Jeff Strahl, Mechanical Engineer

Believes the WTC was brought down by demolition.

He brings up the interesting concept of the "resistance paradox":

Interesting that you note the towers disintegrating, but do not note, or pretend to not note, the contradiction between the lower portions offering no resistance to the falling debris if you wish to explain the short collapse time, vs the top portions disintegrating as if encountering massive resistance. So, which is it, Mr Partridge? Did the lower portions offer zero resistance to explain the short collapse time (videos show the lower portions offering no more resistance than the nearby air), or did they offer high resistance, to account for the upper portions disintegrating ABOVE THE COLLAPSE ZONE, IN MID-AIR?

The fact that the towers collapsed top to bottom, where the only thing that appears to drive the collapse is a huge cloud of dust, is by itself strong proof that the collapses were not simple pancaking events.