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The mechanics of the collapse are really
much more simple than conspiracy theorists would like
you to believe. The heat expanded the steel in the truss
in all directions. As a result they also expanded into the
columns. The trusses/floor system, sagged in the middle
because the columns were preventing the trusses from
expanding in their direction. That led to the bowing of the exterior
columns.
In terms of mass, the
floors were comparable to tree trunks and the columns were
like branches. The floor connections of the long span floors
could support a load of a couple story masses and had an
energy absorbing ability of a couple hundredths of a GJ per
story. The floor connections were like crepe connecting the
floors to the columns. The crepe was sufficient for the
structure in its static organized state but was a weak link
during collapse when the structure in the region of the
collapse front no longer resembled the static organized
state.
Listen to the NIST lead investigator
explain the leading hypothesis for the towers collapse.
After the columns bowed, the weight
was no longer going straight down. Like taking a straw and
bowing it in the middle, it no longer can hold the same
weight as it did when it was straight. The building tried to
transfer the load to the core columns and massive hat truss
on the roof. The
weakened core, weakened by fire and impact, couldn't hold the
massive weight from tilting. As with the perimeter column,
the massive load on the deformed core columns gave way.
Now look at what a REAL
Controlled Demolition looks like...
You can hear the explosives clearly over
the helicopter engine and rotating blades.
The NIST and "Pancaking"
The
massive weight easily caused a "Pancaking" effect
but unlike
the original hypothesis, the pancaking didn't cause the
collapse. It was a result of the collapse.
Update:
Conspiracy theorists are taking the above
out of context in an effort to mislead readers into thinking
the NIST and I are in disagreement. We are not. As I
mentioned above, the pancaking happened AFTER the building
was on it's way down and therefore NOT part of the NIST
investigation. The NIST only studied the collapse until
"Global collapse was inevitable". Any conspiracy theorist
that tells you the NIST said the building NEVER pancaked is
lying. The building didn't pancake CAUSING the collapse but
evidence is strong the building pancaked AFTER the collapse
was "inevitable".
What the NIST observed:
Failure of the gusset
plate welded to the top of the truss chord was again
almost exclusively observed regardless of location. This
may be a result of overloading the lower floors as the
floors above were "pan-caking".
NIST NCSTAR 1-3C Sect
3.5.3
Of course this will be
labeled a contradiction by conspiracy theorists. As if the
NIST can't observe something without studying the behavior
of it.
Let me make this really easy for them...
1) The NIST said, the heat from the fires
sagged the trusses which bowed the columns inward CAUSING
the collapse. Pancaking did NOT cause the collapse. The
evidence I see agrees with this conclusion.
2) The evidence on the ground strongly
indicates, after the collapse began, the building pancaked
spreading the debris as we see below. The NIST never studied
this so how could we be in disagreement?
I recently E-mailed the NIST to verify
this. Here is their response:
NIST did not describe the specific
sequence of events after global collapse initiated. The
progression of global collapse was induced by the
failure of the supporting structure (columns carry
vertical loads; floors hold columns together, they do
not carry vertical loads). NIST's investigation focused on the factors that
led to the initiation of collapse, rather than the
sequence of events after the collapse initiated.
The focus of
the Investigation was on the sequence of events from the
instant of aircraft impact to the initiation of collapse
for each tower. For brevity in this report, this
sequence is referred to as the “probable collapse
sequence,” although
it does not
actually include the structural behavior of the tower
after the conditions for collapse initiation were
reached and collapse became inevitable.
So while they did investigate the squibs
issues and other parts of the global collapse like the
gusset plates failure, they never
studied the "structural
behavior" of the global collapse, as they
did "the
sequence of events from the instant of aircraft impact to
the initiation of collapse". And why
should they? Every paper which passed peer review by
respected scientific journals (The Journal of 911 Studies is not one of them.) on the collapse of the
towers calculates the massive weight of the top sections
would crush the buildings as seen. There are mathematical
calculations which are shown in Bazant's paper (See below) and are peer reviewed. Others
have passed similar papers. The idea that these buildings
could not fall as they did flies in the face of these facts.
Conspiracy theorists are clearly lying
about this in order to paint this site as unreliable. The
irony of their claims seem to be what's most reliable in
their movement.
This also proves the building
was falling apart and could never topple over as conspiracy
theorists imply should have happened.
Below is a close-up of the columns as the top
section falls behind the bottom section.
Can you tell what's
missing here? There is no ejection of debris at the moment
of collapse. The debris builds up slowly as the collapse
progresses. The so called "scholars" say there
were explosives which cut the columns to
begin the collapse. The evidence does not support that
rationalization. What this evidence does support is the
NIST's report which says the columns were pulled in by the
floors which started the collapse. Ironically this video is
a clip from a conspiracy theorist video.
Conspiracy theorists use the original hypothesis - which
wasn't created by the government, and which was wrong - to
say the NIST can't be trusted, but that's the way all
science is. They look at the evidence and create a
hypothesis, test the hypothesis against the evidence and if
new information comes out, they change the hypothesis
accordingly. You would think if the NIST was going to lie,
they would just build the lie around the first hypothesis.
That they changed it only shows independence. Ironically,
Professor Jones has changed his paper numerous times, yet
the conspiracy theorists don't cast doubt on whether his
paper is correct. Proof of the pancaking effect is the core
columns, which can be seen collapsing seconds after the
perimeter columns hit the ground.
If the building didn't pancake, what
happened to the trusses? Assuming they didn't just fly away
it's obvious they fell straight down. More evidence of
pancaking is on ground zero.
Note what's left of the core with most of
the debris from inside the building around it. This photo
was taken in October 3rd so many of the columns were already
picked up but the major debris is located closest to the
core.
Below is another interesting photo. It
shows the perimeter columns laid out as if they simply
tilted over. The only explanation is that the floors went
straight down and the unsupported perimeter columns pivoted
over in large sections.
The video below shows a large
section of perimeter columns leaning over to land flat on
it's face.
Like cutting the top of a milk carton off and slitting
the corner edges - the walls lean over to land flat on it's
face. Some easily hit the Winter Garden building.
Note the WTC
columns laid out as if there were a path to the building.
There are no concrete slabs attached to columns.
With the
floors pancaking straight down, the perimeter walls were
free to lean over in tall sections before breaking off and
coming down. That's what gave them distance.
The above photo
illustrates just how far the perimeter columns could
have gone. If the columns didn't break up as they leaned out
they could have made a path to the Hudson river. Reaching
Building 7 and the Winter Garden would have been well within
reason.
The last piece of evidence is the standing
perimeter columns. You can see what's left of the steel
plates which hold the floors up. The tremendous weight
stripped them off as the floors were on their way down.
As generally accepted
by structural engineering and structural mechanics
experts (though not by some laymen and fanatics seeking
to detect a conspiracy), the failure scenario, broadly
proposed by Bazant (2001), and Bazant and Zhou (2002),
on the basis of simplified analysis, and supported by
very realistic, meticulous and illuminating computer
simulations and exhaustive investigations by S. Shyam
Sunder's team at the National Institute of Standards and
Technology (NIST, 2005), may be summarized as follows:
1. About 60% of the 60 columns of the impacted face of
framed-tube (and about 13% of the total of 287 columns)
were severed, and many more were significantly
deflected. This caused stress redistribution, which
significantly increased the load of some columns, near
the load capacity for some of them.
2. Fire insulation was stripped during aircraft impact
by flying debris (without that, the towers would likely
have survived). In consequence, many structural steel
members heated up to 600±C (NIST 2005) (the structural
steel used loses about 20% of its yield strength already
at 300±C, NIST 2005, and exhibits significant
visco-plasticity, or creep, above 450±, especially at
high stresses that developed; see e.g. Cottrell 1964, p.
299; the press reports right after 9/11, indicating
temperature in excess of 800±C, turned out to be
groundless, but Bazant and Zhou's analysis did not
depend on that).
3. Differential thermal expansion, combined with
heat-induced viscoplastic deformation, caused the floor
trusses to sag. The sagging trusses pulled the perimeter
columns inward (by about 1 m, NIST 2005). The bowing of
columns served as a huge imperfection inducing
multi-story buckling. The lateral deflections of some
columns due to aircraft impact and differential thermal
expansion also decreased buckling strength.
4. The combination of six effects
a) overload of some columns due to initial stress
redistribution,
b ) lowering of yield limit and creep,
c) lateral deflections of many columns due to sagging
floor trusses,
d) weakened lateral support due to reduced in-plane
stiffess of sagging floors,
e) multi-story buckling of some columns (for which the
critical load is an order of magnitude less than it is
for one-story buckling), and
f) local plastic buckling of heated column webs finally
led to buckling of columns (Fig. 1b). As a result, the
upper part of tower fell, with little resistance,
through at least one floor height, impacting the lower
part of tower. This triggered progressive collapse
because the kinetic energy of the falling upper part far
exceeded the energy that could be absorbed by limited
plastic deformations and fracturing in the lower part of
tower. (Bazant,
Verdure, 2006)
For a detailed account of the collapse, do yourself a favor
and READ ALL the NIST FINAL reports. Any conspiracy site
which gives you the old preliminary reports are being
dishonest. There is incredible detail which mirror the
evidence of the event in each of the reports below.
