What really happened ....11 september

[version77]

Quote from man:

wow. it is getting worse by each post. the moment you
do not agree with someone you fall into stereotypes.
my comments have nothing to do with your basic vision
of the subject, but with your inability to debate. and i
am not at all convinced of a conspiracy.

it is really difficult to take anything serious which is
coming from a person with such an obvious lack of
communication skills.

sorry, you are disqualifying yourself on an ongoing
basis. but we can leave it like that. i am the naive
foreigner for you and you are an inable debater for
me.

Whatever, you are the "man"...

Good luck finding someone to "debate" with you on this dying
boring, re-hashing, paranoid about 9/11 thread...

V77.... over and out.

 

[man]

Quote from version77:

Whatever, you are the "man"...

Good luck finding someone to "debate" with you on this dying
boring, re-hashing, paranoid about 9/11 thread...

V77.... over and out.

thnx. good that we both end it before we waste time of both of
us. truly appreciate it.
take care.

 

[dpt]

Sorry, this reply is long.

I thought it necessary to quote two levels of discussion, since otherwise it
would be too hard to follow what's being discussed. Also had to break it into
multiple posts to avoid 10,000 character restriction.

Quote from Bitstream:

Quote from dpt:
No. Not at all. These buildings were unique in design. They're not easily
comparable to other steel frame buildings. The weight was borne in the
towers both by the core and by the perimeter tube columns: neither group
was sufficient on its own to support the buildings. They were about 95%
empty space. If either core or exterior or about half of all the columns
on one floor failed, that floor would give way. That much was known when
they were built, I think.

this is an assumption of yours. those building were very very tough. infact
strong enough to withstand continuous hurricane winds, earthquakes and
multiple boeing 707 crashes.

Remember that what I said here was in response to man's suggestion that if
point heating of the steel beams were a significant factor in initiating the
collapse of the towers, then we would surely expect that more steel frame
buildings would have suffered total collapse due to fire in the past. My
major point here is that the design of the buildings is in many respects
unique and that they are not easily comparable to other steel frame buildings.
This is not an assumption on my part. This is simple fact.

So to reason, as man did, that other steel frame buildings having very
different construction should have behaved the same way as the towers did in
earlier fires that were caused by quite different mechanisms is simply a
logical error.

Your own statement that the buildings `were very tough' is purely qualitative,
of course. To my knowledge: the towers were designed to survive a
direct hit by a major hurricane, and some level of earthquake, that's correct.

But also, to my knowledge, there is no evidence that `multiple' Boeing 707
crashes were ever even considered during the design, and it sounds unlikely to
me on the face of it. Surely no one would have imagined it very likely that
multiple boeing 707s would ever crash into one tower. How many would
`multiple' be, in any event? Would it be as many as 3 or 4, perhaps?

There is reference made in documents that were kept on record with the
Port Authority of New York to an `impact study' that was done of the crash of
a single Boeing 707 into the towers. There's no specific documentation
of the details of this study that has come to light. The conclusion was that
only local structural damage to the towers, insufficient to cause their total
collapse, would have resulted from the impact.

This conclusion seems to have been borne out by the events on 9/11, since had
the deflection of the buildings from vertical caused by the impact of either
Boeing 767-200 (ER) been sufficient to damage either tower on floors very far
away from the impact zone, then we should have expected both to see some
serious immediate damage at distant points on the towers and probably also to
see a collapse following the impact far more quickly than what occurred.

It is certainly not clear that the combined effects of fire and local damage
were looked into in this study, and it's not clear either what impact
velocities were considered for the 707. So I think your assertion that `they
were strong enough to withstand multiple boeing 707 crashes' is an assertion
without basis in fact.

 

[dpt]

and i think u are wrong to say the core was not enough in itself to
support the building ... infact the core is much more stronger than nits make
it up to be...those 47 massive steel columns were not free standing as nist
stated but connected by trusses and they should have survived the
fall.

What are you suggesting? That the entire weight of the building could still
have been borne by the core if the perimeter tube were suddenly completely
absent?

The core was designed to easily support the static weight of the
building as long as the core columns were true and the horizontal forces on
the columns remained balanced. In this case, a large fraction of the weight
of the building was directed vertically down the core, compressing the core
columns vertically. A significant fraction of the weight was also carried by
the perimeter tube.

Potential horizontal buckling of the core columns was actually a design
concern. There was worry that the elevators, on passing rapidly up and down
through the central core, might cause sufficient buckling of the interior
columns to compromise the structural integrity. The elevator shafts were
specially designed to deal with this worry.

Here's a hypothetical collapse scenario, if the perimeter frame tube were
suddenly totally removed.

[0] The outer edges of all of the floors would move downwards under gravity,
since there would be no remaining external attachment points for the floor
support trusses. The downward fall of the floors would lead to enormous and
unbalanced downward and outward pointing forces at all of the attachment
points of the floor support trusses to the central core.

[1] This would produce huge dynamic bending moments on the core columns, which
would not remain true for long. Core columns, when sufficiently pulled out of
line near the attachment points, assuming these didn't fail first, would fail,
and the core would be gradually torn to pieces. The floors would fall off from
the core, and while some of the core might remain standing at the end of the
process, it would be severely weakened.

there's also no reason to believe the fire alone was hot, strong
and widespread enough to weaken half the core or the columns...infact evidence
suggests there were only a couple of fires that firemen thought were easy to
extinguish with just a couple of lines.

Yet, firemen did not manage to extinguish the fires with just a couple of
lines.

I beg to differ with your assertion that there is no reason to believe the
temperatures were high and the fire was strong. Some engineers studying the
collapse have actually published papers arguing that the fires were hot,
strong, and widespread enough to have eventually caused the collapse all on
their own, even without the major structural damage that it is suggested the
impacts caused.

While the jet fuel was burning, certainly, high fire temperatures could be
reached. Fires are evident externally on more than one floor in each tower.
That is widespread by definition. We can't see all the way into the core, of
course. But that is not grounds to suggest that there weren't strong,
sustained and widespread fires there. It would certainly be expected that
there would be. There was considerable combustible material on the planes and
in the towers. The large amount of empty space in the building design would
have allowed all of the debris to be swept directly in towards the core.

Not necessarily. It would depend on the adequacy of the insulation
of the support members in buildings, and again the nature of loading and
temperatures that occurred in those fires.

again, there's no evidence insulation was not adequate.

Adequate is not the right word. I should have said intact rather than
adequate. The insulation was theoretically adequate to protect major
supporting columns for up to 3 hours in a fire naturally, assuming that it was
intact and no metal was exposed directly to fire. These survival times
were specified in the fire codes applicable at the time of design in 1962,
which originated in 1938. In 1968, the requirements of the code were weakened
by as much as an hour for certain interior structures, and the actual
construction was according to the new code. (See executive summary of NIST
report).

There's good reason to believe that the crashes of the airliners could have
stripped the insulation from various structural support members, exposing
areas of bare steel to possibly high fire temperatures. The insulation on some
structural members had been reduced from 2 inches to 1/2 inch during
construction, it appears.

 

[dpt]

That's not at all clear. In those other buildings the frame presumably
remained well enough insulated. There were no airliner crashes in those
buildings, apart from the one into the Empire State building, and that was
a much smaller, slower plane in a building with a lot of exterior masonry
which the towers lacked.

the crash was not what cause the collapse according to nist/fema..infact it
was not even partly responsible for it.

What?!

Sorry, but I have to wonder whether you have ever actually looked at the NIST
report. What you say here is plainly wrong.

I suggest taking a look at the report right now. Turn to page 175 (it's 229 in
the pdf file) of NIST-NCSTAR1 (Draft). The pdf is available here:

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


Section 8.3 is titled Findings on the Mechanisms of Building Collapse.
I'll quote a bit to make it easy:

The specific factors in the collapse sequences relevant to both
towers (the sequences differ in detail for WTC 1 and WTC 2) are:

Each aircraft damaged exterior columns, damaged interior core columns and
knocked off insulation from steel as the planes penetrated the buildings. The
weight carried by the severed columns was distributed to other columns.

Subsequently fires began to grow and spread. They were initiated by the
aircraft's jet fuel, but were fed for the most part by the building contents
and the air supply resulting from the breached walls and fire-induced window
breakage.

These fires, in combination with the dislodged insulation, were responsible
for a chain of events in which the building core weakened and began losing its
ability to carry loads.

The floors weakened and sagged from the fires, pulling inward on the exterior
columns.

The floor sagging and exposure to high temperatures caused the exterior
columns to bow inward and buckle -- a process that spread across the faces
of the buildings.

Collapse then ensued.

Seven major factors led to the collapses of WTC 1 and WTC 2;

Structural damage from the aircraft impact;

Large amount of jet fuel sprayed into the building interior, that
ignited widespread fires over several floors;

Dislodging of SFRM from structural members due to the aircraft
impact, that enabled rapid heating of the unprotected structural
steel;

Open plan of the impact floors and the breaking of the partition
walls by the impact debris that resulted in increased ventilatio;

Weakened core columns that increased the load on perimeter walls;

Sagging floors that led to pull-in forces on the perimeter columns; and

Bowed perimeter columns that had a reduced capacity to carry loads.

So the NIST theory is certainly that the crashes caused damage to the towers,
as well as fires. It's the combination of these that eventually caused the
collapses. Disbelieve the theory if you want, but the NIST clearly said that
this is how the collapses were initiated, and that the crashes were partly
responsible.

 

[dpt]

It's widely suggested that the fuel burned probably no more than
15-20 minutes. But the fires clearly remained burning for at least 1hr and
thus could have kept the steel at high temperature for some time, although not
perhaps as high as 550 C. But 550 C could have been reached initially. That
initial jolt might just start the failure process.

even if that was the case, and according to firemen it was just a
couple of pockets of fire small enough to be controlled by a couple of lines,
heat couldn't be concentrated since steel disperses heat and the construction
and design of the column facilitated the process.

Steel conducts heat, it's true, but if you keep on heating it at a given point
for long enough you will set up a temperature gradient in the steel, with
highest temperature at the point of heating. It's a question of conduction of
heat versus rate of heating.

I've suggested that the timescale to failure is not easy to
predict, but is a very complicated question, one that depends on the precise
way in which the steel deforms under stress and temperature, and precisely how
and when the steel was heated.

agreed, problem is tho that not only melted steel was found but also
evaporated steel and massive amount of sulfur which presence was deemed weird
and unexplainable by nist....and we know in what cases steel evaporates;
certainly not due to fire.

Melted steel was not definitely found, I think. I have seen pictures of stuff
at ground zero that maybe looks to me possibly like melted
steel, pictures taken on days later than 9/11, but what is the evidence that
this is actually melted structural steel and that it was melted on the first
day? I'm not aware of anything solid to prove this.

That evaporated steel was found in any significant amount is practically
impossible to believe. The boiling point of iron is 2861 °C. I think it would
take very special explosives or possibly electrical arcs to produce
temperatures anything like that high.

What's the actual evidence for the claim about the evaporated steel?

 

[dpt]

Yes. The office materials provided, certainly, a lot more but lower
temperature flame.

I think it depends on what you mean by weaker here.

It seemed pretty clear to me from about one or two days after I had seen the
collapse, that a possible failure mechanism was simply that one story near the
level where the planes hit had failed completely, and that the parts of the
buildings above then fell through one story, impacting onto the parts below. I
and some of my friends made a ballpark calculation of what would happen in
this case, within a day or two of 9/11.

yes and it is much easier to explain it out by the use of
explosives. infact it is perfectly fitting.

So you agree that this collapse mechanism is a possibility.

I agree that explosives would be a possible way of cutting the supports on one
floor.

I disagree that it would be very easy to do without getting caught, and I have
problems understanding how one could know what floor to do the demolition work
on in advance.

After all the buildings collapse starting at those floors where they were hit
by the aircraft. So one would either have to wire up many floors for
demolition, or else tell the pilots almost exactly what floor to steer
towards. And then, take a careful look at the paths that the airliners flew on
before they hit the towers. One of them practically missed the South tower, it
hit travelling on a wild curve, at one corner, and in a steep bank.

It's not too hard to estimate what the dynamic stress would be
produced on the lower part of the building if that ever happened, and it's
very easy to see that it is far in excess of what the building was designed to
take. It was designed to be strong enough to support its static weight and a
bit more, and that's all.

hmm...would not be hard? dont think it is a straight case as u make
it up to be.

Well, OK. You might think that it's harder than I say.

But anyway you agree above that this is a possibility.

I'm simply telling you that I actually have done this calculation for
myself, and I'm also saying that it was not that hard for me to estimate what
the dynamic stress would be in the best possible case for the chance of
building survival (perfectly symmetric and uniform fall of the upper stories
onto the lower stories).

The only really difficult part was to know how stiff the structural steel is,
and how much energy bending it might absorb, and to figure out how to model
how the building's floors would respond when the upper part fell downwards and
impacted on the bottom: what it's elastic properties are and so on.

Structural engineers know that sort of thing really well, physicists don't

I'm a reasonably good physicist, and I was able to think of a simple
model (actually more than one) in which I could estimate the numbers by
hand. It would be hard if one didn't know any physics.

I would be happy to provide more detail on what I did if you don't believe
this, but it turns out that some structural engineers who looked at the
question came up with basically the same ideas as I did. The idea
was actually published only very shortly after 9/11.

So the structure it seems to me could have been about as strong as it was
expected (was designed) to be, and still have failed, if something like
half of the supporting beams were cut on any one floor.

So it was weak enough to fail in this manner. Now I frankly don't know
whether this was understood before 9/11. But I think there are no steel
frame buildings that possibly could survive an event in which a
sufficiently large part of the top of the building fell onto the bottom.

that's another assumption.

No, it's not exactly an assumption. It's a prediction, based on my ballpark
calculation, done using known properties of the buildings ... mass density,
elastic properties of the steel, height, size of the stories, etcetera, and a
couple of alternative basic models for the impact of the top of the tower on
the bottom of the tower.

Structural engineers have basically agreed with what I found in published
papers on this question. I certainly wasn't the only one who came to this
conclusion shortly after 9/11, not by any means.

 

[dpt]

as i said the towers were built to withstand multiple jet airliners crashes
and continuous battering of hurricane winds. not sure my self about fire and
heat, but we have an example with madrid bldg that survived intact a fierce
fire spreading throughout the whole structure/floors and lasting for an entire
day...maybe even more.

Multiple jet airliners: I don't think these were ever considered.
Hurricanes, definitely yes.

The Madrid building did actually partly collapse, but it's true there was no
total collapse, there. But the Madrid building is a much more standard design
... there are many more structural columns per unit area of space on the
floors, and there is also much less open space on the floors. In addition,
there was no airliner crash in Madrid, so the insulation on the beams may well
have been in much better condition.

So the conditions of no more than minor structural damage and
intact fire insulation, as it seems to me, could well have been violated in
the collapse of towers 1 and 2, due to the impact damage caused over several
stories, combined with the fires.

the impact damage has nothing to do with the weakening of the
towers and subsequent collapse according to nist.

That's not true, as you can see in the NIST report itself, referenced and
quoted above.

the problem here is the nature of the collapse; sudden and sharing
all the element of a controlled demolition. what int boils down to is that it
can be very easily explained by cutter charges and other explosives present in
the building and extremely difficult if not impossible to attribute it to a
simple fire.

I don't see things the way you do.

While I definitely agree with you that a relatively small number of cutter
charges could have done the job, due to the inherent dynamical instability of
the towers, I think that it's very hard to understand how this could be
carried off in reality, without leaving a single trace, and without being
discovered.

Thanks very much for the links you provided, I
will read more of them when I get more time.

Cheers and good trading to you! Thanks also
the effort put into your response.

I'll respond to man later on.

 

[version77]

Quote from man:

thnx. good that we both end it before we waste time of both of
us. truly appreciate it.
take care.

Cool. And thanks to you also man. Have a good trading day...

 

[wdscott]

NIST Reports, What expert findings?, Theories of collapse?

All the metal debris of WTC1 and WTC2 and WTC7 was gathered, loaded onto cargo containers, and shipped to another country (possible China) for scrap.

I guess without the ability to analyze the metals structural integrity, we will never know what caused the buildings to collapse.

How can one write a theory, or conclude a finding, or make any opinion at all about those buildings. The evidence is gone.

WD