Re: Physics of the 9/11 building collapses?

hetware wrote:

Edward Green wrote:

hetware wrote:

Edward Green wrote:

... 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.

You'd think after 100 years of intensive study by tens of thousands of
engineers and physicists, someone would have figured that out by now...

I didn't say "nobody knows this", I just said I haven't heard an
approved talking head making this point. That's another way of saying
it's not a standard oolie. ...

I've considered pretty much what you are suggesting. It really was my
uncritical assumption until I started having doubts a week ago. I recall
such things as collapsible vacuum cleaner hoses which snap together one
ring at a time. It's not completely unreasonable. But I have yet to see
any model of the collapse beyond efforts to explain what initiated it. All
of the official explanations work under the assumption that the aircraft
impact and subsequent fire were the cause of the collapse. My approach is
to start from the hypothesis that one or more floors did, in fact, give
way. Could dropping the top 20 or 30 floors on the bottom 90 or 80 floors
from 20 or so meters above cause the collapse observed?

Well, now you're asking a hard (as in hard vs. soft) question, so "it
seems reasonable to me" is probably not an adequate answer. However:
dropping 20 to 30 floors of an office tower 20 meters (accepting your
figures) is a pretty large hammer, don't you think? It certainly
doesn't seem unreasonable.

I
also wonder just what the experience base is in the unintentional
collapse of steel frame towers -- rather small, I think. I further
note that although from a distance the twin towers fell approximately
straight down, nearby structures sustained significant damage. The
difference between an unplanned collapse with a high probability of
looking like a controlled demolition and an actual controlled
demolition may be tighter control of the footprint: if professionals
had demolished the tower, taking a chunk out of the the corner of
nearby 7 WTC would have been a process failure. ;-)

There seems to be a huge lesson to learn here. It's one I have known in my
heart from the first time I saw Manhattan. People don't belong stacked up
like corral cells.

Hah. Now we uncover our deep seated prejudices. ;-) I happen to have
been born and raised in Manhattan, so it seems quite natural to me that
people should live stacked up like coral cells.

<...>

Why do you say this? <thermal image of collapse site>

Too much heat.

Supposing this were true, I'm not sure it would be evidence on the side
of explosives. What would be the relative contribution of a sufficient
amount of explosives to do the job, vs. the graviational potential
energy and ordinary combustion?

<snip some other points of argument and rebuttal>

Because they wanted to destroy the WTC and kill as many people as
possible, but were concerned about loss of life or property damage in
nearby buildings?

You are asking about the psychological aspects. I am asking about the
physical evidence.

Ah. But they go hand in hand, from my point of view. We are not
conducting a hard engineering review of all the available data, in
light of expert knowledge of structures. We are having a discussion as
more or less informed laymen of the relative plausibility (appropriate
Bayesian prior) of various scenarios -- at least that's what I think we
are doing. Of course it is of the very nature of Bayesian priors that
they are subjective, but not therefore that their basis is outside the
realm of rational discussion. In particular, the assignment of our
best rational prior probability to one of two possible scenarios (say)
involves all our own prior knowledge, including our knowledge of human
behavior. Humans after all were part of the process, no matter what
happened.

If you want an evil government conspiracy theory, keep it simple.
Postulate that the CIA was in contact with bin Laden,

Why does bin Laden need to have been involved if "the government" pulled it
off? Would it not be convenient to blame some guy nobody likes in the
first place?

I was merely presenting an alternative third scenario to (1) bin Laden
orchestrated it all (2) the evil US government orchestrated it all: (3)
bin Laden orchestrated it mostly, with help from evil elements in the
US government. I wasindicating that, given my own prior experience,
that if you "want" to implicate the US government, I find (3) a vastly
more probable scenario than (1).

I will admit you have me thinking, and while I still find revisionist
histories of class (2) to be in the same category as denial of WWII
genocide or the Moon missions, some of my gut feel that people in
goverment would be _incapable_ of such infamy do not stand up to closer
examination. To wit, I note that the history of the twentieth century
is replete with governments which did delibrately murder vast numbers
of their own people, and, without really trying, I'm aware of at least
one case where it is widely accepted by mainstream history that an
"atrocity" was staged for manipulating public opinion (the Reichstag
fire).

Ok... since it is certainly well attested that humans in power can and
will act the way you seem to be hinting that a certain government close
to us may have acted here, I have to ask myself why I find it so
improbable? Are we a better class of people than those other bastards?
Probably not genetically -- we _are_ them, so to speak. However, for
all the flaws one can find, I think we have a better system of
government than was in place to facilitate all the governmental mass
killings one can think of -- mostly dictatorships.

I'm not saying how likely I find that scenario, but it involves many
less people and much lower levels of implausibility than yours.

What is 'my scenario'?

That parties unknown rigged the towers with explosives?

It's
simply straightforward treason, rather than Hollywood style paranoia.
The old ways are best.

I'm trying to explain the physical evidence, not who done it.

There is overwhelming evidence that aircraft were hijacked, and in fact
hit the towers. Now, if we, for unknown academic reasons, want to
restrict ourselves to the question of whether ensuing events are more
consistent with aircraft impact and nothing else, or with aircraft
impact plus pre-set explosives, you've got me. I can't rule out, from
my lazy layman's armchair, considering nothing but "the physical
evidence", the presence of explosives to help things along. However,
if we step back and begin to consider who would have placed the
explosives, and why and how, my prior on that begins to fizzle to tiny
cinder, not even worth considering. Conspiracies only remain secret if
there are a very small number of conpirators. Oliver North's dealings
and Nixon's activities _might_ have remained undetected -- though they
did not, and they only involved a small number of conspirators.

If you want some unindicted co-conspirators -- which I still have a
feeling is your agenda, despite your claims to be considering only "the
physical evidence", the highest probabilities scenarios would involve
only a minimal number: say, some rogue elements in the CIA who were
secretly helping bin Laden, providing him with intelligence, or finding
ways to quash or misdirect investigation which might have foiled his
plot: that's a conspiracy theory with legs. Forget about controlled
demolition: I'm sorry, but that's just nuts.

.

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