Consensus on WTC collapse?
Chris
why the WTCs collapsed, or is there insufficient evidence to work
with? The general view propograted by the media, as far as I can
gather, is that the initial jet impacts were not necessarily fatal,
but that fires effectively turned the steel trusses into 'licorice',
as described by University of Sydney civil engineering dept:
"However, as fire raged in the upper floors, the heat would have been
gradually affecting the behaviour of the remaining material. As the
planes had only recently taken off, the fire would have been initially
fuelled by large volumes of jet fuel, creating potentially enormously
high temperatures. The strength of the steel drops markedly with
prolonged exposure to fire, while the elastic modulus of the steel
reduces (stiffness drops), increasing deflections."
(see http://www.civil.usyd.edu.au/wtc.htm)
As a scientist but non-engineer, I have several questions about the
plausability of this theory that I would be interested to hear expert
opinions on. For instance:
1. Were the heat and duration of the fire sufficient to sustain to
this outcome?
- I have read claims that they were not, for instance see
http://serendipity.magnet.ch/wtc.html
The author of this web-site doubts the veracity of this claim, and
suggests instead that the towers were imploded from within using
explosives:
"Firstly, much, or perhaps most, of the jet fuel was consumed in the
fireballs which erupted when the planes hit the towers. Furthermore,
it is likely that the jet fuel which managed to enter the towers would
have burnt fairly quickly (jet fuel does not burn slowly like wood).
And finally there were sprinkler systems in place in the towers, and
it can be surmised that these would have hindered the spread of the
fire (by soaking combustible material) even if they had no effect on
the burning jet fuel itself. The Twin Towers were giving off a lot of
black sooty smoke, but there was little fire visible. But to melt
steel you need the high temperature produced by, e.g., an
oxy-acetylene torch. Jet fuel burning in air (especially in an
enclosed space within a building, where there is much smoke and little
available oxygen) just won't do it. And if the steel columns had
melted, would this have produced the implosive collapse observed? If
the columns had melted like toffee they would have bent (not snapped),
causing the upper parts of the towers to buckle and tip to one side
(probably the side where the planes hit). This did not happen. These
considerations (and others, given below, concerning the probable
maximum temperature of the fire) show that the claim that tens of
thousands of liters of burning jet fuel produced a raging inferno and
caused the steel columns to melt is extremely dubious, and does not
account for the collapse of the towers "
any comments on this?
2. Why did the south tower collapse first, when the north tower was
hit first and appeared to receive a more direct impact?
3. How credible is the theory that explosives were used to implode the
buildings in a controlled demolition?
4. Is there any evidence against the explosives theory?
5. How is it explained that the fires appeared to go out (as least
visibly) quite soon after the impacts, yet the steel infrastructure
continued to be weakened by fire?
many thanks
Chris
Brian Whatcott
and the depth of informed comment was not extensive - there was more
than one suggestion that we just wait for the experts to give us an
analysis ( while such experts as were interested, were hindered by the
disposal of damaged structure, and legal impediments asserted by
the NYPA).
The most telling proposition that I read, had it that an accumulation
of debris on one or two floors broke the connections to the exterior
curtain, and a one story fall of such an overloaded floor inevitably
cascaded on all the floors beneath. The connectors provided the
centripetal force at each level as they failed.
This was apparently a well known failure mode of steel structures of
an older curtain wall type (as opposed to the very durable column and
beam design which disperses the frame throughout the body of an
industrial style structure.)
You may take it that the idea of a massive collapse due to chemical
explosives is at about the same level of credibility (at least to my
mind) as the new conspiracy theory that the Pentagon was not in fact
impacted by an airplane, but by a truck carrying explosives. This
latter composition being based on three observations available from
public photographs:
1) A track of gravel was soon filling the lawn exterior of the impact
site
2) the clear aperture in the exterior wall had a smaller cross section
than the undamaged crosssection of the aircraft involved.
3) Recognizable, major pieces of airplane were not seen at the impact
site.
It is praiseworthy to want to make up one's own mind from the evidence
at hand. It is another thing to have enough background to reasonably
interpret accident data in a sensible way.
Brian W
On 24 Mar 2002 16:40:08 -0800, c.cha...@psych.unimelb.edu.au (Chris)
wrote:
Brian Whatcott
Altus, OK
Eureka!
Bob Morrison
> The most telling proposition that I read, had it that an accumulation
> of debris on one or two floors broke the connections to the exterior
> curtain, and a one story fall of such an overloaded floor inevitably
This the one of the best summaries of the failure mode with the
exception that the steel frame was in a weakened condition due to the
intense heat of the fire. Any possible overload capacity (redundancy)
in the system was negated by the fire.
> This was apparently a well known failure mode of steel structures of
> an older curtain wall type (as opposed to the very durable column and
> beam design which disperses the frame throughout the body of an
> industrial style structure.)
The particular curtain wall used in the WTC probably delayed the
collapse. The number and spacing of the exterior columns caused the
curtain wall to act a Vierendeel truss spanning the impact opening. In
a conventional frame structure with the same open floor plan (no
interior columns except at the center core) the collapse would have been
immediate because all one would have needed to do was take out one or
two of the building's exterior columns.
--
Bob Morrison
R L Morrison Engineering Co
Structural and Civil Engineering
Poulsbo WA
Carson Morrison
that the structural steel is being sold for scrap without being
subjected to forensic analysis. There was an article about this by
Bill Manning in the January issue of Fire Engineering magazine. After
enduring a free sign-up, you can read the article at
The article is hightly critical of the investigation run by the ASCE,
calling it "a half-baked farce that may already have been commandeered
by political forces whose primary interests, to put it mildly, lie far
afield of full disclosure." The second half of the article entertains
the theory that:
The structural damage from the planes and the explosive
ignition of jet fuel in themselves were not enough to bring
down the towers. Rather, theory has it, the subsequent
contents fires attacking the questionably fireproofed
lightweight trusses and load-bearing columns directly caused
the collapses in an alarmingly short time. Of course, in light
of there being no real evidence thus far produced, this could
remain just unexplored theory.
This theory is explored in greater detail in Kingsley Hammet's
interview with San Francisco architect Jim Malott in the
November/December issue of Designer/Builder magazine. An excerpt
reads:
"Prior to the advent of the World Trade Center towers, high-rise
buildings shared two vital characteristics. They were supported by a
grid of steel columns, generally spaced about thirty feet apart, and
each interior column was encased in a tough cladding of concrete to
create a fireproof skin designed to withstand a four-hour inferno.
(The four-hour fire rating is the code rule for the columns and major
beams in any large building.) As designed by architect Minoru
Yamasaki, New York's Twin Towers incorporated neither of these
traditional features. And as far as Malott is concerned, it was the
failure of their substitutes - not the initial crash, not the
exploding jet fuel, and not the subsequent fire alone -that lead to
their collapse and the enormous loss of life . . .
"As Malott watched the tragedy unfold, he surmised that the sequence
of events went something like this. when the planes slammed into the
exterior of the buildings, the fuselages and engines broke through a
number of the outside columns while the wings disintegrated as though
being forced through a cheese grater. The bodies of the planes crashed
across the unobstructed floors, smashed into the central cores of the
buildings, and blew the sheetrock off the supporting columns and from
around the stairwells, completely destroying the elevator shaft wails.
Thus, in the first seconds, the four-hour-rated fireproofing was
stripped from the steel core structures and with it went all hope that
the buildings could survive a fire.
"After an hour of this inferno, the now-naked steel columns of the
central core at the impact floors were heated to about 1,600 degrees,
which is the point at which steel loses almost all of its structural
strength. The relatively skimpy floor system, with hung sheetrock,
small-diameter steel bar joists, and the thin layer of concrete,
offered little barrier to the raging flames despite having been rated
as fire-resistant for four hours. Three floors may have collapsed
within the impact area, further tearing fireproofing away from the
core columns. Once the first couple of core columns began to buckle,
Malott speculates, they threw all of their load not onto a neighboring
ring of strong columns protected with fireproofing (which in this
design did not exist), but onto the adjacent columns in the exposed
core, which were similarly denuded of fireproofing by the initial
impact and also were failing under the intense heat. 'The outside of
the building did not fail. It did not get hot enough,' Malott says.
'It was the core that failed.'
"It's time now to go back and rethink the entire concept of the
high-rise structural system, Malott says. Buildings such as the World
Trade Center towers cannot be built to minimum code specifications And
architects must now truly consider the impact of a fully loaded
aircraft or other impact/explosion/fire combination striking another
tower. Future high-rise buildings must be designed with a redundant
system of interior support columns so no failure of any critical part
- be it the core, the skin, or the floor -leads to the catastrophic
collapse of the entire building . . . Ever since the World Trade
Center became the global icon of capitalism, most high-rise buildings
in America have followed its lead and wrapped their steel columns in
some combination of mineral wool and gypsum board rather than
concrete, leaving them susceptible to potentially devastating pancake
failure not in four hours, for which they are theoretically fire
rated, but in less than an hour . . .
"It's interesting to note that while the enormous bomb that exploded
in the parking garage of the World Trade Center in 1993 killed six
people, injured almost 1,000, caused a massive fuel fire, and
collapsed two garage floors, it did relatively little structural
damage to the tower because the basement columns were encased in
concrete . .
[end quotation]
Actually, I've just found a webpage that archives these two articles
and some similar comments from elsewhere. The link is:
Chris
magazine, Bill Manning stops about a whisker short of accusing the
government of some kind of cover-up, or at least a deliberate
obstruction. By keeping the standard of evidence to work with vague,
they could be trying to prevent law suits that might arise if the
fire-theory was confirmed and the building was deemed to have failed
to meet its safety requirements. All this does is feed the fire of
conspiracy theories and gets us no closer to the truth. For whatever
reason, it doesn't look like the evidence will be open to independent
scientific analysis.
I wonder if there is a policy for what proportion of wreckage in these
incidents is put aside for investigation, and what proportion is
immediately sold off. I once read somewhere that the Oklahoma bombing
wreckage ended getting buried somewhere.
Chris
Bob Stahl
<....>
> 3. How credible is the theory that explosives were used to
> implode the buildings in a controlled demolition?
>
> 4. Is there any evidence against the explosives theory?
Good grief.
May we ask whether you are writing a paper or article on this?
--
Bob Stahl
Carson Morrison
Times, which published a story on the report this morning. In broad
outlines, the report seems to support the fire theory advanced in the
sources I posted earlier, and pays some attention to the role of the
easily-dislodged spray-on fireproofing. However, according to the
story, "little evidence collected from the piles of debris contributed
in a meaningful way to the report's conclusions." After yet another
free sign-up, you can read the entire story online at:
Chris
and you would think that because....?
Matt
c.cha...@psych.unimelb.edu.au (Chris) wrote:
> As a scientist but non-engineer, I have several questions about the
> plausability of this theory that I would be interested to hear expert
> opinions on. For instance:
I am neither a scientist nor an enginneer and have absolutely no
qualification to speak on this matter. But hey, I'm interested, and
this is Usenet after all...
> 1. Were the heat and duration of the fire sufficient to sustain to
> this outcome?
> - I have read claims that they were not, for instance see
> http://serendipity.magnet.ch/wtc.html
>
> The author of this web-site doubts the veracity of this claim, and
> suggests instead that the towers were imploded from within using
> explosives:
>
> "Firstly, much, or perhaps most, of the jet fuel was consumed in the
> fireballs which erupted when the planes hit the towers.
According to the summary of the federal report in the NY Times, only
about a third was consumed in the fireball. The rest spilled into the
building and outside.
> Furthermore,
> it is likely that the jet fuel which managed to enter the towers would
> have burnt fairly quickly (jet fuel does not burn slowly like wood).
> And finally there were sprinkler systems in place in the towers, and
> it can be surmised that these would have hindered the spread of the
> fire (by soaking combustible material) even if they had no effect on
> the burning jet fuel itself.
No it can't be surmised. It's a safe bet that the crashes destroyed
many sprinklers in the immediate area, and since the planes damaged the
cores as well, it's likely supply lines to the sprinklers were destroyed.
Furthermore, the author of this page appears to be a layman, as opposed
to someone qualified to speak about fires. I don't mean to make an
appeal to authority, but I think speculations as detailed as the rate
jet fuel would burn, and how effective any working sprinklers would have
been in preventing the spread of the fire, surely require some
qualification. And even an expert might not be able to surmise anything
without more evidence.
> The Twin Towers were giving off a lot of
> black sooty smoke, but there was little fire visible. But to melt
> steel you need the high temperature produced by, e.g., an
> oxy-acetylene torch. Jet fuel burning in air (especially in an
> enclosed space within a building, where there is much smoke and little
> available oxygen) just won't do it.
Many windows broke and there were gaping holes pierced in the sides of
the buildings. I imagine that would provide a plentiful source of
oxygen.
Furthermore, it may not have been necessary to actually melt the steel.
Raising the temperature enough to soften it could have caused beams to
sag, collapsing floors, or columns to buckle sooner than they otherwise
might have.
> And if the steel columns had
> melted, would this have produced the implosive collapse observed? If
> the columns had melted like toffee they would have bent (not snapped),
> causing the upper parts of the towers to buckle and tip to one side
> (probably the side where the planes hit). This did not happen.
It happened on the south tower, which I believe collapsed to the
southeast, the same corner on which the plane struck.
Also, there's no logical reason to suppose bending columns would
necessarily cause the tower to collapse to one side. They could just as
well "cave in" after losing their strength, causing the building to fall
in on itself. This is what seems to have happened, though it still an
open question as to whether the floors broke loose and pulled the
columns down with them or whether the core columns gave way, removing
support from the floors.
> These
> considerations (and others, given below, concerning the probable
> maximum temperature of the fire) show that the claim that tens of
> thousands of liters of burning jet fuel produced a raging inferno and
> caused the steel columns to melt is extremely dubious, and does not
> account for the collapse of the towers "
>
> any comments on this?
His reasoning does not seem particularly astute or qualified in regards
to the fires; I have a hard time accepting his assertions over those of
structural engineers who have been studying the question. If you look
at the rest of the page, it is obvious that he is a complete wacko; for
example, consider his suggestion that Larry Silverstein, who leased the
WTC from the Port Authority, is part of some Jewish conspiracy to bomb
the towers to drum up American support for Israel.
> 2. Why did the south tower collapse first, when the north tower was
> hit first and appeared to receive a more direct impact?
Three factors to consider:
1. Relatively new information indicates the plane that hit the south
tower was going around 100 mph faster than the other one (500+ mph vs
400+ mph). Recall that kinetic energy increases with the square of
speed, so a 100mph difference in speed could make a considerable
difference in the amount of energy suddenly imposed upon the building.
2. The second plane hit lower, so presumably there was more weight being
exerted on the surviving columns on the level the plane hit. That could
contribute to columns buckling faster.
3. The second plane hit the corner of the tower, and during the collapse
the building tilted over in the direction it was hit. This is my
speculation, but such a lopsided hit may have hindered the building's
ability to redistribute the load among surviving columns.
> 3. How credible is the theory that explosives were used to implode the
> buildings in a controlled demolition?
Not very credible, in my opinion. It seems superficially plausible, but
once you read up on how the structure worked, a pancake collapse
resulting from failures of several floors is plausible.
The plane crash attack plan was creative, simple, and elegant. The
terrorists exploited a vulnerabilty they found in commercial air
security. Adding explosives to the equation makes things operationally
far more complicated and risky. And it would be difficult to determine
how powerful a blast you need to collapse the buildings, because no one
could know in advance how much damage the planes would cause. A
controlled demolition involves strategically placed charges, but there
is no certainty of where the planes would strike; these were after all
ametaur pilots, and the United plane nearly missed the south tower. So
the best place to put the charges could vary with where the planes hit
and how much damage they do. There is even a risk the crash could
disable the bombs.
In short, if terrorists had the liberty to place bombs in the building
strong enough to cause major structural damage, they would not have
bothered with the planes. Maybe the planes were just a "diversion" but
at this point we're just squeezing the facts to fit the theory rather
than building the theory from the facts.
> 4. Is there any evidence against the explosives theory?
A better question: is there any evidence FOR it?
> 5. How is it explained that the fires appeared to go out (as least
> visibly) quite soon after the impacts, yet the steel infrastructure
> continued to be weakened by fire?
Where there's smoke, there's fire. That's my uneducated guess, but it's
no more a guess than the claim that there were no fires because flames
were not visibly billowing out of the towers. From the pictures I saw,
in some places there were flames coming out of the towers, and smoke
billowed from multiple floors, even on floors higher than the impact
zones, suggesting there was a lot of fire in the building even if it was
not all burning at along the facade.