Miragememories
Banned
R.Mackey said:"The buckling required for this "freefall" portion, which only affects some of the perimeter, takes place in the seconds before the "freefall." As NIST explains in thorough detail, an eight-story section of the lower perimeter, now unbraced and heavily loaded, buckles. This absorbs energy but leads to little vertical displacement. However, once buckled, those columns have almost no remaining strength, so the next phase is the "free fall."
That "free fall" by the way is approximate. Also it was only measured on one face, and rotation can artificially inflate the apparent downward velocity. You cannot say there was no energy dissipation during this period, only that it was relatively little. But that's what we already expected."
Miragememories said:"From NIST NCSTAR 1-9, WTC 7 Global Collapse Analysis
"In Stage 2, the north face descended at gravitational acceleration, as exterior column buckling progressed and the columns provided negligible support to the upper portion of the north face. This free fall drop continued for approximately 8 stories (105 ft), the distance traveled between times t = 1.75 s and t = 4.0 s.
...a freefall descent over approximately eight stories at gravitational acceleration for approximately 2.25 s, and a decreasing acceleration as the north face encountered resistance from the structure below."
DGM said:"And then concluded:"
Miragememories said:"So much for the NIST's explanation in thorough detail.
Your depiction of what the NIST supposedly reported about free fall is fanciful ad-lib."
DGM said:"That's not all they had to say now is it?"
In the context of free fall, yes.
From what I could tell after reading the whole chapter, Mackey took liberties with the NIST overall global collapse analysis, adding language of his own choosing.
What I quoted was all that I could find of the NIST's supposed detailed explanation of the WTC7, 8 story free fall.
Keep in mind, that little tidbit was a huge leap for the NIST, given that only a few months earlier, after years of investigation and computational analysis, the NIST had somehow overlooked the 8 story free fall and were denying its existence.
Quite the oversight.
MM