Creative Speculation
In reply to the discussion: Martin Sheen: 9/11 Questions 'Unanswered,' Building 7 'Very Suspicious' [View all]tomk52
(46 posts)AC,
There were external steel columns of the Windsor Towers that did survive the fires. The rework was in the process of upgrading the fireproofing of the steel columns. As a result, there were several floors of the building (1 thru 8th, 10 thru 14th & 16th) that had insulation on the outer columns, and several floors (17th thru 28th, 9th & 15th) that did not.
Proving how critical insulation is to steel's survival in a fire, the steel on ALL the floors with insulated steel survived. The steel on ALL the floors with non-insulated steel collapsed.
Concrete being a superb insulator (& the steel in the cores carrying no weight), the cores did fine, as you said.
See the summary at UManchster's fire science web page: http://www.mace.manchester.ac.uk/project/research/structures/strucfire/CaseStudy/HistoricFires/BuildingFires/default.htm