With ductile steel there would be significant deformation of each column before enough load was transferred to adjacent columns. The time for a sequential column failure around the exterior of WTC 7 can conservatively said to take at least many seconds and that is not what we see. The entire exterior comes down as a single unit. The only way it could come down the way we see is for the entire 24 column central core to have been taken out nearly instantaneously which would then pull all of the exterior columns inward at the same time and cause it to uniformly collapse. Now the entire core could not fail nearly instantaneously due to a progressive collapse. This is a serious problem for a natural failure scenario.
The exterior was not stiff enough to be pulled on at one corner of the building and then start falling at the other in a symmetric way..
Tony, I think Chris needs another perspective to understand the discussion. He seems to be assuming that once load is transferred from failed columns to surrounding columns, that these will also automatically fail the instant they face the extra burden. Are you sensing the same thing?
It might help Chris to take another look at the Twins and why the tops did not collapse down for about an hour after the jets took out several columns. I think he might see that even though the load was transferred very quickly from failed columns to surrounding ones, that these surrounding columns did not instantly fail, and not at all for about an hour.