WTC 1 & 2. What happened after collapse initiation?

[Mancman]

You said one bolt had 40-50KN of capacity (or 9.0-11.2kips of capacity). You're off by a factor of two. The design strength of an A307 bolt is 5.52 kips (24.5KN).

Congratulations! If you were a real engineer you would have just gotten a bunch of people killed! And you wonder why no one takes you seriously: you have no clue.

Now then, the correct total design capacity of two bolts is 11.0kips. Can this force be significant in damaging the columns?

Out of interest, what is the corresponding figure for the 1' A490 bolts used on the floor trusses? I'm just wondering what the energy requirement is to shear a floor worth of bolts.

 

[Newtons Bit]

Out of interest, what is the corresponding figure for the 1' A490 bolts used on the floor trusses? I'm just wondering what the energy requirement is to shear a floor worth of bolts.

35.3kips if the threads are included in the shear plane.
44.2kips if the threads are not included in the shear plane.

This includes a phi factor of 0.75. You could divide these numbers by 0.75 and get the average force that the bolts would fail at, but some would obviously fail earlier.

 

[Cuddles]

Why is there even a discussion here, let alone 20 pages of it?

WTC 1 & 2. What happened after collapse initiation?

Collapse. That's what "collapse initiation" means. Nothing to see here, move along.

Now, are there any other questions I can help with that would require anything more than the language ability of a six year old to answer?

 

[cmcaulif]

Free fall collapse for the first few moments? No, I do not write like that.

I paraphrased, and it would seem I did not misrepresent your view as you still contend:

Bazant proposes crush-down and Seffen some magic dynamic overloading, both implying some sort of free fall of the upper block (no collapse yet) and impact as initiation of destruction (apart from local failures due to heat and previous damages setting the WTCs on fire).

This is not true as I have pointed out. If you don't believe me compare Seffen equation 14 to free fall

if the initial displacement of the system (s) is one story height and we let this be negative, since we want to know velocity at the time of the first impact (edit: and let the position in space where this first impact occurs be zero) we get

Displacement = 1/2gt²-s = 0
then
t = sqrt(2s/g)
Velocity = gt = g*sqrt(2s/g) = sqrt(2gs)

Seffen EQ 14 is V = sqrt(2g(gamma*L)*(c-1)/c)
where gamma*L is the height of one story , or s as I have called it for short.

note that (c-1)/c, which corresponds to compaction, is always less than one so the velocity calculated by Seffen eq 14 to determine the initial conditions is always slower than free fall.

I have very little interest in discussing your paper as a whole. I thought I would just point out a factual error.

 

[Heiwa]

I paraphrased, and it would seem I did not misrepresent your view as you still contend:


This is not true as I have pointed out. If you don't believe me compare Seffen equation 14 to free fall

if the initial displacement of the system (s) is one story height and we let this be negative, since we want to know velocity at the time of the first impact (edit: and let the position in space where this first impact occurs be zero) we get

Displacement = 1/2gt²-s = 0
then
t = sqrt(2s/g)
Velocity = gt = g*sqrt(2s/g) = sqrt(2gs)

Seffen EQ 14 is V = sqrt(2g(gamma*L)*(c-1)/c)
where gamma*L is the height of one story , or s as I have called it for short.

note that (c-1)/c, which corresponds to compaction, is always less than one so the velocity calculated by Seffen eq 14 to determine the initial conditions is always slower than free fall.

I have very little interest in discussing your paper as a whole. I thought I would just point out a factual error.

With due regard to Seffen's EQ 14 this compaction is a little strange.

Seffen starts with a tower of uniform density 0.18 and then a moving intermediate block beta x L between an intact (superstrong) upper block and a moving crush front develops where compaction takes place during collapse, i.e. the uniform density increases without, e.g. any friction in this beta x L section and there is no ejection of débris and rubble. Below the crush-front the uniform density is still 0.18. At the end of the collapse the upper block remains intact and the structure below is compacted to infinite density.

None of the assumptions of Seffen has any foundation in reality. And he is a Cambridge lecturer!! Google on Seffen and you find plenty more jokes about this clown.

 

[cmcaulif]

Heiwa, please don't change the subject, perhaps his compaction term can become the topic of another discussion if we can focus and get past this one teeny weeny point.

If you agree or disagree with Seffen's derivation does not change the fact that his model does not show free fall.

I have demonstrated that, contrary to your statements, Bazant(in his 2 recent models) and Seffen do not imply free fall. Can I count on you to fix this error on your website?

 

[Heiwa]

And .....

Given that the steel plate that forms the "table top" (later to become the base of the water tank) is only 5mm thick, how feasible would it be to weld 20mm diameter steel tubes to this in such a way that it stands true? Presumably it would have to be fabricated upside-down and then flipped over? I see what I believe are called jigs involved, to get stuff lined up, and I don't think they're in the budget. The flipping over could prove tricky?

Then .. how feasible is it to lift 60kg steel plates and weld them to this "table top" - one by one - to form the tank? Would the contraption not tip over or collapse around the weld when the first plate is welded on? It strikes me that the way to do it would be to weld up the 4 tank plates into a box and lower them down onto the "table top", to keep the whole thing strong and stable. But this amounts to 240kg of steel, which would require heavy lifting equipment and several people, I'd imagine.

Pehaps an engineer here could comment on the consequences of getting the legs even a few degrees out of true? Or warped during the welding of the "spandrels"

Although I know nothing about steel fabrication, I'm beginning to wonder if Heiwa is even a welder by trade. But I could have got it all wrong about the construction issues here. Just guessing, based on many years of improvising d-i-y jobs.

I am glad that you have started construction! The weights of the parts were chosen to be handled by two persons.
You start to weld the four 75 cms tubes to the table top on flat ground at the corners. Welding leg length is 1-2 mm. And then you weld the spandrels between the tubes. Then you turn the table upright on a solid floor. Reason that the legs are 75 cms is to get the correct slenderness ratio (between spandrels).
Then you tack weld the first tank 5 mm wall on top of the table. It needs some temporary support and then you tack weld the second wall to the table top and the first wall. Now, these two walls support themselves. So it is easy to fit the remaining walls. Then complete the welding - leg lenght 1-2 mm at all joints. Not very difficult.
But it can be simplified. In lieu of the four 5 mm walls fit a steel cage above and line it with a tarpaulin and fill it with the correct amount of water. In that case put a layer of insulation material between the tarpaulin and the table top so the tarpauline will not be damaged later by heat. The objective is simply to be able to load the table so that the legs are compressed to 0.3 yield. I chose 5 mm walls of a water tank as I am used to handle plates like that. The welding is easy. To use water as the weight seems the easiest.
The table will easily carry double the weight (stress in legs then 0.6 yield) but then you have to increase the tank.
I realize that you clever guys can improve on the model. Pls advise your progress.

 

[Newtons Bit]

The photos show some diagonal bracing of the core structure seperate from the crane supporting structure.

in this picture, for example I can see six diagonal braces:

.........whatreallyhappened.com/IMAGES/wtc1_core.jpg

Perhaps they were helping to support the cranes and later removed. Do you have evidence that they were?

Given that the lateral system was composed of the exterior moment frames, we can conclude that the core was not comprised of braced frames. An interior braced frame core would render the super expensive exterior wall completly pointless.

Sometimes you need to have a basic knowledge of structures before you make assumptions.

 

[Heiwa]

Heiwa, please don't change the subject, perhaps his compaction term can become the topic of another discussion if we can focus and get past this one teeny weeny point.

If you agree or disagree with Seffen's derivation does not change the fact that his model does not show free fall.

I have demonstrated that, contrary to your statements, Bazant(in his 2 recent models) and Seffen do not imply free fall. Can I count on you to fix this error on your website?

I use 'near free fall' or 'nearly free fall' (and rarely only 'free fall') in the texts so it should be clear what we are talking about. Pls copy/paste a sentence where 'free fall' can be misunderstood.

In descriptions of Bazant and Seffen fantasies I have just copied/pasted some of their statements direct from their papers:

Seffen uses 'near-free falling' (without definition - how near?).

Bazant says 'so the upper part starts falling down onto the lower part below the critical floor, gathering speed until it impacts the lower part. At that moment, the upper part has acquired an enormous kinetic energy and a significant downward velocity'.

It sound as if Bazant means near or nearly free fall.

Enormous kinetic energy is not very scientific as not very much energy is released. Significant velocity? Scientific? The velocity could only have been 3 m/s!

Anyway - what happens before contact is of little importance. No destruction of lower structure has even started.

So no need to change my text, but thanks for the observations.

 

[cmcaulif]

I use 'near free fall' or 'nearly free fall' (and rarely only 'free fall') in the texts so it should be clear what we are talking about. Pls copy/paste a sentence where 'free fall' can be misunderstood.

In descriptions of Bazant and Seffen fantasies I have just copied/pasted some of their statements direct from their papers:

Seffen uses 'near-free falling' (without definition - how near?).

That is defined by his equations and you could calculate how near by comparing the result from the equation I provided to his. This is the difference between a qualitative and a quantitative argument.

you use the term "free fall" in a potentially confusing way more than once from the very outset of this article. Again you are implying no resistance, which is not modeled and is not the case in reality.

Bazant says 'so the upper part starts falling down onto the lower part below the critical floor, gathering speed until it impacts the lower part. At that moment, the upper part has acquired an enormous kinetic energy and a significant downward velocity'.

It sound as if Bazant means near or nearly free fall.

yes, which implies resistance, and is not "free fall", which implies no resistance. I just wanted to make sure you are making the distinction.

So no need to change my text, but thanks for the observations.

thats just about what I expected, bye.

 

[Toke]

I dont see what is proved/disproved by this setup.

Things don´t just scale up/down lineary, the greeks figured that out.*

Scalemodels are used for evaluations of aestics and planning of acces/workspace.
If you have the knowlegde to make an accurate model you already know how it would act in the aspect it is accurate in.

The strengt of a colum depends on the square of the length, why should this model be more accurate than the clip with the chickenwire and concrete block

*I read of some armoury that collapsed for them

 

[GlennB]

I am glad that you have started construction! The weights of the parts were chosen to be handled by two persons.
You start to weld the four 75 cms tubes to the table top on flat ground at the corners. Welding leg length is 1-2 mm. And then you weld the spandrels between the tubes. Then you turn the table upright on a solid floor. Reason that the legs are 75 cms is to get the correct slenderness ratio (between spandrels).
Then you tack weld the first tank 5 mm wall on top of the table. It needs some temporary support and then you tack weld the second wall to the table top and the first wall. Now, these two walls support themselves. So it is easy to fit the remaining walls. Then complete the welding - leg lenght 1-2 mm at all joints. Not very difficult.
But it can be simplified. In lieu of the four 5 mm walls fit a steel cage above and line it with a tarpaulin and fill it with the correct amount of water. In that case put a layer of insulation material between the tarpaulin and the table top so the tarpauline will not be damaged later by heat. The objective is simply to be able to load the table so that the legs are compressed to 0.3 yield. I chose 5 mm walls of a water tank as I am used to handle plates like that. The welding is easy. To use water as the weight seems the easiest.
The table will easily carry double the weight (stress in legs then 0.6 yield) but then you have to increase the tank.
I realize that you clever guys can improve on the model. Pls advise your progress.

I have a lot of trouble visualising 1.8 tonnes of water and steel being supported by 4 x 1mm welds. In fact I can hardly visualise a 1mm weld at all. Sounds like small-scale soldering to me. Maybe I need to learn more about steel fabrication?

 

[tanabear]

I've already explained to you, in this thread, patiently, endlessly, that we already have models, of collapse, initiation, etc., the whole nine yards. I've explained that all of this is consistent with the evidence, including video, recovered pieces, structural models, different formulations. All, obviously, to no effect.

Sorry for wasting your time.

NIST did not analyze the behavior of the towers after collapse initiation. This is why I started a thread on the topic. Where can I see models of the collapse?

“World Trade Center disaster investigators are refusing to show computer visualizations of the collapse of the Twin Towers despite calls from leading structural and fire engineers, NCE has learned. Visualisations of collapse mechanisms are routinely used to validate the type of finite element analysis model used by the [NIST] investigators?"
New Civil Engineer, October 6, 2005

If what NIST is saying is actually true then why not show the video/photographic evidence? Why rely on computer animation?

Heiwa, please don't change the subject, perhaps his compaction term can become the topic of another discussion if we can focus and get past this one teeny weeny point.

If you agree or disagree with Seffen's derivation does not change the fact that his model does not show free fall.

I have demonstrated that, contrary to your statements, Bazant(in his 2 recent models) and Seffen do not imply free fall. Can I count on you to fix this error on your website?

Bazant and Verdure state in their March 2007 paper, Mechanics of Progressive Collapse: Learning from WorldTrade Center and Building Demolitions,

"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."

So you are admitting that this 3.7 meter drop is something that was made up by Bazant? Was there ever any evidence to support this hypothetical assumption?

If not, then where did such an idea come from? Was it just made up to find reasons to support the official theory?

If so, then the primary defenders on the government's case are promoting falsehoods in a tragedy that killed thousands of people. That sounds kind of serious to me.

Bazant writes in the same paper,

"The subsequent progressive collapse was not simulated at NIST because its inevitability, once triggered by impact after column buckling, had already been proven by Bažant and Zhou’s (2002a) comparison of kinetic energy to energy absorption capability."

Here Bazant is saying that NIST did not simulate the actual collapse because it had already been shown to be inevitable by Bazant and Zhou in their 2002 paper. But if there 2002 paper contains assumptions that never happened then the official investigation by NIST is flawed or at best incomplete.

 

[R.Mackey]

No, it isn't. NIST answered the question it was intended to answer, and answered it well.

You don't understand Dr. Bazant's work, either. Your complaints are sheer foolishness.

 

[cmcaulif]

Bazant and Verdure state in their March 2007 paper, Mechanics of Progressive Collapse: Learning from WorldTrade Center and Building Demolitions,

"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."

So you are admitting that this 3.7 meter drop is something that was made up by Bazant? Was there ever any evidence to support this hypothetical assumption?

If not, then where did such an idea come from? Was it just made up to find reasons to support the official theory?

What are you talking about? Bazant makes very clear the cause of initial failure, which essentially amounts to columns on one floor losing stability. Of course a drop will occur then because there is no more static equilibrium.

Bazant's quote is correct because once the columns fail (remember collapse initiated with the buckling of an exterior wall, which then unloaded onto a weakened core) downward acceleration must begin. Since the columns that are providing the resistance were heated, and at this point are in the post buckled stage, there was indeed little resistance. This is still a far cry from no resistance, which is what I take issue with since seemingly pedantic language can lead to snowballing of errors.

If you are looking for visual evidence of the drop, a poster called gregory urich made an excellent frame by frame power point. I do not know where the thread has gone, perhaps a more regular poster can link you to it.

Bazant writes in the same paper,

"The subsequent progressive collapse was not simulated at NIST because its inevitability, once triggered by impact after column buckling, had already been proven by Bažant and Zhou’s (2002a) comparison of kinetic energy to energy absorption capability."

Here Bazant is saying that NIST did not simulate the actual collapse because it had already been shown to be inevitable by Bazant and Zhou in their 2002 paper. But if there 2002 paper contains assumptions that never happened then the official investigation by NIST is flawed or at best incomplete.

If by 'flawed assumption' you are referring to the drop of the upper block, see above. Also, please indicate what made you think I was admitting the drop was made up, I have no Idea where you got that from.

NIST was never charged to study collapse beyond initiation, however, I would have liked to see them develop a dynamic model. There are a few difficulties with a finite element analysis, even if cost was no object. But it would have been interesting to see how they would develop the physics in a mathematical model. It was their judgment that B&Z's work made this unnecessary.

We do however have dynamic models developed by Bazant, Seffen, and one of my professors mentioned a university in Japan has developed a dynamic collapse model as well(I'll follow up on that).

 

[Heiwa]

you use the term "free fall" in a potentially confusing way more than once from the very outset of this article. Again you are implying no resistance, which is not modeled and is not the case in reality.

I use "free fall" only describing the upper block alleged drop or vertical displacement due to alleged simultaneous local failures of the columns prior to "impact" and any destruction of the lower structure.

To clarify I have added a little note in the paper.

However, it doesn't matter if the displacement of the upper block is "free fall" or something else at initiation. As soon as contact takes place, destruction of the upper block would start absorbing strain energy and waste energy as friction. The whole interface between the upper block structure and the lower structure changes ... and you have to analyse that!

Not just say, like NIST, that sufficient energy could not be absorbed due to lack of strain energy in the structure ignoring friction, or, like Bazant and Seffen, that the upper block does not absorb any energy of any kind.

Evidently the upper block would start to fail at contact and the local destruction of the lower structure would soon be arrested, which I hope you agree to? That's the essential message in my papers.

 

[JihadJane]

Given that the lateral system was composed of the exterior moment frames, we can conclude that the core was not comprised of braced frames. An interior braced frame core would render the super expensive exterior wall completly pointless.

Sometimes you need to have a basic knowledge of structures before you make assumptions.

You are assuming that am claiming that the Towers cores comprised of braced frames. I'm not. I was responding to a poster who asserted that all there were no diagonals in the core whereas the photos I posted do show some diagonal bracing. The is nothing in the NIST report that I can find explaining the function of these components.

 

[JihadJane]

Experts............

There is a huge amount of information about the WTC structure in the NIST reports, via: http://wtc.nist.gov/

Jane, you might find that sometimes people here seem to be lacking in patience. This is because all of these issues have been discussed countless times. The "search" facility here can be useful, as can researching via the InterWebThingy.
Just strolling in and demanding "do you have evidence they were (removed)" will probably get people ratty, mainly because you can find out the construction method for yourself.
Evidently. Happens all the time!

Thanks for your kind comment, GlennB. Actually posters here (presumably because of JREF's moderation policy) seem relatively patient. My normal experience of 911 believers is mostly of people in an apparently permanent state of almost sociopathic rattiness so I appreciate your more humane approach!

I notice that 911 believers are rarely shy about rudely demanding evidence from 911 sceptics. I often ask for legally admissible evidence connecting bin Laden to the attacks but have yet to receive any. It seems reasonable to keep asking for it.

I am aware of the Twin Towers' construction methods. I have yet to find anything in the NIST report about the diagonal units shown in the photos I posted. However, it is an unimportant point. I consider discussion about the Towers' collapse to be somewhat of a red herring. Nearly all the physical evidence was prematurely destroyed forcing NIST and others to rely on almost completely computer hypotheticals for their "studies". Nothing can be proved about the Towers' physical behaviour during their apparently explosive disintegration.

Arguments based on hypothetical computer models will go on for ever in the absence of physical evidence.

----------------------------

 

[funk de fino]

I am aware of the Twin Towers' construction methods. I have yet to find anything in the NIST report about the diagonal units shown in the photos I posted. However, it is an unimportant point. I consider discussion about the Towers' collapse to be somewhat of a red herring. Nearly all the physical evidence was prematurely destroyed forcing NIST and others to rely on almost completely computer hypotheticals for their "studies". Nothing can be proved about the Towers' physical behaviour during their apparently explosive disintegration.

Arguments based on hypothetical computer models will go on for ever in the absence of physical evidence.

----------------------------

NIST took the steel that they wanted. They had a choice what to use. All the steel was forensically examined and catalogued prior to NIST getting it. This is confirmed by Brent Blanchard. There was no absence of physical evidence. There is now.

 

[JihadJane]

NIST: "The scarcity of physical evidence..."

NIST took the steel that they wanted. They had a choice what to use. All the steel was forensically examined and catalogued prior to NIST getting it. This is confirmed by Brent Blanchard. There was no absence of physical evidence. There is now.

Extract from the statement of Dr. William Jeffrey, Director, National Institute of Standards and Technology:

“The scarcity of physical evidence that is typically available in place for reconstruction of a disaster led to the following approach:

*Accumulation of copious photographic and video material. .....”

‘The Investigation of the World TradeCenter collapse: findings, recommendations, and next steps’, 2006, page 59:

http://commdocs.house.gov/committees/science/hsy24133.000/hsy24133_0f.htm

The process of gathering of WTC physical evidence was a battle against the swift removal and recycling of the steel. It was haphazard, underfunded and carried out by volunteers. They looked for samples from the impact/fire zones but hardly found any. In the case of WTC7 no steel was preserved:

http://wtc.nist.gov/pubs/NCSTAR1-3ExecutiveSummary.pdf.

Mechanical and Metallurgical Analysis of Structural Steel (Draft), E.1, Overview.