I’ve melted many a piece of steel in a coal forge. I’ve also melted steel with a propane, acetylene and Mapp gas cutting torch.
Shucks, I’ve even got steel red hot in a common wood stove. Forged my first knife heated in a wood stove.
What probably happened on 9-11 is the fires caused the bolts holding the I beams to lose their temper, and they sheared off causing the entire floors to collapse and pancake on the ones below them.
weren’t I-beams, they were open web trusses, far quicker to lose structural integrity in a quick high temp environment. The sag of the joist over-stressed the joist/load bearing wall connection, further contributing to the floors collapsing. The spray on fire-proofing’s poor insulation contributed to the rapidity in loss of strength. High winds, ever present at the upper floors, provided the bellows effect of stoking the flames. On that cloudless morning the evidence of wind force was nit present until the fires were fully engaged. Present in the videos from Jersey and Brooklyn sides.