ozeco41
Philosopher
Don't forget the infinite rigidityC7 moment frame.Oh, what happened to the indestructible moment frame?
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A Thought:
Isn't Internet engineering great. You can rewrite the rules for every post.
Don't forget the infinite rigidityC7 moment frame.Oh, what happened to the indestructible moment frame?
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Correct. NIST is describing their computer model which does not fall as a unit nor does it fall at FFA. They admit that their model does not match the observed collapse.*The fundamental question is: when a group of columns fails at a lower floor, can the floors & columns above be held up & supported by their lateral connections? Or will the collapse of lower columns progress to the roof?
If, and only if, the columns & floors above a lower collapse can be supported by their lateral connections, can the remaining portion of the upper block "fall as a unit".
There are two unequivocal proofs that NIST says that the upper core collapsed BEFORE the outer shell (i.e., NOT as a unit), and not simultaneously with the outer shell.
The vertical collapse happens between 14 & 16 seconds on this timeline. The horizontal progression of collapse happens between 16 & 21.5 seconds.
PROVES that the collapse progressed from the collapse floors to the roof AS IT HAPPENED.
Here again, NIST explicitly shows that their models do NOT show all external walls collapsing simultaneously, but rather collapsing in a complex sequence, each releasing (in 1 or 2 steps) over a period of about 5 seconds.
One last thing to note: These graphs also show that NIST's structural modelers do NOT believe that the external walls went "into free fall". If they did, these load vs. time graphs would have an infinite (straight up) slope as the load reduced instantly to zero. The slopes are steep, but they are not anything close to vertical. Especially for the north wall.
These graphs show exactly what the accurate analysis of the fall data of the north wall show: they did not fall "at free fall", but rather at an acceleration substantially less than free fall.
The final report does not include that darkened area as damage. There is no sign of frame damage and that is too perfect to be debris damage IMO.Oh, what happened to the indestructible moment frame?
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The final report does not include that darkened area as damage. There is no sign of frame damage and that is too perfect to be debris damage IMO.
http://www.internationalskeptics.com/forums/showpost.php?p=8143236&postcount=3781
Right, it's arguable that NIST didn't consider the whole damage to the building.The final report does not include that darkened area as damage. There is no sign of frame damage and that is too perfect to be debris damage IMO.
http://www.internationalskeptics.com/forums/showpost.php?p=8143236&postcount=3781
Hi Tom/TFK,Edited to main points for brevity because I agree with the conclusion.
Correct. NIST is describing their computer model which does not fall as a unit nor does it fall at FFA. They admit that their model does not match the observed collapse.*
The quote from page 55 of the final report that says the entire upper part of WTC 7 moved downward as a single unit is referring to the observed collapse.
*NCSTAR 1-9 Vol.2 pg 612 [pdf 274]
The results of this scenario were consistent with the observations except that the screenwall on the roof fell downward before the west penthouse.
In the NIST model, the horizontal collapse takes place over a period of about 5 seconds, but the observed collapse of the core columns under the screenwall and west penthouse takes about 1 second.
* * * * * * * * * *
In part 18, Chris Mohr said that "only one perimeter wall of 8 of those stories is known to have collapsed at free fall acceleration*."
This statement is incorrect. At very least, the north and west wall fall together at FFA.
Furthermore
NIST clearly stated [and it can be seen] that the entire upper portion [minus the part that had already collapsed] fell as a single unit in the "observed" collapse.
*Chris Mohr acknowledges that north wall collapsed at FFA.
The camera 3 video and the "New footage" video clearly show the north and west faces falling as a single unit at the same rate - FFA.
Note that the SW corner, where the debris damage was, is falling with, not before the north wall.

Edited to main points for brevity because I agree with the conclusion.
Correct. NIST is describing their computer model which does not fall as a unit nor does it fall at FFA. They admit that their model does not match the observed collapse.*
Hi Tom,
Ryan Mackey once claimed in an email to me that 8 floors held on at one point inside Building 7 during this period, but I don't see evidence of this in the NIST Report.
A question: I can't reconcile your statement that "These graphs show exactly what the accurate analysis of the fall data of the north wall show: they did not fall "at free fall", but rather at an acceleration substantially less than free fall." How does that statement, and the graph 12-61, reconcile with NIST's measurement of part of the roofline of the north face descending "at gravitational acceleration" for 2.25 seconds? Your statement seems to contradict that.
David Chandler seemed to explain the discrepancy in terms of fraud on NIST's part. If I understand his claim, it's that NIST at first averaged out the collapse speed of the perimeter walls over a longer time in order to gloss over the 2.25 seconds of freefall. Their acknowledgement of 2.25 seconds of gravitational acceleration of the roofline of part of the north face came after the public comment period and appeared in the final report, but not the draft report.
Can you clarify how to reconcile Figure 12-61 with NIST's graph showing gravitational acceleration for 2.25 seconds?
Tom,
When you get to answering my freefall question, here is another one: you said, "NIST says that the upper core collapsed BEFORE the outer shell (i.e., NOT as a unit), and not simultaneously with the outer shell." I think that is understood by everyone: that it's the outer perimeter walls that sort of fell as a single unit, not the core columns which went first in any analysis.
Now you're in my area of expertise,
Has been trumped. I doubt if he will return.
You still don't have an accurate assessment of my position.Hi Tom/TFK,
So if I understand Chris7 correctly, he is saying that the original computer model of the NIST Draft Report shows no freefall acceleration of any part of Building 7, but that in the final report, NIST acknowledges freefall of the top of Building 7 which fell as a single unit (he acknowledges internal collapse prior to this but still says freefall acceleration of the outer perimeter walls).
"within the margin of error" implies that it was not FFA. That is wrong. The error was 1/10th of 1 % or a difference of 0.001. The difference is NEGLIGIBLE - TOO SMALL TO BE CONSIDERED. Anyone who understands the nature of this analysis knows that the negligible difference is due to the FACT that an exact measurement cannot be made from a video.I acknowledge freefall within NIST's margin of error
There is no sign of variation. The moment frames would not allow different rates of fall. You are just injecting your unsupported desire to say they "may" be different.as measured at one point along the roofline of of the north perimeter wall, for 2.25 seconds. Eyeballing the videos, I also agree with Chris7 that it looks like at least the north and west walls fell together, to a gross order, but there may be subtle variation in different parts of the walls' rate of descent (here C7 and I disagree).
Anyone who understands the process knows that the variation is because the measurements are being taken from a video and are not exact. That is why many dots are plotted, the software computes the average, gives a number (9.81 m/s2) and draws a line. NIST clearly said "at gravitational acceleration" because they understand this.[FONT="]Looking at the graph in the NIST final report, I see slopes slightly exceeding freefall (but within the margin of error). Closer analyses show those slopes of greater than FFA may well represent momentary collapse rates for a total of one second of localized greater than freefall. (Here Chris7 and I also disagree).
My position is: The "entire upper portion" includes all the exterior columns and most of the core columns [all but the 3 that were taken out ~6 seconds before the rest of the core].
This is demonstrably wrong. The fall of the WMP overtook that of the roofline, beginning above it and disappearing below it. The core columns on that side had to have failed prior to the collapse of the N face.