Yet Another Structural Engineer
A guy purporting to be a structural engineer, has this to say:
You all seem to be oblivious or intentionally obtuse, even to the point that you will not accept a "truther" point that the towers were composed of steel reinforced concrete. Of course with a tower structure of this height/base ratio it is almost required that the frame be constructed of steel beams, but the bulk of the building, all of those open spans like ceilings/floors, walls, those are constructed of steel reinforced concrete, as I stated earlier, not just concrete.
I have some grave doubts as to whether this guy has any real involvement in structural engineering. The World Trade Center towers were constructed of steel and glass. The floors were indeed concrete, but 4 inch slabs poured over steel decks. You don't have to reinforce concrete floors. The "walls" were not constructed of steel-reinforced concrete, as anybody with a modest familiarity with building materials would know; they were taped and painted drywall (Although the towers were old enough that some walls might be sheetrock).