New guy here: Questions for official hypothesis

[Sizzler]

I am currently going through my own process of research to understand the 9-11 debate.

My question is for those that know the official hypothesis inside and out.

From what I've gathered so far;

The first theory was:

1. Truss failure leads to collapse initiation.
2. Complete collapse a result of progressive failure (pancaking/domino/etc)

FEMA would endorse this theory.

NIST would later endorse a different theory.

1. Trusses were strong enough to cause column bowing when floors sagged
2. Perimeter columns bowed too much causing collapse initiation

But NIST ends there.

Further scientific studies now endorse this ‘complete’ collapse mechanism.

1. collapse initiation via NIST hypothesis
2. top section crushed down causing complete collapse and was destroyed upon impact with the debris pile (Bazant's new paper)

_______________

My questions:

1. Is the above correct? (I know it is simplified, but is it basically right?)

2. Why were there two studies, NIST and FEMA?

3. Has the FEMA theory of pancaking been rejected?

4. Is there a difference between progressive collapse and pancaking?


Help from the debunkers on board would be great!

Thanks guys.

 

[WildCat]

2. Why were there two studies, NIST and FEMA?

The FEMA study was just a quickie, didn't get too far into the meat and bones of the matter. The NIST investigation was thorough, and made with the goal of recommending changes to existing building codes and practices.

3. Has the FEMA theory of pancaking been rejected?

Yes and no. The collapse initiation was not a strict pancake-style event, but everything after that was.

4. Is there a difference between progressive collapse and pancaking?

None that I know of, pancaking is more informal.

 

[BenBurch]

1. Yes.

2. Because they had different goals. The NIST study was aimed at modifications to building and fire codes. FEMA as I understand it was aimed at understanding the actual mechanisms and to understand how best to respond to such an event in the future.

3. There could have been multiple mechanisms all happening in the buildings. The question is what was the biggest contributor.

4. Not much.

 

[WildCat]

1. Trusses were strong enough to cause column bowing when floors sagged
2. Perimeter columns bowed too much causing collapse initiation

But NIST ends there.

Close enough, but NIST did calculate that the mass above the crash floors was more than enough to cause complete collapse.

 

[Sizzler]

The FEMA study was just a quickie, didn't get too far into the meat and bones of the matter. The NIST investigation was thorough, and made with the goal of recommending changes to existing building codes and practices.


Yes and no. The collapse initiation was not a strict pancake-style event, but everything after that was.


None that I know of, pancaking is more informal.

Thanks for the quick reply. Your answer for my question #2 makes a lot of sense. Who pushed for the NIST study to be done?

Can anyone else confirm his answers for questions #3 and #4 and/or add anything else?

Thanks guys.

 

[Sizzler]

Close enough, but NIST did calculate[/url] that the mass above the crash floors was more than enough to cause complete collapse.

thanks for the link.

 

[Brainster]

Thanks for the quick reply. Your answer for my question #2 makes a lot of sense. Who pushed for the NIST study to be done?

Can anyone else confirm his answers for questions #3 and #4 and/or add anything else?

Thanks guys.

For #3 and #4, see NIST's FAQ #2:

NIST’s findings do not support the “pancake theory” of collapse, which is premised on a progressive failure of the floor systems in the WTC towers (the composite floor system—that connected the core columns and the perimeter columns—consisted of a grid of steel “trusses” integrated with a concrete slab; see diagram below). Instead, the NIST investigation showed conclusively that the failure of the inwardly bowed perimeter columns initiated collapse and that the occurrence of this inward bowing required the sagging floors to remain connected to the columns and pull the columns inwards. Thus, the floors did not fail progressively to cause a pancaking phenomenon.

 

[Sizzler]

NIST’s findings do not support the “pancake theory” of collapse, which is premised on a progressive failure of the floor systems in the WTC towers (the composite floor system—that connected the core columns and the perimeter columns—consisted of a grid of steel “trusses” integrated with a concrete slab; see diagram below). Instead, the NIST investigation showed conclusively that the failure of the inwardly bowed perimeter columns initiated collapse and that the occurrence of this inward bowing required the sagging floors to remain connected to the columns and pull the columns inwards. Thus, the floors did not fail progressively to cause a pancaking phenomenon.

Thanks for the link.

I'm curious about the core columns now though. How does NIST describe their failure?

 

[R.Mackey]

Thanks for the quick reply. Your answer for my question #2 makes a lot of sense. Who pushed for the NIST study to be done?

Can anyone else confirm his answers for questions #3 and #4 and/or add anything else?

Thanks guys.

FEMA itself pushed for a more thorough investigation, in its final report.
Numerous experts in industry and media (e.g. Bill Manning of Fire Engineering Magazine) pushed for it as well.
Ultimately, Congress made the decision, and there were several champions within the Capitol.

As for the progressive vs. pancaking question, the NIST FAQ describes the difference as noted above. Also, NIST ran a calculation estimating what would happen if a single floor fell completely free, as an appendix in NCSTAR1-6, and found that it would not lead to a collapse of the floor impacted, even taking damage and weakening into account.

Regarding pancaking later, once the collapse was well underway, the fact that large pieces of the core columns actually remained standing for some seconds afterward suggests that this is so. During such a chaotic event, "pancaking" is a gross oversimplification, but the fact is that many stories worth of core remained after the rest of the structure had been stripped away, so it's probably a good guess. Early on, however, the floors did not fall on their own, but must have remained attached since we saw the perimeter walls pulled inward at the start of collapse.

 

[R.Mackey]

Thanks for the link.

I'm curious about the core columns now though. How does NIST describe their failure?

NIST describes the core columns being overloaded in the minutes leading up to collapse, through a combination of impact damage, thermal weakening, and creep, as the heated upper structure sagged slightly, placing additional stress on the core columns. The sagging floor systems and thermal expansion / contraction of the floor systems also must have been a significant factor, though this is downplayed by NIST since their models could only incorporate creep and thermal expansion in a piecewise fashion, and they were forced to simplify these effects when assembling the global collapse model. Arup et al. believe the thermal expansion issue is key, and I agree with them.

The core was partially suspended by the hat truss later in the fires. NIST describes the total load borne by the core and the perimeter sections as a function of time in its reports, and the load gradually shifts away from the core to the perimeter, until the perimeter buckles.

See NCSTAR1-6 for more details.

 

[FactCheck]

1. Is the above correct? (I know it is simplified, but is it basically right?)

Basically

2. Why were there two studies, NIST and FEMA?

http://www.nist.gov/testimony/2002/abwtc.html

3. Has the FEMA theory of pancaking been rejected?

Only that pancaking CAUSED the collapse has been rejected, not that it never happened.

4. Is there a difference between progressive collapse and pancaking?

That's like the difference between Evolution and Natural Selection. Evolution happened, be it from Natural Selection or some other mechanism. A progressive collapse happened on 9/11, be it from pancaking or some other mechanism.


I would like to point out the NIST never said pancaking never happened after the building started to collapse. There is VERY strong evidence of pancaking, both during the collapse and on ground zero after the collapse.

http://www.debunking911.com/collapse.htm

You can clearly see the floors go on video and photos as the windows are blown out and debris is pushed out floor by floor. The debris cloud seperates at the corners of the building as if the corners were intact for most of the collapse. There is much more evidence supporting pancaking after the collapse began on my link above.

 

[Sizzler]

Thanks for the info guys.

I am very comfortable with my understanding of the NIST report now.

However NIST's analysis ends after collapse begins.

I am a bit confused with the current hypothesis for 'complete' or 'global' collapse mechanism.

Can someone link me to a scientific paper that describes a global collapse theory after collapse initiation?

What is the leading theory and paper on this?

 

[Gravy]

Can someone link me to a scientific paper that describes a global collapse theory after collapse initiation?

What is the leading theory and paper on this?

Hi, Sizzler. There's no "leading theory" per se. The structural engineering community accepts that that once the collapses began, they had to progress to the ground. The calculations are relatively simple for a competent engineer. NIST describes this in their December FAQ (see questions 1 and 10). Here are some independent papers that confirm the complete collapse scenario (cut and pasted from my site, which is linked in my signature).

WTC collapse papers with Zdenek Bazant as lead author
​

May, 2007: Collapse of the World Trade Center Towers: What caused it and what didn't Co-authors Le, Greening & Benson. Refutation of controlled demolition theory. Discusses matching of video record with progressive collapse equations, "free-fall" claims, concrete crushing (and how much TNT equivalent would be needed to do that crushing), air pressure & ejection of air, spread of dust cloud.

June, 2006: Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions Co-author Verdure. PDF.

Excerpt (applies to link above and below): The kinetic energy of the top part of the tower impacting the floor below was found to be about 8.4x larger than the plastic energy absorption capability of the underlying story, and considerably higher than that if fracturing were taken into account (Bažant and Zhou 2002a). This fact, along with the fact that during the progressive collapse of underlying stories the loss of gravitational potential per story is much greater than the energy dissipated per story, was sufficient for Bažant and Zhou (2002a) to conclude, purely on energy grounds, that the tower was doomed once the top part of the tower dropped through the height of one story (or even 0.5 m).​

Bazant & Zhou, 2001-2002: Why Did the World Trade Center Collapse?—Simple Analysis

Other explanations of the tower collapses​

November, 2007: Structural Engineer Keith Seffen'smathematical model of WTC tower progressive collapse (PDF. Due to appear in the Journal of Engineering Mechanics, Vol. 134, No. 2, February 2008)
BBC News article about Seffen's paper

Dr. Frank Greening's papers on the Collapses, Energy Transfer, "Tipping," Concrete Pulverization (PDFs)

Physicist Manuel Garcia's Counterpunch articles on the physics of the WTC collapses Pt.1– Pt.2– Pt.3

 

[Gazpacho]

3. There could have been multiple mechanisms all happening in the buildings. The question is what was the biggest contributor.

More specifically, NIST's goal was to figure out how to make similar buildings not collapse, and not how to make them collapse more gracefully. Therefore the details of the collapse were much less important than the initiation.

 

[Quad4_72]

Thanks for the info guys.

I am very comfortable with my understanding of the NIST report now.

However NIST's analysis ends after collapse begins.

I am a bit confused with the current hypothesis for 'complete' or 'global' collapse mechanism.

Can someone link me to a scientific paper that describes a global collapse theory after collapse initiation?

What is the leading theory and paper on this?

Really not too much to it. Do you really expect the intact portion of the towers to simply stop the momentum of thousands of tons of steel, concrete, building materials, etc from the collapsing upper portions?

 

[Architect]

Just to endorse Mck's comment, progressive collapse refers to a very wide range of failure modes and is correct. Pancake collapse was originally used to describe a very specific failure of cast and lift slabs, but has become more widely (and innacurately) used.

Ronan Point, for example, is a progressive collapse rather than a pancake but is occasionally described as such.

 

[Gazpacho]

Can someone link me to a scientific paper that describes a global collapse theory after collapse initiation?

To understand why this is not really a fair request, you have to consider the difference between engineering and physics.

A standing skyscraper and a collapsing skyscraper are both subject to the laws of physics. However, nobody is going to model a standing skyscraper by brute-force application of physics. Instead they are going to consider that the building is close to some nominal state (standing straight up). Then they will simplify the physics to just what is needed to accurately model the behavior of the building near that state.

A collapsing skyscraper has no nominal state to speak of. It is an out-of-control system. It is outside the scope of engineering.

 

[Sizzler]

Thank you Gravy.

That'll keep me busy for a night.

 

[Sizzler]

Really not too much to it. Do you really expect the intact portion of the towers to simply stop the momentum of thousands of tons of steel, concrete, building materials, etc from the collapsing upper portions?

I don't really know what to expect.

That's why I asked for scientific papers describing it.

Again, thanks gravy.

 

[rwguinn]

IS anybody else getting a sense of potential deja moo here.
I awit developments with worm on tongue..