Building Collapses in Rio

For the record, I consider the collection of inane assertions regarding design FOS to be soundly put to bed. If you do not personally agree, then we must agree to disagree because I don't play the endless repetition game forever. Point has been made, made well, and it stands unchallenged except by challenges to my person, not my arguments.

FOS is meaningless in a messy collapse.

Originally posted by ANOK

Originally posted by PhotonEffect
I've asked ANOK & friends repeatedly, at what floor should the collapse have completely arrested. But I can't seem to get any sort of a straight answer; or even a monkey's guess.

You have, I don't recall.

But who knows? How can anyone answer that question, and why do you think it makes a difference?

Because it's the equivalent of (for example) Bazant's work from your dissenting perspective. Several researchers have elaborated models which indicate a gravity collapse is natural and expected for the towers. You, and others of similar ilk, have railed for years about how it's impossible and how it violates laws of physics, yet in all that time have provided nothing substantive except armchair pseudophysics and wildly waving arms to demonstrate the truth of your claim.

Saying it doesn't make it so. However, in physics and engineering mechanics, there are at least mostly objective ways to say things and arbitrate any ensuing disputes. There may be no firm or satisfactory resolution, often there is not. But the first step is to take it from vague, wordy concepts and translate it into mathematical relations. Like it or not, the language of physics is mathematics, and the reason is the lack of ambiguity. Your assumptions and your process are explicit - quantified! - and transparent for review. It documents your thinking process in a precise manner.

If either your assumptions are questionable or your framing of the problem arguable or incorrect, these facts can be discovered independently and called into question. It's the way it works.

You are trying to shortchange the process by essentially proclaiming your gut tells you otherwise, everybody needs to stand down and listen up because, even though YOU haven't bothered taking Physics 101, those who've worked successfully through Physics 497 and 503 couldn't possibly know as much as your gut.

You've got nothing else, at least originating with you. Surely, as such a passionate questioner of the OS, you've read Szamboti's Missing Jolt paper? No? You should. It's one of the best formal arguments against the OS mechanics out there (Charles Beck's may be better). But that isn't saying much; it's riddled with flaws, most elementary and some fatal. At least he tried!!!!!

reply to post by IrishWristwatch

I realize you apparently exist for the sole purpose of riding my ass, but all I have to do is scroll past your posts as I encounter them, which isn't difficult. SnowCrash continues his trend of handing you your ass at every turn. You should stop embarrassing yourself, especially if your secret thrill is believing that I'm reading your tripe.

Let us be clear here Irish, because you still seem to be under the illusion that you have some claim to being an "expert" of some sort.

You are a layperson too Irish.

You have no standing on your qualifications alone to question David Chandler, never mind Zdenek Bazant.

Your ideas are not rigorous as you pretend they are, they are little more than jargon, the calculations you do do are unconnected to any rigorous model and there is no display of any attempt to develop a logical chain reasoning for your disjointed ideas.

Now, I am last person to insist on either qualifications as an arbitrator of debate, but in the absence of credentials and anything resembling mathematical formalism beyond post hoc single step calculation one would hope you have some solid empiricism or at the very least a convincing intellectual framework to start from from.

Yet you claim to not be a solid supporter of ROOSD, the half-digested zombie framework that it is, and you don't offer anything approaching an alternative aside from, if I recall correctly, a single cartoon model that is at best a parody of Bazant's own (while you decry his method in the same breath).

Then the joke of it all all, the kicker, is that you deny the scientific method and any attempt to establish truth by empirical means.

Let me be perfectly clear here Irish, you have NO standing to call anyone a layperson based on your performance in this question. The only thing you have going for you is an ability to phrase things in a certain sagacious way that leads the uninitiated to believe you have some standing YOU are a layperson in this question as much as a person with a undergrad degree in psychology is a lay-psychologist. You have no standing to be setting the rules, you have no standing to decide who kicked whom's butt, you have no standing to decide what principles are put to bed and no longer up for discussion.

Maybe if you had a paper of your own your criticism of Szamboti would have more currency, but you don't have even that, as far as actual work done goes you are little more than an average run of the mill internet hero.

"'There are two ways of doing calculations in theoretical physics,' he said. 'One way, and this is the way I prefer, is to have a clear physical picture of the process you are calculating. The other way is have a precise and self-consistent mathematical formalism. You have neither.'

-Enrico Fermi
www.nature.com...

reply to post by Darkwing01


Here's the thing. You just wrote a lot of nothing in there. There's nothing contained in your post but a lot of ad hominem whinging.

To be quite frank, calling Irish a layman is rubbish in light of his degree, and more importantly, demonstrated knowledge. In a forum full of droolers who are constantly harping on "the physics and engineering" while knowing less about it than even an engineering dropout, I can see why his presence bothers you.

In the land of the blind, the one eyed man is king.

If you want to have some kind of argument, you're going to have to make some kind of relevant, non-personal points.

reply to post by Darkwing01


Why don't you hold that same standard for yourself and fellow truthers? Oh right, that would mean the end of the truth movement, which is build on baseless assertions, a lack of understanding in physics and lies.

reply to post by IrishWristwatch


I kind of miss the point of these calculations. What exactly does it matter that in a uniform density distribution the acceleration of an accreting mass converges to a certain value? How is that related to the WTC? It seems to me that, depending on the type of construction, with a building collapse you can have any amount of acceleration, form 0 to g, with g being an asymptote. In case of the WTC tower it turned out to be about 2g/3. (and I also don't understand how density is defined by H/M. Shouldn't that be M/H?).

Anyway, I do understand how conservation of momentum dictates that average acceleration is lower (or converges to a value lower) than g. But I think almost anyone would agree to that.

Edit:I gave it some more thought, and I think I get the point you are trying to make. Which is that acceleration increases as falling mass increases. With increasing mass, resistance of the material becomes insignificant, and only inertia plays a significant role. And you tried to explain this point with your hypothetical situation.

In simple words, 1kg of mass hitting a window will be slowed down more than 1000kg of mass hitting that same type of window.

Originally posted by -PLB-
reply to post by IrishWristwatch

 

I kind of miss the point of these calculations. What exactly does it matter that in a uniform density distribution the acceleration of an accreting mass converges to a certain value? How is that related to the WTC? It seems to me that, depending on the type of construction, with a building collapse you can have any amount of acceleration, form 0 to g, with g being an asymptote. In case of the WTC tower it turned out to be about 2g/3. (and I also don't understand how density is defined by H/M. Shouldn't that be M/H?).

What is a COLLAPSE?

The building may have come down at 2/3rds G but is it possible for the top 15% of any building over 1000 feet tall to force down the structure below at 2/3rds of G?

Now if something destroyed the structure below that fast then it is possible. But is that what we mean by collapse?

We are playing semantic games with the word COLLAPSE. But the Laws of Physics do not care about semantics. Words just confuse people who do not understand what is going on. But buildings over 1000 feet tall cannot have uniform density. So playing mathematical games based on that assumption is complete nonsense. It just awes people that are intimidated by the math.

Regardless of what destroyed the buildings the Physics Profession has made an ass of itself by not demanding accurate data on the towers. What are the LAYMEN supposed to do when the EXPERTS abdicate their responsibility?

psik

reply to post by psikeyhackr

We are playing semantic games with the word COLLAPSE. But the Laws of Physics do not care about semantics.

No you are playing semantics.

Regardless of what destroyed the buildings the Physics Profession has made an ass of itself by not demanding accurate data on the towers.

No the physics profession has done fire testing on the truss design used in the wtc.
It showed deck buckling in as little as 10 minutes and truss buckling in as little as 16 minutes.

Here is the link to the 202 page report that the physics experts did. It has steel and concrete distribution specifications so it should really make your day.
Your assertion that the physics experts sat in their arm chairs and did nothing is flat out WRONG.

You could have looked up this info but you prefered to hand wave.

It’s not the physics profession that has made asses out of themselves.

Originally posted by psikeyhackr
The building may have come down at 2/3rds G but is it possible for the top 15% of any building over 1000 feet tall to force down the structure below at 2/3rds of G?

Your error is in assuming the resolution of Chandler's video measurements is adequate, then taking his questionable uniform acceleration measurement as a static quantity, ignoring the fact that acceleration will fluctuate each collapse iteration.

Averaging out based on inadequate data is bad idea. So is assuming acceleration will be uniform and then proceeding to calculate structural resistance based on this assumption.

Another error is assuming column-on-column impact not as a theoretical model favoring collapse arrest but as an actual occurrence, then deriving expected decelerative behavior from that premise and then screaming bloody murder when it's not seen in the (resolution-challenged) measurement data.

I hope you'll get it now but I doubt you will. Shame.

Challenge my last comment as much as you will, but in that case answer me this: which analysis, flawed or not, is at least appropriate in terms of expectations about acceleration, Chandler's or Szamboti's? One of those two expects, or implies, uniform structural resistance over time, and one of them does not. Why is that? And what does one analysis say about the other?

Originally posted by Darkwing01
Let us be clear here Irish, because you still seem to be under the illusion that you have some claim to being an "expert" of some sort.

You are a layperson too Irish.

You have no standing on your qualifications alone to question David Chandler, never mind Zdenek Bazant.

And... shortly thereafter...

Originally posted by Darkwing01
Now, I am last person to insist on either qualifications as an arbitrator of debate (...)

In fact, you appear to be the first person to do so, just like Rob Balsamo, and both of you are clueless mountebanks. Take a technical position and defend it. Name-dropping of scientists you can't hold a candle to, prancing around your bastardization of the 'scientific method' and hand waving formal mathematical analysis with sophist cotton wool isn't going to cut it, Darkwing.

Originally posted by -PLB-
reply to post by IrishWristwatch

 

I kind of miss the point of these calculations. What exactly does it matter that in a uniform density distribution the acceleration of an accreting mass converges to a certain value? How is that related to the WTC?

You got it in the edit

It seems to me that, depending on the type of construction, with a building collapse you can have any amount of acceleration, form 0 to g, with g being an asymptote. In case of the WTC tower it turned out to be about 2g/3. (and I also don't understand how density is defined by H/M. Shouldn't that be M/H?).

Thanks for spotting the error! Notice it doesn't affect the result, because I don't actually use it...


Edit: the purpose, really, was to show that convergence is not to g. Obviously, the viable range is 0-g, and it isn't going to oscillate, but intuition might lead one to expect the long term limit to be g, since a smaller and smaller percentage of the impacting block mass is swept up. However, more per unit time is swept up. It leads to a balance around g/3. Even with no structural resistance. Even with structural resistance, if the resistance is insufficient to cause arrest (though this hasn't been shown here).

Originally posted by psikeyhackr
But buildings over 1000 feet tall cannot have uniform density.

Absolutely true. It's also true that no physical object is a mathematical point, no 'flat' surface perfectly planar, no oscillation truly linear, and so on. That doesn't stop calculations which use such idealizations from being useful or even accurate when applied to real world problems. I wanted to show the sort of effect momentum exchange alone causes on a simple system. I succeeded.

This is one of the way to learn things, but I understand very few people are interested in learning anything beyond the skills they picked up as toddlers. Getting some people to even learn to read is like pulling teeth. Thinking's not for everyone, I heartily agree.

So playing mathematical games based on that assumption is complete nonsense. It just awes people that are intimidated by the math.

Well, I hope you weren't awed.

Originally posted by samkent
reply to post by psikeyhackr

 

We are playing semantic games with the word COLLAPSE. But the Laws of Physics do not care about semantics.

No you are playing semantics.

So you can point at a 200 page report that I burned to DVD four years ago. BIG DEAL!

Why don't you tell us where in that report they specify how many inches the floor assemblies actually sagged in the middle due to the heat tests in furnaces. Isn't that what you are trying to make a big deal about?

psik

Regarding this last exchange: It only takes one introductory physics class, not even close to an undergrad degree, to separate the skilled from the lay person on this matter. Idealizations and approximations are used to great success all the time in physics. If you're smart enough to understand that without taking a class, great. Most aren't.

The first time you encounter a derivation like: "in order to solve the equation of motion for a simple harmonic oscillator, we will assume infinitesimal deflection..." you'll either get over the hump or be left behind. What? Solving for the motion of an oscillator by assuming no oscillation! Nonsense! Ridiculous!

No, effective.

Originally posted by IrishWristwatch
Edit: the purpose, really, was to show that convergence is not to g. Obviously, the viable range is 0-g, and it isn't going to oscillate, but intuition might lead one to expect the long term limit to be g, since a smaller and smaller percentage of the impacting block mass is swept up. However, more per unit time is swept up. It leads to a balance around g/3. Even with no structural resistance. Even with structural resistance, if the resistance is insufficient to cause arrest (though this hasn't been shown here).

I can see how this applies to your example of a material with a uniform distribution of mass. But I can't see how this is applicable to building collapses. A building consists mostly of air where acceleration is close to g. So I would expect acceleration converging rather to g than to g/3, if we ignore air resistance.

Just imagine a similar building where the height of the floors is twice as much (2h). That would result in a higher acceleration of the collapse than in the case of a floor with hight h. I don't think the acceleration converges to the same value in both cases, and the further the floors are apart, the close you get to a=g.

Originally posted by IrishWristwatch

Originally posted by psikeyhackr
But buildings over 1000 feet tall cannot have uniform density.

Absolutely true. It's also true that no physical object is a mathematical point, no 'flat' surface perfectly planar, no oscillation truly linear, and so on. That doesn't stop calculations which use such idealizations from being useful or even accurate when applied to real world problems. I wanted to show the sort of effect momentum exchange alone causes on a simple system. I succeeded.

My Python program makes it possible for anyone to create a table with whatever mass distribution they want to see how it affects collapse time. 12 seconds is the minimum with what you would call constant density. Making it bottom heavy increases the time.

breakfornews.com...

I call the program a kludge because it uses a fixed time base. The impacts will not occur exactly on 1/100th of a second intervals. But that makes the program easy to understand and the error is still less than 2%.

Dr. Sunder says the north tower came down in 11 seconds. So how can it be 8% faster than a magical program that ignores the necessity of destroying the physical supports that held the building up?

The 9/11 decade is an endless debate of a physical and logical absurdity.

psik

Originally posted by psikeyhackr
My Python program makes it possible for anyone to create a table with whatever mass distribution they want to see how it affects collapse time. 12 seconds is the minimum with what you would call constant density. Making it bottom heavy increases the time.

Thats odd, as the calculations are independent of the mass. After all, when you increase the mass of the lower floors, the mass of the top floors increase with the same amount.

Originally posted by -PLB-

Originally posted by psikeyhackr
My Python program makes it possible for anyone to create a table with whatever mass distribution they want to see how it affects collapse time. 12 seconds is the minimum with what you would call constant density. Making it bottom heavy increases the time.

Thats odd, as the calculations are independent of the mass. After all, when you increase the mass of the lower floors, the mass of the top floors increase with the same amount.

Tell that too all of the people who say that the columns at the top of the WTC were 1/4th of an inch thick but at the bottom the steel was 5 inches think.

Reality does not give a damn about mathematics. Let's see you build a 1000 foot skyscraper with the same amount of steel on every LEVEL.

One can judge from experiment, or one can blindly accept authority. To the scientific mind, experimental proof is all important and theory is merely a convenience in description, to be junked when it no longer fits. To the academic mind, authority is everything and facts are junked when they do not fit theory laid down by authority. "Doctor Pinero" in Life-Line (1939) by Robert Heinlein

psik

Originally posted by -PLB-
I can see how this applies to your example of a material with a uniform distribution of mass. But I can't see how this is applicable to building collapses.

Ah, then it was a useful exposition!

A building consists mostly of air where acceleration is close to g. So I would expect acceleration converging rather to g than to g/3, if we ignore air resistance.

This is where intuition can lead you astray, and was part of the purpose of working the equation of motion. Before I say why, let me tell you that I accidentally 'discovered' the g/3 limit in simulations of a discrete slab model, that is one where the masses are concentrated at 'floors' with only void in between, as you describe. So I already know that the limit holds true for discontinuous mass distribution, as the simulator knows nothing of the equation I listed or its property of convergence. All this particular solver knows about is F=ma and small time steps.

Your intuition seems to be correct. How can this be reconciled?

Just imagine a similar building where the height of the floors is twice as much (2h). That would result in a higher acceleration of the collapse than in the case of a floor with hight h. I don't think the acceleration converges to the same value in both cases, and the further the floors are apart, the close you get to a=g.

What really happens is, the further apart the floors are, the longer it takes to converge on the limit. Scale up the interstory distance, it scales the time to achieve convergence.

If you note the velocity curve I posted earlier, the initial acceleration is g, diminishing a bit right away, but radically diminishing after about 10 seconds. If it were more than 10 seconds until the first collision, obviously the acceleration remains identically g over that period. However, at the very first collision (assuming one story mass is initially dropped), the velocity of the impactor is halved - no matter what that velocity is. Therefore, the average acceleration over that entire interval has just been cut in half, too. So much for averaging g, eh?

By the next collision, the two masses have dropped in freefall a story's distance, bringing the average back up. Then another collision, and the combined velocity is reduced by a third. Average goes back down; not as much, but the collision came quicker than the first. And so it goes on to infinity - and g/3.

The equation of motion I derived is independent of mass, but is contingent on a continuous distribution. It is fair to ask if the continuous derivation is applicable to a discrete distribution, so it is a great question you pose. Clearly, the behavior is different, but in this case the limit is the same. On some level, though, that is to be expected since there is no distinct point where a discontinuous change is found when going from discrete to continuous in that limit. Imagine a series of masses so small and tightly spaced that, at the scale of the entire structure, the mass distribution approximates a continuum. It is a discrete system, so it must behave as such, yet it is for all practical purposes a continuum, so should approximate the properties of continuous media.

In fact, this is exactly what happens, and the discrete system approaches the dynamics of the continuous system. There are just a lot of smaller jolts spaced closely together such that it looks close to the continuous curve. I don't have an illustration of that handy, but I can show you the jolts of a discrete system. Here is a graph showing three different discrete system simulations with radically different driving masses on top:



All exhibit the jolting, but all are tending towards the same asymptote, which demonstrates another universal property: the convergence is applicable for ANY initial driving mass. ANY structural resistance. ANY mass distribution which averages to a constant over large scales. The difference is in the approach, not the limit being approached.

Now, let's consider a real building. It is mostly air, but it is most decidedly NOT discontinuous in the vertical dimension. In terms of support, which MUST be swept up too if full accretion, it is in fact continuous. Add a little eccentricity to the upper block and, voila, all illusions of slabs going wham-wham discretely vanishes.

So, yes, the limit (but not the precise curve) for even a structure which is mostly air is correctly given by the continuum relation. It is an extraordinarily powerful expression with much broader applicability than intuition might indicate. That's why I posted it. It is, as I said, almost magical.

Thank you for an interesting exchange. Seriously. Woefully lacking in most circles.