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    2/25/11 Answers from NIST to Questions by Chris Mohr, Journalist Print E-mail
    Sunday, 13 March 2011 21:43

    The following written answers were provided to Chris Mohr, Investigative journalist, by NIST (National Institute of Standards and Technology) on 2/25/11 in preparation for the debate that Mohr had with AE911Truth in Boulder, CO on 3/6/11. Listen to that debate here.


    From: "Newman, Michael E." < This e-mail address is being protected from spambots. You need JavaScript enabled to view it >
    To: Chris Mohr
    Sent: Fri, February 25, 2011 10:23:53 AM
    Subject: Answers to Your Questions


    Chris,

    Below are the answers to your questions as requested. We apologize for the delay in getting these to you but we wanted to be certain that we provided you with the most complete and up-to-date responses that we could. Hopefully, these will help you as you prepare for your debate.

    Thanks for your patience. Let us know if we can be of further assistance.

    Best wishes,

    Michael

     

    -------------------------------------------------------------------

    1) Just making sure I understand sag vs pancake etc., getting clear on the difference and why the pancake theory popularized on public TV several years ago is no longer accepted. Also is there photographic evidence of sagging steel structures and steel columns being pulled inward? I do have figure 2-12 with the lattice overlay of inward buckling. I'll be using a lot of slides and videos (as will Richard) and visuals work well for this audience.

    NIST’s findings do not support the “pancake theory” of collapse, which is premised on a progressive failure of the floor systems in the WTC towers (the composite floor system—that connected the core columns and the perimeter columns—consisted of a grid of steel “trusses” integrated with a concrete slab). Instead, the NIST investigation showed conclusively that the failure of the inwardly bowed perimeter columns initiated collapse and that the occurrence of this inward bowing required the sagging floors to remain connected to the columns and pull the columns inwards. Thus, the floors did not fail progressively to cause a pancaking phenomenon.

    The change from “truss failure and pancake collapse” to the “weakened trusses that did not completely fail causing inward bowing of the perimeter columns and a non-progressive collapse” was acknowledged in the second of two NOVA TV documentaries about Ground Zero. The first program, “Why the Towers Fell” in 2002, discussed the truss failure/pancake collapse theory postulated by the Building Performance Assessment Team study (done by the Federal Emergency Management Agency and the American Society of Civil Engineers) that was the precursor to our more comprehensive investigation (which was under way at the time the program was produced). The follow-up program, “Building on Ground Zero” in 2006, corrected their previous report with a discussion of the “inward bowing” mechanism.

    2) Making sure I understand how to calculate the kinetic energy of the fall. Besides f=ma, what are the factors that determine how much more force gravity adds to a falling object? Richard Gage says there is not enough kinetic energy for the collapse to continue, but with the f=ma formula it seems that an object hits with 9.8 times more force just in the first second (assuming not much elasticity... and concrete and steel aren't all that elastic). By the way, I will be dropping a 25 pound dumbbell on a bathroom scale from 6 1/2 feet up. That's only half a story. In my first debate with a local 911 guy I crushed the scale completely. It's not scientific but I think it does demonstrate how even 25 pounds in free fall quickly generates enough force to crush a scale designed to measure the weight of a 300-pound object!

    NIST estimated the elapsed times for the first exterior panels to strike the ground after the collapse initiated in each of the towers to be approximately 11 seconds for WTC 1 and approximately 9 seconds for WTC 2. These elapsed times were based on: (1) precise timing of the initiation of collapse from video evidence, and (2) ground motion (seismic) signals recorded at Palisades, N.Y., that also were precisely time-calibrated for wave transmission times from lower Manhattan (see NCSTAR 1-5A).

    As documented in Section 6.14.4 of NIST NCSTAR 1, these collapse times show that:

    “… the structure below the level of collapse initiation offered minimal resistance to the falling building mass at and above the impact zone. The potential energy released by the downward movement of the large building mass far exceeded the capacity of the intact structure below to absorb that energy through energy of deformation.

    Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass.”

    In other words, the momentum (which equals mass times velocity) of the 12 to 28 stories (WTC 1 and WTC 2, respectively) falling on the supporting structure below (which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum) so greatly exceeded the strength capacity of the structure below that it (the structure below) was unable to stop or even to slow the falling mass. The downward momentum felt by each successive lower floor was even larger due to the increasing mass.

    From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse. Neither the duration of the seismic records nor video evidence (due to obstruction of view caused by debris clouds) are reliable indicators of the total time it took for each building to collapse completely.

    3) The tops of WTC I and II have been compared to pile drivers pushing the building through a natural collapse. But since both the top and bottom of the buildings were of similar structural strength, it looks to me like the bottom of the building was like a pile driver for the top as well. As the top of the building loses its structure while crashing down onto the very strong steel supports of the bottom part, how does the structural collapse of the top affect its ability to keep pushing down on the bottom of the building?

    Since the stories below the level of collapse initiation provided little resistance to the tremendous energy released by the falling building mass, the building section above came down essentially in free fall, as seen in videos. As the stories below sequentially failed, the falling mass increased, further increasing the demand on the floors below, which were unable to arrest the moving mass.

    In other words, the momentum (which equals mass times velocity) of the 12 to 28 stories (WTC 1 and WTC 2, respectively) falling on the supporting structure below (which was designed to support only the static weight of the floors above and not any dynamic effects due to the downward momentum) so greatly exceeded the strength capacity of the structure below that it (the structure below) was unable to stop or even to slow the falling mass. The downward momentum felt by each successive lower floor was even larger due to the increasing mass.

    From video evidence, significant portions of the cores of both buildings (roughly 60 stories of WTC 1 and 40 stories of WTC 2) are known to have stood 15 to 25 seconds after collapse initiation before they, too, began to collapse. Neither the duration of the seismic records nor video evidence (due to obstruction of view caused by debris clouds) are reliable indicators of the total time it took for each building to collapse completely.

    4) How could the towers have collapsed almost straight down? I have good answers (building was 95% air by volume, no lateral force like an earthquake pushed it to the side, etc). Still, I can't quite answer their assertion that a mostly straight-down collapse would have required that hundreds of structural supports all fail at once, that the randomness of natural fires creates asymmetrical collapses.

    In the absence of any lateral forces acting on the falling mass, gravity will cause the mass (upper stories of the building) to collapse straight down. Core members were still standing after the rest of the building had collapsed.

    5) Do you have an explanation for the iron microspheres in the WTC dust? Controlled demolition theorists assert this is evidence of very high temperatures during the collapse, well over 2000 degrees, which leads them to thermites. The "911 debunkers" claim the microspheres are in printer toner, burnt garbage ash, concrete, etc but I can't find evidence of this.

    NIST did not study the “microspheres.” The body of available evidence does not support the theory that thermite or nanothermite was used to demolish the WTC Towers or WTC 7.

    As far as the “microspheres” that were claimed to have been found at Ground Zero, there are two arguments against their being linked to thermite or nanothermite. First, there is no "chain of custody" for the samples. They cannot be traced back to anything "used" in the towers or WTC 7, or for that matter, or to any of the these three buildings at all.

    Secondly, even if the samples could be conclusively linked to one of the three WTC buildings, there are hundreds of possible sources for the samples reported. For example, the alternative theory groups have often cited a U.S. Geological Survey paper, “Particle Atlas of World Trade Center Dust Report,” as documenting the chemical signature of thermite. However, a review of the actual paper (http://pubs.usgs.gov/of/2001/ofr-01-0429/chem1/) shows that the authors state that "the trace metal compositions of the dust and girder coatings likely reflect contributions of material from a wide variety of sources. Possibilities include metals that might be found as pigments in paints (such as titanium, molybdenum, lead, and iron), or metals that occur as traces in, or as major components of, wallboard, concrete, aggregate, copper piping, electrical wiring, and computer equipment. Further detailed SEM studies of dust and beam coating samples are needed to develop a better understanding of the residences of metals in the samples. A detailed review of the materials used in construction, and the elemental composition of materials commonly found in office buildings would also be useful to understand more completely the potential sources and compositions of the materials in the dusts." There is NO mention of thermite or nanothermite as a possible source.

    6) For Building Seven, if column 79 had failed, weren't there redundant support structures somewhere to shift the load to, at least partially? It seems that all big buildings are designed with structural redundancies. How can one column's failure bring the whole building down? I do see an eight-second time period on the video of the Bldg 7 collapse after the east penthouse goes down. Is that when the structural load shifted momentarily before the global collapse?

    The heat from the uncontrolled fires caused steel floor beams and girders to thermally expand, leading to a chain of events that caused a key structural column to fail. The failure of this structural column then initiated a fire-induced progressive collapse of the entire building.

    According to the report's probable collapse sequence, heat from the uncontrolled fires caused thermal expansion of the steel beams on the lower floors of the east side of WTC 7, damaging the floor framing on multiple floors.

    Eventually, a girder on Floor 13 lost its connection to a critical column, Column 79, that provided support for the long floor spans on the east side of the building. The displaced girder and other local fire-induced damage caused Floor 13 to collapse, beginning a cascade of floor failures down to the 5th floor. Many of these floors had already been at least partially weakened by the fires in the vicinity of Column 79. This collapse of floors left Column 79 insufficiently supported in the east-west direction over nine stories.

    The unsupported Column 79 then buckled and triggered an upward progression of floor system failures that reached the building's east penthouse. What followed in rapid succession was a series of structural failures. Failure first occurred all the way to the roof line-involving all three interior columns on the easternmost side of the building (79, 80, 81). Then, progressing from east to west across WTC 7, all of the columns failed in the core of the building (58 through 78). Finally, the entire façade collapsed.

    7) Your official 2008 report says that Building 7 fell at 100% of free fall acceleration for over two seconds of the collapse. Even if the major support structure had collapsed, it seems there would have to be SOME resistance to the collapse. How is this possible?

    In the draft WTC 7 report (released for public comment on Aug. 21, 2008), NIST stated that the north face of the building descended 18 stories (the portion of the collapse visible in the video) in 5.4 seconds, based on video analysis of the building collapse. This time period is 40 percent longer than the 3.9 seconds this process would have taken if the north face of the building had descended solely under free fall conditions. During the public comment period on the draft report, NIST was asked to confirm this time difference and define the reasons for it in greater detail. That was done for the final WTC 7 report (released Nov. 20, 2008).

    To further clarify the descent of the north face, NIST recorded the downward displacement of a point near the center of the roofline from first movement until the north face was no longer visible in the video. Numerical analyses were conducted to calculate the velocity and acceleration of the roofline point from the time-dependent displacement data. The instant at which vertical motion of the roofline first occurred was determined by tracking the numerical value of the brightness of a pixel (a single element in the video image) at the roofline. This pixel became brighter as the roofline began to descend because the color of the pixel started to change from that of the building façade to the lighter color of the sky.

    The analyses of the video (both the estimation of the instant the roofline began to descend and the calculated velocity and acceleration of a point on the roofline) revealed three distinct stages characterizing the 5.4 seconds of collapse:

    * Stage 1 (0 to 1.75 seconds): acceleration less than that of gravity (i.e., slower than free fall).
    * Stage 2 (1.75 to 4.0 seconds): gravitational acceleration (free fall)
    * Stage 3 (4.0 to 5.4 seconds): decreased acceleration, again less than that of gravity

    This analysis showed that the 40 percent longer descent time—compared to the 3.9 second free fall time—was due primarily to Stage 1, which corresponded to the buckling of the exterior columns in the lower stories of the north face. During Stage 2, the north face descended essentially in free fall, indicating negligible support from the structure below. This is consistent with the structural analysis model which showed the exterior columns buckling and losing their capacity to support the loads from the structure above. In Stage 3, the acceleration decreased as the upper portion of the north face encountered increased resistance from the collapsed structure and the debris pile below.

    8.) Your report says that the Building 7 fires were scattered on several floors, that was not one huge fire. How do I reconcile this information with a global collapse of a steel framed building for the first time ever.

    Debris from the collapse of WTC 1, which was 370 feet to the south, ignited fires on at least 10 floors in the building at its south and west faces. However, only the fires on some of the lower floors-7 through 9 and 11 through 13-burned out of control. These lower-floor fires-which spread and grew because the water supply to the automatic sprinkler system for these floors had failed-were similar to building fires experienced in other tall buildings. The primary and backup water supply to the sprinkler systems for the lower floors relied on the city's water supply, whose lines were damaged by the collapse of WTC 1 and WTC 2. These uncontrolled lower-floor fires eventually spread to the northeast part of WTC 7, where the building's collapse began.

    As stated previously above, the heat from the uncontrolled fires caused steel floor beams and girders to thermally expand, leading to a chain of events that caused a key structural column to fail. The failure of this structural column then initiated a fire-induced progressive collapse of the entire building.

    9.) In Appendix C of an earlier FEMA report (http://wtc.nist.gov/media/AppendixC-fema403_apc.pdf), there is talk of sulfidized steel. Chemistry is a weak spot for me; I understand physics better. Richard Gage makes a big deal about this Appendix and his assertion that it is not dealt with in the subsequent NIST report. From the 1000 or so pages I have read of your report, I haven't found it either, and I see much more physics than chemistry in your report. That said, I have to try to find an answer to this question of how there was melted and sulfidized steel. Is there a chemist at NIST who has researched this? So far I have come up with this:

    a) Sulfidized steel melts at a lower temperature than regular steel (I have read figures of both 1800 and 2200 degrees F).
    b) Gypsum, which is 18% sulfur, was used as fire insulation for some of the steel beams and trusses.
    c) I don't know how steel is sulfidized. Is mere proximity of steel and sulfur during a fire enough to sulfidize steel?
    d) If so, could some steel have been sulfidized in the WTC fires, causing some steel to melt at the lower temperatures of the WTC fires? Or is there another explanation? Or is there no explanation yet? Except for this I have so far been able to find alternative explanations for melted steel in the rubble (such as melted aluminum from airplanes and cars in the basement garages).

    The steel sections used in the other WTC buildings (WTC 3, 4, 5, 6, and 7) were conventional sections and were not marked. Thus it was not possible to conclusively trace the piece studied in the FEMA report to a particular building. It is also not possible to determine how and when the sulfidation occurred. It is important to note that NIST found that the steel only needed to heat sufficiently to lose a substantial amount of its strength and stiffness, which occurs at a temperature well below the melting point.