Quote Originally Posted by gamolon View Post
Based on what calculations or FEAs do you make this claim?
Based on a knowledge of the elements at that area and how they were connected, and observations of how the building behaved. I suppose we could go through the demand/capacity ratio for that column compared to it's neighbouring cores, but it does seem somewhat strange that you appear to be leaning toward a simultanious failure of the North perimeter columns around floor 96.

Quote Originally Posted by gamolon View Post
How do you know the trusses didn't bend/shear at the perimeter column facade when column 508 dropped?
I'm sure they did, but that's not the question. The building is failing in the one way zones initially. Column 146 on the North face is the furthest east column who's descent is not arrested. The two way zone to the NE then follows just after. As this is all happening the roofline is descending more or less evenly.

The initial movement at the North face panels reflects the damage pattern sustained by them.
Un.jpg
The green panel falls, the yellow one falls a little and stops, the red one doesn't descend at all, the yellow circle's at floor 96 and column 508 is just west (to the right) of opposite perimeter 151 which is the centre column of the red panel. What would be breaking the spandrel connections above and west of it, if 508 had failed opposite it ? The building at the North, is failing initially in the one way zone only.