Velocity loss is observable in every Verinage demolition and it would be in any demolition where gravity is all that is used to break the full structure after an organized fall.
This (the "
is observable in every Verinage" bit) may incidentally be true since
a) Verinage is indeed an "
organized fall" (WTC wasn't)
b) No Verinage has been undertaken so far where the top part is 15 floors or more
However, it is not true, as you insinuate, that
velocity loss must be observable for collapse to proced to completion.
There is a positive (downward) acceleration of the top part of g caused by gravity. As Verinage organizes an impact, this
acceleration must be reduced. However, since the impact is never fully instantaneous but instead loss of KE occurs over a finite time interval, deceleration is a function of that time interval and the KE loss incured by the impact. It often will be,
but doesn't have to be, more than g, thus resulting in loss of
velocity.
Additionally, we must ask:
Where is a deceleration observed? Answer: At the plane/level of impact. If however you observe some building feature much higher up (say a roofline 13 storeys higher), that feature may be sufficiently insulated, by elasticity and by plastic failures lower down, from the mass that actually causes the crushing that no velocity loss is observed there, even when there is velocity loss at the crushing interface.
Thus, your claim that there must be loss of velocity is plainly FALSE. It happens to be true in a number of other collapses, but may be absent.
...
It is the velocity loss which is observable and it would take over a second to regain the velocity...
This is plain nonsense.
This implies that the velocity loss is >= 9.8 m/s.
However, it can be shown (e.g. B&Z, even if you correct their numbers) that energy dissipation per story is only a fraction of PE differential of 1 story, hence loss of velocity due to crushing is only a fraction of the velocity gained by falling 1 story, or a fraction of a second.
