Re: Physics of the 9/11 building collapses?

Sam Wormley wrote:

ABarlow wrote:

I guess then the question really is, why did the building that wasn't
hit by an aircraft collapse? If you accept the premise that the damage
from the aircraft was sufficient to bring down the WTC 1 & 2, you are
still left with the problem with explaining how the building that
wasn't hit by the aircraft, WTC 7, and suffered only superficial damage
from debris, suddenly collapsed without warning. At best, it means that
the building must have had *major* structural flaws that were
exacerbated by the collapse of the other two buildings...

http://wtc.nist.gov/pubs/NCSTAR1ExecutiveSummary.pdf
http://wtc.nist.gov/pubs/NISTNCSTAR1Draft.pdf

http://wtc.nist.gov/

http://wtc.nist.gov/pubs/NISTNCSTAR1Draft.pdf

"The final report on the collapse of WTC 7 appears in a separate
report".

http://wtc.nist.gov/pubs/#draft

"The NIST investigation of the WTC 7 building collapse is not yet
complete. The report on the WTC 7 collapse investigation will be
released in draft form for public comment and posted on this web site
as soon as it is available".

"Last updated: 4/6/2004"

So, two years later and they still haven't come up with a draft?

I did find the following nugget in the first reference:

"...the fire alarm system in WTC 7, which was transmitted to a
monitoring service, was on "test" on the morning of September 11, 2001
since routine maintenance was being performed. Under test conditions
(1) the system is typically disabled for the entire building, not just
for the area where work is being performed, and (2) alarm signals
typically do not show up on an operator console".

Since I happen to be qualifying at this moment as fire safety director
of an office tower about the same size as WTC 7, with an alarm system
of about the same vintage, I can say that the first statement is true
but misleading, and the second statement is probably false. For what
that's worth.

What I expect happened to WTC 7 is the following. Scattered fires were
allowed to burn unchecked for hours, because, in view of the collapse
of towers I and II, and the loss of life, it would have been foolish
for on scene commanders to risk personnel to fight fires in an
evacuated building. As we all know now, structural steel is coated
with thermal insulation to delay the onset of softening and failure
from the heat of a fire. However, such protection is not absolute, but
time rated. Since the fires were not extinguished, structural steel
was eventually heated to the softening point, starting, at some initial
location, a catastrophic chain reaction failure.

I haven't heard an approved talking head making this point, but it
seems probable that the lesson to take away from the WTC collapses is
that the thrilling drop-in-place results of the professional demolition
experts are not really that hard to achieve after all -- it's hard to
make a large structure _not_ fail in this way. The reason lays in a
scaling argument: if we nudge a block standing on end, it tips over.
If we nudge an office tower, it may _start_ to tip over, but because of
scaling and loading and the fact that most of the "structure" of the
building is empty space, we have far less excess strength to play with,
and the building doesn't tip far. The compressed corner fails,
allowing the top to drop straight down. Office towers don't fall over
like building blocks: to tip and rotate, you need a fulcrum, but the
part of the frame which might form a fulcrum is failing more quickly
than anything else.

OTOH, and not that I want to give any ammo to conspiracy theorists --
including those who haven't even bothered to check out the references
you give them -- but your shot from the hip here with large caliber
citations is a bit wide of the mark. WTC 7 seems to have fallen
through the cracks of the investigation.

.

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