Reply #36: You're talking about the melting point of steel under no other stresses.

[Bolo Boffin]

And you don't have to get to the melting point anyway to have problems. You have to get to the softening point, the point at which steel has "plastic" deformations.

Plastic here means that the steel changes shape and will keep the changes permanantly, as opposing to bending back and forth but returning to the original shape.

Factor in the increased weight stress when other supports were destroyed and transferred their weight to other crucial joints supporting their own weight load to begin with.

Factor in increased wind stress, because the structural design meant to minimize wind movement of the towers had been compromised. The tops of the towers were flopping back and forth in the wind, basically. Since we're dealing with a lot of mass, you wouldn't see much more movement than normal, but those joints were being wrenched back and forth in the wind, generating more heat stresses in the structural steel.

Under these increased stress factors, the softening point of steel falls well into the range of temperatures produced by the WTC fires.