NIST Uses Lame Floor Collapse Mechanism to Explain the Fate of WTC7
As IF a floor collapse can pull a complete building down symmetrically at perfect free-fall speed--
Investigators have focused on the east side where the long floor spans were under most stress.
They think fires burnt long enough to weaken and break many of the connections that held the steel structure together.
Most susceptible were the thinner floor beams which required less fireproofing, and the connections between the beams and the columns. As they heated up the connections failed and the beams sagged and failed, investigators say.
I guess it "worked" so well before, they decided just to use it again!