The Obligatory 9/11 Thread Part II

[Xaihe]

What evidence do you have that there was any steel bigger than nails in that building?

I don't see any indication of girders.

- Why are you asking this question?
- Where does this objection even come from?
- Does this mean that you think the composition of a building or model is important and that it should have a certain minimum amount of steel?

Were WTC 1 and WTC 2 skyscrapers?

What holds up skyscrapers?

Does the steel have to be properly distributed for a skyscraper to hold itself up?

For any building to collapse straight down completely doesn't it have to destroy all of its own supports? Have you seen me ask about the TONS of STEEL and TONS of CONCRETE that were on every level of the buildings before now. Is this something new for me? This ongoing pseudo-debate focuses on limited areas at different times and people act like I have forgotten about other related aspects. Just because I talk about collapse doesn't mean I forget that STEEL HAD TO GET HOT ENOUGH for the collapse to start. I have said there were three reasons for needing to know the distribution of steel many times. So how much steel was in the vicinity of the impacts. So the amount of steel on every level should have been settled long ago.

psik

Why do you demand the same standards for skyscrapers as for smaller buildings and scale models? I'll repeat my question: Does this mean that you think the composition of a building or model is important and that it should have a certain minimum amount of steel? I really hope you know the answer is "no" and that it's the same with every other objection you've given to reject models and buildings that can collapse completely.

[psikeyhackr]

What other strategy have you got?

About mass distribution... here are two runs of a step-wise 1D algebraic accretion model where the total mass is the same in both runs, but one has uniform story masses while the other has mass increasing linearly going down, such that the bottom story is 100 times heavier than the topmost. Model uses a 10/90 split on a 100 story structure, rigid top and debris zone, stretch (inverse of compaction ratio) of 0.0. Graph compares velocities of the two runs as a function of elevation (not time) for momentum-only:



horizontal : elevation in meters
vertical : velocity of descending mass in m/s
blue : uniform mass
red : mass gradient 1:100

Collapse times are 11.52 sec for the uniform mass distribution, 14.15 sec for the bottom-heavy. 25% increase in time and less than 3 seconds' overall difference for a 100 fold change in distribution ratios.

Adding in a conservative per-story fail energy (~0.38mgh where m is the accumulated mass above and h is full story height) increases the collapse times by approximately 3 seconds for both. The order of effect between introducing fail energies and using an absurd mass distribution is then comparable. I'm sorry I don't have any graphs handy of what happens when discontinuous spikes (e.g. mechanical floors) are introduced into the mass distribution; there are bumps, not too large for a realistic distribution, pretty big for 100x.

Suffice to say that, if actual mass distribution is known to story granularity to within +/- 50%, the mass distribution will have little impact on the overall mechanics in a model such as the one I offer, which is essentially the Greening model with stretch, though stretch is not used here.

Edits: corrected stretch value; forgot to mention the graph and stated collapse times are crush down phase only.

But what are the reported collapse times of the north tower?

Dr. Sunder of the NIST says ELEVEN SECONDS.

http://www.pbs.org/wgbh/nova/tech/debun ... ories.html

But 11 seconds is less than your magical collapse without supports. And you can just CLAIM that the energy required to collapse each level would add 3 seconds. What real data do you have for that energy?

There are collapse time estimates less than 11 seconds however.

http://www.911myths.com/html/wtc_collap ... mates.html

But even with your CLAIMED conservative and comparable minimum of 3 seconds the total of 14 seconds looks peculiar. But how did you compute the time due to the falling mass losing energy from crushing itself? Where did you mention that? In my model the falling portion lost energy crushing its lower two loops in addition to the stationary loops below. That is the nice thing about physical models. They don't allow you to forget REAL PHYSICS.

Computers have the Garbage In, Garbage Out problem based on the ASSUMPTIONS OF THE PROGRAMMER.

Adding in a conservative per-story fail energy (~0.38mgh where m is the accumulated mass above and h is full story height) increases the collapse times by approximately 3 seconds for both.

I asked you about that 38% before.

http://www.rationalskepticism.org/consp ... ml#p629107

But before a collapse can occur the downward force has to exceed that peak which would have to include the safety margin for that building. So your 38% is based on the ASSUMPTION that the collapse would continue and you have no proof that the peak force could be exceeded at EVERY LEVEL.

You are saying that a level can be crushed by 38% of its static load capacity because that is the force you are applying which is the AVERAGE over the collapse of that level. It had to have been designed to hold more than that AVERAGE but you are multiplying that force times the height of the level to get the amount of energy expended to do the collapse ACCORDING TO YOUR ASSUMPTION.

You are choosing not to question if the PEAK FORCE can be reached at every level. You are setting the PEAK FORCE to mg which would mean a building with no safety margin whatsoever. Do you really believe skyscrapers are designed that way? Assume the collapse and compute backwards to make sure you get a collapse. But it only takes one level for the peak to not be reached and the collapse would stop. You can't build a physical model that perfect. It takes 12 to 15 washers to crush a single loop. A loop has to be tested to destruction to find its limit. That is why I have 11 single loops at the top.

Most sources say the core was 50% stronger than necessary. Your math is at a perfect edge that cannot exist in the real world. My physical model is REAL WORLD.

Your velocity computation is based on NO SUPPORTS then you don't do anything to see if that peak force is satisfied and just do energy absorption based on the average. But gravity is not completely free to add energy because that would only happen with ZERO FORCE pushing up from below.

GARBAGE INDEED!

That 38% goes very well with your 1000 m/s. Create some complicated computer crap and presume no one will figure out the absurdity of the flaw in the assumptions.

You should go back to smileys. They are more intelligent.

psik

[psikeyhackr]

Why do you demand the same standards for skyscrapers as for smaller buildings and scale models? I'll repeat my question: Does this mean that you think the composition of a building or model is important and that it should have a certain minimum amount of steel? I really hope you know the answer is "no" and that it's the same with every other objection you've given to reject models and buildings that can collapse completely.

The standard is that the structure must support itself. For 1300 foot buildings that is no mean trick.

Because my model uses paper and is as weak as possible the distribution of strength is made obvious. Because the material is so strong the distribution is not as great and obvious in short buildings.

I have got two different models with completely different designs that demonstrate completely different phenomenon. More things happened to the twin towers than just a collapse. ALL OF THE PHENOMENON must be explained. You people act like the objective is to win a debate in some limited area. KD made up some 38% crap and CLAIMS it can explain the collapse but his theoretically perfect assumptions give collapse times greater than many estimates of the real event.

My impact model is to demonstrate that the mass and distribution of mass affects the structures response to sheer fources. How important is wind analysis to the design of a building less than 20 stories tall? My collapse model doesn't need excess strength to handle the wind. But any increase in the amount of steel in the tower for wind resistance would probably affect collapse behavior also. So the advantage of my model is control and repeatability. Looking at videos of the collapses of short buildings may be emotionally satisfying to some people but it doesn't mean much when the number of stories can't even be determined in the video. There is no way to tell if the walls were weakened in any way and the distribution of mass would be different from a 110 story tower that had to use steel.

Which KD demonstrated with his graphic.

psik

[Kat Dorman]

psikeyhackr, your last post to me is uncharacteristically focused on the true technical issues. Many questions deserve and require a detailed response and I haven't time at the moment to do it. Not sure if I can until next week. One thing that's easy right now is this:

I asked you about that 38% before.

I did actually explain that somewhat here but, looking back at it, it's not only incomplete, what's there is a lousy explanation.

Peak static capacity = FOS x LOAD = FOS x mg

Assume an FOS of 3 for purposes of calculation.

Peak static capacity is not equal to average dynamic capacity over full compaction of the supports. An assumed value is needed for that as well. Based on Bazant's load-displacement curve, which is backed by classical engineering formulations, which is in turn backed by enormous amounts of physical experimentation and empirical data on axial compression of steel columns, the value is around 13% of peak capacity.

3.0 x 0.13 = 0.39

The values which are nice round numbers as input to the formulas I use result in a value of 0.38.

These are all assumptions and ballpark estimates. But you have to start somewhere, and there's no point in pretending that well-explored properties and common construction standards are complete unknowns. These are GOOD nominal estimates.

Of course, the real values could diverge from these nominal values. But, before you continue to go off on GIGO, you need to know that the reasons I've done many thousands of runs was to try the huge number of combinations of possible values in these calculations. For example, running with FOS in small increments from 1.0 to 10.0 while holding the other parameters constant. Then, incrementing one of the other parameters (e.g., stretch) and doing it all again. And repeating until wide ranges of all parametric combinations have been checked.

In fact, I'm sure my off the cuff estimate of thousands of runs is way off, given the combinatorics. Many millions of runs is more like it. Mass distribution, mass shedding, average dynamic capacity, velocity dependent sinks, you name it - even heights, number of stories, inhomogeneous distributions, impact velocities (yes, including one series at 1000 m/s just to see what would happen). Arrest is possible under a variety of circumstances. Your physical model is one of them. I've plugged in estimates based on your documentation and arrived at similar results.

It's not garbage in. It's every possible combination of inputs in. There's a huge difference. I'm sorry I can't present the aggregate results of years of exploratory data analysis in a single post. I have, however, documented aggregate results in great detail, such as time allows. In the post you reference, I am presenting a range of results between two extremes of mass distribution while picking benchmark (stretch = 0) or nominal (maxwell line at 0.38mg) values to remain constant. The focus was on variation in mass distribution, not those other things.

Do you want thousands of graphs in an attempt to explain the grand picture in every post, or only one graph sufficient to get a very specific and limited point across? I've never tried to imply that one graph tells the whole story, or that the simulations are of a tower. It's a complicated subject. That short post of mine you cite is way too much for most people as it is. At least you seem to get the gist of some of it. Stop trying to play one post as the be-all and end-all of words on the subject. It's meant to be instructive, nothing more.

The collection of links I gave in my last post are a response to your implication that I have nothing but ridicule on my side. That was false.

[Xaihe]

Why do you demand the same standards for skyscrapers as for smaller buildings and scale models? I'll repeat my question: Does this mean that you think the composition of a building or model is important and that it should have a certain minimum amount of steel? I really hope you know the answer is "no" and that it's the same with every other objection you've given to reject models and buildings that can collapse completely.

The standard is that the structure must support itself. For 1300 foot buildings that is no mean trick.

Because my model uses paper and is as weak as possible the distribution of strength is made obvious. Because the material is so strong the distribution is not as great and obvious in short buildings.

I have got two different models with completely different designs that demonstrate completely different phenomenon. More things happened to the twin towers than just a collapse. ALL OF THE PHENOMENON must be explained. You people act like the objective is to win a debate in some limited area. KD made up some 38% crap and CLAIMS it can explain the collapse but his theoretically perfect assumptions give collapse times greater than many estimates of the real event.

My impact model is to demonstrate that the mass and distribution of mass affects the structures response to sheer fources. How important is wind analysis to the design of a building less than 20 stories tall? My collapse model doesn't need excess strength to handle the wind. But any increase in the amount of steel in the tower for wind resistance would probably affect collapse behavior also. So the advantage of my model is control and repeatability. Looking at videos of the collapses of short buildings may be emotionally satisfying to some people but it doesn't mean much when the number of stories can't even be determined in the video. There is no way to tell if the walls were weakened in any way and the distribution of mass would be different from a 110 story tower that had to use steel.

Which KD demonstrated with his graphic.

psik

If the standard is that the structure must support itself, then why do you go on about steel and wind? And why is this building not good enough? It really doesn't matter if the walls were weakened in any way, because the building is still self supporting, until they start pulling at it. Control and repeatability? I really do believe that demolition companies have those collapses for the most important parts under control and repeatability should be obvious. Where, under this standard, does the distribution of mass matter, as long as the structure supports itself?

Not good enough? Here's another. They didn't even need to use explosives, they just pulled it down close to the top and let the weight collapse the rest of it.
[youtube]http://www.youtube.com/watch?v=bL5bkxS2cFU[/youtube]

Keep in mind if you have objections such as how they are not analogous to the WTC that is irrelevant. You asked for any model. Well there you go!

The standard is that the structure must support itself.

That standard is met, isn't it?

[Kat Dorman]

The standard is that the structure must support itself. For 1300 foot buildings that is no mean trick.

For a paper loop and washer model...

KD made up some 38% crap...

As I explained above, I chose a nominal and sensible value based on the known properties of steel columns in axial compression. That's a far cry from making up crap, but you're entitled to your opinion.

...and CLAIMS it can explain the collapse...

But you're not entitled to lie. I do not, have not, claimed any such thing. Show where I've said anything of the sort. You can't.

...but his theoretically perfect assumptions give collapse times greater than many estimates of the real event.

I'll get to that. Not that I haven't already, but I've grown accustomed to going around and around with you on the same subjects. I can guess that you don't pay attention, but it's also possible you don't understand.

How important is wind analysis to the design of a building less than 20 stories tall?

Paper loop and washer model...

There is no way to tell if the walls were weakened in any way...

Argue with yourself:

So your idea of some perfect material that can be right at the edge of collapse and can all give simultaneously is nonsense. The material must stand over time even if weakly.

It is demonstrating the physical principles involved in a gravitational collapse with AS WEAK AS practically possible crushable supports.

So if a heavier structure was made as weak as possible it would not really be on the verge of collapse. It would have to be able to stand reliably for a time.

So it exhibits the unavoidable characteristic of the vertical supports resisting and absorbing energy from any mass falling from above and trying to crush them.

The problem is any material strong enough to support the STATIC LOAD can't be so weak that it is easy to destroy with the DYNAMIC LOAD. So all of the people who choose to believe or PRETEND TO BELIEVE that the collapse was possible must assume such a material exists.

The model is as weak as possible but it should be obvious from the video that it can support its own weight.

But it cannot be made weak enough to completely collapse but still be strong enough to support the static load.

...and the distribution of mass would be different from a 110 story tower that had to use steel.

Paper loop and washer model...

Which KD demonstrated with his graphic.

How many times do I have to tell you that's NOT distribution of mass?


And now I'll turn my attention to your more serious points. Hopefully, there's something of merit there. I get no joy out of you being wrong, believe it or not.

[Kat Dorman]

But what are the reported collapse times of the north tower?

Dr. Sunder of the NIST says ELEVEN SECONDS.

http://www.pbs.org/wgbh/nova/tech/debun ... ories.html

First of all, I'm not responsible for what Sunder says. I believe he's wrong. Yes, he is speaking from authority and there's no reason for you to take my word over his. But I'm not obligated to defend or support a claim I believe to be false. I've had very few kind words for NIST's analysis of either the towers or building 7. On the other hand, I have spent a lot of time criticizing them because I've seen compelling evidence to indicate they were wrong on a number of fundamental, important items. To me, this is just another one. I find it highly unlikely.

All the same, suppose he's correct. What might that imply? Now is the time you finally need to pay attention to this, since you didn't before:

Suffice to say that, if actual mass distribution is known to story granularity to within +/- 50%, the mass distribution will have little impact on the overall mechanics in a model such as the one I offer, which is essentially the Greening model with stretch, though stretch is not used here.

Emphasis provided to drill home the obvious. My claims are for my model, not the towers. The model is a 1D full accretion system. Basically, that's what your physical model approximates and vice versa. Whatever the tower collapses were, they were not one dimensional. I've hardly made a single argument about the tower collapses since I've been here; everything you take potshots at is typically accompanied by a disclaimer like the above, which you fail to notice.

So if the towers were to actually collapse faster than is possible based on what a 1D full accretion model allows, what can one conclude? The tower collapses did not conform to a radially symmetric full accretion system. That might be a significant revelation IF the claim of an 11 second collapse were true and IF it weren't already painfully obvious from videos.

But 11 seconds is less than your magical collapse without supports.

You seem to think momentum-only in a 1D model dictates some sort of cosmic speed limit in a 3D collapse. It doesn't. Lateral deflection and mass concentration, column bypass, inelastic collisions, mechanical affects like cleaving and elastic waves transmitted ahead of the physically moving debris can all act to reduce collapse times. It's painfully obvious you've considered none of these factors.

This is the kind of thing that econ41 has been trying to get across to you for some time. I know I'm arguing about the results of 1D models, not the actual towers, but you don't. It's really time for you to get on board with that. My models and your model are simplifications which can help in understanding the particulars of collapse mechanics, if properly interpreted (i.e. in accordance with basic physics and engineering, not wild intuition).

But I don't buy the 11 seconds, anyway. All I'm saying is, if it were true, neither my models nor yours provide a speed limit for the towers.

[Kat Dorman]

And you can just CLAIM that the energy required to collapse each level would add 3 seconds.

My reasoning is given above, also the limits of applicability. If you had the knowledge and skill to make your Python program do the same, you could confirm the conditions under which it is true. Pity.

What real data do you have for that energy?

You asked this before I responded with an explanation of the 38%. That explanation should suffice, but if it doesn't, I'll remind you that enormous amounts of real data, gathered over decades, using real steel and real columns, was used to derive an analytical expression for the load-displacement relation. Moreover, the validity of using an equivalent average force over the entire distance of crushing (Maxwell construction) is well established from both theory and practical experience - not limited to steel columns.

It works when I plug your model's data into it.

There are collapse time estimates less than 11 seconds however.

Yes, and I find them of very low credibility for very good reasons.

http://www.911myths.com/html/wtc_collapse_time_estimates.html

Did you do anything besides Google this and post the link? Of the 9 claims:

- 5 explicitly claim times under 10 seconds
- 1 gives a range which goes as low as 10 seconds
- 3 explicitly claim times of 14 or more seconds

Of the 6 which allow for less than 11 seconds:

- 1 refers to the time given by the 9/11 Commission Report (a POS, IMO)
- 5 have reference links

Of the 5 which have links:
- 3 are "Page not found"
- 1 is Thomas Eagar's article
- 1 gives a range between 10 and 14 seconds

Thomas Eagar: I have even less respect for that fatass windbag than I do Sunder. The last time you brought his work up on this forum, I wrote a long post detailing the provably false statements in his article. Just because he's part of the official story doesn't mean he isn't full of shit. But you can believe THAT part of the official story if you want to, be my guest.

The last one says 'According to testimony provided to the 9-11 Commission, the tower fell in 10 seconds. Other data shows it took closer to 14 seconds." It is not an independent source for the 10 second figure, and mentions DATA SHOWS it took closer to 14 seconds.

That's a small amount of support for the notion of less than 11 seconds. The sole sources in the entire page are Eagar and the Commission. Eagar proven to be ignorant of tower construction, and the Commission (generously speaking) was a non-technical work. Whose 'testimony' was it? Someone on the scene with a stopwatch and an unobstructed (yet safe) view? Perhaps Thomas Eagar testified.

On the other hand, REAL DATA indicates around 14 seconds or more for the internal collapse progression to merely reach ground (here's a non-broken link for you). Bazant calculates around 14 seconds for the north tower and correlates with the ground velocity seismic data. Cling to 11 seconds if you must, but the evidence is stacked against it.

[Kat Dorman]

But even with your CLAIMED conservative and comparable minimum of 3 seconds the total of 14 seconds looks peculiar.

Well, what can I say to that? It looks peculiar to you. That's OK.

But how did you compute the time due to the falling mass losing energy from crushing itself? Where did you mention that?

It's a rigid top approximation. Before you take this as some kind of sign to go off about the unrealistic nature of a rigid top, let me again remind you of things I've told you time after time but you've ignored:

- Results from computations using a non-rigid top are not very different from rigid, except for the roofline displacement
- The difference is the roofline falls FASTER
- Motion of the center of mass is virtually identical
- Total collapse times nearly the same
- I've done tons of those calculations, too
- I was trying to minimize factors and keep it simple, as I said above

In my model the falling portion lost energy crushing its lower two loops in addition to the stationary loops below. That is the nice thing about physical models. They don't allow you to forget REAL PHYSICS.

All true.

Computers have the Garbage In, Garbage Out problem based on the ASSUMPTIONS OF THE PROGRAMMER.

The only garbage assumption being made here is by you, assuming that garbage is necessarily being fed into each and every computation. This is a provably false assumption, and I have done so in this thread, on this page.

But before a collapse can occur the downward force has to exceed that peak which would have to include the safety margin for that building. So your 38% is based on the ASSUMPTION that the collapse would continue and you have no proof that the peak force could be exceeded at EVERY LEVEL.

You are absolutely right!!! Thank you. I will address this next.

[Kat Dorman]

You are saying that a level can be crushed by 38% of its static load capacity because that is the force you are applying which is the AVERAGE over the collapse of that level.

Correct. This is the so-called "Maxwell construction", a physical law of nature, expressed in a simple mathematical form, and borne out each and every time by experiment. It only applies when the supports are completely crushed. If the stories are crushed (and a couple of other conditions are true, which I will explain only if you're interested) it is a valid means of doing the dynamics of crushing a level.

It had to have been designed to hold more than that AVERAGE but you are multiplying that force times the height of the level to get the amount of energy expended to do the collapse ACCORDING TO YOUR ASSUMPTION.

It's not an assumption, it's a fucking law of nature - one which you are ignorant of.

This brings us to... what happens if there isn't sufficient energy to crush a level? Then the Maxwell construction can't be used.

You are choosing not to question if the PEAK FORCE can be reached at every level.

Number one astute observation you've made recently, perhaps in forever.

Correct, I am choosing not to question if the peak force can be reached at every level. But you wouldn't know that from the graphs, because they don't tell that story. All of my computational environments are capable of accounting for peak force, only one of them allows me to choose not to! All of them give results which agree to story level detail, whether the Maxwell construction is used in the one environment or not.

There are three environments:

1) A storywise crush calculator (discrete algebraic model)
2) A physics engine
3) A extended finite element program

The first only supports a rigid top, because two degree of freedom calculations (that is, where the upper block can crush too) cannot be done in the discrete algebraic method. The other two can support non-rigid tops but do not have the overall flexibility of the first. They can also suffer from being too realistic sometimes (example: the vibration you had a cow over is actually quite realistic for 1kg metallic masses in collision - you ever heard metal ringing? Duh). I end up with an artifact of the test configuration rather than a demonstration of a fundamental principle.

Therefore I frequently use the first environment, even though it can't do a collapsing upper block and despite its story resolution limit. I programmed this (many times, many ways) myself, and I've included a setting to indicate whether to run with a Maxwell line equivalent average force over an entire story, or to section the story into elastic, peak plastic, and minimum plastic step value approximations to the actual chosen load displacement. This is not as precise as the other two environments, which are both iterative force/constraint solvers of different architectures, but it is sufficient to establish arrest or no arrest at each level.

That's not to say the Maxwell line option can't arrest. When I model your model, I use the Maxwell line and I come up with the same number of stories crushed, only mine are necessarily all in the bottom block when using the first method. It arrests just fine.

If I know that there's no way a particular configuration will approach arrest, based on more detailed runs, I use the Maxwell line. After all these trials, I have a pretty good feel for what will arrest. From a theoretical standpoint, it's very simple: Maxwell line above mg arrests, everything else doesn't. Constant FOS or DCR means the same Maxwell line AND DCR at every level, so that's a no-brainer. If it gets over the peak in the first collision, by definition it will get over every subsequent peak.

Your model has an average Maxwell line above mg; that's WHY it arrests. There's no other reason, it's not a fucking mystery. I knew that before making the loops and load testing them. The loops crush by deforming into a slightly stronger structure when at minimal compaction. You basically wiped out the peak, barely strong enough to stand, but with...

A MAXWELL LINE ABOVE MG!


The questions were:

- is it strictly the resistance of the loops as resistive force, or were vibration/friction/air expulsion sinks necessary to achieve arrest?
- what was the approximate load-displacement curve for paper loops?

The measurements answered these questions. Make it strong enough (or in your case, spongy enough), it will arrest.




PS - the Maxwell line technically CANNOT be used to model your model for the reasons I haven't yet discussed; nevertheless, it's so good that it comes close enough, anyway.

[Kat Dorman]

You are setting the PEAK FORCE to mg which would mean a building with no safety margin whatsoever.

Incorrect. See previous post and earlier post explaining the 38%. The average is a little less than 13% of peak static capacity, and therefore 38% of imposed load at a factor of safety of 3.

Do you really believe skyscrapers are designed that way?

Yes. I think a FOS of 3 (actually demand to capacity ratio of 1/3) is quite damned realistic; the construction standard FOS value is 2.5, so it's actually conservative.

Assume the collapse and compute backwards to make sure you get a collapse.

Not really. At worst, the story-wise computations with the Maxwell line are a few stories off IF arrest is possible. Because there's no fuzzy in a given run, it produces hard numbers. There's no "almost pregnant"; if it's going to arrest, the story-wise method will capture it no more than one story late if the DCR is constant or nearly so.

But it only takes one level for the peak to not be reached and the collapse would stop.

Correct, and I hope you understand after all this explanation that I'm not overlooking that fact.

I'm not that stupid.

Sometimes, it's not even a close call. Like when you have a factor of safety of three, but the load displacement characteristics of a steel column. Do YOU get it now? Are you ready to take your Python program up several notches?

You can't build a physical model that perfect.

No, you can't, and thats one of the best reasons for doing it numerically! Who wants the fucking artifact of washers clandestinely locking up on a dowel, when that is simply a vagary of the test setup? I don't want to (e.g.) carve out the dowel under toothpicks so the washers don't bind. Washers are not floors or stories in a building!

It takes 12 to 15 washers to crush a single loop. A loop has to be tested to destruction to find its limit. That is why I have 11 single loops at the top.

That's great. I'm not being sarcastic. But that's the static limit, don't forget.

Most sources say the core was 50% stronger than necessary.

Oh hell, it was probably stronger than that. But a lot of it was still standing after most of the floors hit ground. Open your eyes and look at any number of videos. If you demand all the core to be crushed, you're not modeling the towers, period. I'm not, for the nth time.

Your math is at a perfect edge that cannot exist in the real world.

True, but it is a virtue as I said. Not if you want to model the towers, but very good if you want a model to demonstrate principles - and a lot of them.

My physical model is REAL WORLD.

True, and it also has artifacts associated with being a dinky little model with paper loops and washers on a dowel, which has nothing to do with real world conditions of buildings, let alone skyscrapers. That's why your dismissal of the verinage is BULLSHIT. You really think the percentage of total height dropped has more to do with reality than whether the model is a BUILDING or not? Do you realize how bizarre that is?

[Kat Dorman]

Your velocity computation is based on NO SUPPORTS...

The velocity graph shown is for the no support run.

...then you don't do anything to see if that peak force is satisfied...

That's just muddled. The "no support" trials had....

NO SUPPORTS!

So there is no peak force in those runs, Einstein, by definition. Try again.

...and just do energy absorption based on the average.

An entirely different set of computations, WITH supports. Peak force business explained above. Not a problem on my end. Problem is in your comprehension.

But gravity is not completely free to add energy because that would only happen with ZERO FORCE pushing up from below.

False. Have you ever heard of a free body diagram, psikeyhackr? Or made one? It's a simple diagram depicting the forces on an object with their direction and magnitude. You should do one here and learn this once and for all. If there is a net force on an object, it will accelerate. Gravity applies a constant downward force. Supports (ALL supports in the real world) provide a non-constant resisting force in compression.

If the resistive force is less than the gravitational force, even by the tiniest bit, the load will accelerate downward.

If the load accelerates downward, it gains kinetic energy. This energy comes from lost height - change of potential energy. The notion that it can only gain KE when there's zero force pushing up is an embarrassment coming from someone who has invested thousands of words in mocking the institutions of physics. They've got it right; YOU make a mockery of PHYSICS itself.

The grade school kind!

[Kat Dorman]

Now, psikeyhackr, I have given detailed explanations to every statement in your post, albeit peppered with derision. I know you don't care about that - you've said it so many times I want to puke - but I see no reason not to respond with negativity in the face of all you dish out.

You can't just ask a question, you have to make false assumptions about what I'm doing, ignore answers already given, and throw a good measure of mockery in. You don't even deserve any answers, as ill-equipped as you are for every aspect of this debate, from social skills on up to technical skills.

But I give you answers, and this isn't the first time, or the 10th time, or even the hundredth time...

What do I get from you?

GARBAGE INDEED!

That 38% goes very well with your 1000 m/s.

You are utterly incompetent at most physics and logic, from what I can tell from our interactions. (Moderator, please note this is an objective fact, not an ad-hom, not even an opinion; it can be objectively determined from what he's written, as the basic laws of mechanics are not subject to interpretation) You need to spend a lot less time copying and pasting your own unique brand of physics on hundreds of forums and pick up a fucking book.

Create some complicated computer crap and presume no one will figure out the absurdity of the flaw in the assumptions.

I understand you don't get it. Don't put it on me.

Usually, the more certain you are about some 'fact of physics', the more likely it is you're dead wrong. Stop posting and READ A BOOK. LEARN SOMETHING. Then you'll understand that building a physical model doesn't prevent you from being a bull in a china shop when it comes to the underlying physics.

You should go back to smileys. They are more intelligent.

They're what you understand, apparently.

[Dudely]

part of my argument against a gravitational collapse is that a lighter, weaker portion of the building should not be able to crush stronger heavier portions and certainly not accelerate in the process.

[youtube]http://www.youtube.com/watch?v=bL5bkxS2cFU[/youtube]
Note: the lighter, weaker portion of this building was able to crush the stronger, heavier portion. And it accelerated (well, until there wasn't enough accumulated mass because it was running out of floors). Yes I know it's not the right weight/distribution,/etc. but then neither is your paper loop model. You dropped it FAR further than the distance of one floor. The video shows perhaps 30% of the weight crushing all of the rest of the floors. Even subtracting out the collapse of floors you can't see due to the dust if you were to run the same thing against your model you would not get the same result. given that we have a (albeit very rough) model that does something similar (but with a greater % of mass) and it does NOT match what your paper loops would do that means your paper loop model is wrong. You cannot modify your paper loop model in a way that would reflect what you see in this video.
Where's my prize?

Additionally, your comment about how we don't know exactly what it did to the building is kind of strange. Why would they employ a demolition technique that doesn't actually destroy the building? Why are you jumping all over stupid shit and pretending like it's relevant? If you can show me some math explaining why the demolition in video above actually arrested and we just can't see it because of the dust then I'd love to see it (I'm not joking- I actually would love to see that). Otherwise your incessant whining and bizarre nitpicking is irrelevant. "Physics doesn't care" what you think about progressive collapse. Concrete and steel buildings are "incapable of caring" what your paper loops did. What matter is what those loops showed and what can be applied in regards to the collapse of steel framed buildings. I'm afraid to say it's not much.


Progressive collapse is possible and is employed daily in the demolition industry. Pulling as shown in the above video is common when it is too dangerous to enter the building to set explosive charges. If you would like to contact the companies and inform them that what they are doing is not possible because you crushed some paper loops with washers I'm sure you can find their contact info. There are a lot of them.

[psikeyhackr]

You are saying that a level can be crushed by 38% of its static load capacity because that is the force you are applying which is the AVERAGE over the collapse of that level.

Correct. This is the so-called "Maxwell construction", a physical law of nature, expressed in a simple mathematical form, and borne out each and every time by experiment. It only applies when the supports are completely crushed. If the stories are crushed (and a couple of other conditions are true, which I will explain only if you're interested) it is a valid means of doing the dynamics of crushing a level.

It had to have been designed to hold more than that AVERAGE but you are multiplying that force times the height of the level to get the amount of energy expended to do the collapse ACCORDING TO YOUR ASSUMPTION.

It's not an assumption, it's a fucking law of nature - one which you are ignorant of.

This brings us to... what happens if there isn't sufficient energy to crush a level? Then the Maxwell construction can't be used.

You are choosing not to question if the PEAK FORCE can be reached at every level.

Number one astute observation you've made recently, perhaps in forever.

Correct, I am choosing not to question if the peak force can be reached at every level. But you wouldn't know that from the graphs, because they don't tell that story. All of my computational environments are capable of accounting for peak force, only one of them allows me to choose not to! All of them give results which agree to story level detail, whether the Maxwell construction is used in the one environment or not.

There are three environments:

1) A storywise crush calculator (discrete algebraic model)
2) A physics engine
3) A extended finite element program

The first only supports a rigid top, because two degree of freedom calculations (that is, where the upper block can crush too) cannot be done in the discrete algebraic method. The other two can support non-rigid tops but do not have the overall flexibility of the first. They can also suffer from being too realistic sometimes (example: the vibration you had a cow over is actually quite realistic for 1kg metallic masses in collision - you ever heard metal ringing? Duh). I end up with an artifact of the test configuration rather than a demonstration of a fundamental principle.

Therefore I frequently use the first environment, even though it can't do a collapsing upper block and despite its story resolution limit. I programmed this (many times, many ways) myself, and I've included a setting to indicate whether to run with a Maxwell line equivalent average force over an entire story, or to section the story into elastic, peak plastic, and minimum plastic step value approximations to the actual chosen load displacement. This is not as precise as the other two environments, which are both iterative force/constraint solvers of different architectures, but it is sufficient to establish arrest or no arrest at each level.

That's not to say the Maxwell line option can't arrest. When I model your model, I use the Maxwell line and I come up with the same number of stories crushed, only mine are necessarily all in the bottom block when using the first method. It arrests just fine.

If I know that there's no way a particular configuration will approach arrest, based on more detailed runs, I use the Maxwell line. After all these trials, I have a pretty good feel for what will arrest. From a theoretical standpoint, it's very simple: Maxwell line above mg arrests, everything else doesn't. Constant FOS or DCR means the same Maxwell line AND DCR at every level, so that's a no-brainer. If it gets over the peak in the first collision, by definition it will get over every subsequent peak.

Your model has an average Maxwell line above mg; that's WHY it arrests. There's no other reason, it's not a fucking mystery. I knew that before making the loops and load testing them. The loops crush by deforming into a slightly stronger stucture when at minimal compaction. You basically wiped out the peak, barely strong enough to stand, but with...

A MAXWELL LINE ABOVE MG!


The questions were:

- is it strictly the resistance of the loops as resistive force, or were vibration/friction/air expulsion sinks necessary to achieve arrest?
- what was the approximate load-displacement curve for paper loops?

The measurements answered these questions. Make it strong enough (or in your case, spongy enough), it will arrest.

PS - the Maxwell line technically CANNOT be used to model your model for the reasons I haven't yet discussed; nevertheless, it's so good that it comes close enough, anyway.

You seem to think people are interested in your complicated demonstrations.

The point is that your 100% is EXACTLY equal to mg which means that the maximum strength at every level is EXACTLY EQUAL to all of the weight above.

That cannot be produced in the real world. There is always variation in man made items. No two of my paper loops are EXACTLY identical. No two of the perimeter wall panels could have been EXACTLY identical. So a 33 level structure or a 100 level structure cannot be built where the strength of the supports at every level is EXACTLY EQUAL to the weight above. All that can be done is a statistical analysis can be made of the strength of the supports then something slightly stronger can be mad to assure that it is never too weak. I bet every level would be 5% to 10% greater than mg. So what would that do to your collapse time? Could it even collapse?


It is IMPOSSIBLE for me to even build such a model where 100% = mg because there is no way to determine the exact strength of every loop. You have simply created another perfect virtual reality which cannot exist in reality and which no building is, or can be, or would be built to conform to. And then you expect people to be impressed by all of your complexity and talk about MAXWELL.

Mathematics is not physics and physics is incapable of giving a damn about mathematics. But a building where the maximum strength of a level is as close as possible but still greater than the weight above makes no sense whatsoever. But that is what my physical model is an attempt to be. And it arrested. Ten ounce washers would make a better model but would be lots more work test for minimum strength.

100% = mg, 1000 m/s, 100 Hz oscillation

Mathematical never-never land.

psik

[psikeyhackr]

Note: the lighter, weaker portion of this building was able to crush the stronger, heavier portion. And it accelerated (well, until there wasn't enough accumulated mass because it was running out of floors). Yes I know it's not the right weight/distribution,/etc

So why are you bothering to talk about it?

You can't even see how much if any of the building is left. You can't even be sure how many stories there were.

"Physics doesn't care" what you think about progressive collapse. Concrete and steel buildings are "incapable of caring" what your paper loops did.

Exactly, the dowel makes it IMPOSSIBLE for my washers to get off center and consistently crush one side more than the other and fall down the side. My model cannot explain why neither tower allowed the top to fall down the side. The core would help make that more likely compared to a normal grid skyscraper design.

Additionally, your comment about how we don't know exactly what it did to the building is kind of strange. Why would they employ a demolition technique that doesn't actually destroy the building? Why are you jumping all over stupid shit and pretending like it's relevant?

I DON'T KNOW WHAT DID IT. I am not talking about what other people CLAIM to know. I think we have to agree that the buildings held themselves up for 28 years and they withstood the wind. I saw one site which claimed the wind reached 100 mph on 6 occasions. Since I don't waste time on the holographic planes crap I think we can agree that the towers were hit by airliners.

We also know that the towers were completely destroyed.

So eiter they were completely destroyed as a result of the airliners and fires or SOMETHING ELSE WAS INVOLVED. I DO NOT KNOW WHAT THAT SOMETHING ELSE WAS. I am not trying to say what you think you know about it. I have no control over the emotional certainty of YOUR MIND.

Now how are we supposed to understand how the towers held themselves up if we don't have accurate data on the distributions of steel and concrete? How you can be certain without accurate data is beyond me.

Where have I ever said anything about this THEY and their DEMOLITION TECHNIQUE?

psik

[Kat Dorman]

You seem to think people are interested in your complicated demonstrations.

You think that was complicated?

The point is that your 100% is EXACTLY equal to mg which means that the maximum strength at every level is EXACTLY EQUAL to all of the weight above.

No, I just got finished saying the peak capacity was 3mg. Not mg. Just got finished saying it. It's not complicated, it's simple arithmetic.

[Dudely]

Exactly, the dowel makes it IMPOSSIBLE for my washers to get off center and consistently crush one side more than the other and fall down the side. My model cannot explain why neither tower allowed the top to fall down the side. The core would help make that more likely compared to a normal grid skyscraper design.

Because floors are not discrete objects. You can't "topple" a skyscraper and more than you can topple a sand castle. Show me a single case where a skyscraper fell sideways. I think you're getting emotional and asserting certain incorrect physical properties on skyscrapers. How would it be physically possible for a large chunk of building to stay in one pieces as it is pushed to the side? And what would push it? You do know gravity pulls down, right? Not sideways?

Plus the towers DID fall outward as much as would be expected. In fact, they fell so erratically that they took out a chunk of WTC 7 hundreds of feet away- causing enough damage to trigger an evacuation of emergency personnel and eventually (after extended time and fire) topple it.


Psiky, show me just ONE CASE where a real, actual, steel and concrete building had a chunk of the top come down and it DIDN'T cause a progressive collapse. I could not possibly care less about your worthless paper loops- show me REAL physics with the actual materials and sizes involved (or their direct analogies). You've been shown time and time again computer models, videos of collapses, and raw data and math all describing how progressive collapse is not just possible, but expected. Now it's your turn.

[Dudely]

Now how are we supposed to understand how the towers held themselves up if we don't have accurate data on the distributions of steel and concrete? How you can be certain without accurate data is beyond me.

You seem pretty capable of figuring it out:

The concrete slab alone was about 600 tons

http://knol.google.com/k/official-theory-of-9-11-wtc-tower-near-free-fall-collapses-violates-laws-of#comment-1hwr2894wxokh.lkuwyb

Lets go through a bit of logic:
I have a friend who is an architect. He's been through 6 years of schooling, helped design and build Daniel Radcliffe's apartment in New York, and is currently taking a series of 7 exams to get certified- each one taking months of studying to prepare for.

When he is asked a question on one of his exams like "will this building hold up when you cut X supports on floor Y" do you think he needs to be spoon-fed the data? Do you think being off by, say, 1% is going to mean the difference between a progressive collapse or an arresting collapse? Do you think he would be incapable of figuring out how much everything weighed? Do you think his calculation would be so inaccurate that his subsequent modelling would be fatally flawed?

The reason you have not seen those numbers anywhere is made clear by your comment I linked to above. Even YOU were able to calculate them fairly accurately. It is not generally common for architects or engineers to interrogate blueprints and builders from 30 years ago so they can be sure the numbers are spot on. Turns out calculating them again now is often more accurate than using numbers from back then because of how much finer we can make the calculations what with all these computers and their processing power.

Where have I ever said anything about this THEY and their DEMOLITION TECHNIQUE?

I was talking about the video I posted, not WTC. That should have been obvious. Do you even fully read my posts?

[Kat Dorman]

Do you even fully read my posts?

Rhetorical, of course.