P1, einsteen, femr, I agree with all points mentioned.
Femr, nice to see you are still around.
Concerning the symmetry claim:
A close-up of the roofline descent shows the building interior fail slightly before the exterior walls.
In the quality video clip
http://video.google.com/videoplay?docid=3132857754400064872&q=south+tower+collapse+close+up&total=27&start=0&num=10&so=0&type=search&plindex=7#We notice, in order:
1) East Penthouse Collapses from left to right (In the OP of "column 79? Oh, really?" thread there is well-documented smoke suction from behind the east penthouse before it collapses)
2) Rest of penthouse collapses, all supporting columns seem to lose strength simultaneously. Do you see the penthouse "wiggling" after the east side falls but before the rest of it falls?
3) The whole outside of the building follows closely behind. There is maybe a one second delay between the simultaneous failure of the penthouse columns and the equally simultaneous faiure of the entire perimeter.
We know that the whole penthouse fell slightly before exterior of the building because we can the penthouse disappear within the building in the video.
This helps confirm the probable order of column failure. The interior columns failed just before the exterior frame, pulling the exterior inwards and over the interior.
The early fall of the penthouse allow the building to fold inwards while falling.
For column failure, it seems to mean column 79, 80, 81 fails first (hence smoke suction followed by the east penthouse). This is followed by a near simultaneous failure of all inner columns holding up the penthouse as the above video seems to show. Just a second after we see the penthouse start to move the rest of the building starts to move.
I think this is pretty interesting. It seems to confirm what Dr G has said about the entire building moving together and not just some "exterior shell".
It shows how the building pulls the exterior slightly inwards and why the rubble shows the outside of the building folded over the inside.
This is pretty cool because we can see collapse of interior columns via early penthouse movement. In a sense we are looking at a building (penthouse) on top of another building. Contrast in motion of the two buildings allows us to see inner vs exterior column failure. We can see a slight delay between interior column failure and exterior failure by the way the entire penthouse slowly disappears into the building in the video.
