I'd add to Jim Green's well-reasoned response another
clear inference from the NOVA program he mentioned.
Namely, the WTC design relied on light weight steel
floor trusses as tension members to join the outer
steel columns to the inner steel columns, thereby
providing the necessary rigidity to keep the whole
structure plumb. When the first floor truss/wall
joints failed, the entire structure was doomed,
including the central stairwell located inside the
inner column structure. I recall having seen another
program where it was stated that the use of this
design would now be seriously re-examined.
The very large skyscraper recently built in Kuala
Lumpur(sp?) uses reinforced concrete as its central
core. Its designer (on the same NOVA program) claimed
that this design would leave the central core intact
(along with its enclosed stairwell) even if the office
floors should pancake and collapse.
Another comment in the NOVA program that went by
rather quickly was made by, I believe, a NYFD official
who stated that it is "common knowledge" that a fire
cannot be fought in a high-rise building. Does anyone
on the list recall what floor was quoted as the
"cutoff"? The NOVA program indicated that the great
majority of the jet fuel ignited in a fireball outside
the building. There was plenty of fuel in the building
to produce a fire hot enough to cause structural
failure of the steel. This would seem to suggest that
all WTC-design buildings are vulnerable to collapse in
a major fire that starts on a high floor. It would be
interesting to follow this (presumably) ongoing safety
review. John Barrere
__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software http://sitebuilder.yahoo.com