- indeed, from the maximum energy expenditure claimed in Le and Bazant's paper, over a factor of 100. Hoffman identified energy being expended for crushing the concrete. heating the concrete and the suspended gases, and vaporization of the water. Any rough validity to these energy expenditure calculations would imply that these collapses cannot be caused by fire-induced gravitational collapse as Le and Bazant presume in this paper.Hoffman is arguably one of the most well respected 9/11 truth researchers due to his careful nature. He has produced a prodigious number of very well researched pages on his three web domains and his pages have always scored well on Google searches. And he has disassembled many debunking arguments, like those of Popular Mechanics and National Geographic. So there is indeed a reason to believe that there is at least a rough validity to his calculations, even though his work on this topic is incomplete. 911review.com notes that, "Hoffman admits that there is substantial uncertainty regarding several assumptions used to obtain the energy estimates -- in particular those regarding the contribution of turbulent mixing to the size of the dust cloud. The promised Version 4 of the paper will employ a more flexible approach for computing energy estimates."
At least one academic paper has attempted to explain the rapidity of the collapses by promoting a questionably applicable mathematical model alleged to predict a nearly frictionless total collapse. Since that model has each tower neatly pulling itself down at near the speed of free-fall, there would be very little heat produced to drive the dust cloud expansion.The academic paper cited is by Bazant and is reproduced in full at that link with refutations added in red colored text throughout.
It is claimed by some that the dust cloud was cold. However, New York Daily News photographer David Handschuh was quoted as saying, "I got down to the end of the block and turned the corner when a wave-- a hot, solid, black wave of heat threw me down the block. It literally picked me up off my feet and I wound up about a block away." Firefighter Timothy Julian also described the dust cloud as being hot.
1D equation cannot model the Towers collapses correctly, because the horizontal dimension is very important in the physics of those collapses. This includes the squibs repeatedly shooting out in this horizontal dimension, the South Tower's top segment making a sudden shift in the horizontal direction in its collapse, very large pieces hurled out from of both Towers having considerable momentum and kinetic energy in this horizontal dimension. There are large streams shooting out in the horizontal dimension with large debris coming out from the Towers -- not only with a downward component, but also an upward component in the case of the North Tower. These effects are all neglected in a 1D model, yet they are very important processes in the Towers collapses."Debunkers" do not think these processes are important. Here is a page that I and a few others authored at AE911Truth debunking several claims of "debunkers" relating to squibs. Included is the fact that calculations performed by Grabbe show that the horizontal ejection rate of the squibs is disproportional to the floor and debris descent speeds that are allegedly responsible for them. One point not in the article, is one made by blog contributor Adam Taylor. In his video, "9/11 Smoking Guns: The Squibs," he demonstrates that a squib in the South Tower that appears approximately 40 stories below the demolition wave, forms approximately three seconds into the collapse. If something was falling through the building to cause the squib, as "debunkers" have claimed, it would have to be falling faster than gravitational freefall, which is impossible.
As to the South Tower's shift, Jim Hoffman writes:
The sudden slowing of the rotation of the South Tower's upper 30-story block as it disappeared into the burgeoning explosion is the basis for a particularly obvious disproof of the collapse theory. The top began to topple at an accelerating rate, rotating about 20 degrees in two seconds so that its roof overhung its base by at least 80 feet at one point. Why, instead of toppling off of the base, did it telescope into the base?He then goes on to refute "debunker" Ryan Mackey on this point:
In Mackey's tortured scenario, the columns on the east side of the Tower -- those directly under the center of mass of the rotating and falling top -- were somehow able to catch the top and impart the force necessary to reverse the rotation. That implies that the columns on the far side and the core -- which, being offset from the top's center of mass, would apply increasing torque to accelerate the top's rotation as it toppled -- had somehow ceased to interact with the top. If that were true, why didn't the west perimeter wall, unscathed by the top, remain standing -- why was it erased like the rest of the Tower's base in such a systematic top-down fashion?As to the "very large pieces hurled out from of both Towers having considerable momentum and kinetic energy" consider this beam:
Mackey's theory, though incredibly far fetched, may be the best that collapse theory supporters can offer. The behavior of the South Tower's top so clearly reveals that the top and bottom sections were disconnected -- i.e., there was no crush zone -- that even grade-school children quickly grasp this proof of demolition.
As blog contributor Scootle Royale wrote:
...It was somewhere between 6.7 and 6.8 seconds. The north tower was 417 meters tall, and WTC7 was 186 meters tall, so the distance between the two roofs was about 230 meters. The amount of time it would take to freefall that distance in a vaccum is about 6.85 seconds. So even if this beam was dropped from the height of the roof of the north tower at the exact moment the tower started to collapse, it still wouldn't have reached the roof of WTC7 in under 6.8 seconds. Put simply, this steel beam had to have been falling significantly faster than freefall. Obviously this is impossible unless it was launched downwards by something, such as an explosion.Addressing his fourth stated goal, which relates to the third, Grabbe writes:
Finally, I challenge Le and Bazant's statement at the beginning of their paper where they say "All the objections of the proponents of the controlled-demolition hypothesis have been shown invalid." In particular, that is not correct in their response to the recent comment by Bjorkman (Bjorkman, 2010; Bazant et al, 2010). Commentor Bjorkman challenges the validity of the 1D model based on observations, as well as on an earlier critique by MacQueen and Szamboti (2009). Bjorkman states that equations are not needed to see from observations that Le and Bazant's model is wrong. Le and Bazant disagree with that, responding that equations are vital. However, questions of the collapse of the Towers are at least 2D because of important features observed in the horizontal direction. Le and Bazant's 1D gravitational equations for that analysis are not adequate, and they cannot counter Bjorkman's objection unless they present a quantative model of the Tower that is at least 2D in their equations of motion.
Furthermore, Bjorkman provides the following:
Scootle affirmed the above point by making speed-time graphs of the motion of four different verinage demolitions, where the columns on the central floors are weakened to crush the bottom section. The first three were tracked at an angle, however, he notes that "in all three cases there's an initial acceleration and then upon impact the acceleration abruptly ceases and a deceleration trend begins. This is exactly what we would expect using basic physics and common sense." The fourth was tracked from a great frontal view:
And here's an After Effects speed-time plot...In comparison Scootle mapped out the North Tower and provided the following:
Can't get much clearer than that really!
Three points were tracked. This was a bit more difficult because of the smoke. The graph below is of all three tracks together.
I think that's pretty clear! Just like Chandlers' analysis and MacQueen & Szamboti's analysis, my tracks have produced a reasonably straight line. For at least two seconds the north tower accelerated constantly, further proof of the lack of jolt.
The three [four] Verinage demolitions are perhaps the closest real-world examples we have for comparison to the North Tower, and they clearly behave differently. The fact remains that what happened to the north tower was unprecedented, regardless of how much you wanna exaggerate the tilt!Bazant et al. did author a Closure, which Bjorkman called "the most shameful Closure in structural damage analysis history" in his response. Is he right? Well, his response also included a challenge that puts his money where his mouth is, offering 10,000 Euro to anyone who can "come up with some other type of structure that really can collapse from top down," when the mass of part C is 1/9 the mass of part A.
If his opponents cannot find a way to collect the money offered, then it is certainly possible that they have written "the most shameful Closure in structural damage analysis history." Here is the only attempt I'm aware of thus far:
As Bjorkman noted, "A heavy disc on a pin that breaks the weak fastenings of other discs to same pin is not a collapse of anything. The only things broken are the weak fastenings while the discs and the pin remain intact, the discs having displaced a little.
This experiment with concrete blocks is much more representative:
Even this egg experiment is more representative than the first above:
0 comments:
Post a Comment