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Reply #104: WTC test [View All]

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lcwilson Donating Member (1 posts) Send PM | Profile | Ignore Wed Jul-05-06 12:31 PM
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104. WTC test
I consulted a standard handbook - Perry's Chemical Engineers'
Handbook, Sixth Edition, page 23-65.  It has a nice graph of
the stress (load on the beam due to the weight of the building
above it) versus temperature giving the rate of creep (beam
starting to deform and fail).  Two important points that are
broad generalizations: below about 800 F, the rate of creep is
so low that you don't need to worry about it.  At about 1200
F, carbon steel can only support a stress of 600 psi with an
acceptable rate of creep, versus the typical design spec of
30,000 psi at room temperature.  This is a reduction in the
strength of the beam of 50 times, well past any safety factor.

The reason the rabbit hutch test failed is because the WTC had
walls and kept the heat in.  Redo the test with a thermocouple
to see how hot the fire can get when you have good insulation
around it and a good chimney to draw the air in.  My son's
forge regularly gets to the point that the steel starts to
melt (2800 F), using only charcoal and a blower.  When the
steel gets hot enough, it will fail.  When your test
reproduces the conditions in the WTC, it will fall down as

Perhaps we can get the opinion of a real mechanical engineer
or fire safety engineer.  I am a chemical engineer and know
enough to stay away from serious designs and get the right guy
to do the design for me if I need something like this. 
However, I have worked in labs for 20+ years and done some
experiments at these temperatures, etc. so this critique of
the rabbit hutch experiment is based on sound science.
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