Lyrandar
Thinker
- Joined
- Apr 28, 2010
- Messages
- 211
NIST says WTC 7 had 2.25 s of free fall. They also say the lower columns buckled causing the building to come down. That means buckling removed completely eight stories of structure. The buckling had to be simultaneous over all columns because all four corners came down at the same rate. Since buckled columns all have some resistance not none at all, the columns all had to simultaneously snap. Plus, this all had to happen in the .6 seconds before the free fall period as the building fell two measly feet.
The problem with this is that we might still see gravitational acceleration even if the columns are still providing a minimal amount of resistance. This is why, I would assume, NIST uses the term "negligible" and not "none" when talking about the support provided by the columns. You are somewhat correct in your assertion that a bent column will probably still have resistance, I think, but I'm not sure where you're getting your certainty that the column has to snap entirely before its resistance drops to a negligible level.
Either way, the claim that the columns snapped simultaneously inside .6 seconds is not, in fact, implicit in NIST's claim, since the required conditions for NIST's claim can be satisfied by seriously damaged or weakened columns as well as completely destroyed ones.
