OOS Collapse Propagation Model

[ozeco41]

These personality driven conflicts are a waste of time.

Oystein raised the issue of "meta-process" and it would be an interesting study. There seem to be two main classes of reasons or goals for involvement in these forums. I am -check my 8 year record - firmly in the sector where interest is in understanding and explaining the events. My personal focus on explaining which was what brought me to forum discussion back in 2007 - again check my record.

The other sector has a focus on "argument" in the sense of proving others wrong - winning or losing.

--and that pair of statements is itself "meta-process" which is a blind spot to many and will probably attract ridicule. One other member who routinely expresses interest in the "meta-process" level is Major_Tom with his recognition of "memes". Note that no one seems prepared to address those matters. I've deliberately stayed away and explicitly stated why - given the make up of members I doubt it could be discussed meaningfully. BUT note also that some members resort to ridicule. A strong sign that they do not recognise the issue - let alone have the ability to discuss it. And Major_Tom as always on this forum "leads with his chin" by making his assertions as false generalising.

And "explaining by reasoned argument" will never win against "argument for arguments sake" - AKA "Win at Any Cost". That was the reason I abandoned participating in this thread in 2014.

And both those assertions are "meta-process" though the second should be understood by all.

[JOKEwith SeriousMessage] We need two new words to replace "argument" to help reduce the conflicting goals - the difference between "argument" and "argument"!![/JOKEwith SeriousMessage]

 

[JSanderO]

So lets discuss how fires in a plane damaged tower made the top section... in whatever state it was in... to become "un-moored" and drop down... Let's dp 1WTC or 2WTC.

What mechanisms with the core... would do that and how did they do it?

 

[ozeco41]

Might as well get this out of the way...

It's an interesting issue even tho OT.

It was a good effort by R Mackey representing the leading edge of debunker common wisdom when it was used for that Hardfire project.

It served its purpose and R Mackey was a significant leader of the "debunker" cause through that era. It needed to be better than the T Szamboti et al truther version. It was.

We now know better. Understanding has advanced. And if you are interested in understanding the actual mechanisms and/or the shortcomings which are not comprehended in R Mackey's use of it - set up the thread.

It could be as controversial as this thread for the same reasons of lèse majesté.

 

[ozeco41]

Agreed but that seems to be what this forum is for, conflict between Ideas, to waste time.

Neatly summarised and exactly the same point I just made in more formal language responding to Sander.

JSO you might want to read Dr. Greenings report, so might you, Ozeco41.
www.911myths.com/WTCREPORT.pdf

I'm familiar with it. I'm sure you would find it interesting - probably attractive because his reasoning follows your preferred approach starting from details or one aspect which is "lower in the taxonomy"

My preference is - and is unlikely to change - to work from the bifgger picture AND known facts - engaging details only as and when they become relevant. Put bluntly from my perspective his approach is arse about. Like most truther arguments which start from a not understood anomalous issue and never put it reasoned and coherently in context.

My perspective is that you must know WTF you are talking about BEFORE you apply the maths. And what he is discussing is a mechanism. You cannot apply maths/energy/velocity measurement to anything UNLESS you know what you are applying those factors to. That should be self evident but it isn't. I wont take the risk of identifying debunkers examples BUT it is the fatal error T Szamboti made with "Missing Jolt". It is the fatal error by Sz et al claims that tilt will not prevent axial impact of columns. And numerous others. False starting point or undefined starting point == recipe for false argument.

Decide what you are talking about THEN apply the maths or energy or...whatever other factor.

So Greening loses my respect in his introduction
His second paragraph starts: Agreed - good start. So what "mechanics" are we talking about FG?

...his next sentence:

True - maybe - if you need to follow the energy transfers BUT

He has jumped over the key step.

How can you follow the path if you haven't described the mechanism you are tracing through?

 

[ozeco41]

So lets discuss how fires in a plane damaged tower made the top section... in whatever state it was in... to become "un-moored" and drop down... Let's dp 1WTC or 2WTC.

What mechanisms with the core... would do that and how did they do it?

I've already done it Sander. I'm not aware of any other member attempting to present an overall comprehensive and coherent argument.

The topic is both compound and complex. Compound in that it involves a lot of factors. Complex at two levels - first that many of the factors are complicated in themselves - second in that combining them adds another layer or two to the complication. It is full 3D + T = four dimensions.

Most people shouldn't need to go there - including those for whom "19 Terrorists Did It" is sufficient then those who want to dig a bit deeper "The Top Block fell and from there global collapse was inevitable". Whilst most in the engineering profession would be satisfied with "it was a heat driven cascade failure after some initial impact damage...so what?" And the WTC specific details would probably be of little help to those intent on making their own new building more resistant to progression failures.

 

[Major_Tom]

My perspective is that you must know WTF you are talking about BEFORE you apply the maths. And what he is discussing is a mechanism.

Yes, that is best. But he didn't know the specific mechanism when he wrote the paper. He didn't know what was 'inside all that dust'.

He has jumped over the key step.

Because he honestly did not know at the time he wrote. But if you don't know, the energetics approach is the best approach.

Energetics is better than trying to derive differential equations for the crush front and the roofline like Bazant does in BV and BL. Because if you do it like Bazant did, you may start believing that you differential equations "prove" there can be no 'crush up' before 'crush down', like David Benson clearly did in the quotes I provided earlier.

How can you follow the path if you haven't described the mechanism you are tracing through?

You can only do it in the most generic of terms: general energy.




It really is a question of perception. Each of their papers show how each author perceived the mechanics of the collapsing buildings at the time they wrote their papers, just as the R Mackey diagram shows how he and the NIST perceived the WTC1 collapse initiation motion. R Mackey merely drew the movement as it was described in the NIST reports.

 

[WilliamSeger]

So lets discuss how fires in a plane damaged tower made the top section... in whatever state it was in... to become "un-moored" and drop down... Let's dp 1WTC or 2WTC.

What mechanisms with the core... would do that and how did they do it?

I like this one:

Review of Causes of WTC Collapse

Although the structural damage inflicted by aircraft was severe, it was only local. Without stripping of a signifcant portion of the steel insulation during impact, the subsequent fire would likely not have led to overall collapse (Bažant and Zhou 2002a; NIST 2005). As generally accepted by the community of specialists in structural mechanics and structural engineering though not by a few outsiders claiming a conspiracy with planted explosives, the failure scenario was as follows:

1. About 60% of the 60 columns of the impacted face of framed tube and about 13% of the total of 287 columns were severed, and many more were signifcantly deflected. This caused stress redistribution, which signifcantly increased the load of some columns, attaining or nearing the load capacity for some of them.
   
2. Because a signifcant amount of steel insulation was stripped, many structural steel members heated up to 600°C, as confirmed by annealing studies of steel debris (NIST 2005) the structural steel used loses about 20% of its yield strength already at 300°C, and about 85% at 600°C (NIST 2005); and exhibits signifcant viscoplasticity, or creep, above 450°C (e.g., Cottrell 1964, p. 299), especially in the columns overstressed due to load redistribution; the press reports right after September 11, 2001 indicating temperature in excess of 800°C, turned out to be groundless, but Bažant and Zhou’s analysis did not depend on that.
   
3. Differential thermal expansion, combined with heat-induced viscoplastic deformation, caused the floor trusses to sag. The catenary action of the sagging trusses pulled many perimeter columns inward by about 1 m, (NIST 2005). The bowing of these columns served as a huge imperfection inducing multistory out-of-plane buckling of framed tube wall. The lateral deflections of some columns due to aircraft impact, the differential thermal expansion, and overstress due to load redistribution also diminished buckling strength.
   
4. The combination of seven effects — (1) Overstress of some columns due to initial load redistribution; (2) overheating due to loss of steel insulation; (3) drastic lowering of yield limit and creep threshold by heat; (4) lateral deflections of many columns due to thermal strains and sagging floor trusses; (5) weakened lateral support due to reduced in-plane stiffness of sagging floors; (6) multistory bowing of some columns for which the critical load is an order of magnitude less than it is for one-story buckling; and (7) local plastic buckling of heated column webs — finally led to buckling of columns (Fig. 1b). As a result, the upper part of the tower fell, with little resistance, through at least one floor height, impacting the lower part of the tower. This triggered progressive collapse because the kinetic energy of the falling upper part exceeded by an order of magnitude the energy that could be absorbed by limited plastic deformations and fracturing in the lower part of the tower.

 

[JSanderO]

I don't buy the sagging trusses pulled the columns inward... Where? That much?

This is the facade led failure.

 

[JSanderO]

I've already done it Sander. I'm not aware of any other member attempting to present an overall comprehensive and coherent argument.

The topic is both compound and complex. Compound in that it involves a lot of factors. Complex at two levels - first that many of the factors are complicated in themselves - second in that combining them adds another layer or two to the complication. It is full 3D + T = four dimensions.

Most people shouldn't need to go there - including those for whom "19 Terrorists Did It" is sufficient then those who want to dig a bit deeper "The Top Block fell and from there global collapse was inevitable". Whilst most in the engineering profession would be satisfied with "it was a heat driven cascade failure after some initial impact damage...so what?" And the WTC specific details would probably be of little help to those intent on making their own new building more resistant to progression failures.

Ozzie,
Well yeah and this is why we had a few lame ideas sketched out which were generic and likely incorrect. Columns missed / moved out of alignment to allow the top to drop... I don't see anyone explaining it... HEAT don't make columns boogie...

NIST said the sagging trusses pulled the facade in.. BOWED them.. what got the whole damn thing (ALL the columns) out of alignment so it could drop. Or maybe it was almost all of them...

Guesses anyone?

 

[DGM]

I don't buy the sagging trusses pulled the columns inward... Where? That much?

This is the facade led failure.

Do you "buy" that they could pull them in at all?

 

[Dave Rogers]

I don't buy the sagging trusses pulled the columns inward... Where? That much?

The inward bowing of the perimeter columns is an observation rather than an inference; it was photographed from a helicopter several minutes before collapse initiation. The inward collapse of the perimeter columns at the point of initiation was also observed and filmed in the South Tower. Is it the mechanism you dispute, or the authenticity of the observations?

Dave

 

[Crazy Chainsaw]

Yes, that is best. But he didn't know the specific mechanism when he wrote the paper. He didn't know what was 'inside all that dust'.



Because he honestly did not know at the time he wrote. But if you don't know, the energetics approach is the best approach.

Energetics is better than trying to derive differential equations for the crush front and the roofline like Bazant does in BV and BL. Because if you do it like Bazant did, you may start believing that you differential equations "prove" there can be no 'crush up' before 'crush down', like David Benson clearly did in the quotes I provided earlier.





You can only do it in the most generic of terms: general energy.




It really is a question of perception. Each of their papers show how each author perceived the mechanics of the collapsing buildings at the time they wrote their papers, just as the R Mackey diagram shows how he and the NIST perceived the WTC1 collapse initiation motion. R Mackey merely drew the movement as it was described in the NIST reports.

Correct MT, Frank at that time didn't know the structure few did.

The problem is model abstractions vs reality, the tilt is not all that Nist messed up.

 

[JSanderO]

The inward bowing of the perimeter columns is an observation rather than an inference; it was photographed from a helicopter several minutes before collapse initiation. The inward collapse of the perimeter columns at the point of initiation was also observed and filmed in the South Tower. Is it the mechanism you dispute, or the authenticity of the observations?

Dave

I don't dispute the observation. I question the cause. It doesn't feel right to me that some wimpy trusses at 80" oc could pull in those facade panels. I am going to go out on a limb and say they can't! I think bowing was likely BUCKLING from re distributed loads and the buckling favored to floor load side.

 

[DGM]

I don't dispute the observation. I question the cause. It doesn't feel right to me that some wimpy trusses at 80" oc could pull in those facade panels. I am going to go out on a limb and say they can't! I think bowing was likely BUCKLING from re distributed loads and the buckling favored to floor load side.

That would be right. They favored the truss side because that's the way the sag would pull them. The NIST never said only one force (truss sag) was acting on them (that's a "truther" claim)

 

[Bravin Neff]

I don't dispute the observation. I question the cause. It doesn't feel right to me that some wimpy trusses at 80" oc could pull in those facade panels. I am going to go out on a limb and say they can't! I think bowing was likely BUCKLING from re distributed loads and the buckling favored to floor load side.

What was wrong with Newtons Bit's explanation?

http://www.internationalskeptics.com/forums/showthread.php?postid=3465131#post3465131

 

[ozeco41]

I don't dispute the observation. I question the cause. It doesn't feel right to me that some wimpy trusses at 80" oc could pull in those facade panels. I am going to go out on a limb and say they can't! I think bowing was likely BUCKLING from re distributed loads and the buckling favored to floor load side.

Sander I and others have explained this many times.

As Dave Rogers says The observed FACT is that there was Inward Bowing.

The historic debate over sagging trusses as the SOLE cause was wrong - both sides wrong - in interpreting it as SOLE cause.

The reality which you identify is that there was also load re-distribution. It is near certain inference that redistribution INCREASED the load on those columns.

There were likely other factors but I ASSERT that the other factors were probably secondary - not significant.

So we have two factors. (1) An inwards pull from sagging joists and (2) an applied axial load which is increasing through re-distribution.

Those need to be added and the key is that columns under an axial load will continue to bend/buckle without further load increase once the bend/buckle passes a critical point. And from memory that critical point was only a matter of a few inches.

SO the joist sag pull in ONLY needs to bias the direction of buckling.

It does NOT have to achieve even that first bit on its own little lonesome.

The total loading and amount of buckling passing beyond the critical point is the clue.


And - covering my arse - I dismissed those other secondary factors BECAUSE even if I have missed any of them they would only make the situation worse.

 

[ozeco41]

What was wrong with Newtons Bit's explanation?

http://www.internationalskeptics.com/forums/showthread.php?postid=3465131#post3465131

It is most likely overkill for Sander - and addresses a far wider scope.

Sander's question was specific - hence my deliberate choice to start with the basics.

Newtons Bit's explanation includes the principle I just expressed in layman's terms:

The other limit state is P-delta. When the exterior column is pulled inwards, it deflects. This deflection(Δ) generates a moment, specifically P2*Δ. This moment, creates more deflection, which further magnifies the moment, creating more moment, and so forth. P-delta has two outcomes: the moment reaches equilibrium at some point, or becomes unstable and continues to grow. This phenomenon can be easily shown with a simple experiment. Take a straw and try to compress it between your fingers. It has a surprising amount of strength. Now push the middle in slightly. This is p-delta.

 

[ozeco41]

The problem is model abstractions vs reality, the tilt is not all that Nist messed up.

That must qualify as understatement of the week.

 

[ozeco41]

Hey Sander try this even simpler version:

I am going to go out on a limb and say they can't! I think bowing was likely BUCKLING from re distributed loads and the buckling favored to floor load side.

You are on the CORRECT limb - you are just short of the end of the limb. Agreed "they can't" AND the little bit of force from the sagging is what caused the "buckling favored to floor load side".

 

[JSanderO]

Sander I and others have explained this many times.

As Dave Rogers says The observed FACT is that there was Inward Bowing.

The historic debate over sagging trusses as the SOLE cause was wrong - both sides wrong - in interpreting it as SOLE cause.

The reality which you identify is that there was also load re-distribution. It is near certain inference that redistribution INCREASED the load on those columns.

There were likely other factors but I ASSERT that the other factors were probably secondary - not significant.

So we have two factors. (1) An inwards pull from sagging joists and (2) an applied axial load which is increasing through re-distribution.

Those need to be added and the key is that columns under an axial load will continue to bend/buckle without further load increase once the bend/buckle passes a critical point. And from memory that critical point was only a matter of a few inches.

SO the joist sag pull in ONLY needs to bias the direction of buckling.

It does NOT have to achieve even that first bit on its own little lonesome.

The total loading and amount of buckling passing beyond the critical point is the clue.


And - covering my arse - I dismissed those other secondary factors BECAUSE even if I have missed any of them they would only make the situation worse.

Ozzie,

This may be a minor point or just quibbling about words. I see the movement inwards like this.

The facade columns had axial loads from above... that was the MAJOR load by far... The they had some APPLIED loads via the truss seats on the core side of the column. THIS WAS AN ASYMMETRICAL load from the get go.

So if you overload the facade... past the yield strength it WILL buckle... And which way would it go? As it is "restrained on the core side" it would have to push the slabs out of the way... Or if the slabs broke or maybe.. maybe sagged they would exert some lateral force... in the core direction.

BUT if a there was a break in the floor and the floor was hanging from the facade...wouldn't this junk of floor pull the facade which was buckling toward the core?

How can we determine which is was? Sagging trusses or hanging floor slabs? That is if these two cause produce the same inward buckling direction?

Weren't there some section of floors which could be seen dropping? What is the force on the trampoline when some one jumps on it? It's a kind of sagging but it's not from heat... but deformity from impact.