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Posted by RicodJour on April 24, 2006, 1:42 pm
Osiris88 wrote:
>
> I have heard some say that World Trade #7 collapsed "at the speed of
> gravity" as opposed to having floor after floor pancake on themselves,
> which I gather would be slower. Is that correct?
Once the floors start pancaking down, do you expect the next floor down
to have a longer elapsed time to failure or shorter? Shorter of
course. The perceivable change in acceleration, or slowing down of
gravity forces due to resistance of the building's structure, is hardly
something someone can look at and say, "Yep, that sure looks like
around 10 meters/second^2."
R
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Posted by Frankendrip on April 24, 2006, 5:16 pm
"RicodJour"
> Osiris88 wrote:
>>
>> I have heard some say that World Trade #7 collapsed "at the speed of
>> gravity" as opposed to having floor after floor pancake on themselves,
>> which I gather would be slower. Is that correct?
>
> Once the floors start pancaking down, do you expect the next floor down
> to have a longer elapsed time to failure or shorter? Shorter of
> course.
Unless there was greater and greater structural support at each consecutive
floor below, which is not to necessarily say that this is or was the case.
> The perceivable change in acceleration, or slowing down of
> gravity forces due to resistance of the building's structure, is hardly
> something someone can look at and say, "Yep, that sure looks like
> around 10 meters/second^2."
Yes, there should be natural chaotic variability to mess with predicability,
so I think pancaking buildings won't fall according to gravity alone.
There'll be issues of syrup-consistency, which can often be correlated to
its temperature and sugar content for example, as well as how much butter
there is, how light and fluffy each cake is, and maybe even the angle at
which the cook whacks the stack, and what he uses to do so, etc..
And speaking of stack-whacks, here's a little tune/video:
http://www.sfu.ca/~rmacinty/wing.mp4
--Wing of The Plane, by Severed Heads
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Posted by on April 25, 2006, 1:55 pm
Osiris88 wrote:
> Before anybody bashes me, I am not a conspiracy nut. I was talking to
> a friend the other night and we discussed this. I would like your
> input and expertise, thanks.
>
> I have heard some say that World Trade #7 collapsed "at the speed of
> gravity" as opposed to having floor after floor pancake on themselves,
> which I gather would be slower. Is that correct?
>
> I am not an architect or an engineer, so I was hoping that maybe some
> folks here could illuminate the subject. My point of view, as a
> layman, is that the building would not collapse so perfectly because of
> debris from the twin towers. Am I correct or is there a possible
> explanation that architecture people might be able to describe? Or
> other?
>
> If this has been covered before then I apologize, but I would really
> like to learn more about this. Thank you for your time in educating
> me.
See
http://wtc.nist.gov/pubs/WTC%20Part%20IIC%20-%20WTC%207%20Collapse%20Final.pdf
for a general overview of how WTC 7 collapsed.
It doesn't really make sense to distinguish between floor pancaking and
global collapse, as buildings are not monolithic structures, but
structures made up of separate of parts (columns, beams, struts,
floors, cladding, etc.) Depending on the design, failure of any of the
critical structural parts can cause partial collapse, partial
pancaking, global collapse, global pancaking, or nothing at all.
WTC 7 was a particularly unique example because unlike the vast
majority of other buildings, this building had a structural system that
transferred load from the new building system to an existing structural
grid of a prior building. See the above document. Just from the line
drawings you should be able to grasp that WTC 7 had some particularly
critical columns, unlike most other skyscrapers where there is some
structural redundancy.
As for a 'neat collapse', most buildings will little structural
redundancy, particularly in the center core, will collapse onto their
own footprint. given the nature of their component construction. Large
buildings don't act like trees.
Marcello
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Posted by Pierre Levesque, AIA on April 25, 2006, 10:13 pm
> "Pierre Levesque, AIA"> wrote
>> "Don"> wrote
>>> So, 2 pressurized 6000 gallon diesel fuel tanks on the 5th floor caused
>>> the blaze that caused column 79 first then columns 80 and 81 to fold
>>> like stepladders, correct? What caused the tanks to ignite?
>>
>> Ummm, ftom the heat generated from the collapse of WTC 1 a mere 60 feet
>> away??? That's right, 60 away feet from a building that was 1368 feet
>> tall...
>
> Not to pick nits here or argue, I'm just asking.
> Diesel doesn't ignite, it does its damndest to NOT ignite.
> Wasn't the fire up on the 80th floor or some such, roughly 800' away from
> the diesel tanks?
> I'll assume that the jet fuel that poured down through the building(s)
> brought flames with them as well, which then brought the heat to Bldg 7?
> I'll also assume that the diesel tanks were not right up against the wall
> closest to the burning tower (60' away).
> That brings me to wondering how a fuel that is pretty non-ignitable,
> inside steel tanks, could be brought to ignition by a heat source 60+ feet
> away?
>
The other fires were likely electrical fires or fires caused by the extreme
heat of the tower 1 collapse. As you say, the final reports don't conclude
that the diesel fuel fire made any difference if it was even burning when
the global collapse occured.
> Can I also assume that when column 79 buckled (stacked dominos), it then
> caused the corner of the penthouse to drop, which was the catalyst, ala
> pancake, for the rest of the building 7 collapse?
Yes, that's the likely major cause along with all the other weaknesses
caused by the other fires... the structural collapse occured just as the
tower 2 collapse happened. Extreme heat from the fires weakened major
structural components. Also recall that the vibrations caused by the tower
1 collapse could understandably have loosened fireproffing and maybe even
some structural connections.
here's another interesting report with really good structural analysis:
http://tinyurl.com/4gabz
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Posted by on April 25, 2006, 11:04 pm
Pierre Levesque, AIA wrote:
>
> > Can I also assume that when column 79 buckled (stacked dominos), it then
> > caused the corner of the penthouse to drop, which was the catalyst, ala
> > pancake, for the rest of the building 7 collapse?
> Yes, that's the likely major cause along with all the other weaknesses
> caused by the other fires... the structural collapse occured just as the
> tower 2 collapse happened.
??? If I recall WTC 7 collapsed 6-7 hours after both Twin Towers had
come down, like 4 or 5 in the afternoon.
Reading the final reports of WTC 1 and 2 is very illuminating, and also
depressing. Some rather astonishing details.
Marcello
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