Strength of Metals - Strength versus Temperature

Note that there is no abrupt knee in the green curve…or any of them. Heat is not transferred instantaneously and at no point do any of these metals suddenly lose strength as it heats. Steel heats slowly and gains strength to about 425F then weakens as it heats after ~700 F, the point at which it is again at room temperature strength. A weight put on the heating steel would be let down slowly. NIST reports show that all steels in the buildings were from 5% to 100% stronger than specified. Also, the safety factors in the buildings were from 3X to 5X above design forces which included 145 mph hurricane wind stresses.