How does this Domino Tower Collapse relate to 9/11 Collapses

Definitely this one:

 

It's a total, progressive, axially symmetrical top-down collapse of a slender tower without explosives, so in a sense, it is a token of intellectual honesty often forwarded by some members of the "9/11 truther community".

The domino tower experiment defuses the somewhat common misconception that 9/11 skeptics claim it is outright impossible to achieve such a total progressive collapse without explosives. It does however demonstrate that, if not explosives, certain other, additional, assumptions must be made about the structure to allow for its self-disassembly.

 

The debate consists of two diametrically opposed views:

1.) additional assumptions must be made to explain the unprecedented and unique way the Twins fell (explosives, steel-eating termites, alien space laser beams)

2.) the Twins' fall was entirely natural, expected and inevitable

Hence, any experiment that professes to demonstrate how the Twins fell without such forms of additional energy input must necessarily bear some semblance with a house of cards or a domino tower or a similar Rube-Goldberg machine setup, or, in other and more scientific words, be extremely metastable, and have the energy required to overcome the force holding them up already built in. So it is not so much an attempt at dismissal as it is an attempt at formulating the argument in a clear and concise manner, at getting to the point and bringing matters to a head.

Put even more simply: models that do somewhat mirror the Twins' collapses and arguments that try to "normalize" such a behaviour dismiss the Twin Towers, and insult the engineering feat that realized them, as "domino towers" and "houses of cards", as death traps engineered, on purpose, with a "self-destruct" mode - whereas the opposing (minority) view holds that in general, skyscrapers are quite stable structures, and that a lot of thought goes into making them stand up, and thus, the collapse should necessarily have arrested sooner or later.

By falling, by and large, just as the Twins fell.

That the Twins were extremely metastable systems which had the energy needed to overcome the force that held them up already built in - in one form or another - and required only very little energy input to powerfully release all their potential energy.

 

To the extent that planes have become quite "natural" ever since the Wright Brothers' first takeoff, and to the extent that building fires have been quite "natural" ever since humans have decided to engineer their dwellings outside of caves, it is, for all intents and purposes, quite "natural" to expect a plane crashing into a building every now and then and a fire to ensue in the process.

It would seem that, despite years of lurking and several weeks of serious ketchupping through previous related threads, I am still utterly unfamiliar with some of the rites, habits and customs of Metabunk - is it usual to pretend all preceding discussion has never occurred? I am, for example, quite surprised to find the planes and the fires becoming a topic when discussing the collapse again although previous threads on the collapse made abundantly clear that the initiation of collapse is a premise taken for the sake of the argument, and may (since a lesser building than the Twin Towers would have been forgiven for allowing initiation to take place), in the spirit of "A Simple Analysis", be generously assumed and modeled by simply dropping the smaller upper part of the tower on the taller lower part.

It was intended as a summary of the argument presented by supporters of the official explanation and/or opponents of alternative explanations. Close study of the threads "Use of scale modeling", "Deny the inevitability" and "Rate of Crush" - or the official literature, for that matter - will surely reveal that this is the gist of the message, not a misrepresentation, nor an invalid paraphrasing of the viewpoint taken by "debunkers". Once initiated, there was no way the lower part could have arrested the progression of collapse - "there is no way to deny the inevitability". There is, as far as I can see, not much room for interpretation errors in this matter, which does not mean I am not open to correction.

The point is that the domino tower falls like the Twins. Whether or not the Twins were built and engineered like a domino tower is a different matter. If those who deny the presence of steel-eating termites and space alien laser beams also dismiss a domino/Rube Goldberg machine/house of cards/any other form of chain reaction mechanism and dismiss Bazantian crushing scenarios -- what else can possibly explain that and how the Towers fell in a reasonable manner? I have only one last analogy left, and that is Genady Cherepanovs Dutch Tear hypothesis - but that would be worth its own thread, if anyone is interested.

We are, however, not operating in an information vacuum, we are making a comparison. The 500mph plane crash and the ensuing kerosene deflagration triggering one hour of office fires are "very little energy" compared to the powerful energy conversion they - as some claim, they alone - caused: all potential energy was converted into kinetic energy and deformation.

It's a simple numbers game. Estimates for the kinetic energy of the plane impact range from ~3-6 GJ (it should be noted that the structural response of the towers is really hard to make out, except by close analysis of the Myers video which shows a slight, but distinct northwards sway of the tower. It is fair to say that in a macroscopic sense, the towers hardly budged in response to the impact).

A famous estimate for the kinetic energy after a free fall drop of the upper 15 floors on the rest is 2.1 GJ (although Szamboti et al have shown this to be an unreasonably high estimate). The equivalent energy of the 1993 basement car bomb was in the range of 3-5 GJ also, IRRC - just for comparison.

Estimates for the weight and mass distribution of the whole structure vary wildly, but assuming a lower bound of ~440 GJ (for 250,000 tons, CoM @ 180m), the statement that apparently - at least by the assertions of supporters of the official explanation and opponents of alternative explanations - "very little energy" sufficed to cause the Twins to release all their potential energy stands on solid ground mathematically by any measure.

This kerosene deflagration indeed looks like only very little of the chemical energy was available to cause much damage to the steel structure of the building, other than blowing out the window panes on three (!) sides of a few floors, ripping off a few aluminium panels and leaving a few scorch marks - and getting the office fires started. But if I understood correctly, this thread is about the collapse progression - I will gladly share some salient features of the fireball in a different discussion.

That is the point made by those who claim that explosives (or other forms of additional energy that do not traditionally belong into an office building) were needed to bring down the Twins the way they came down, yes.

(Note, by the way, that it does not suffice to build a tower from dominos to ensure progression of collapse. They must be arranged intelligently, meticulously and purposefully to achieve that aim. The approach to building a stable tower is a completely different one, even with dominos, and arrest of a top-down collapse could easily be achieved, even without welds and bolts - solely through the friction between the dominos).

The collapse is - in proportion - a little on the slow side, I confess, but other than that, I have yet to find anything remotely resembling the Twin Tower collapses as much as the domino tower collapses do in terms of axial symmetry, lateral distribution, smoothness of progression and completeness.

 

The domino tower is enough to refute a couple or so of the most fundamental errors made by a number of CD truthers.

You probably recognize the class of "Newton's law" arguments, populated e.g. by David Chandler, that roughly go like this:

• On each level, the structure could bear the full load above, plus some nice margin of error / factor of safety.
• As the collapse progresses, the standing part would alway exert the full force of m*g upwards against the falling mass, of not messed with.
• Since that falling mass accelerates at 0 < a < g, the lower part actually only exerts an upward force of 0 < m*(1-a) < m*g
• Therefore, the standing structure must have been messed with - on every level all the way to the ground, or else the collapse would have arrested

The premises of these arguments are all true[ETA: See footnote] for the domino tower, but the experimental result refutes the conclusion.
The conclusion is thus disproved.


Aka is correct to describe both the domino tower and the WTC towers as "metastable": They are only stable as long as the full assembly is in their as-designed state (or sufficiently close to it), but very unstable once they leave their design envelop.
One such deviation from the design envelop could be simply the fact that the top part is moving down at a speed beyond what buildings are designed to withstand (e.g. to survive seismic accelerations). Or that some key connection, or a set of connections, is severed.

The domino tower thus may have some limited usefulness in demonstrating a simple principle: That of metastable structures.

[ETA] Actually, 0 < a doesn't seem to be satisfied throughout. It looks like the domino collapse alternated between accelerating and decelerating, averaging nearly zero after it first started. It may be useful to think about why the vertical progression never completely arrests. This tower seems to be nearly a limiting case and may as such have additional usefullness.
I am indeed reminded of the old results by the the911forum guys (achimspok? femr2? reported by Major_Tom) who claimed, IIRC, that the WTC collapse front reached a terminal velocity (not acceleration) - something which I have aways doubted, as my own spreadheet sims of a CoM-driven pancaking of floors tends to converge on a final acceleration.

 

Different mechanism, different results. Bazant's methodology converges on g/3 (that's you, too, right?), Seffen on g/2, and reality 0. Or so it seems. There's velocity dependence involved.

 

Is there any analog, a similar physical phenomenon, is there anything this process, this sequence of action of an object upon itself can be compared with?

I have offered, as working analogue physical processes and phenomena, so far:

- A house of cards
- A domino tower
- A Dutch Tear
- A slinky dropped from the roof
- A Rube-Goldberg machine
- The sped-up footage of a burning candle

...and it is with some conviction that I say they beat:

- A hammer dropped on a glass table
- A barbell dropped on a soda can
- A bowling ball dropped on the head of a truther

...by far in terms of energy signature; time history, overall behaviour and visual similarity.

That is indeed a hypothesis that has been in circulation for a while.

...which is a beautiful way to explain the concept of metastability.

A piece of wood is metastable too. It is relatively stable at room temperature, but once "initiated", it will burn (do heat work) and slowly fall to a lower and more stable state - ash.

I largely agree, but please clarify: does setting up the tower deliberately in a very special and completely counterintuitive way (from the viewpoint of building a stable tower) to ensure its collapse not qualify as "messing" with the standing structure on every level all the way?

Measurement would be futile with all the fine granularity involved, but merely from eyeballing I would agree and even say that is another good reason to find that actually, the domino tower seems to mimick the real thing quite well - it also reaches a "terminal velocity" (if the uppermost "fountain" is counted - I think Chandler shows in Acceleration and Serendipity that the ejecta from the windows continue at the initial roofline acceleration or so).

PS: Hi OWE

 

This is the analogue I offered at physorg in 2008. It was not well-received; ignored at best. There's little effective difference between no connections and trivial ones.

 

akaREYON?

 

The one, at your service!

There should be a discernible difference between a building being in the way all the way and a building getting out of its way to get out of its way...?

1. A demolition method
2. deceleration of progression

None getting anywhere near the similarity the domino tower has with the Twins' collapse pattern.

A bookshelf held together with magnets so wobbly and delicate it can rise to 18 floors at most and only if nobody sneezes (no offense, really not - you know I think it's great, the first of its kind, unique, the magnets were a brilliant idea and you have all my respect for all the work, time and money you put into it, and I'm not dissing you at all with this - but in comparison with the domino tower, as far as visual similarity with the Twins goes, it really still needs a lot of work and fine-tuning).

 

Just for clarity, verinage is not a method that would work on steel frames.

 

Greetings!

Maybe. I'm still trying to get my head around the statement.

It is the propagation of a defect. I'm not sure that treating it like a building is proper, once the phase transition starts. It's something else entirely.

 

Hi OWE - this series of related discussions more your area of interest than mine for reasons which should be obvious to you.

Save me scouring the sources - isn't the BIG difference that femr et al measured the real event and others did theory calculations?

If that is so you know where I would go. If I'm wrong I'll retreat back into my shell.

 

I agree there, yes. Verinage (a form of controlled demolition) is much more comparable to the WTC collapses than the "natural" collapse of a tower of dominoes.

 

Yes. femr2, achimspok and I all measured and got roughly the same result. Of course, measuring the leading front is not the same as an aggregate metric, but for an extrema it suffices. And, if you extrapolate the constant velocity from the region measured to ground level, it's within an acceptable band of collapse time.

So that's reality compared to theory, correct. However theory need not be so disconnected from reality. Depends on whose theory it is. David Benson's vertical avalanche formulation does have velocity dependence and can achieve terminal velocity.

 

Emphasis mine - that is the key here, you know how to name things. I would say it "liquefies", except that the top would buoy in a liquid that is denser. So it either must turn into a gaseous state or densify first (also according to Newton's impact depth formula).

Exactly!

I disagree! I was incorrect when I thought vérinages start in the middle - in fact, the patent says the top 1/3 would be enough - and that they expect something remaining upright and needing an excavator. And as Chandler shows, the roofline and collapse front decelerate - whereas the real towers' collapse front - and the dominos - hit terminal velocity and keep it up until the bitter end.

Are there any regulations or benchmarks on how fast a building is allowed to disassemble itself before it becomes "unacceptable"?

 

Haha! I just meant that if one adds the time the measurements started to the extrapolated time to reach ground, the figure is close to generally accepted values for the collapse time. I mention this because it might seem that a terminal velocity would lead to a collapse time longer than observed.

 

I agreed with Mick on the basis of verinage being a form of controlled demolition.
Verinage would be the equivalent of pulling some dominoes out of the middle, jenga style.

 

Thanks - my "Old Farts" memory vindicated.

Understood of course. BUT - As always - my problems arise when the relationships are not "connected' - not defined and there are lots of loose hanging inferences that the theory somehow is relevant to whatever. Mostly my focus on the real WTC events but same goes for anyone's abstract model - if the logic is loose or none existent discussion can wander all over the planet.

I think you mean WHAT the theory says - not WHO wrote it - i.e. how well the theory ties to either reality or the model.

 

Yes, although the exception is that if I say it, it's better.

 

Modesty inhibits several responses.

 

Except for the "deliberately" part, I agree with this sentence fragment.

 

Agreed. The vulnerability to progression arose from the OOS Tube in Tube design. A deliberate feature of design. But not intended to ensure progressive collapse. The building design intended that it not reach progression within the design parameters. But under the massive trauma - way outside design parameters - progression and progression to global collapse were both inevitable. Easily demonstrated/explained/proved by direct access to the physics of the real event. Hence my concerns that models can demonstrate what happens but the quantitative physics is easily applied directly to the real event.

The bigger picture issue of engineering design and regulatory code philosophy is "Should buildings be designed for "soft fail" when taken beyond the design envelope" And that is circularly redundant - because it effectively extends the design envelop. The question of "ultimate soft fail" philosophy is still valid but not relevant here.

 

I am not aware of when, where and through what mechanism Bazant arrived at g/3, but that's what I got: By modelling pure momentum transfer of floors pancaking inelastically. No strength, force or energy of anything considered (connections can be thought of as holding the floors just barely, but requiring practically zero force/energy to disconnect once tapped on ever so lightly). That seems as far away from anything Bazant has modeled in his WTC papers as I can think of. Or I missed that part (quite likely, given that I never truly studied any of them after B&Z )

I am of course aware that my model is missing a great deal of reality - mostly the columns, but also elastic components, mass shedding, etc. I would not be surprised in the slightest if someone added one or several of these factors to my model and came up with a terminal acceleration of 0.

What I meant to say is: We might get inspired to think about what factors lead to terminal velocity by looking at the domino tower.
I think in the domino tower, the main reason why collapse doesn't accelerate on average is that all the descending mass is shed as fast as it acrues.
And also perhaps because the main failure mechanism pieces sliding and toppling sideways, not failing in the vertical.

 

The reason you get the same result is that the discrete algebraic solution in the limit of infinite stories / infinitesimal story height reduces to the continuum solution of Bazant. Plus the fact that realistic structural dissipation functions do not contribute to the acceleration limit, just prolong getting there as the structural resistance increases. Your model is the Greening model, and is exceedingly useful for exploration of the solution space, as it's a great deal more flexible than the analytic approach (which ends up having to be solved numerically anyway).

The key is there has to be a natural dynamic equilibrium, which means drawing in velocity as a term somehow. As velocity increases, resistive force increases. Mass shedding (as you note below) is a parameter which can drastically alter the characteristics of the dynamics, and it is physically reasonable to suppose a velocity dependence of some sort.

Excellent point. Clearly the mechanism is entirely different than the tower collapses, which might lead to premature dismissal of the instructive value it offers.

Are there parallels? If one looks at the problem framed in terms of "propagation of defect (phase transition)", there are. This puts the tower collapses (but not verinage) in the same class of systems as toppling dominoes, card houses, growth of cracks in crystals, fiber strand breakage, polymer disordering, and so on. It could be argued that this approach will not lead to typical equations of motion so is inappropriate to the study, but I say that all of the classical mechanics formulations to date fail to capture the dynamics anyway.

 

Both do demonstrate, as Oystein pointed out above, the fallacy of the supposed violation of Newtonian physics.
Both however are structures that have each level's "floor" support the entire portion of the structure above. In that, they do not represent the twin towers structures which transfer each floor pan load individually to the columns.
An analogue for this difference would be parallel versus series electrical circuits, and we know they behave very differently.

Demonstrate propagation of compressive forces. Since there is no evidence of shattered columns I don'the see how this relates to the TTs except perhaps how the seismic record shows the entire collapse.

By definition it can be anything arrangement you wish. OK it's a propagation of energies.

Now that's reaching. Is this supposed to bolster a Judy Wood argument?

.

Never intended as an analogue to collapse but as a demonstration of a single aspect, dynamic forces.

Same as previous with added emotional aspect.
Verniage also does not mimic the tower collapses in that it destroys vertical structural members directly while the towers came down due to loss of the horizontal members which laterally supported the vertical columns. (Bazant's calculations aside)
So, Mick's model: It satisfies the condition that floor loads are individually transfered to columns as in the towers.It also mimics the mode of collapse in that floor destruction leads column failure. Your beef seems to be that column section splices are too flimsy. However if you built this with three 4X4 continuous columns, those columns would still topple after removal of the floors. Build it in three dimensions with large continuous columns would make the fully connected structure much more stable but destroy the internal lateral supports between columns and they will still topple!

 

Yes,,,, IF the tower is tall enough.
Analogue would be skydiver in free fall. Eventually air friction force equals gravitational force and net acceleration reduces to zero. It is of little consequence if the jumper is just leaping off of a six foot step ladder. A shorter structure than the towers may well not see acceleration drop to zero.

Of course there is no mass shedding [for a skydiver]

 

Indeed. The Tacoma Narrows Bridge was not deliberately designed for failure either but it's design led to its failure.

 

Here is how I understand "Mechanics of Progressive Collapse" and I hope OWE will be so kind to correct me where I'm wrong.

ü=g-F/m

where ü is only typographically an Umlaut for convenience, it is the second derivative of u, the unit height: the acceleration.

If it is further assumed that the load-displacement curve is a given F(u), the effective acceleration only depends on how much mass is shed - so all that is needed is an arbitrary constant or function for that parameter which can then be used to fine-tune and reverse engineer the velocity history.

And since the area under F(u), let us call it E[elasticplasticpot], is smaller than E[gravpot], this is in essence a mathematical way of saying "for every meter height, there is on average less Newtons upwards force in the way than necessary to decelerate the kilograms of the tower against the gravity of the planet."

So far, Oysteins model (if I understand correctly) derives U, an optimum of the energy going into deformation/pulverization/etc/friction (in short: heat) to achieve optimum v, from perfectly inelastic collisions. So far, a Dirac impulse is assumed here, which is of course unrealistic (which does not matter because the Twin Tower floors did not hover mid-air) but extremely useful for analysis because it sets a baseline for the relations between a (downwards acceleration) and g (gravitational acceleration) for every meter.

The domino tower is built with the "cube" technique, which works like this:

and usually progresses at an angle, they "fall over" progressively:

Same with domino walls.

So I'm definitively not saying the domino tower is a perfect illustration, or that the Towers were built like such. The math is a completely different one in this case - more "runaway" and self-propagation than the "crushing" scenario.

Which might explain the terminal velocity aspect though, maybe.

My point was only that is the next best thing visually of something disintegrating from top to bottom, but I'm happy we're having this discussion about a mathematical model.

That's a nice strawman you're building there, it would be a shame if somebody came to knock it over!

Explaining the WTC collapse with the Tacoma Narrows Bridge is like explaining zero point energy with a steam engine. When Galloping Gertie fell, she fell like other suspension bridges fell. The Twins fell unlike anything ever.

 

Pet peeve:
Deceleration is NOT imho, a reduction in acceleration, but rather a change in the sign of acceleration.
To use it for both situations just makes the term horribly ambiguous.

 

The strawman is simply a result of misapplication of physics by others. I guess you also missed it when Oystein ( I now note my new tablet'so annoying autocorrect) said the same thing.

I am not "explaining" the WTC collapses with the TNB collapse. I am pointing out that a design peculiarity that allows for collapse need not be a deliberate feature the engineer built in.

 

I understand. And I refute it by pointing out, by means of the domino tower model, that there is a measurable, energetic difference between "shit happening" and "a plan coming together", between failure due to stupidity and neglect and a perfect chain reaction, between dumb accident and blatant purpose, between ordo ab chao and intelligent design. .

 

So far so good. (How do you do subscript?)

So we have ma - the upwards force - and mg, the gravitational force. When it stands, they are in equilibrium. ma must do the virtual work of keeping it up, even if there is additional momentum - gold bullions, storms, books, people, elevators, doors. For that, the "stiffness" of the structure is chosen so that ma = kd (stiffness times displacement), so that for most displacements arising from additional momentum, the structure stays in equilibrium by pushing back with as strong an ma as necessary to stay where it is and, most of the times, simply by virtue of its mass.

When it falls, ma is considerably smaller than mg the whole way, though. There is a lever between the ma that keeps the tower up and the ma that decelerates the propagation front to terminal velocity and thus the effective fall rate by a few m/ss.