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The start of the South Tower collapse seen from the
southwest
Some General
Observations Any attempt to discuss
the
collapse of the World Trade Center towers
must come to terms with the enormous emotional trauma that these events
inflicted on the American psyche. That horrendous emotional wound demands
that the utmost honesty and seriousness are applied when raising questions about
the fundamental nature of those events. But we must not let a
misplaced sense of propriety make us feel unable to ask technical questions
about the nature and causes of the collapses, especially if the true answers to
these questions lead to the realization that the collapses were indeed
controlled demolitions. For that would force us to face the
realization that an undertaking of that scale and complexity could only be
undertaken with the active cooperation of elements in our own government. And
yet, far from dispelling these doubts by aggressively pursuing the truth about
9-11, that government at every level has done everything possible to prevent a
meaningful investigation. The scene of an enormous
crime has been systematically scrubbed of all useful evidence, as FEMA, the
agency in charge blandly asserted that it is "not an investigative agency"
and that "this will not be a Flight-800 type investigation."
This absolutely unique
catastrophic failure of two sophisticated high-rise towers
is treated as the most
banal sort of everyday event, even as tourists are forbidden from taking pictures of
the crime scene. This lack of interest in doing a thorough forensic analysis of the
crime scene, and the haste to dispose of the physical evidence are hard to
understand as anything other than a cover-up. There seems to be an official
government commitment to learning as little as possible about the events of September
11, and to making the investigations themselves as
secret as possible.
Despite this loss of the
physical evidence, a number of videos of the collapses
exist and have been made
available on the internet. These are copies of
broadcast television
footage that are available from a number of sources, and
show no evidence of
editing or image manipulation. The archives of the various
networks should be able
to verify the authenticity of the clips, but in view of the
close agreement between
various sources and various views, fakery seems very
unlikely. I believe that
a careful analysis of some of the major qualitative
features of the events
that these videos show allows us to exclude the
possibility that these
were simple gravitational collapses due to structural
failures induced by the
collisions and fires. That may seem like a strong
statement, but remember
that if a proposed explanatory model for the collapses
does not account for
major objective features of the events as witnessed, it
cannot be accepted as an
adequate explanation for the events witnessed.
The Popular Models
Though there has been no
official explanation released so far, there seems to be
a popular consensus more
or less as follows: heat from the fires weakened or
softened the trusses
that supported the floors. Either from sagging or thermal
expansion of the
trusses, the attachments of the outer end of the trusses to the
outer steel framework of
the buildings were broken. This would presumably
happen to the floor or
floors above the impact sites, where the fires would have
burned hottest. The loss
of these attachments is then said to have caused
entire floors or
sections of floors to fall, leading to a chain-reaction collapse.
These models generally
ignore the fact that the very substantial core of the
building, a 27 x 40
meter rectangular pillar consisting of 44 large steel box
columns interspersed
with about one hundred elevator and utility shafts, should
have remained standing
as the relatively light floors fell down around them. The
brackets attaching the
inner ends of the trusses to the central core would shear
off under the impact of
a floor falling from above, causing the floors to slide
down around the core
like records on a spindle. But yet, in both collapses, when
the dust settles the
building is completely gone, including any trace of the central
column structure.
The most difficult
feature of the collapses to account for is that the buildings fall
in almost exactly the
time it would take for an object to reach the ground from
the height of the roof.
Several careful analyses of the video evidence show that
the fall occurs in ~9
seconds, within measurement error of the free-fall time.
At the moment of collapse
the building still has considerable resistance to vertical
compressive loads, even
if a little local weakening exists at the level of the crash
and fire. The central
core is still mostly intact (especially in the south tower,
where any significant
heating would have been near the corner the plane struck,
and the core could not
have been hit by major parts of the plane) and much of the
outer frame is still
intact at this point. The energy to overcome this resistance
can only come from the
gravitational potential energy of the building. The
dissipation of that
potential by doing the mechanical work of crushing structural
materials must be
subtracted from the force available to accelerate the upper
part of the building,
and this must result in a significant slowing. One estimate
by a structural engineer
at MIT article estimated 30% of the gravitational potential
being used to crush the
building, probably a conservative estimate since it does not account for the energy
needed to pulverize
the concrete and eject powder and debris laterally at
high speeds. For any this value
of resistance consistent with the real-world strength of the columns there would have
been a very observable slowing. Intuitively it's plain that the only
way a building can fall at free-fall speed is for there to be no resistance at
all... as if
the whole building had suddenly liquefied, or if a wave of liquefaction
(i.e. demolition wave) had traveled
down at or above the rate of free fall.
Why The Immense Dust
Clouds?
In trying to
understand what actually happened during the collapse of
the World Trade Towers,
perhaps the most glaring problem with the "official" models is their
inability to explain the enormous dust clouds generated by the collapses. Even early
on, when the tops of the buildings had barely started to move, we saw the characteristic
jets of fine dust (mixed with larger chunks of debris) being shot out very
energetically from the building. During the first few seconds of a
gravitational fall nothing is moving very fast, and yet from the
outset what appears to
be powdered concrete can be seem blowing out to the
sides, growing to an
immense dust cloud as the collapse progresses.
The floors themselves are
quite robust. Each one is 39" thick; the top 4" is a
poured concrete slab,
with interlocking vertical steel trusses (or spandrel
members) underneath.
This steel would absorb a lot of kinetic energy by
crumpling as one floor
fell onto another, at most pulverizing a small amount of
concrete where the
narrow edges of the trusses strike the floor below. And yet
we see a very fine dust
being blown very energetically out to the sides as if the
entire mass of concrete
(about 400,000 cubic yards for the whole building) were
being converted to dust.
Remember too that the tower fell at almost the speed of
a gravitational
free-fall, meaning that little energy was expended doing anything
other than accelerating
the floor slabs.
Considering the amount of
concrete in a single floor (~1 acre x 4") and the
chemical bond energy to
be overcome in order to reduce it to a fine powder, it
appears that a very
large energy input would be needed. The only source for
this, excluding for now
external inputs or explosives, is the gravitational
potential energy of the
building. Any extraction of this energy for the
disaggregation of the
concrete would decrease the amount available for
conversion to kinetic
energy, slowing the speed of the falls. Yet we know that
the buildings actually
fell in about 9 seconds, only slightly less than an
unimpeded free-fall from
the same height. This means that very little of the
gravitational energy can
have gone toward pulverizing the concrete.
Even beyond the question
of the energy needed, what possible mechanism
exists for pulverizing
these vast sheets of concrete? Remember that dust begins
to appear in quantity in
the very earliest stages of the collapses, when nothing is
moving fast relative to
anything else in the structure. How then is reinforced
concrete turned into
dust and ejected laterally from the building at high speed?
Puzzling Evidence: the
Videos
The
video "Ground level close-up of WTC south tower "
(Slow-motion
of beginning of clip)
shows the WTC south tower
very soon after it starts to collapse, looking up from
directly below the
building. The cameraman quickly realizes that he is in danger
and turns to run, only
to be pursued by the immense dust cloud that issues from
the collapse. Though the
view of the building is brief, looking at it in slow motion
reveals some peculiar
features. At the very start of the clip we can see how
perfectly even the
collapse is, advancing with what looks for all the world like
rows of explosions
progressing in a perfectly straight line around the building,
and advancing down in an
extremely uniform way. As the demolition wave
advances there is only
dust and smoke where the top of the building used to be,
and a great quantity of
dust mixed with small pieces of structural steel is ejected
out horizontally at high
speed. To account for this very rapid ejection of debris
without the use of high
explosives, especially in the early stages of the collapse,
seems quite impossible.
If you look closely as
the wave travels down it seems to spare the corners,
perhaps letting them lag
behind to help keep the implosion aligned. The
demolition wave is
clearly advancing ahead of the actual collapse of the
structure, and speeds up
as it travels down. The delays between demolition
charges would have to be
very precisely controlled to create this effect,
suggesting to me that
each floor was wired to a separate detonator, with control
of the sequencing most
likely done remotely. This would also allow the collapse
to be triggered from the
point of impact of the plane to make it look more
realistic. Such
sequencing could easily be done from a laptop connected
wirelessly to the
towers, as long as each floor could be detonated
separately.**
Soon the photographer is
running away to escape the dust cloud, holding the
video camera at his side
and pointing back. As he runs you can see an
enormous cloud of dust
chasing people down several blocks of the surrounding
streets. The cameraman
and the people with him are running full tilt to get away
from the dust flow,
which seems to rapidly fill all the streets for a several block
radius around the site.
"South Tower Dust Pillar" also shows an interesting view of
the immense tower of
dust that is all that remains of the WTC South Tower as it
begins to flow down and
race out along the surrounding streets.
The other striking thing
visible at the beginning of this clip is how much very
fine concrete dust is
ejected from the top of the building very early in the
collapse. Since it
should at most be accelerating under gravity at 32 ft. per
second per second,
things would actually be moving quite slowly at first,
reaching about 200 mph
at the end of the ~1400' fall if nothing slowed it
down. It is very hard to
imagine a physical mechanism to generate that much
dust with concrete slabs
bumping into each other at 20 or 30 mph. And the
extreme fineness - I
have heard it described as like talc - and uniformity of the
dust makes its origin
quite puzzling.
This huge amount of very
fine dust seems to virtually fall in place, much of it
within the outlines of
the former building. This created a pyroclastic flow, or
perhaps more properly a
turbidity current: a slurry of dust and air much denser
than the air around it,
that can accelerate to considerable speeds as it falls. This
is the dense cloud that
chases the cameraman down the street for several
blocks, and can be seen
in several of the videos. From what I understand the
surrounding area for
several blocks radius was covered by several inches of very
fine concrete dust,
which would seem to account for most of the concrete in the
structure. And there
seem to have been very few macroscopic chunks of
concrete found at the
sites, much less the pile of broken but not pulverized
floors that one might
reasonably expect to find after the dust cleared.
The Afterglow
This is perhaps the
strangest feature of the collapse: in both collapses, the
videos show a bright
glow that develops as the bulk of the dust cloud hits the
ground. A good example
of this is "Close and medium view north tower-
(starts about 1:45 into the
clip)
At 45 seconds into the video,
just as the dust
cloud from the North Tower collapse hits the ground,
there is a sudden very
bright glow that develops. It may seem at first that this is
some kind of video
artifact, but a similar glow is seen in several views, and occurs
at the same point in the
collapses. This can also be seen in "Both collapses -
bright afterglow at 1min
07sec.mpg"
"Bright afterglow of
south tower collapse.avi"
http://ontario.indymedia.org/local/webcast/uploads/bright_afterglow_of_south_tower_collapse_.avi
starts after the South
Tower has fallen, but a very bright and persistent glow can
be seen where it had
been. The beginning of "Both collapses - bright afterglow at
1min 07sec.mpg"
shows the South Tower afterglow, and the sudden "ignition" of
the North Tower
afterglow at 1 min. 07 sec., which is so bright that it almost
burns out the image.
I have no explanation to
offer for this effect, and have heard no accounts of it
being seen by witnesses.
Is this something that shows up on video (near UV?)
but is not visible to
the naked eye? All I can say is that it seems to be real, and
occurs with both
collapses.
** Actually the sequence
of the south tower collapse is a bit strange as seen in the
video clip
"Close-up of top of South Tower"
http://ontario.indymedia.org/local/webcast/uploads/--_close-up_of_south_tower_collapse.mpg
First we see the top of
the building start to tip to one side as a monolithic block,
which we would expect to
continue to rotate and topple to the side. Instead,
almost as soon as it
starts to tip, the building below it starts to collapse, allowing
it to drop straight
down. There are very visible rings of explosions that start at
the level where the
building has begun to tip and travel rapidly down the building.
And instead of
continuing to topple to the side, the top portion actually
telescopes into itself
at the same time that it sinks effortlessly into the building
beneath it. Before it
disappears into an immense dust cloud, we see the distance
between the roof and the
bottom of the upper section actually collapse to less
than half its original
height. This is especially remarkable because it is essentially
in free fall at this
point, so there should not be any internal forces causing it to
collapse on itself.
The attached video,
close-up north tower.mpg, shows the beginning of the collapse of WTC-1.
I suggest viewing it
frame by frame: a number of very well-defined explosions can be seen.
home.attbi.com/~jmking/wsb/html/view.cgi...
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