The 9/11 Forum

Wildbear wrote:China conducted a demolition which bore some similarities: http://www.rtve.es/alacarta/videos/television/vuelan-edificio-mas-alto/566780/

I know, I'm credited in the post at 911blogger that introduced this demolition, which is why I said:

SnowCrash wrote:Not even the top-down controlled demolition examples we know about look this catastrophic.

I was specifically referring to the 104 meter tall, 34-floor rain garden building demolition in Zhongshan, 2009-08-13.

More elaborate reply later.

Bear,

I think that there was no requirement to crush or destroy the column's axially load capacity once the collapse/destruction of the twin towers began.

The columns were bystanders and victims of the floor destruction. The columns of course supported the floors, but the floors provided the required bracing for the columns. If you destroy or sufficiently weaken a column, it can no longer support the floor it supports or the axial load bearing down on it. If you remove the bracing from a column it becomes more slender, weaker and less stable. If it is too tall and thin.. to slender it will self buckle and likely snap apart at the weakest point in its length... which happens to be the joint / splice locations.

The floor destruction proceeding downward not only was a destructive drive dislodging the floors from the columns, but it fractured those floors and forced all the air inside the towers at each floor... 18,000 cu yards of it to disburse outward with great force... in fact some of the air was pressurized to result in as much as 400mph winds. This over pressure not only pushed against the facade... like forcing air into a bellows... but likely destroy the contents ON / between each floor. Even slight outward bulging of the facade would stress the panel to panel connections and the weakest ones would fail. It's always the weakest link which will go first and the other links are then *spared*.

The ejected materials are likely explained by lateral impulse from overpressure... both air and from the accumulated rubble of the collapse... which pushed outward much the way sand or gravel does when poured into a cardboard container. Look at any construction site which has this material delivered in 1 cu yard cardboard containers on pallets - they are always bulging outward. The contained material is always exerted an outward force on the container... as well as down (M).

Strong as structural connections are... they are usually weaker than the members they joint... and will be the weak link and fail first. And with respect to the twins... this seems to be in play related to the dismantling of many of the columns in the frame.

Wildbear wrote:

femr2 wrote:Splendid. So do you agree that any debris falling/emerging from the footprint above that point is irrelevant, as the actual point of destruction is lower down in the tower ?

I agree that debris emerging from the footprint is irrelevant in that it is not participating with impact and crushing.

Not quite what I asked. I'd suggest debris emerging from the footprint has already participated in impact and crushing, or it wouldn't be crushed. Agreed ?

Again, my (leading) question is to clarify with you that, regardless of the cause of the "crush front", everything you see above that is not going to be relevant to the cause of that crush front. Agreed ?

However, I feel that it is still relevant with regard to mass and energy considerations.

Why ? You're now hopefully aware of the ROOSD process in enough detail to know that numbers bandied around "out there" have very little to do with reality.

Presumably you have already done calculations and concluded that even with the amount of energy being expended pulverizing concrete and other interior materials, there is still enough energy available in the crush front to cause failure of the columns and sustain a downward acceleration of the crush front.

Correct. Also bear in mind that crushing is not a separate process. Also bear in mind that not too many columns buckled in the sense used in many calculations. Instead the OOS floor regions were stripped from the core, and the core kind of prised apart at the seams by falling mass. The core floors themselves were thicker than the OOS regions, and there was plenty of mass in there to break core beam connections once the OOS region support had gone.

the load being experienced by the columns in the lower portion of the building is decreasing; thus increasing the margin between the load that they are experiencing and the maximum load allowed by the factor of safety, and thus making buckling due to overload less likely.

Again the core columns did not buckle in any great numbers, but instead broke at the joins between 3-storey sections or fell outwards in multi-column sections.

Which raises another question: how many buckled columns, due to vertical overload conditions and not horizontal impact, were found in the debris?

A small proportion.

femr2 wrote:As long as there's enough mass acting at that crush front (which we've worked out to bo about 3 storeys worth) then the rest of the mass (many floors worth by the time of that photo) is not necessary and is quite at liberty to fall out wherever it pleases without affecting the crush front propogation. Yes ?

If the mass is "enough", then yes. Does 3 storys worth of mass apply through the entire height of the building, from top to bottom?

Yes (almost). The floor connections were pretty much constant throught the tower height, apart from the MER floors, which were stronger.

Do you have an explanation handy for what appears to be trails of white smoke coming from the ends of pieces of steel flying through the air?

Dust ?

Mr Bear doesn't seem to understand the ROOSD hypothesis.

The destruction of the towers was not a single type mechanical event.. like an explosion... or multiple explosions doing the same thing up and down the tower. And key is that it DOES NOT involve column buckling for the most part. There WAS column buckling associated with the initiation... what got the ROOSD going... but that was not a ROOSD mechanism.

As femr2 and others have explained quite well.. The ROOSD was the destruction of the FLOORS... both inside and outside the core. FLOORS not columns. We use the term the columns were *stripped* of the floors... The ROOSD mass also destroy most of... a sufficient amount of... the bracing which:

1. held the columns laterially in a rigid frame... one atop the other (they wer3 composed of 36' long sections with splices MUCH MUCH MUCH weaker than the column sections themselves.

2. jostled the unbraced and now partially braced columns breaking many of the connections and allowing the column above to move laterally and drop.

3. leaving the still connected columns one on top of the other...of a slenderness ratio which made them extremely unstable. As bracing was destroyed.. slenderness ration of the column increased... instability increased and in some cased caused self buckling

4. provided an accumulating mass... which could not be contained within the facade as it descended.. and exerted lateral force on the facade breaking it apart... including removal of the lateral bracing and increasing the slenderness ratio making the facade absent floors unstable and *easily* pushed outward.

5. With the floor system being identical except for the stronger mech floors... once the ROOSD was going... threshold mass achieved to drive the floor destruction... every floor below was essentially going to see the same overloading and yield to it. If floor 91 could not support or arrest the descending mass... neither could 55 or 62 etc.

But without the floors... and the bracing... none of the columns could remain stable and frame was easily torn apart and shattered into the pieces it was built from. The collapse was like an intense 15 (or so) rock crusher / agitater... and in this case the *rocks* were rather flimsy concrete slabs and building contents. When 10's of thousands of tons of material is raining down on a floor in the twins... it doesn't have much of a chance or surviving to tell a tale.

femr2 wrote:

Wildbear wrote:I agree that debris emerging from the footprint is irrelevant in that it is not participating with impact and crushing.

Not quite what I asked. I'd suggest debris emerging from the footprint has already participated in impact and crushing, or it wouldn't be crushed. Agreed ?

Agreed, if this is in fact a gravitational collapse.

femr2 wrote:Again, my (leading) question is to clarify with you that, regardless of the cause of the "crush front", everything you see above that is not going to be relevant to the cause of that crush front. Agreed ?

Yes, if the collapse is gravitational. If there are explosive charges going off, they could be going off at multiple levels, resulting in debris emissions at multiple levels simultaneously or at different times. If this were the case, what is seen happening above the "crush front" would be just as relevant to understanding the destruction of the building as the "crush front" itself. I just spent some time looking at a WTC1 collapse video and still images, and the appearance that I am seeing is that the strong emissions do appear to be occurring at multiple levels simultaneously. Specifically, the leading pattern of emissions appears to be occurring at the center of the building, while other strong emissions are occurring along the sides at higher levels. If there is a bellows effect occurring, it does not appear to be occurring uniformly across any single floor. It looks like the left-center-right emission pattern may be resulting in three distinct "banana peel" clouds on each side of the building. Others who have studied the video and photographic evidence in greater detail may know more about what's going on with these emission patterns.

femr2 wrote:

Wildbear wrote:the load being experienced by the columns in the lower portion of the building is decreasing; thus increasing the margin between the load that they are experiencing and the maximum load allowed by the factor of safety, and thus making buckling due to overload less likely.

Again the core columns did not buckle in any great numbers, but instead broke at the joins between 3-storey sections or fell outwards in multi-column sections.

Agreed. Regardless of the cause of building failure, I would think it improbable that the columns would buckle all the way to the ground, for any reason. Even widespread buckling at the impact point seems improbable to me (I doubt that the fires were that hot, or that their duration was long enough); but that topic goes in a different section of the forum.

Wildbear wrote:

femr2 wrote:

Wildbear wrote:I agree that debris emerging from the footprint is irrelevant in that it is not participating with impact and crushing.

Not quite what I asked. I'd suggest debris emerging from the footprint has already participated in impact and crushing, or it wouldn't be crushed. Agreed ?

Agreed, if this is in fact a gravitational collapse.

The cause of destruction is irrelevant.

femr2 wrote:Again, my (leading) question is to clarify with you that, regardless of the cause of the "crush front", everything you see above that is not going to be relevant to the cause of that crush front. Agreed ?

Yes, if the collapse is gravitational.

I disagree, as I say, regardless of the cause of the crush front, whatever is going on far above the crush front is irrelevant to the crush front.

If there are explosive charges going off

Then the behaviour of the ejecta would be very different...MUCH faster.

I must ask you to focus on the crush front, so that you fully understand what can be seen.

Do you agree that regardless of the cause of the crush front(s) that THAT is where the destruction of the building is ocurring ? If you want to assume "explosives" at this point in the discussion, fine, but it is important to remain focussed on the consequences of that crush front destruction.

Agreed ?

Mr Bear,

You ought to look into how these columns could buckle and likely did. The 47 columns were mostly 36' in length except at the mech floors but even then they were not very different in length. There were 38 sections making up each column... one atop the other. As the axial loads increased as you move down, the lower you descend the larger the cross section and axial capacity of the column. Most were built up from plates welded up to floor 50...several of the perimeter of the core were built up from plates extending further up the towers. There was a transition to rolled sections where a strong enough cold rolled H section was available.

The connections of column to column were obviously much weaker than the cross section above and below the connections. The connections were more or less to position the columns for erection, as there was little lateral loads at the column splices. However these joints do provide some structural continuity.

The columns were held *in column* that is their plan position by the bracing. The bracing restrained the column from moving laterally. Bracing was attached to the typical columns at about 3', 15' and 27' from the bottom of each column and the bracing supported the floor slabs.

Some of the bracing was set between the columns and some of was set outside (along side) the columns. This is true for the bracing of the long axis of the core for rows 500, 600, 900 and 1,000. All bracing is connected to columns with *bream stub outlookers*. For the bracing placed outside the column (not in the CL axis) these were very short beams... attached with the use of angles, bolts and welds to the side of the column and to the web of the bracing. The bracing which was connected to the CL of columns was also connected by beam stub outlookers at each end... so the bracing was made up of two short segments - the beam stub outlookers and a longer length of a steel WF H section. Again the weakest point would likely be in the connection of the beam stub outlookers to the column and the longer H sections.

The strength of a column of a given type of steel... such as A36 steel which has a yield strength of 36K PSI... is related to a ratio of its cross sectional area and its unbraced length. That is... as column of given cross section can be used as a short, medium or slender column with its yield capacity decreasing as its unbraced length increases. The length of a WTC column was over 1,300 feet not considering the sub basement parts... the braced length was under 12 feet which was the floor to floor height where the bracing was attached. For any given region... when the bracing is removed... from any cause... the strength of that section is reduced.

When a column fails from buckling the stress causes the column to compress and bow outward. You can take a thin stick and push downward against a resisting bearing surface...the stick will bow outward and if the load is large enough.. snap at mid section. If the column were made from segments it would likely fail at the joints between segments... which are weaker than the column section itself. The sort of failure can cause the column section to spring outward.. normal to the axial load.

A slender column has an upper limit as well. Beyond that slenderness ratio.... it will self buckle... it can't even support its own weight. Of course bracing will reduce the unbraced length and enable the column to stand and carry axial loads.

The ROOSD collapse of the floors regardless of whether an entire floor was destroyed in the same instant... resulting in increasing the unbraced length of the columns... reducing the load capacity... and making it less stable. It's likely that the post initiation column failures were the result of loss of bracing (from ROOSD) and attendant loss of load bearing capacity exceeding the safety factor. Rather than the columns crushing down and buckling... the failures occurred at the splices... springing the column off in 36' sections.

The core columns surviving the floor collapse toppled as a result of *Euler buckling*... that is their slenderness ratio was too high and they buckled from their own weight... again failing at mid length.. kicking out sections breaking at the splices... leaving the top section with no internal stress....not support and they plunged straight down... like an icicle falling from a roof.

The remaining columns... after the floor collapse broke apart from Euler buckling or as a result of impact with the ground which again failed the weakest point - the splice.

Consider the massive core columns which were box sections. Regardless of how strong the full pen welds were joining them together, these welds were a tiny fraction of the strength of the box section. When a 9 story (3 segment) box section topples...the welds break and the columns are almost completely intact... lying about on the ground.

The destruction of the columns post initiation was NOT from fire, explosives... but from gravity and mechanics.

It's that simple.

SanderO: Thank you for that detailed description, it's appreciated. Yesterday I went looking looking for similar information, such as dimensions and column/beam connection methods, among some NIST documents; particularly NCSTAR 1-6. I didn't find much of what I was looking for - I was probably looking in the wrong place (though it seems like it should have been relevant there). Your hypothesis sounds plausible and could be what happened (or a close approximation). However, plausibility of a hypothesis is not confirmation, and I feel that further investigation and analysis is essential before any conclusions are drawn.

SanderO wrote:It's that simple.

Good. Now we just need testing to confirm that it's not only simple, but physically possible, and probable, under the assumed conditions. Until then, I acknowledge the hypothesis, but I'm not committing to it.

femr2 wrote:Then the behaviour of the ejecta would be very different...MUCH faster.

I feel that this is an expression of too much certainty under conditions where there are many unknowns. If explosives and/or incendiaries were used, we do not know what kind were used, we do not know where they were placed, we do not know how much was used, we do not know how they were timed, etc.

I am unwilling to commit to anything where I either do not fully understand what I am committing to, or where there are too many unknowns or too much speculation, or where contradictory evidence appears to exist. I am not saying that I think you are wrong; I am just saying that you appear to be asking me to agree in a situation where I do not yet feel comfortable in expressing agreement. Please proceed, but with understanding that there are limits to what I am prepared to agree to. If your presentation appears solid enough, at some point I may be willing to go back and say, "yes, I now agree to that."

Wildbear wrote:I feel that this is an expression of too much certainty under conditions where there are many unknowns. If explosives and/or incendiaries were used, we do not know what kind were used, we do not know where they were placed, we do not know how much was used, we do not know how they were timed, etc.

Good point.

I am unwilling to commit to anything where I either do not fully understand what I am committing to, or where there are too many unknowns or too much speculation, or where contradictory evidence appears to exist.

Most sensible.

Thanks, OneWhiteEye. It's nice to be in an environment where I'm not berated for not mindlessly kowtowing to one school of thought or another.

And for the others: I hope my feedback will be taken constructively, and not cause any offense or frustration. I hope that we are all pursuing the same objective here and will be open-minded about it.

I hope that we are all pursuing the same objective here and will be open-minded about it.

I hope I don't tar you by praising you, but it feels like there is finally a sane person on this forum who understands that, beguiling as the ROOSD hypothesis is, it does not rise to the level of theory because certain members of this forum studiously object to moving to the hypothesis testing phase of the scientific method.

They are offended by lack of immediate acceptence of their theory but they refuse rise above description of the visual record in visual terms as if that constitutes science somehow.

"All science is either physics or stamp collecting." - Ernest Ruhterford

I fear there is an awful lot of stamp collecting going on here, however well meaning. Heaven knows I have tried to explain this to people here, but they seem completely enamored by their own ideas.

Maybe you will have more luck, I wish you godspeed, for what it's worth.

Darkwing wrote:certain members of this forum studiously object to moving to the hypothesis testing phase

Nonsense. Feel free to build whatever you please to confirm or clarify your own understanding.

Berating others for not doing what you want them to is not the way to go.

In short, if you feel that physical model testing of the ROOSD hypothesis is required for your personal progression, get off your ass and get to work.

We've spent hundreds, if not thousands, of hours cross-checking minute visual cue information against the suggested mode of progression, and built virtual models (such as my asynch model) which further suggest the plausability of the ROOSD hypothesis.

If you need to build a SCALE model, I wish you well, though I personally would use the significant funds that would take for something more personally gratifying and worthwhile.

If you need to build a SCALE model, I wish you well, though I personally would use the significant funds that would take for something more personally gratifying and worthwhile.

What I am getting at is that if it doesn't have predictive power and is not falsifiable it is not science. No amount checking, explaining and describing an historical event will ever amount to a scientific treatment.

If you don't like scale models that is fine. There are other ways to attempt to falsify an hypothesis. But insisting that a hypothesis is not falsifiable because it is based on extensive observation only reinforces the conclusion that it is unscientific.

Usually it is the prerogative of the person putting forward the hypothesis to put forward ways in which it may be conceivably be falsified by failing to correctly predict the outcome of some experiment. It doesn't have to be scale models.

Darkwing wrote:What I am getting at is that if it doesn't have predictive power and is not falsifiable it is not science.

Is science the only means to know something? Can science establish the truth value of everything?

What was I thinking five seconds before I started writing this post? Please feel free to use science in any way you please; good luck. You'll never know for sure what I was thinking. But I do.

You might be able to guess, and you may be right. How do you prove it? How do you go about falsifying your hypothesis about what was on my mind? Is it even necessary to know with certainty to act meaningfully on information?

I think it's important for both the yayers and the nayers on a given topic to recognize the mutual gaps which sometimes exist in the common language of discourse. If you don't know that Euler buckling exists, it's not even part of your worldview constructions let alone your arsenal of tools for explaining observed phenomena.

If the phenomena you are observing is indeed Euler buckling, and you have no concept of it, you will be at a total loss to explain what you're seeing. I'm not talking about the name for something, I'm talking about the something itself. It may be possible for you to leverage your observation into a true understanding of the phenomena - and then might be tempted to name the effect after yourself not knowing it's taught in undergraduate structural classes.

The issue is - ignorance. I don't mean it in a disparaging sense, just that when you don't know something you are ignorant of it and can't make use of it to aid in further understanding. Many discussions I see are steeped in incredulity at very well understood phenomena and invariably go off course into pointless bickering because one side simply cannot accept that the boundaries of their knowledge on a particular subject may end right where standard freshman coursework begins.

On the other side of the fence, someone who is comfortable with a subject may not approach it with the necessary rigor to differentiate the cases where looks can be deceiving, simply because of a rote familiarity and habit of reaching for the same old tools when solving a problem.

Here, in this thread, the explanations DO come off as "this IS what happened" as opposed to "this COULD be what happened" and naturally that reflects personal confidence of those telling the tale. So long as that is understood, what's the problem? Of the two conditions I've raised in this post, ignorance of well-understood principles of physics and engineering seems to me a much bigger obstacle towards obtaining representational models. If you don't know about Euler buckling, you cannot explain the fall of certain core segments towards the end of collapse. You will resort to some f***king magic to explain your observation, whereas a structural engineer will not only be able to call it for what it is, they will be able to predict the threshold at which it would occur.

Most of what I see here are remedial explanations of very basic engineering concepts which your average person does not know. They cannot be faulted for not knowing; though elementary it is also specialized and there is no expectation the general populace should be conversant. However, if members of the general populace choose to inject themselves into conversations of this nature, it is essential they get up to speed on certain tools and vocabulary such that they are not fatally impeded by their ignorance.

Like discussing disease vectors when you have no concept of the existence of a microbial world, your position will be stilted by what you don't know. It's really as simple as that. Now, you learn the rules, examine things carefully, and if it still doesn't make sense - then you may have something, but at least you'll have the means to articulate it in such a way that others will be able to objectively reconstruct what you claim to be discrepant.