In a recent interview with the BBC, Roland Angle claimed that NIST did not have any explanation for the 2.25 seconds of essentially free fall descent observed during the collapse of World Trade Center Building 7, saying:
But NIST actually DO have an explanation for that, in their report on their collapse, and summarized in the FAQYou've got to understand that the way that that building collapsed was unprecedented. You had a forty seven story steel frame building that collapsed in just under just around seven seconds, which is just about freefall speed. And measurements of the video showed that the first two and a quarter seconds of the collapse was an absolute freefall speed, which means that there was no resistance, which means that all 82 columns in the building were not acting at all for a distance of about eight floors.Now that's an impossibility. The columns were there. What what could possibly have caused those columns not to be acting, not to be giving any resistance to the collapse of the building at all? Well NIST doesn't have an answer for that. They admit, NIST's reports at actually admitted that there was two and a quarter seconds of freefall, and yet they don't have any explanation for how that could occur. It certainly wouldn't occur under the premise that they have, which is that the girder failed and therefore there was a progressive collapse those those collapses even if they did occur would take time there's no way that the building collapse at freefall speed under their scenario. They have no explanation for that.
Their explanation is the buckling of the exterior columns (which happened after the collapse and buckling of the interior columns). Since a buckled column supplies only a tiny fraction of its designed resistance to vertical load, the result is very close to freefall.
11. In a video, it appears that WTC 7 is descending in free fall, something that would not occur in the structural collapse that you describe. How can NIST ignore basic laws of physics?
In the draft WTC 7 report (released Aug. 21, 2008; available at http://www.nist.gov/el/disasterstudies/wtc/wtc_draftreports.cfm), 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.
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 approach taken by NIST is summarized in NIST NCSTAR Report 1A, Section 3.6, and detailed in NIST NCSTAR Report 1-9, Section 12.5.3.
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:
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.
- 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
AE911 Truth must be aware of this, so it's rather misleading on their part to suggest otherwise. It's fine to disagree with a complex analysis, but not to claim it does not exist.