Steel is surprisingly vulnerable to heat. Steel gets progressively softer as its heated but there is a sudden increase in plasticity at around 900F "black heat" - just below red heat. Its entirely plausible that the burning fuel raised a section of the steel frame to this temperature and started the collapase.

If you hear hoofbeats - guess horses not zebras!
altagid Reviewed by altagid on . 9/11 re-revisited/pentagon Its Interesting, that the engine found at the pentagon does not look like it came from an 757 boeing---Do they still think thats an engine from a 757---I guess my eyes are lying to me again...Still no proof that a plane hit the pentagon..... Rating: 5