Questions About the Pancake Theory for the WTC North Tower Collapse

[spooked911]

Does the official pancake collapse model say that the floors collapsed and cascaded down from around the core structure, and that the core initially stayed intact? This could make some sense, although the progressive collapse should have stopped at floors 75 and 76 where there were solid beams holding the floors instead of trusses. The other problem is that in videos and photos, we see no signs at all of the core staying intact as the initial floors fall down. Rather there is just an incredibly violent disintegration of the top thirteen floors and a rapid downward explosive global collapse.

Or, does the official pancake collapse model say that the floors collapsed and cascaded down from around the core structure, and that this brought down the core structure at the same time? I think this would have to be the model to account for the video and photographic evidence, but it absolutely makes no sense that the incredibly strong WTC core would collapse from the floor plates that surrounded it falling down.

Certainly, it is ludicrous to think that on floor 97, where the collapse started, that the core columns and exterior columns ALL failed exactly at that same time, initiating a rapid high energy collapse. Rather, damaged columns and fire weakened columns would give way slowly and there would be a drooping, not a sudden fall.

So--anyone care to explain exactly how a pancake collapse of one floor started the total global collapse of WTC1?

[AZCat]

1. Why is it ludicrous?

I find it quite the opposite. Perhaps an explanation is in order.

A few definitions
stress: The force applied to a material divided by the area over which it is applied. For beams (columns) the area used is generally the original cross-sectional area. Stress has units like pounds (force) per square foot (area) or "psi" in Imperial units and newtons (force) per square meter (area) or "Pascals".

strain: The normalized change in a dimension of a member (length, for example), or (new dimension - old dimension)/old dimension. Strain is unitless but often can be seen labelled as inches per inch or something like that. This is basically a measure of how much a beam is stretching (under tension) or squishing (under compression).

A quick assumption
The weight held by the remaining structural members didn't change (much) during their failure, so we can treat it as a constant.


In materials science, there is something known as "Young's Modulus", or the "Modulus of Elasticity". This is the number that, for particular kinds of materials, defines a quasi-linear relationship between stress and strain. In other words, if you know how much force is being applied to a beam, you can figure out the change in length.

This quasi-linear relationship only lasts over a certain range of stresses, because the material begins to undergo some changes that affect how it reacts to stress. An example "stress-strain curve" can be seen at the wikipedia. Notice the initial linear region and how it tails off until the point labelled "Fracture". The maximum stress doesn't always occur at that point, but it does in this graph.

That maximum stress point is what we are concerned with. If we assume that the cross sections of the structural members in the WTC don't change during failure, then the stress applied to those members is dependent only on the weight carried by each member.

If structural members begin to fail they no longer can carry the weight they previously did, and that weight is shifted to other members increasing the stress on each of them. If a large number of the members are already loaded close to their ultimate strengths then failure of a few members can cause a cascade of failures, and it can occur very rapidly. In fact, the speed of the failures feeds itself because the strain of the members causes heat buildup within the member itself, and under the appropriate conditions it can be adiabatic and can cause "strain hardening" in the member, particularly around stress risers.


If you have any questions please don't hesitate to ask. I may not have explained everything clearly.

[pox americana]

2. Translation: because the TeeVee tells me so.

That's not particularly charitable but you didn't address the topic and my question is, which program did you watch?

[AZCat]

4. I have absolutely no idea what you mean.

Are you sure you responded to the correct post?

[pox americana]

6. Come on now, confess.

You watched the Nova and/or National Geographic 9/11 programs, didn't you?

[AZCat]

7. Actually...

I don't have a TV, so no - I did not watch the Nova and/or National Geographic 9/11 programs.

[pox americana]

8. Well don't be the last on your block to get one.

So you didn't see the WTC collapses on 9/11?

[AZCat]

9. That I did see.

I was house-sitting for some friends who, strangely enough, were scheduled to fly back home that Tuesday from New York. After I heard about the first plane from a neighbor (he asked about my friends) I watched tv continuously until I had to leave for class. I saw both towers collapse that morning.

[pox americana]

11. Okay then think carefully about what you saw.

I'm guessing that some engineering professor explained the whole picture for you according to NIST gospel (maybe it was even Leslie Robertson, who travels the land preaching the official word), but keep in mind that learned professors taught that the world was flat for the first 1500 years of this era.

[AZCat]

12. I don't know who Leslie Robertson is.

When I began discussing the collapses with professors of engineering it was well before the NIST began its investigation, so I don't see how the "NIST gospel" would have had an impact (since it wasn't written yet).

[pox americana]

13. He was a lead WTC structural engineer, now a Princeton professor.

Here's an article on a lecture he gave last night at Notre Dame:

World Trade Center Engineer Speaks
By Bridget Keating
The Observer
Published: Thursday, September 22, 2005

Students and faculty filled the auditorium of Bond Hall Wednesday for a lecture by Leslie Robertson, the lead structural engineer for the World Trade Center Towers and president and founder of the engineering firm Leslie E. Robertson Associates. . . . Robertson, a current Princeton professor, captivated the audience with information about innovations in structural engineering, his current projects and the future of the industry.

<snip>

At age 32 and with his tallest project at 22 stories, Robertson became the lead structural engineer for the World Trade Center, whose towers reached 110 stories each.

He describes them as "strong, robust, redundant and light." He explained that the towers were designed to resist the accidental impact of a Boeing 707. The impacts of the Boeing 767s, commandeered by the terrorists on Sept. 11, 2001, even though larger and flying much faster than 707s, were unable to bring down the towers.

It was the ensuing fire fueled by thousands of gallons of jet fuel that was too much for the fire-resistive systems, he explained.

http://www.ndsmcobserver.com/media/paper660/news/2005/09/22/News/World.Trade.Center.Engineer.Speaks-994609.shtml

[AZCat]

14. Now that you mention it...

I think I have read articles containing quotes from him. I just didn't recognise the name. I don't know if he's been to my kneck of the woods to give a lecture.

[petgoat]

20. The NOVA program may be available on DVD in a library near you,

AZCat. When you watch it keep in mind that the animations of the
"zipper" truss failure are extremely dishonest because they omit the
lateral trusses that join all the floor trusses together. Note also how
the graphics minimize the robust nature of the core structure.

Remember while watching it that while the "zipper" theory supposes that
the trusses are anchored to the perimeter columns by very weak "clips",
the NIST hypothesis is that the trusses were so strongly anchored that
sagging floors were able to buckle the perimeter columns.

Take special note of the testimony of Brian Clarke. He walked down
from the South Tower right through the fire zone. He said he saw some
flames, but no blazing inferno. He stopped around the 30th floor to
make some phone calls and then walked away down the street. When his
friend said the tower might fall, Clarke said "No way. Those are
steel-framed structures."

[AZCat]

26. Again - no tv. n/t

[spooked911]

3. I understand what you are saying, but even you are saying that the columns

could not have failed all at once-- rather there would be shifting of strain, some elasiticty and plasticity to the columns but eventually they succumb to the strain. Which is what I was saying. It is ludicrous that all the columns would give way at the same time

But since you seem to undewrstand the collapse so well, perhaps you could explain to me the following:

1) when floor 97 collapsed, how many columns were weakened by the fire? Where were they?

2) Did the floor come detached from its bracings before or after the column failure, or did it stay attached to the core and outer columns during the collapse?

3) why did the floor collapse occur symmetrically and why wasn't there a partial collapse on one side first?

[AZCat]

5. Perhaps I wasn't clear

Yes, you are technically correct - the failures would not have happened at the same time - but under rapidly increasing loads the columns would have failed quickly in succession.

I tried to make it clear that I wasn't explaining the whole collapse sequence. I perceived a misunderstanding of the mechanics of failure and I tried to share a little knowledge.

[spooked911]

10. Again, can anyone explain how a pancake collapse of one floor started the

total global collapse of WTC1?

[vincent_vega_lives]

15. It's the difference between a mass at rest vs at motion

take a brick, place it gently on your head, you skull does a nice job of supporting it (if you can balance it).

Now take same brick, and drop it on your head from a height of say... 12 feet.

I think you will notice a slight difference.

The point is the mass of the building above the point of collapse obtains sooooo much more "weight" when it is in motion than when it is at rest, it makes supporting it a practical impossibility, and that repeates itself almost all the way down to the ground. I say almost because mass is lost (thru dispersion) during the process. That's how those firefighters survived on the lower floors.

Before you start mentioning examples of 4 or 5 story brick & mortar buildings collapsing only one story duing an earthquake, don't because you are committing a relational fallacy. The strength to weight ratio is much greater in the smaller structure. The same way you can take a toy metal car and drop it from 12' and it will sustain little or no damage. Take a real car and drop it from same height and, well, I think it may not fair quite as well.

[spooked911]

16. You are not answering the question. I asked how the pancake collapse

started and if the core went with the first floor or collapsed after the first several floors collapsed. If the former, how did that happen? If the latter, why didn't we see the core projecting out from around the collapse early on?

[vincent_vega_lives]

17. I take it then you don't disagree with anything I posted?

That's a start.

How did the collapse start? I guess you can't research this yourself?

Core columns were compromised by the aircraft impact damage and then the fire. Sagging floor trusses caused the exterior walls to bow inward as much as 55" in some places.

Projecting out from the collapse? Not clear how you think that would happen.

[spooked911]

18. What is there to disagree with in your post #15? That is common sense.

But I have asked a specific question about the pancake colapse that no one seems willing or able to answer. Once again-- when did the core start collapsing and how did it start? I know the NIST doesn't talk about this, as far as I have been able to tell. They just talk about a couple of floors collapsing and assume that it will induce a global collapse.

[vincent_vega_lives]

19. Why wouldn't it cause the building to collapse?

No such thing as "global collapse". It is sequential BTW..."chain reaction" if you will.

[spooked911]

21. still not interested in answering the question, I see.

[vincent_vega_lives]

22. Its been answered over and over

But what's the point, everytime I post something you have no answer for, you just ignore it, and pretend it never existed.

[pox americana]

24. No, this question has not been answered.

You probably think it has because you're certain that the federal government is working hard to make us safer. Have another pancake.

[spooked911]

25. Once more with feeling: HOW DID THE CORE COLLAPSE EARLY ON?

That is all I have wanted to know and this is what you and LARED and others never can seem to answer.

[vincent_vega_lives]

30. How couldn't it?

All the information I have seen leads me to believe that the damage caused by the aircraft + the removal of the fireproofing + the fires = collapse of the towers. One or even two of any combination of the three most likely would NOT have resulted in the towers collapsing.

BTW The core was not some stand-alone separate structure, it was part of a structural system that included the truss system and perimeter columns.

[spooked911]

35. Don't you have any more details than that?

Question-- do you think the core columns failed evenly or more on one side?

[vincent_vega_lives]

37. Initial

On the side struck by the aircraft, then a very rapid sequential failure throughout.

All the detail you need can be obtained from the primary source..the NIST report.

[spooked911]

39. They have no details on how the progressive collapse proceeded past the

first floor failure.

Here's an experiment you can try--

Fill a large steel pot with a few bricks so it weighs twenty pounds or so, then put it on a grill composed of two hundred wires from wire coat hangers. Have 160 of the wires on the outside but have 40 wires on the interior also supporting the grill. Put a wire and asbestos pad on top of the wires to act as a floor. Now, cut twenty of the outside wires on one side, ten on the inside on the same side and build a pyre out of sticks and newspaper under the pot, soak it with some kerosene then light it. Now see what happens.

Will the pot--

a) suddenly fall stright down as the all wires heat up, weaken and give way at once?

b) will some of the wires weaken and the grill and pot will sag on one side and then slowly droop down into the fire?

c) will the wires hold the weight of the pot just fine until the fire burns out?

[vincent_vega_lives]

40. Kidding right?

You didn't actually try that brick experiment I suggested did you?

:rofl:

[petgoat]

41. "try that brick experiment"

You don't have to. Obviously the wires hold up the pot just fine.

As a thought experiment it brings up an important point: the perimeter
columns functioned as tensile elements, and the compressive forces were
taken by the core.

[vincent_vega_lives]

42. I meant the one I suggested

You know to test the difference in a brick at rest and one in motion upon one's head?

[spooked911]

43. Not kidding. I see once again you cannot answer my question.

And I think my experiment is a little more representative of the WTC collapse than yours.

Are you afraid to try it?

[vincent_vega_lives]

45. Yes

Sounds like a good way to burn my yard down. :nuke:

[petgoat]

46. "burn my yard down"

So do it in your neighbor's yard when he's out of town.

Here's a record of the experiment:



http://covertoperations.blogspot.com/2005/10/can-hydrocarbon-fires-weaken-steel.html

(Thanks to spooked911 for the link)

http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=125x56653#56739

I assumed the wires were in tension. It never occurred to me that
they'd function in the configuration shown.

[rman]

23. maybe you mean momentum.

mass doesn't change with velocity.

[philb]

27. If it is assumed that the initial failure was a top block of floors

falling on a floor about the level of the plane hit that was damaged,
what caused the pulverization of the top block? What fell on it?
What forces pulverized it?

And was the central core collapsing at the same time and in similar manner to the area outside the core? If so, what about chistophera's pictures of the standing core? If not, what caused the core to collapse?

And why all of the reports of explosions by firemen, policemen, engineers, janitors, and others at the site?
Were they all just confused?
And what about the physical harm(burns,etc.) suffered by those who reported being mangled and burned by the explosions, such as in the basement and at ground level before the collapse?
http://www.flcv.com/firemen.html

[pox americana]

29. That's a good question.

However the cores were constructed it's pretty clear that they weren't stacks of chessboards and could not have "pancaked" in the way we're supposed to believe the floor diaphragms did.

They were also narrower and denser and much more likely to topple from a failure point than to somehow power down to their foundations.

[vincent_vega_lives]

31. "pancaking" is a misnomer

as the "pancakes" did not survive the process.

[pox americana]

44. Yes, but a conveniently deceptive one.

It produces a mental image of sequential vertical failure when the photographic evidence shows that the explosive forces were horizontal.



Just another big banana nut lie.

[pox americana]

28. Another question: if every floor "pancaked," every column buckled.

But out of 63,140 above-ground perimeter and core columns, I have yet to see one showing clear signs of compressive load failure (buckling). But I've seen hundreds, if not thousands, showing no signs whatsoever of any failure, as in the photo below.



So where's the evidence of "pancaking"?

[vincent_vega_lives]

32. Its what you are seeing when you watch a video of the building

collapse. Perhaps "pancake" is a poor word to use as a description as it implies the floors stacked neatly upon one another. It was anything but that. It was an incredibly violent and explosive process that results in the perimeter columns being smashed outward, the concrete floors (and everything between them) being pulverized, and the mighty core columns being rendered apart. The reason for the standing lower structure is due to the dispersion of the mass of the building on the way down. It simply ground itself apart.

[petgoat]

33. "the perimeter columns being smashed outward,"

If I'm not mistaken, the NIST report alleges that the perimeter columns
were buckled inwards by sagging floors.

Of course they have no evidence for this notion.
,

[LARED]

34. Correction

The NIST has photographic evidence that the perimeter columns bowed inward as a precursor to collapse.

No matter if you believe in CD or global collapse the perimeter columns were forced outward once the collapse started.

[petgoat]

36. "NIST has photographic evidence that the perimeter columns bowed inward"

Photos which, as Jim Hoffman points out, are useless because hot air
induces distortions like the wavery effect you get over hot asphalt in
the desert.

You'd think somebody would have picked a buckled column out of the pile,
but apparently they didn't.

[vincent_vega_lives]

38. Only just prior to the collapse obviously!

I'm talking during the collapse.

They have examined a great deal of structural components from the buildings, what makes you think there is no evidence?