Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns

[ergo]

Correct on "No CD" but it is not the topic. The thread is about a challenge to prove some engineering aspects of WTC1/WTC2 collapse. Ergo keeps trying to derail the thread.

It was never my intent to derail the thread. I just want readers of the thread to realize that this is not an explanation of the collapse initiation of WTC 1 and 2. And even as a hypothesis, it is incomplete.

The situation is that enik, Newtons Bit and ozeco41 are in full agreement on the engineering principles and 95% agreement in the details. and the 5% difference is of no consequence other than to the engineers looking at the details.

That's great. But it should also be noted that you three as well are clearly rejecting the NIST model of collapse initiation. Not surprising for Enik, but for supporters of the government version of events, I think that's really interesting.

 

[ozeco41]

It was never my intent to derail the thread.

Noted as to lack of intent.

I just want readers of the thread to realize that this is not an explanation of the collapse initiation of WTC 1 and 2...

Take care with the generalisations. I agree that "..this is not [a complete] explanation of the collapse initiation of WTC 1 and 2.

And even as a hypothesis, it is incomplete.

True or partially true at two different levels:

True at the level of overall collapse initiation - it does not fully explain collapse initiation. It is merely one of the probable mechanisms. An actual observed mechanism as applied to WTC1. RThat is not the levle of tghe OP of this thread.

Partially true at the lower systemic level of the challenge which is the OP the enik v Newtons simplified model is incomplete as I have identified several times in this thread and numerous times in other threads. However the accuracy difference between the simplified model and the more complete and vastly more complicated real situation is why I stated "95% agreement". And I also said that I doubt that properly quantified difference would be significant other than as an engineering detail. I could explain it qualitatively (have done elsewhere on other occasions) but proving it would require a much more extensive FEA. And I doubt that such is feasible as I have already said.

...That's great. But it should also be noted that you three as well are clearly rejecting the NIST model of collapse initiation...

Not so - you are making the classic error of false generalisation which is M_T's trademark. I have no doubt about the accuracy of NIST in the broad picture viz aircraft strike causing damage and unfought fires, more damage accumulates resulting in a cascading failure of impact and fire zone leading to "global collapse" with no CD needed or practised at either critical stage.

There are lower level details where I either disagree or am agnostic to NIST finding. One agnostic example is the argument of "core led" v "perimeter led" where some folks get excited over which came first. I am yet to see anyone show why it matters.

My position is simple - when the cascade initiation process dropped the top part of tower both core and perimeter columns had failed.

Not surprising for Enik, but for supporters of the government version of events,...

My agnosticism on Governmemt or NIST or any other authority has been on published record on several forums since early 2008. My explanations are mine - not parroted Government or NIST. Primarily to avoid the truther tactics of repeatedly switching objectives in discussion - as explained recently in this thread..

I think that's really interesting.

Could be except you seem to be basing your interest on a misreading of my position. I'll leave it to enik and NB to explain their positions if they want to.

 

[enik]

But catenary sag is a very effective force multiplier.

You are wrong on this quote¹, unless you can supply calculations or a model to prove otherwise², in which case you would have been successful in my challenge³.

1 Nonsense - it is a simple statement of a true fact.
2 Calculations are both irrelevant and inapplicable to proof of truth of the simple factual concept.
3 Ridiculous. It is only remotely relevant to that old challenge.

I hope I got these quotes embedded correctly. Oz has stated that truss sag is a very effective force multiplier. I say "hogwash".

So Oz, please show me with a model or calculations how truss sag is a very effective force multiplier. This is key to your argument with Tony on the other thread and as a former engineer, should not be difficult for you to prove and thereby sucessfully end this challenge.

 

[Grizzly Bear]

OZ can speak for himself, but as far as I'm concerned with the OP and what the latest bump addresses... isn't the eccentric loading of the columns due to the "pull" element of the floor failures the "force multiplier"? Non-axial loads have a tendency to lower the yield strength substantially in comparison to a structure who's load path is axial....

I'm not sure where an FEA model is required to make that apparent. But as far as the OP is concerned... I didn't originally join into the thread, but it seems that there've been mentions of the fact that the OP suggests an argument against the "pancake theory of collapse" which is neither relevant nor being used in the context of the other thread. The concept of how the columns misaligned and how there was a great deal of lateral forces involved with their failure is referred to in a different context than the way your OP treated it originally is why I ask for clarification.

 

[enik]

Oz quite clearly stated that "catenary sag is a very effective force multiplier". If he wants to go back into the other post and issue a correction to his statement, then I will let him off the hook.

Here is one quote directly from the NIST report 1-6D page iii and the basis for this challenge:

The finite element analyses (FEA) of the global models and of the component and subsystem models showed that the key structural responses that led to the collapse of the towers were as follows: 1) floor sagging caused by the failure of thermally-weakened truss members, resulting in pull-in forces between the floor and the exterior wall…

There was no mention of eccentric loading nor p-delta with reference to the perimeter columns. If you find mention of either in the NIST report, please point me to it.

 

[beachnut]

Oz quite clearly stated that "catenary sag is a very effective force multiplier". If he wants to go back into the other post and issue a correction to his statement, then I will let him off the hook.

Here is one quote directly from the NIST report 1-6D page iii and the basis for this challenge:
There was no mention of eccentric loading nor p-delta with reference to the perimeter columns. If you find mention of either in the NIST report, please point me to it.

Will this lead to opening the door to CD? What it the goal? What is your overall conclusion, and how will this work out? There was no CD on 911, why did your theory fail? Was it due to evidence, or what?

The "hogwash", is that engineering for something? Do you have a goal after 12 years? Is this a thermite backdoor thing? How does this relate to the silly 911 truth stuff, aka, the theme of this sub-forum? lots of questions, no answers?

Darn, back to NIST, 1-6D...

 

[jaydeehess]

OZ can speak for himself, but as far as I'm concerned with the OP and what the latest bump addresses... isn't the eccentric loading of the columns due to the "pull" element of the floor failures the "force multiplier"? Non-axial loads have a tendency to lower the yield strength substantially in comparison to a structure who's load path is axial....

I'm not sure where an FEA model is required to make that apparent. But as far as the OP is concerned... I didn't originally join into the thread, but it seems that there've been mentions of the fact that the OP suggests an argument against the "pancake theory of collapse" which is neither relevant nor being used in the context of the other thread. The concept of how the columns misaligned and how there was a great deal of lateral forces involved with their failure is referred to in a different context than the way your OP treated it originally is why I ask for clarification.

That is what I thought as soon as ozeco used the term. A stiff component tilt would produce an eccentric load but an caternary sag of the floor would further shift the center of mass and increase the non-axial loading.

 

[jaydeehess]

Oz quite clearly stated that "catenary sag is a very effective force multiplier". If he wants to go back into the other post and issue a correction to his statement, then I will let him off the hook.

Here is one quote directly from the NIST report 1-6D page iii and the basis for this challenge:
There was no mention of eccentric loading nor p-delta with reference to the perimeter columns. If you find mention of either in the NIST report, please point me to it.

"Led to collapse", not that it was the direct cause of the failure of core columns.

 

[enik]

That is what I thought as soon as ozeco used the term. A stiff component tilt would produce an eccentric load but an caternary sag of the floor would further shift the center of mass and increase the non-axial loading.

Too bad oz didn't clarify himself on the other thread. Besides, a caternary sag still would not produce the required pull in force.

 

[ozeco41]

OK folks - this mini discussion arose because enik challenged me over a very simple technical point that I made in this post.

In that post it was nothing more than an explanatory comment to assist Tony Sz to understand some reasoned argument that I had put to Tony. The reason being that Tony claimed that enik had proved something and I suspected at that time that Tony was overstating what had actually been demonstrated.

In a simple lay persons example what I said was that if you tie a rope between two fixed points - say between two columns - and then pull the rope sideways it will result in:
1) A force pulling the columns together;
2) ...which will be multiple times larger than the pull you apply sideways to the rope.

How many of you have used that simple fact to:
p) tighten a load tie down in a car, truck or trailer;
q) used it to pull a bogged vehicle clear - with a rope taut between vehicle and a tree/post - push rope sideways and vehicle moves. Re tauten rope and repeat till clear of bog;
r) add as many homely examples as you wish. The mechanism is simple and obvious.

Rotate from horizontal to vertical and that is the mechanism of "catenary sag pull in". And the "engineering" application to WTC collapse is no more complicated than the "lay persons example".

And the ONLY point I was using it for was to say that "pull in is a lot more that downwards force" That is simple fact. Enik denies my use of it - his record in the other thread is of derailing to assist Tony Sz's false claims/denials etc. That purpose of derail is why I have several times refused to follow enik's derail efforts - refused to help him derail a thread.

So let's look at what enik has said:

I hope I got these quotes embedded correctly. Oz has stated that truss sag is a very effective force multiplier¹. I say "hogwash"².

So Oz, please show me with a model or calculations how truss sag is a very effective force multiplier³. This is key to your argument with Tony on the other thread⁴ and as a former⁵ engineer, should not be difficult for you to prove⁶ and thereby sucessfully end this challenge⁷.

1 Actually I said 'catenary sag'. My comment was generic - not limited to WTC collapse.
2 He is wrong - the pigs will miss their bath.
3 No calculations needed. This is a trick which enik and T Sz deploy regularly. Neither does "reasoning" very well hence the demand for "calculations".
4 I was not arguing with Tony in that post and the comment was in support of requests for clarification.
5 I'm not aware that (i) I had been excommunicated OR (ii) my brain reformatted, wiped clean and re-booted.
6 I don't have to prove what is axiomatic obvious.
7 Ball is in enik's court to stop the silly games.

Oz quite clearly stated that "catenary sag is a very effective force multiplier". If he wants to go back into the other post and issue a correction to his statement, then I will let him off the hook¹⁰.

Here is one quote directly from the NIST report 1-6D page iii and the basis for this challenge:¹¹There was no mention of eccentric loading nor p-delta with reference to the perimeter columns. If you find mention of either in the NIST report, please point me to it¹².

10 I'm not on a hook - here is no hook to be on. (And, to pre-empt an obvious come back, I mean enik's metaphorical hook.)
11 Yet another derail attempt. Please try to maintain focus enik. We are not discussing NIST. My claim is true so if you find NIST in support of your challenge NIST is wrong. And I won't bother going there because it will be a derail of a derail of a derail of a ....
12 More evasion and derails.

Will this lead to opening the door to CD? What it the goal?

Not if I can help it. He has at least two goals a) derail the other thread - foiled for now; AND b) continue his ongoing taunting of me - which isn't causing me loss of sleep. Big boy, thick skin etc...

Now Grizzly has it all in perspective:

OZ can speak for himself,...

Yes. And quite well IMNSHO. (I never did Modesty 101. )

but as far as I'm concerned with the OP and what the latest bump addresses... isn't the eccentric loading of the columns due to the "pull" element of the floor failures the "force multiplier"? Non-axial loads have a tendency to lower the yield strength substantially in comparison to a structure who's load path is axial....

Spot on. Actually a read of this thread will show many of my posts which explain the issues.

I'm not sure where an FEA model is required to make that apparent...

It isn't but enik has a narrow focus on FEA - he is good at using it most times but it isn't the answer to a maiden's prayer. it needs to be used in a valid context and supported by sound reasoning. Two areas where I have previously criticised enik's claims. Read this thread for examples of enik's "narrow focus" on FEA causing him to lose the plot.

FEA is a modern complicated structural engineering calculator. And very good. BUT claiming that "FEA proves something" is equivalent in the language of my generation of engineers to saying "my slide rule proves". That quaint analogy neatly shows the failure of a lot of FEA based engineering on these 9/11 discussions---but I will leave that attractive side track.

That is what I thought as soon as ozeco used the term. A stiff component tilt would produce an eccentric load but an caternary sag of the floor would further shift the center of mass and increase the non-axial loading.

Yes - up to your usual; >>>90% standard.

Too bad oz didn't clarify himself on the other thread...

There was no need in the context I used the statement AND I will not follow your derail tricks as you have found on several occasions.

... Besides, a catenary sag still would not produce the required pull in force.

...and that claim is a valid topic for this thread whether it is true or not. It is a derail for this mini discussion which should now be over.

My statement "But catenary sag is a very effective force multiplier" is true, was true when I made it and was a valid explanatory point in the context of that original post.

 

[Tony Szamboti]

OK folks - this mini discussion arose because enik challenged me over a very simple technical point that I made in this post.

In that post it was nothing more than an explanatory comment to assist Tony Sz to understand some reasoned argument that I had put to Tony. The reason being that Tony claimed that enik had proved something and I suspected at that time that Tony was overstating what had actually been demonstrated.

In a simple lay persons example what I said was that if you tie a rope between two fixed points - say between two columns - and then pull the rope sideways it will result in:
1) A force pulling the columns together;
2) ...which will be multiple times larger than the pull you apply sideways to the rope.

How many of you have used that simple fact to:
p) tighten a load tie down in a car, truck or trailer;
q) used it to pull a bogged vehicle clear - with a rope taut between vehicle and a tree/post - push rope sideways and vehicle moves. Re tauten rope and repeat till clear of bog;
r) add as many homely examples as you wish. The mechanism is simple and obvious.

Rotate from horizontal to vertical and that is the mechanism of "catenary sag pull in". And the "engineering" application to WTC collapse is no more complicated than the "lay persons example".

And the ONLY point I was using it for was to say that "pull in is a lot more that downwards force" That is simple fact. Enik denies my use of it - his record in the other thread is of derailing to assist Tony Sz's false claims/denials etc. That purpose of derail is why I have several times refused to follow enik's derail efforts - refused to help him derail a thread.

So let's look at what enik has said:

1 Actually I said 'catenary sag'. My comment was generic - not limited to WTC collapse.
2 He is wrong - the pigs will miss their bath.
3 No calculations needed. This is a trick which enik and T Sz deploy regularly. Neither does "reasoning" very well hence the demand for "calculations".
4 I was not arguing with Tony in that post and the comment was in support of requests for clarification.
5 I'm not aware that (i) I had been excommunicated OR (ii) my brain reformatted, wiped clean and re-booted.
6 I don't have to prove what is axiomatic obvious.
7 Ball is in enik's court to stop the silly games.


10 I'm not on a hook - here is no hook to be on. (And, to pre-empt an obvious come back, I mean enik's metaphorical hook.)
11 Yet another derail attempt. Please try to maintain focus enik. We are not discussing NIST. My claim is true so if you find NIST in support of your challenge NIST is wrong. And I won't bother going there because it will be a derail of a derail of a derail of a ....
12 More evasion and derails.

Not if I can help it. He has at least two goals a) derail the other thread - foiled for now; AND b) continue his ongoing taunting of me - which isn't causing me loss of sleep. Big boy, thick skin etc...

Now Grizzly has it all in perspective:
Yes. And quite well IMNSHO. (I never did Modesty 101. )

Spot on. Actually a read of this thread will show many of my posts which explain the issues.
It isn't but enik has a narrow focus on FEA - he is good at using it most times but it isn't the answer to a maiden's prayer. it needs to be used in a valid context and supported by sound reasoning. Two areas where I have previously criticised enik's claims. Read this thread for examples of enik's "narrow focus" on FEA causing him to lose the plot.

FEA is a modern complicated structural engineering calculator. And very good. BUT claiming that "FEA proves something" is equivalent in the language of my generation of engineers to saying "my slide rule proves". That quaint analogy neatly shows the failure of a lot of FEA based engineering on these 9/11 discussions---but I will leave that attractive side track.

Yes - up to your usual; >>>90% standard. [qimg]http://conleys.com.au/smilies/clap.gif[/qimg]
There was no need in the context I used the statement AND I will not follow your derail tricks as you have found on several occasions.
...and that claim is a valid topic for this thread whether it is true or not. It is a derail for this mini discussion which should now be over.

My statement "But catenary sag is a very effective force multiplier" is true, was true when I made it and was a valid explanatory point in the context of that original post.

I believe in order to get true catenary action it needs to be a cable being deflected. In other words, it can't have any stiffness against bending. The trusses, even when sagging, still had stiffness in the vertical direction and would not transmit all of the vertical deflection as longitudinal tension.

NIST could not get the trusses to apply enough lateral load to the perimeter columns in their FEA to cause them to pull inward and fail. They needed to add an artificial lateral load.

 

[ozeco41]

I believe in order to get true catenary action it needs to be a cable being deflected....

That is true in a narrow interpretation of the word. I was simply following the terminology which has been in use. Call it "pull in due to sagging" if you prefer - or suggest another option.

However recognise that my purpose in this mini discussion was to dispel enik's misunderstandings about a simple technical fact. That issue and nothing further. I have no interest in reopening this current topic nor entering it unless someone once again reflects untruthfully on my statements.

Terminology aside - it is a minor point - the two issues that you raise need to be kept in perspective.

First the issue you raise about "stiffness" is, ironically, one I explained in my draft post but took out in the interest of reducing post length. C'est la vie.

In other words, it can't have any stiffness against bending. The trusses, even when sagging, still had stiffness in the vertical direction and would not transmit all of the vertical deflection as longitudinal tension.

Disagree with "can't have any" - agree with "not transmit all" (Which, in reverse, means "would transmit some")(Aren't those two in conflict?) Despite that issue of conflict I agree with what I think you are trying to say.

Remember I'm not discussing whether there was or was not enough pull in. This discussion arose from comments on another thread because you claimed enik had proved something and I suggested that from my memory he had not proved as much as you claimed. I made a simple technical comment in explanation and enik subsequently disagreed with that comment. If anyone wants to discuss the matter of enough pull in - i.e. how much he has proved - let them do it. Here in this thread. The only reason this mini-discussion is here is to resolve the simple technical point I made and enik misunderstood.

Recall also that I have already offered to discuss these mechanisms leaving CD on the table as an option simply to avoid the polarised positions that either side takes. Neither you nor your other opponents have shown any interest in that proposal. To make that explicit it means that my comment on pull in remains the same whether due to sagging alone OR due to your claimed core collapse (OR both )

Now to your second issue:

...NIST could not get the trusses to apply enough lateral load to the perimeter columns in their FEA to cause them to pull inward and fail. They needed to add an artificial lateral load.

An interesting observation but, bottom line, it is irrelevant to this mini discussion. I don't give a damn about what NIST found - whether it was right or wrong. I have never relied on NIST findings and don't intend to start. This thread is about an enik challenge to prove a technical fact. NOT about "Prove NIST wrong/right". If someone wants to prove NIST was wrong let them start a thread. One member has but has stubbornly declined to either what they got wrong or present any argument in support.

Why someone would OP "NIST was wrong" but not follow through to support the claim is not worth commenting on.

 

[Tony Szamboti]

First the issue you raise about "stiffness" is, ironically, one I explained in my draft post but took out in the interest of reducing post length. C'est la vie.

Disagree with "can't have any" - agree with "not transmit all" (Which, in reverse, means "would transmit some")(Aren't those two in conflict?)

I didn't actually mean the trusses would not have any catenary effect if they have any stiffness at all, just that it is markedly less due to it having vertical stiffness and most of its deflection not being transformed into tensile loading at their ends, like a flexible cable would. Most of the vertical load on the truss would have still been supported by its flanges vertically and very likely only a small percentage by horizontal tension.

It is very likely only the flexible cable that can be considered as having mechanical advantage (and being a force multiplier) due to its deflection being full transformed into high tensile loads at its ends.

Enik basically got the same FEA results that NIST did in that the sagging did not produce lateral loads sufficient to pull in the perimeter columns.

 

[NoahFence]

Any thoughts about the fellow on the 105th floor that reported to 911 he could see the 98th floor when he looked down, 20 minutes before collapse?

that's pretty indicative of floors sagging, isn't it?

 

[ozeco41]

I didn't actually mean the trusses would not have any catenary effect if they have any stiffness at all, just that it is markedly less due to it having vertical stiffness and most of its deflection not being transformed into tensile loading at their ends, like a flexible cable would...

No problem - that is what I thought you meant.

It is very likely only the flexible cable that can be considered as having mechanical advantage (and being a force multiplier) due to deflection causing high tensile loads at its ends...

I don't agree BUT the point is moot - remember the only reason I made the comment was in an explanation for you directed at your comment. So if it doesn't help you throw it out. I'm currently only sorting out enik's misunderstanding about the purpose of my comment. Nothing hangs on it at this stage except enik has been trying to take issue for whatever reason.

...Enik basically got the same FEA results that NIST did in that the sagging did not produce lateral loads sufficient to pull in the perimeter columns.

My focus in this thread back in March was on the history of false arguments about whether or not joist sagging alone could pull columns in 54". People from both sides including engineers were forgetting that it was not a single factor. "Pull in" didn't need to do it all, it only needed to start bowing - past a critical point (Euler -- P Delta - call it whatever) the bowing would self sustain. So "pull in", whether sag induced or dropped core induced, starts and eccentricity makes it self sustaining. See Newtons Bit's FEA based agreement to that and my comments at posts #119 & 120. The subsequent posts also interesting WRT enik's claims.

Meanwhile I have been reasonably persuaded by the work of femr et al that the initiation could well have been core led. No one has responded to my queries over the past year or two as to "Why does it matter?"? Clearly it matters to your CD scenario.

So the claim, if true, that joist sag wasn't enough doesn't faze me. Remember that I have been prepared to explain the cascade mechanism >>initiation >>progression either with CD out of consideration for genuine sceptics OR with CD on the table for convinced truthers. Leaving CD in play as an option only slightly complicates the explanation process.

(Side issue remember that we cannot prove "No CD" by reasoned technical arguments. Two main reasons - the logic problem of "cannot prove a negative" AND the specifics of WTC collapse analysis.

So "CD or Not?" will always fall back onto arguments based on aspects outside the technical domain.)

 

[ozeco41]

Any thoughts about the fellow on the 105th floor that reported to 911 he could see the 98th floor when he looked down, 20 minutes before collapse?

that's pretty indicative of floors sagging, isn't it?

Tilt actually. I take it that his line of sight was outside the building. The floor joist sagging was internal and even at high tilt it would have been out of line of sight.

 

[Tony Szamboti]

No problem - that is what I thought you meant.
I don't agree BUT the point is moot - remember the only reason I made the comment was in an explanation for you directed at your comment. So if it doesn't help you throw it out. I'm currently only sorting out enik's misunderstanding about the purpose of my comment. Nothing hangs on it at this stage except enik has been trying to take issue for whatever reason.
My focus in this thread back in March was on the history of false arguments about whether or not joist sagging alone could pull columns in 54". People from both sides including engineers were forgetting that it was not a single factor. "Pull in" didn't need to do it all, it only needed to start bowing - past a critical point (Euler -- P Delta - call it whatever) the bowing would self sustain. So "pull in", whether sag induced or dropped core induced, starts and eccentricity makes it self sustaining. See Newtons Bit's FEA based agreement to that and my comments at posts #119 & 120. The subsequent posts also interesting WRT enik's claims.

Meanwhile I have been reasonably persuaded by the work of femr et al that the initiation could well have been core led. No one has responded to my queries over the past year or two as to "Why does it matter?"? Clearly it matters to your CD scenario.

So the claim, if true, that joist sag wasn't enough doesn't faze me. Remember that I have been prepared to explain the cascade mechanism >>initiation >>progression either with CD out of consideration for genuine sceptics OR with CD on the table for convinced truthers. Leaving CD in play as an option only slightly complicates the explanation process.

(Side issue remember that we cannot prove "No CD" by reasoned technical arguments. Two main reasons - the logic problem of "cannot prove a negative" AND the specifics of WTC collapse analysis.

So "CD or Not?" will always fall back onto arguments based on aspects outside the technical domain.)

A lot of people have shown the collapses of the North Tower and WTC 7 to have been core led. In both cases the core can be observed to fall a split second before the exterior.

Don't forget that the late Danny Jowenko showed exactly where he would places charges if he were asked to bring down buildings with those types of construction. That would be in the core, which he called the heart. See this video just after 2:30 minutes http://www.youtube.com/watch?v=k3DRhwRN06I.

 

[erwinl]

A lot of people have shown the collapses of the North Tower and WTC 7 to have been core led. In both cases the core can be observed to fall a split second before the exterior.

Don't forget that the late Danny Jowenko showed exactly where he would places charges if he were asked to bring down buildings with those types of construction. That would be in the core, which he called the heart. See this video just after 2:30 minutes http://www.youtube.com/watch?v=k3DRhwRN06I.

Is that why there are videos of the collapse of the North tower where the core can be observed to be still standing (even if only for a short time) after the rest of the building has collapsed?

 

[Tony Szamboti]

Is that why there are videos of the collapse of the North tower where the core can be observed to be still standing (even if only for a short time) after the rest of the building has collapsed?

That is nothing but a 50 story remnant of the full central core and it is hard to understand why you seem to be implying that the core did not collapse first and that the full core somehow survived for a short time. The same type of remnant survived for a short time in the South Tower collapse.

We are talking about the initiation and progression in the early stages of the collapse starting at the 98th floor in the North Tower. There was no surviving core structure for 48 stories down from there. It is very likely that the collapse was allowed to self-propagate after a large number of stories were demolished and some columns in the lower core would have had more of a chance to survive the propagation, but then fell due to their slenderness.

 

[ozeco41]

A lot of people have shown the collapses of the North Tower and WTC 7 to have been core led. In both cases the core can be observed to fall a split second before the exterior.

Good oh. The "core" v "perimeter" led issue has not been of great significance to me. Since the initiation stage meant both core and perimeter had failed why does it matter which went first. Unless someone needs the sequence to support an argument. I can wait till such an argument is made.

My foci on WTC collapse events has been:
1) Explaining rather than combative arguing;
2) Oriented towards lay persons or engineers who simply did not understand the probable or observed mechanisms.

With CD as an easily addressed issue provided reasoned discussion rather than debating tricks.

Then confronting poor logic, poor argument from either side - actually from all four sides in the days before we had only two "sides".

Through 2007-8-9 those were viable options. Not so today with the paucity of reasoned objective material.

OK - I just caught your on the fly edit - this bit added:

Don't forget that the late Danny Jowenko showed exactly where he would places charges if he were asked to bring down buildings with those types of construction. That would be in the core, which he called the heart. See this video between after 2:30 and 3:25 minutes http://www.youtube.com/watch?v=k3DRhwRN06I.
Today 02:24 PM

I am military engineer trained. So the way I first looked at WTC collapse was by "put yourself in the enemies boots" AKA how would I bring them down if given the task by the General.

The trick would be matching how it actually fell so that the CD vanishes into the prima facie cause of Aircraft impact and fires.

Bringing them down not the problem - hiding it before during and after is the challenge. I decided I could mimic the mechanism BUT not keep it hidden/secret/confidential.