Analysis of WTC collapses by Nemec and Suranova

[Dave Rogers]

The buckling and yielding of the columns were taken into accont in our solution. It's influence is considered in the coefficient kappa in the differential equation.

I'm not suggesting you didn't account for it. I'm saying that your accounting didn't allow for the columns fracturing at any point, and so was a very great overestimate.

And as I have written above, even when omitting all column resistance, the speed of the collapse should have been much slower than observed.

Then you got your calculation wrong. Many conservation of momentum analyses have been done, and all give collapse times close to or slightly less than the observed collapse time. If everyone agrees except you, I suspect it might not be everyone else who's wrong.

Our result based on the law of coservation of momentum is congruent with that of prof Kuttler, who based his solution on the law of conservation of energy.

Kuttler's paper is utter nonsense, and blatantly dishonest as well. My comments on it are here.

Dave

 

[alienentity]

To: Captain Swoop

We have only shown, that the cause of the collapse of the Twin towers must be different, than the impact of the planes and fire only. In my previous contribution I have written that the falling mass could not hit a motionless mass, because then the collapse would be slower, even with the omittance of column resistance. The only physical explanation of the observed collapse is, that the mass must have begun to fall before it was hit by the falling mass. The authors of the paper, as academinians and technicians, would like to stand on pure science and not introduce speculations pertaining to the fact that the motionles mass started fo fall before it was hit by the falling mass. But some possible cause you can find on web.

To Dave Rogers

The buckling and yielding of the columns were taken into accont in our solution. It's influence is considered in the coefficient kappa in the differential equation. And as I have written above, even when omitting all column resistance, the speed of the collapse should have been much slower than observed. Our result based on the law of coservation of momentum is congruent with that of prof Kuttler, who based his solution on the law of conservation of energy.

It appears you are falling into the common trap of assuming (incorrectly) that the upper mass fell as an intact block onto the lower structure, more or less perfectly.
Nothing like that happened, so your assumptions will produce incorrect results. We already can observe that a significant 'tilt' and inward bowing/buckling of perimeter columns occurred, making the idea of axial, column-on-column impacts irrelevant to a discussion of reality.
Since the floor systems were also falling inside the outer columns, there was further destabilization of the perimeter sections, which were free to fall outward in chunks, providing very little resistance to collapse.
Upper tower blocks, for as long as they can be seen, fall inside and outside the perimeter columns due to this tilt. We can expect such motion to cause the 'peeling' effect which is observed.

Your assumptions about the time taken to collapse have little bearing on the actual event.

This is why the engineering community by and large is not very interested in this line of inquiry.

 

[Oystein]

Hello Martina,

welcome to the forum, and my respect for daring to face the criticism!

...
To Oystein:
You have mentioned the so called “pancake collapse”, where one or more falling slabs hit another slab. The connections are broken and a further slab is falling.

Not just the floor slabs are impacting other floor slabs - columns from both perimeter and core are doing the same.

You see, when the top block starts to descend (and tilt) as a unit all the columns across one floor have already buckeled, and the lateral geometry of the building is not in its "as build" state any longer. Most perimeter column ends from above will now miss and bypass their counterparts below. There are then three possibilities for each column: It will pass outside the wall, within the wall (between adjacent columns) or inside the wall. In the latter case, those perimeter columns will impact floor slaps and penetrate them easily.

This could have happened, but it was not observed.

Quite the contrary: It was very much observed, both on videos and on the failure modes observed on steel debris, that pretty much all floor-to-column connectors failed by overwhelming impact forces from above, indicating that the floor slabs were overloaded; while at the same time very few columns buckled and not many column-to-column connections broke initially. For a very large part, it was absorved that the perimeter walls peeled away in large undestoyed slabs after the floors inside had crushed down.

The inner core of the building, where were no slabs (only columns), would remain standing in such a case.

You are certainly aware that, when the floor joists disconnect, the core columns lose important lateral bracing, the unbraced length increases, and makes the columns more vulnerable to Euler buckling, right? So with enough floors removed, column capacity drops below actual load.

However I hope you are aware that indeed it was observed that the cores remained standing 50 to 75 stories high (if I rememeber correctly) for several seconds after the floors and perimeter had already fallen, before succumbing to Euler buckling?

Acceleration of the collapse would be much slower than it was observed, as well.
The simulation programs are based on the explicit method. The boundary conditions are simple. The building stands on rigid subsoil.
...

Hmm I am not sure I understand this information, or can gleen actionable information from that paragraph


You did not comment on my surprise to find that your paper has not referenced any paper by Zdenek Bazant - I am sure you are aware that Bazant has written a series of papers on the mechanics of the WTC collapses, with a comparable approach as yours? He commits some of the same errors when he focuses on column-resistance and ignores the actual collapse propagation mechansism through the floors as weakest points. Even then, Bazant has determined that the dynamic forces would overwhelm the load-bearing capacity of the columns by an order of magnitude once the top "block" has reached a downward velocity equivalent to that reached after about story free-fall.

I would have expected a paper like yours to explain how your model or assumptions differ from Bazants to account for the different result!

So direct question to you: Have you studied Bazant and Zhou; Bazant and Verdure; Bazant, Le, Greening and Benson; and Bazant and Le?

 

[Major_Tom]

Ivan, the most probable collapse progression modes of WTC1 and 2 are described in a book.

The book is available at my website, linked at the bottom of this post. The progression modes are in section 2.1 of the book.

Feel free to ask any questions you may have.


Problems with the latter 3 Bazant papers in section 2.6 of the book.

 

[Andy_Ross]

Way to spam your book dude!

 

[Micromegas]

"The presented theory of dynamics of the collapse of high building is based on the law of conservation of momentum, which is one of the fundamental laws of mechanics." Doesn't this law only apply to isolated systems? Was the WTC an isolated system?

I was thinking this myself. I can understand why amateurs writing nasty comments on Youtube videos would make the mistake of applying the Law of Conservation of Momentum to the collapse of the Twin Towers. However, hearing an alleged engineering expert make the same mistake makes me wonder whether this "expert" either doesn't know what the LoCoM is or assumes her audience doesn't.

Either way, poor work.

 

[ergo]

I was thinking this myself. I can understand why amateurs writing nasty comments on Youtube videos would make the mistake of applying the Law of Conservation of Momentum to the collapse of the Twin Towers. However, hearing an alleged engineering expert make the same mistake makes me wonder whether this "expert" either doesn't know what the LoCoM is or assumes her audience doesn't.

Either way, poor work.

How does the modeled collision not conserve momentum?

 

[Micromegas]

How does the modeled collision not conserve momentum?

I'll answer your question with a question: what force adds momentum to a collapsing structure?

 

[ergo]

How about just answering it with an answer, since your question is not going to help you.

 

[TheRedWorm]

How about just answering it with an answer, since your question is not going to help you.

Why don't you answer your own question. Let's see what you think.

 

[Micromegas]

Why don't you answer your own question. Let's see what you think.

They never have any clue. It's just never not funny.

 

[dafydd]

How about just answering it with an answer, since your question is not going to help you.

Hint. The answer begins with G.

 

[The Big Dog]

Hint. The answer begins with G.

and continues with a saucy little "R" note?

 

[Micromegas]

Hint. The answer begins with G.

and continues with a saucy little "R" note?

My first is in EGO, but isn't in PHONE
My second's in CORNER but never in CONE
My third and fourth letter are both in EVADE
My third's not in DEVIL, the fourth's not in SHADE
My fifth's found in RING, not however in GROUND
My sixth is in PETAL, but in LEAP won't be found
My last is in PARTY, but in TRAP doesn't fit
Good luck with this riddle, you thick truther ****

 

[swright777]

^^ Good stuff!

 

[Oystein]

Nom'ed twice :thumb

 

[Martina Juranova]

So you are 'Just asking questions'?

Seems a bit of a cowardly cop out to me.

Why don't you stand up and say what you think happened you obviously don't think it was a combination of crash damage and fire.

What else could it be?

What else could it be? E.g. a controlled demolition. But we don’t want to speculate.

 

[Martina Juranova]

It looks like you used the wrong formula for the inertial force of a falling mass (1.7) F_a= Bma
Where B = portion of the falling total mass above (building mass minus the mass that falls outside of the building)

Dave Thomas calculates this force to be F_dynamic= sqrt (2Kmgh) where h = drop height.
His experiment confirms this formula.

http://www.nmsr.org/nmsr911a.htm

Like Oystein mentioned above, why did you not reference Bazant as you both used the same Ideal Model assumptions, that of simultaneous and square column impacts, which did not happen in the Actual Event.

The inertial (or fictitious) force is by Newton’s 2nd law determined as the product of mass and acceleration acting against the acceleration. The Fdynamic you have mentioned is a quite different force. In our case the actual mass is B*m, so the inertial force is Fa= B*m*a.

As for not referencing Bazant, in the conference proceedings we had only 4 pages available. So the paper had to be very shortened. Besides our theory, the dynamics of the collapse of a high building is general, and does not depend on Bazant’s papers. Please read our paper mentioned in my first contribution, where we had more space and Bazant is cited.

 

[Martina Juranova]

To me this paper is puzzling at best. Some statements:

1. The resistive force of the columns was defined as

F_N = m*g*s*k

But is this equation correct? I think, that m*g equals the weight of the upper part and that s and k are material constants of the columns. But the weigth of the upper part was previously defined as

G = m*g*b

where b is a correction factor as not the total mass of the upper part impacted the lower part. Shouldn't this term be incorporated in F_N, too?

2. Could someone explain table 1 to me? I'm not an engineer and I have no clue how to interpret the data of this table.

3. I have the same problems with fig. 4 and 5. What do this colours mean?

4. The most interesting part of the paper:



a. Why do the authors believe this parameters to be true?

b. So the upper part is expected to fall 80 m, which equals 21 floors. What happens to these floors?

Ad 1) The columns were designed to the weight of all the mass above with a safety factor, i.e. m*g*s. This is the ultimate force which a column can carry. But due to buckling the average resistance of the columns would be much lower. To obtain the average resistance we made a computer simulation of the postbuckling response diagram of a column (se Fig. 2. and 3.)

Ad 2) The table introduces the collapse extents and pertinent times for several variations of the parameters s and α

Ad 3) The pictures 4 and 5 illustrate the deformed shape of the building obtained utilizing two independent computer programs based on the explicit method. The pictures demonstrate that the collapse would stop after about 70-80 m for setting the values of the parametres as the authors regard as probable.

Ad 4a) The values of parameters are briefly discussed in article 3.1. Here I will clarify the probably most important parameter, the safety factor. The safety factor generally is the ratio of the ultimate force and the maximal possible force of the design, i.e. force due to an extreme combination of loading, including wind and seismicity. For stability (buckling) the value of the safety factor is often taken as 3. Our parameter is not exactly the safety factor, but it is the ratio of the ultimate force and the actual force at the time of the collapse. This value should be higher than the safety factor, therefore at the time of the collapse the building was not fully loaded and no hurricane, or seismicity was in occurrence, nevertheless we have used the value s=3 as a conservative estimation.

Ad 4b) As you can see in figures 4 and 5, approximately 21 floors on the falling front were destroyed, and the remaining floors above and the lower remaining ones partly deformed, or intact.

 

[Martina Juranova]

Couple of questions:

1. "The presented theory of dynamics of the collapse of high building is based on the law of conservation of momentum, which is one of the fundamental laws of mechanics." Doesn't this law only apply to isolated systems? Was the WTC an isolated system?

2. "The inner core of the building, where were no slabs (only columns), would remain standing in such a case." Are you aware that substantial portions of the core remained standing after the initial collapse?

3. Are you aware of verinage demolition?

Ad 1) No structure is completely isolated. But the principle of isolation was known already to the founder of mathematical mechanics Archytas of Tarentum and is still widely used in analyzing structures. We could add to our solution e.g. aerodynamic drag, probably the most important influence not taken into account. The differential equation would be a little more complicated. Nevertheless the pertinent force would act against the motion and would cause further slowing of the collapse.

Ad 2) No substantial parts of the core remained standing after the initial collapse. When seeing the videos we cannot see any standing columns above the front of the destruction except the lower part, where only several columns remained standing.

Ad 3) Sorry, I don’t understand the word „verinage“.