ЗЫ: From this useful website:

Metals lose about 50% of their strength at 60% of their melting temperature. This is common knowledge and may be found in any undergraduate text regarding "Fracture and Deformation of Materials."

If the approximate melting temperature of steel is 2750 F [1510 C] then the material would be plastic at 1650 F [900 C].
And also:

the Popular Mechanics article (and NIST report) mentions that pockets of the World Trade Center reached 1800 degrees F [980 C]. This would put the steel temperature in those locations at around 1600-1700 degrees F [870-930 C] , which is far above the 1100 degree F [590 C] mark that steel loses 50% 40% of its structural integrity.
The second quotation contains a slight error, which I've corrected in red. You can easily Google for yourself to confirm that 1100 F [590 C] is widely considered by firefighters to be a critical "failure" temperature for structural steel in buildings, although the loss in strength at this point is only about 40%, and the 50% loss in strength occurs closer to 1650 F [900C]. But in either case, the maximum temperatures in the WTC fires were even hotter, although still much less than the melting point of steel.

По-видимому, кампания дезинформации ЦРУ настолько распространенная, что участвуют в ней и металлурги и пожарные инженеры!!!