Douglas Watts of Augusta, Maine wrote:
The nature of the collapse of the WTC 1, 2 and 7 towers is of interest because of their marked resemblance to the intended goal of a controlled demolition (ie. a building falling quickly and within its own footprint). Basic probability suggests that 3 buildings structurally weakened by completely uncontrolled damage would tend not to all fall in such a markedly similar fashion to each other, nor in a fashion so highly similar to that of a controlled demolition. Out of three buildings, all other things being equal, one would expect that through probability alone, one building would sway or topple sideways, just as a coin randomly lands on heads or tails in three tosses.

I am also intrigued about the ability of burning jet fuel and combustible building debris near the top of a building to so thoroughly weaken the steel supports of a building adjacent to the localized heat source that the entire building collapses very quickly rather than the weakened steel at the top of the building giving way and the top of the building sliding off and falling while the unweakened steel near the base of the building remains relatively intact. This bothers me because it seems counter-intuitive, and would constitute an enormous design flaw for a multi-story steel building. By definition, a first order task for engineers would be to design a very tall steel building in such a way that a severe fire in the top 3/4s or 2/3s of the structure would not cause the entire structure to disintegrate, which clearly occurred at WTC1, 2 and 7. This, by definition, would represent an extremely unsafe building design.

Assuming that burning jet fuel acted like a cutting torch at the impact point of the jets at WTC1 and WTC, and the jets struck the buildings on one side, not all four sides at once, this would cause heat to be concentrated near the impact point with lesser amounts of heat with distance from the impact point. Thus it seems to me the building would most likely be sheered at the floors in which the impact occured, because this was where the temperature reached a point to weaken or actually melt the steel. Because of this, one would expect the building to careen and sway prior to collapse, or even lose large chunks of itself, first at the point of impact, and only afterwards spreading outward, upward and downward from the initial point of impact and subsequent fire.

As an analogue consider a house fire which begins in the second floor, well above the foundation. In general, the fire will move upward and begin to consume the roof. Rare is the house fire in which only the top floor is actually aflame, yet those flames cause the unburned and relatively cool foundation of the house to completely buckle and collapse. It seems to me that if this behavior were the norm, firefighters would not risk entering a house with a roof fire through the ground floor due to the imminent risk of the entire building collapsing on them, even if the ground floors were not burning and at normal temperatures.

As morbid as it may sound, the poor firefighters of the NYFD became tests of this hypothesis. Had the blazing fires in the upper floors of WTC1 and 2 somehow caused the ground floors to be superheated or otherwise obviously unsound, the firefighters would not have entered the buildings and conducted such extensive rescue efforts. These men and women do understand the physics and behavior of building fires. If all fire science indicated that a fire 60 floors up could cause an entire 110 story building to instantaneously collapse, the NYFD firefighters would not have entered the building in the first place. These issues trouble me, so if people who know more on these technical subjects can enlighten, it would be appreciated.