Regarding live loads etc, I think each floor assembly was rated to take something like ten times its own weight, static. John Goss said eleven. But in the more conservative case, WTC1, there were at least ten floor assemblies, plus the top mechanical floor (heavier than a standard floor assembly), plus the hat truss, plus the roof, and all the contents, which included heavy stuff like elevator winches etc. Oh, and there’s an aircraft in there too. That lot has to come to more than eleven times the weight of a floor assembly, so even if we gently lowered it onto the highest floor assembly below the damaged zone, it’s too much, the floor’s going to go. The floor is only four inch concrete on one inch bar joists, no way it can hold that lot. And it wasn’t gently lowered; it was dropped 3.7 metre at 2/3g. No way. Not worth calculating. It’s not going to hold, and the next floor down is even worse of course. Collapse ensues.