Softening of Steel
NIST theory relies on dramatic softening of steel
to achieve "column instability".
Recall that:
NIST determined that there was no evidence that any of the samples
had reached temperatures above 600 ºC.
(p 90/140)
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FEMA Report:
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In the mid-1990s British Steel and the Building Research Establishment
performed a series of six experiments at Cardington to investigate the
behavior of steel frame buildings.
These experiments were conducted in a simulated, eight-story building.
Secondary steel beams were not protected.
Despite the temperature of the steel beams reaching 800-900 C
(1,500-1,700 F)
in three of the tests
(well above the traditionally assumed critical temperature of 600 C
(1,100 F), no collapse was observed in any of the six experiments).
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