OK addressing the post...
"the walls around the impact site slowly bowed in minutes before the collapse, this was the girders cooling and shrinking back in"
That's truly hilarious. IF the girders expanded in the first place they could only shrink back to the original size. And that is only IF the temperature retured to where it started. If you think the beams heated up enough to expand (and i sure don't) how did they cool with any sort of ongoing fire? How could they possibly cool below the temperature they were before the fires?
What you are saying is preposterous. Forget what happens at the swimming pool, when it comes to steel girders shrinkage and expansion is NOT more than a fraction of a percentage. The expansion rate you are talking about would mean mile long bridges would have 50 foot gaps in them on cold days.