Originally Posted by Tony Szamboti
I do see some
deformation of the east side exterior while the east side interior is collapsing: Windows break on several floors.
I suggest that the facade was very stiff. It could withstand the collapse of one row of core columns (79-81) and and the accompanying pull on exterior columns 44 plus 43 and 45, being still braced by column 46 (that had a beam going to c76) and the east wall. Perhaps floor beams detached from the exterior before the exterior was torn apart; the window breakage however indicates some stress and strain and deformation of the window framing.
Later, when the core collapsed in rapid progression from east to west, and the lateral bracing through floor beams (tying exterior columns 46 through 55 to core columns 76 through 58) was lost, it took far lesser forces to pull in the facade.
Of course that is also just a story.