Please excuse me if this guy's work concerning Greening's model is already well plowed ground around here. I found it late yesterday afternoon while searching for some information on the distribution of the debris piles and posted a picture from it. I didn't have time to read through it until just a few minutes ago. Imagine my surprise when I saw he used the pretty much the same example I came up with for what he calls the "dissociatiated materials" in the collapse mass.

I've put a link at the bottom to a picture of what is purported to be the remains of the core in wtc 2 which stood briefly after the initial collapse. As with the much noted "spire" in wtc 1, all the material in these formations could not have contributed to the collapse as they were standing (if only briefly) after the collapse wave passed....BUT all of their material/mass would be real close to dead center in the debris pile. So, wouldn't you have to subtract their mass from the destructive material driving the collapse as well as subtract it from the material in the heart of the debris piles?

Anyway, fwiw/fyi:


http://www.studyof911.com/articles/BsB092306/

Greening assumes all steel, concrete, aluminum, etc., falls straight down with falling mass only increasing.

Destroyed floors did not re-combine to form a single, focused mass again, as suggested by Greening’s calculations, but broke up and were mostly ejected during the collapses, and thus contributed a small fraction of the total mass available to the continuing collapse, again, easily equating to 90% of the total mass being ejected throughout the collapses as shown by the heavy debris spread area alone in the FEMA diagram, and Ground Zero photos showing a clear lack of significant debris piles in the footprints of both buildings (remembering that most additional mass remaining within the footprints can rather safely be attributed to vertical core collapses after the perimeter and truss collapses, and not any type of pancake mechanism).



However, the mass that did continue downwards within either building, and could have contributed some theoretical “driving mass” to its collapse, would have been dissociated (disconnected steel members, destroyed concrete floor slabs; not a single, solid mass). This is important to remember, as dissociated material is easier to deflect than a single, focused force. As an example of this, would you rather have fifty pounds of gravel dumped onto your head from a height of 10 feet, or a single, fifty-pound rock dropped from the same height? A fifty-pound log, or fifty pounds of large woodchips? A fifty-pound steel beam, or fifty-pounds of nuts and bolts?



Intuitively, one would likely opt for the dissociated material always, and for a good reason: broken-up material is not going to exert as much energy upon a single point upon an impact, because the smaller pieces are less focused and more easily deflected; their energy is not focused solely downward upon a single point, but upon multiple points in multiple directions. If a falling solid object impacts something, though the great majority of the object may not actually make contact, the rest of its mass will nonetheless transfer energy efficiently. This is the same principle that allows a hammer to deliver much more impact force than a thin cylinder of the same diameter, though only the flat face of the either may actually make contact. With dissociated material, even such as separated steel beams and pulverized concrete, this is cannot be the case, and the material would simply be deflected rather than delivering the amount of energy that would be available if the material made up only a single solid mass.

Greening’s calculations assume only single masses falling, and never dissociated materials, let alone dissociated materials that are mostly falling over the sides of the collapsing buildings and are thus providing absolutely no mass to the alleged pancake collapses. These assumptions are not only unrealistic, but they are also extremely generous to pancake collapse theory, whereas a rigorous proof of even the possibility of such a theory should allow for the very realistic probabilities of less-than-ideal circumstances. Instead, Greening makes assumptions that prove his model to be impossibly generous to the theory that he is attempting to defend.

Greening assumes that each floor weighed the same in his calculations (he simply divides the building weights by the number of floors), the first floors to drop would have had equal or less structural mass than the floors onto which they dropped. Mechanical floors were an exception, since the mechanical floors (the windowless bands on the Towers in roughly intervals of thirds: 41st and 42nd floors, and 75th and 76th floors) had reinforced trusses, with I-beams spanning between the perimeter and core columns, and apparently encased in concrete. Floors 1 through 9 seem to also have been reinforced.[9]



Therefore, a progressive collapse would meet increasing opposition from one floor to the next, as the core columns thickened, and upon reaching the mechanical floors and lowest floors the Towers. This would indicate that the collapses would require more and more energy to continue without losing significant velocity, but instead, we observed little to no collapse velocity loss from initiation to completion with either Tower, despite thickening columns, dissociated falling material, and most of the total mass being ejected outwards from initiation to completion, and not falling straight down into the footprints.



This collapse behavior would seem more than a little counter-intuitive without considering additional sources of energy within the Towers, and yet it is an issue that has never been addressed in any form by any investigative releases relating to the Twin Tower collapses.

There simply could not have been a linear progression in terms of mass, momentum, etc., from each floor to the next, as individuals like Dr. Greening have assumed. At least 80%, (and probably closer to 90%) of the masses of either building were moved out of the way of the collapses themselves, during the collapses

http://algoxy.com/psych/images/wtc2.core.tall.jpg image of wtc 2 core standing after collapse