holy fuck you're dumb...

so you think that because the bottom of the building weighs more then the top of the building can't fuck it up as it falls into it?

LOL

there is no "force pushing up" it's a compromised system, it's a building that has had it's top cut off... it's not a matter of mass vs mass it's a matter of falling mass impacting a static structural support system that either can or cannot "catch" the weight of the building above.

this happens on a floor by floor basis.

once the building's top sections are falling they are going to blow out each floor they impact... it's the single floor vs the entire weight of the building above with inertia behind it.

once the fires cooked the damaged areas long enough, it reached a point where it could no longer hold the weight of the building above and that damaged area failed, allowing the building above to begin freefalling.

once you have that much weight in motion, you're asking the floor directly below the damaged area to "catch" that building.

never going to happen, it just becomes more weight that is falling into the floors below.