Two levels must break simultaneously. The bottom level of the falling mass and the top level of the stationary mass. Those two levels collapsing had to take energy out of the system.
No, both assertions are wrong. There is no requirement for two levels to break at the same time, and both videos show this is not the case at all.
The initial floor failure happened
before there was any large-scale motion in the structure. Basically, the strength of the failure floor diminished below the static load requirement (see NIST for a vastly more detailed explanation).
Then motion sets in,
then the cascade takes place.
There is no reason why two floors would have simultaneously fallen below their static loads, but if this happened, we would instead get twice the initial gravitational potential release, and this would precipitate the collapse even faster.
The intial collapse is basically driven by thermal energy, not gravitational energy. Only a minor amount of downward creep contributed to the initial collapse. Thus, the initial collapse
does not take energy out of the system in the method you propose.
Since the falling mass would have to be moving faster than gravity would accelerate the stationary mass then momentum was lost getting the crushed level going. Then the next level is going to slow things down more. And the next, and the next,...
I can't parse this first sentence. Restate, please.
Remember,
with every floor that fails, you gain a new
m g h amount of energy. The descending mass slows, but only a bit, and then
it accelerates. You're concentrating on the slowing but ignoring the acceleration. That's why you're confused.
80 levels below versus 30 above and the lower ones must be heavier and stronger but you want to believe gravity is going to make up the difference though you haven't been demanding info about the quantity of steel and concrete on each level all of this time. BELIEF without DATA very smart.
Non sequitur. You can set up the equations using a wide variety of mass distributions, enough to bracket any reasonable amount of mass on any floors, and show that the collapse still happens as expected. You don't need precise knowledge (which, again,
is available despite your claims to the contrary) to prove it will collapse. You only need this level of precision if you're trying to match the timing of collapse to within a few tenths of a second. See BLBG for details.
That is why I say LEVELS not floors. It is all of those core and perimeter columns that must have broken in that scenario not the floors. And FEMA said the perimeter columns were only at 20% of their load capacity so they had plenty of extra strength that had to be broken.
I say "floors and floor trusses," but whether you say potAto or potahto the result is the same. The impulse felt on collision is much higher than five times the static load, so the excess capacity in the perimeter columns is not enough to make a difference. Besides, the design reserve capacity in the core columns was a mere 1.67. There's no reason to cherry-pick the perimeter columns. That reserve also is diminished substantially when bracing mechanisms fail, i.e. the upper section suddenly becoming detached.
But the NIST tells us that one plane had 5 tons of cargo and the other had 9. That must have made all of the difference. ROFLMAO
Again, non sequitur. Nobody, including NIST, has claimed this was a significant factor. I find your complaints poorly reasoned and difficult to follow.
