The government maintains that the Twin Towers were each hit by aircraft and the subsequent fires weakened the steel in the upper stories, initiating a gravity-driven "pancake collapse," as illustrated in Figure 30. There are many problems with this hypothesis. The most obvious problem with it is the near free-fall speed of the destruction of these buildings (see Billiard Balls). A second problem is the paucity of remaining material. Where are the concrete floors? Where is the office furniture? Where is the office machinery? Where are the filing cabinets? Where is the wall board? Where are the bookcases? They were not there, so most of it appears to have turned to dust.
An illustration of what a "pancake collapse" would look like. The rubble pile should be at least 1/8 of the original building height (12.5%).
An illustration of what the actual destruction looked like. The rubble pile was no more than 2% of the original building height. Both towers went "poof."
http://www.drjudywood.com/articles/D...WarsBeam3.html