"The strength of steel remains essentially unchanged until about 600°F. The steel retains about 50% of its strength at 1100°F. The steel loses all of its capacity when it melts at about 2700°F. However, for design purposes, it is usually assumed that all capacity is lost at about 2200°F."

So at 1,100 degrees F, the steel in the WTC lost 50% of it's strength.

A structure designed to support 100 tons would only support 50 tons. Resulting in TOTAL collapse of the structure at 1,100 degrees F

https://www.aisc.org/steel-solutions-center/engineering-faqs/11.2.-steel-exposed-to-fire/#9370