Reply #4: If the collapse was initated by a floor subsystem, then

[Kevin Fenton]

(1) Why is this not visible through the big holes in the towers? Surely, the part of the floors at the impact holes should be (one of) the first part(s) to go?
(2) Why are the walls bowing inwards? NIST claims that the walls (south wall of north tower and east wall of south tower) were bowing inwards. If the link between the core and the perimeter was broken, then how could failed floor trusses pull the perimeter inwards? Or do you disagree with NIST on this point?
(3)(a) Where in the floor subsystem would the failure initiate? Are you saying a truss would "snap" or come apart at a join?
(3)(b) Even if a floor truss failed (and obviously some of them did after the impact), then why would that lead to further failure of other trusses, given that this does not seem to have happened around the impact areas?
(4) How many floors do you think have to collapse before the fall becomes visible? The firemen on the 78th floor of the South Tower didn't report any floor collapse.
(5) The floors of the technical floors aren't lightweight concrete. How come the floor subsystem collapse did stop there?

"My belief is that there was some sort of failures that happened some time before the obvious collapse was triggered. I can easily see floors sagging down on lower floors and superloading the floors for quite a while until a sudden failure occurs."
That's about the most common sense thing you could say, but as far as I can see you're in a small minority here (as far as concerns floor system failure gradually overloading other floors) - most of the other explanations advanced by those who think the towers collapsed "naturally" don't involve floors being gradually overloaded - Eagar thinks the angle clips went all of a sudden, FEMA thinks the trusses failed in rapid succession and NIST thinks the trusses were so strong they pulled the building over. If you could agree on one theory, I'd find it more convincing.