Comment: Very important point.

"resistance on a steel frame assembly"
You see, everyone assumes there was a steel frame assembly to offer resistances. If you study the unique design of the towers, there was none for the vast majority of the floor space. The steel structure resistance was confined to 27% of the square footage, clustered in one rectangle (the core). The 73% was floor spans with no structure underneath. The spans were 60 feet in two directions, 30 in the other two, and again, no structure underneath. The floor joists were lightweight trusses, sandwiched between the outer wall and the core, attached with an "L" bracket you could hold in your hand. That's all the resistance there was for all the jumbled falling mass.
Not only that, if you understand the cores were not fully severed at the time of collapse, you will know the floors beneath the airplane impact zones were weakened and dislodged due to the excessive stress upon the core.
Lastly, at least one core was still standing post collapse:
http://enki.hubpages.com/hub/911-Misdirection#slide210683