Building Collapses in Rio

Originally posted by DrEugeneFixer

Originally posted by psikeyhackr
I do not give a damn about those details of structural engineering..
psik

Apparently not, or you would know something more about it by now than what you read on ATS.

Originally posted by psikeyhackr

Structural engineers are just pretending it is complicated...

It's all a plot to make you look dumb.

Have you ever considered that the four "2d arrays of steel arranged perpendicularly" taken along with the slab and truss systems, constitute a "3D array of steel and concrete". Thus, by your own (faulty) logic, it should be able to resist lateral loads.

The slab and truss system provide areas 35 and 60 feet wide which was the whole point of the design. That was not the distance between the columns in the core. That is why the core was able to provide that rigidity. The trusses and floor slabs just had to transfer the lateral force of the wind from the exterior.

Like I said, SKYSCRAPERS ARE OLD TECHNOLOGY. Trying to make a big deal of structural engineering when the Empire State Building is 80 years old is ridiculous. Structural engineers will need to be laughed at when this crap is settled. Can't even discuss the distributions of steel and concrete down the towers.

Laymen are people who can be convinced that they are stupid by people making things unnecessarily complicated. Like all of the computer scientists who never explain von Neumann machines even though they are everywhere now.

psik

Originally posted by psikeyhackr
Like I said, SKYSCRAPERS ARE OLD TECHNOLOGY. Trying to make a big deal of structural engineering when the Empire State Building is 80 years old is ridiculous.

Holding forth on issues you know nothing about-- now that is ridiculous. And it's getting old.

I see that you ignored my point that the perimeter columns, and slabs together comprise a three dimensional arrangement of structural elements. If this is the requirement to resist lateral forces (as your logic implies) then why can't the perimeter columns and floor slabs resist lateral forces?

Keep in mind, I'm only asking this WITHIN the logic that you have laid out.

Originally posted by psikeyhackr
Laymen are people who can be convinced that they are stupid by people making things unnecessarily complicated.

Charlatans are people who knowingly hold forth on topics they don't understand, usually by deliberately false simplifications.

Kool-aid drinkers are people who unknowingly hold forth on topics they don't understand, usually by mistaken oversimplifications that they get unknowingly from liars.

Suckers are people who fail to educate themselves and fall into the fallacies and errors of Liars and Kool-Aid drinkers through laziness.

Laymen are people who recognize their own lack of knowledge and experience, and either educate themselves on a subject by study, or defer to people with greater knowledge.

Originally posted by DrEugeneFixer

Originally posted by psikeyhackr
Like I said, SKYSCRAPERS ARE OLD TECHNOLOGY. Trying to make a big deal of structural engineering when the Empire State Building is 80 years old is ridiculous.

Holding forth on issues you know nothing about-- now that is ridiculous. And it's getting old.

I see that you ignored my point that the perimeter columns, and slabs together comprise a three dimensional arrangement of structural elements. If this is the requirement to resist lateral forces (as your logic implies) then why can't the perimeter columns and floor slabs resist lateral forces?

Keep in mind, I'm only asking this WITHIN the logic that you have laid out.

Three dimensional with joints made how? People trying to convince us that the buildings came down because of the weakness of the truss joints have shown pictures of those joints often enough. Look at the joints between the spandrels and the perimeter columns. The core had joints like that in 3-D but the truss joints could flex and that is why the visco-elastic dampers were there.

So you can accuse people of knowing nothing when you make no comment about the trusses being 35 and 60 feet long when spaces between columns in the core were nothing like that. The floors just linked the 2-D support of the exterior to the 3-D support of the core but the core provided the rigidity. Structural engineers can just try to keep us in AWE. So what happens when most people don't buy it?

psik

Originally posted by Darkwing01
Actually, sorry for the mistake, I retract that apology since you kinda failed to meet the terms I offered. Apologies for failing to notice at the time.

I'll take being correct over getting an apology, any day. You don't understand the difference between models and systems being modeled. Open systems are studied all the time. I get the impression you think systems must somehow be made closed before a model is acceptable.

In your example of the perpetual motion machine, it's clear you feel system has to be expanded to include the guy turning the crank. You say:

"External inputs" are not external to the logic of the model, they are only external to some pre-defined subsystem within the model.

You put quotes around external inputs as if there's something wrong the phrase, and assert that 'external' really means internal to the system and only external to a subsystem. This is false and once again shows you to be totally devoid of hands-on experience with physics problems of any kind. You're a greenhorn, and it shows badly.

Ok, let's go ahead and do what you want. Let's include the guy turning the crank in order to make a 'closed' system, which you claim needs to be done before any proper analysis can be done. Now the guy turning the crank is part of the system, we can close the system according to your prescription and do the analysis correctly, right?

Except where does the energy for the guy to move his muscles come from? You say he's an energy source? Well, can he run forever like a perpetual motion machine? It seems all you've done is pushed the perpetual motion machine into another object, the guy. You can say he's like a battery, in that he stores a finite amount of energy. Well, how much? What is his mechanical power limit?

Energy-wise, all you've done pushed back the question of where the energy comes from what turns the crank to what animates the body. You see that? Of course not! You may as well define the crank handle to be a rocket, for all this silliness does to help.

Now, you have to add organs and metabolism and food and air to explain the energy from the guy, who is now the new perpetual motion machine within your tidily 'closed' system.

But that's not the only problem; really it's the smaller of the two. The big problem is, how does the man apply the force to turn the crank? Let's say only one hand is in contact with the machine, the one turning the crank. From Newton's 3rd, we know that whatever force the man applies to the crank to turn it is matched by a force of the same magnitude and opposite direction applied by the crank to his hand. Two equal and opposing forces net to zero force! How the hell does he turn the crank?

It's the classic horse and cart problem from physics, the one your hero David Chandler is so fond of. Too bad he isn't here to hand you your ass, you might listen to him. Even he understands something like this.

How can the horse pull the cart when the cart is pulling back equally? Inquiring minds want to know! Should I stop here and let you answer, Darkwing? hahahaha!!!

The reason the horse can pull the cart is the same reason that the guy can turn the crank. The force between animal and object is not the only force on the animal. The other one is the ground. The horse's legs push against the ground and the ground pushes back. This satisifes the third law but leaves forces unbalanced on the horse and subsequently the cart, so the cart moves. So it is with the crank. In order to turn the crank another force must be introduced on the guy's body. Of course, he could always use his other hand to grab the machine and apply force to keep himself relatively stationary with respect to the crank.

But what if he doesn't? I specified ONE hand touching the machine and, if that's the system, that's what you have to model. You're going to have to expand your system even further to include whatever it is applying force if you want to satisy your demented requirement of having a closed system. If the man is standing on the ground, guess what you'll have to include? That's right, the earth. Not just a part of it, ALL of it.

Continued....

reply to post by DrEugeneFixer


I'll ask again, if the towers came down because of the weak truss connections, then why did the weak joints not fail when the trusses supposedly pulled in columns much more massive than themselves?

That is a contradiction you need to address.

Now, the earth can be considered an effectively closed system, but still not isolated. I could replace the guy cranking the machine with a motor powered by solar energy. If sunlight falls on its solar collector (how would we know? Must we also include the immediate surroundings into the system as well as the earth?), energy is introduced from somewhere else.

Ok, let's do that. The machine and motor (with solar cell and battery) are exposed to the sun during the day. That's right, we've now enlarged the system to include not only the earth, but its rotation as well. But, so far, hahahahaha we haven't expanded the system to include the sun, sooo....

The battery accumulates excess charge during the day which powers the motor all night long. The machine runs day and night; from where or what does the energy come? Jesus, we've still got a perpetual motion machine!

In your concept of physics, we now need to include the sun to account for the energy and 'close' the system. But where the hell does the sun's energy come from? Nuclear fusion? Are you ABSOLUTELY sure of that?

Do you get the point yet? Of course not. You're incapable of understanding this.

You could always fix the situation by defining a BOUNDARY of the system, like I would do, and establish an input of solar flux to account for energy entering the system from the external environment. That option is not open to you according to your mistaken notions of science. You must not only add the sun, you must account for its means of energy production, otherwise guess what you still have?

A perpetual motion machine.

In your understanding of the scientific process, nothing could ever get done.

Continued...

Me? I'd make it a whole lot simpler. I'd leave the system definition as the simply the machine and call it an open system. The boundary of the system would be the crank, and external input is a force applied to the crank. This accounts for the mechanical work done on the system by the environment. Simple. OPEN!!!!!!!!!!!!!!!

Of course, how would we know the magnitude of force (or torque) actually applied to the crank as a function of time? That problem exists whether the problem is handled your way or mine. The answer is, you can't, not with the information available. It's arbitrary. If a guy is turning the crank, the amount of force applied is subject to his volition and whim. Without knowing the force function, nothing more can be said about the system's ACTUAL behavior.

However, we CAN specify the action of the system under the influence of an EXTERNALLY imposed force F(t), if the properties of the SYSTEM are well understood. We can set up and solve the equations of motions for the OPEN SYSTEM subject to external arbitrary force such that, if a force function is given, the action of the system is known (predictable).

In fact, since the system of interest is the alleged perpetual motion machine, that's the only solution we're after. We don't care if it's a person or a motor turning the crank; both are capable of supplying an ARBITRARY force over time. Well, hell, if we solve the equation of motion for the machine given arbitrary force, we don't need to know or care what's turning the crank.

And that's how physics is done. Open system, closed logical model.

Something you intuitively know, but have no idea how to express in the language of science. So, not having actually solved a problem like this, let alone hundreds, you ascribe meaning to terms according to your own understanding, which is wrong.

Your way: expand the system spatially all the way out to the sun, and conceptually through all the processes from nuclear fusion to the photoelectric effect, and everything in between, so that it can be a "closed" system. This is what you say is necessary to account for the dynamics of an infinitesimally insignicant machine located somewhere in a sun-earth system. When all we're interested in is the little machine...

I laugh in your general direction.

It's also the foundation of your error in your critique of Bazant. You fail to account for the fact that the system under study, a tower, is an open system with the boundary condition of coupling to ground. You forgot about ground, but Bazant didn't. The only error is yours, and it's colossal. An error no freshman physics student would make.

I always understood what you meant with your imprecise concepts and terminology, and was initially going to agree. What you probably meant was that all matter and energy crossing the boundaries of the system must be properly accounted for. That's what I said in correcting you, referring to external input. But I realized that what you wrote did not match your intent, and what you wrote was wrong. So I told you so. Once told, you still disagree.

I'm not going to agree with you when you're wrong, just to get an apology I'm owed and deserved many times over, going a long ways back. From someone who deserves not one iota of further consideration.


Prediction: as you read this line, you are guilty of not reading all the words preceding it. This is one of the reasons you still have no understanding of physics. For all our interaction, you could've absorbed enough to get through the first two years of an undergrad degree, by osmosis.

Originally posted by IrishWristwatch
From Newton's 3rd, we know that whatever force the man applies to the crank to turn it is matched by a force of the same magnitude and opposite direction applied by the crank to his hand. Two equal and opposing forces net to zero force! How the hell does he turn the crank?

I'm sure you meant this in jest, but it needs some clarification: the equal and opposite forces as predicted by Newton's third law do not actually cancel each other out or net to zero force, because they do not act on the same object. E.g. if you push your hand against the wall, the wall pushes back on the hand. Two forces on two different objects. However, without friction with the floor, the person turning the crank would just slide backwards, making his/her force application ineffective.

This also underscores the point about equal and opposite forces not necessarily resulting in equal and opposite damage: slam your hand against the wall hard enough, the forces will be equal and opposite, but your hand will break and the wall will not.

Expand this analogy to two similar objects, e.g. two eggs, drop them onto each other and one might break while the other stays intact, both might break, or none might break.

Bazant postulates a compacted layer of rubble which, as IWW explained, exerts its mass on the floors below before the upper 'block' impacts, then acts as a shock absorber and this somehow prevents the upper block from disintegrating.


This is if I understand it correctly, so correct me if I'm wrong. I'm not saying I agree with Bazant that this is the true, real mode of collapse but as far as I understand it, this is why Newton's Third Law isn't violated in his paper. It's internally consistent in that sense, but that doesn't make it the be all end all of WTC collapse studies.

(@ ANOK & others)

Originally posted by snowcrash911

Originally posted by IrishWristwatch
From Newton's 3rd, we know that whatever force the man applies to the crank to turn it is matched by a force of the same magnitude and opposite direction applied by the crank to his hand. Two equal and opposing forces net to zero force! How the hell does he turn the crank?

I'm sure you meant this in jest, but it needs some clarification: the equal and opposite forces as predicted by Newton's third law do not actually cancel each other out or net to zero force, because they do not act on the same object. E.g. if you push your hand against the wall, the wall pushes back on the hand. Two forces on two different objects. However, without friction with the floor, the person turning the crank would just slide backwards, making his/her force application ineffective.

No, read again. Or read on. When I am talking about the action-reaction pair alone, which is (e.g.) the hand pushing against the wall, the net force IS zero. The equal and opposite forces as predicted by Newton's third law DO cancel each other out to net to zero force, it is the OTHER forces on the body which don't.

It is only by inclusion of all the forces acting on the bodies in question that the mechanics are resolved. So, yes, action-reaction pairs net to zero by definition, which was my point in the text you quote. I then go on to include the other forces acting on the bodies to resolve the issue of why there's motion. Exactly what you just did.

And I wholeheartedly agree with IWW on his lucid explanation of closed and open systems.

Thermodynamics is a complex topic easily misunderstood and misrepresented.

If only Steven Jones hadn't started working on a perpetual motion machine, he might still be able to claim some semblance of credibility. If he claims his device taps into a heretofore unknown energy source, then his device shouldn't be developed under the rubric of 'overunity' but 'revolutionary alternative energy', and if it does not, then his device is physically impossible. It's a lose-lose situation for him.

Tragic.

Originally posted by IrishWristwatch
No, read again. Or read on. When I am talking about the action-reaction pair alone, which is (e.g.) the hand pushing against the wall, the net force IS zero. The equal and opposite forces as predicted by Newton's third law DO cancel each other out to net to zero force, it is the OTHER forces on the body which don't.

Hmmm, I apologize if I was being a bit dense here, but, I humbly quote my favorite online free physics textbook:

To students, it often sounds as though Newton's third law implies nothing could ever change its motion, since the two equal and opposite forces would always cancel. The two forces, however, are always on two different objects, so it doesn't make sense to add them in the first place --- we only add forces that are acting on the same object. If two objects are interacting via a force and no other forces are involved, then both objects will accelerate --- in opposite directions!

(...)

it doesn't make sense to refer to the equal and opposite forces of Newton's third law as canceling. It only makes sense to add up forces that are acting on the same object, whereas two forces related to each other by Newton's third law are always acting on two different objects.

I bet I'm probably misunderstanding something you are saying... This is just how I've always understood it. More explanation? :-)

Originally posted by snowcrash911
This also underscores the point about equal and opposite forces not necessarily resulting in equal and opposite damage: slam your hand against the wall hard enough, the forces will be equal and opposite, but your hand will break and the wall will not.

Absolutely.

Expand this analogy to two similar objects, e.g. two eggs, drop them onto each other and one might break while the other stays intact, both might break, or none might break.

Now, I'll play devil's advocate for a moment. The counterargument to this is supposedly that the top is actually weaker. Even Bazant assumes a 15% reduction in capacity for the overlying story. How do two similar things, but one a bit weaker, come into roughly symmetric contact and the stronger loses?

Answer (with minor corrections):

Bazant postulates a compacted layer of rubble which, as IWW explained, exerts its mass [correction: static weight plus force from change in monentum] on the floors below before [correction: AS] the upper 'block' impacts, then acts as a shock absorber and this somehow prevents the upper block from disintegrating.

That's it. That's all of it. Otherwise you have crush up. Exclusive crush up, or mixed direction? I haven't yet explored solutions in this domain, so I can only speculate (in relatively learned fashion, mind you). For Bazant's other conditions, my guess is there would be exclusive crush up followed by arrest if the initial debris layer were not included.

Can you dig that? I really think there's a high probability of this. I'll say it again for the hard of hearing: WITHOUT THE INITIAL DEBRIS LAYER AT FIRST IMPACT, BAZANT'S MODEL WOULD PROBABLY PREDICT ARREST.

In essence, this is what all the wannabe physicists have been saying, isn't it?

But we can never get to truly interesting conclusions like this while all time is spent wallowing in the funk of the unschooled!

If we could get there, we could then examine why Bazant's model really fails as a descriptive model. That might happen over at the 9/11 Forum while Darkwing is suspended, but it won't happen here. Too much knuckle walking.

This is if I understand it correctly, so correct me if I'm wrong. I'm not saying I agree with Bazant that this is the true, real mode of collapse but as far as I understand it, this is why Newton's Third Law isn't violated in his paper. It's internally consistent in that sense, but that doesn't make it the be all end all of WTC collapse studies.

You are correct. Let me quote the bastard, emphasis mine:

Newton’s Third Law: The discusser is not correct in repeatedly
claiming that Newton’s third law is violated in the paper
and particularly in concluding that the “two-phase collapse
scenario is scientifically implausible because it ignores
Newton’s third law and the equal but opposite upward force
dictated by it.” As explained at the outset in every course on
mechanics of materials, this law is automatically satisfied,
since all the calculations are based on the concept of stress or
internal force, which consists of a pair of opposite forces of
equal magnitude acting on the opposite surfaces of any imagined
cut through the material or structure. This concept is so
central to the discipline of structural mechanics and self evident
to structural engineers that Newton’s third law is
never even mentioned in publications.

Critics of Bazant should start by reading Bazant!

Originally posted by IrishWristwatch
You are correct. Let me quote the bastard, emphasis mine:

Newton’s Third Law: The discusser is not correct in repeatedly
claiming that Newton’s third law is violated in the paper
and particularly in concluding that the “two-phase collapse
scenario is scientifically implausible because it ignores
Newton’s third law and the equal but opposite upward force
dictated by it.” As explained at the outset in every course on
mechanics of materials, this law is automatically satisfied,
since all the calculations are based on the concept of stress or
internal force, which consists of a pair of opposite forces of
equal magnitude acting on the opposite surfaces of any imagined
cut through the material or structure. This concept is so
central to the discipline of structural mechanics and self evident
to structural engineers that Newton’s third law is
never even mentioned in publications.

Critics of Bazant should start by reading Bazant!

I remember first reading those comments by Bazant and thinking they were a cop-out... but all it was .... was that his calculations led to somewhat counterintuitive results, pressing down hard on the sore spot in the 9/11 Truth Movement: reliance on 'intuitive physics'... a pitfall. Simple intuition is often bad counsel in these matters.

Hence "aluminum cannot penetrate steel", etc. etc.

reply to post by IrishWristwatch


I don't have such a deep understanding of Bazants model as you have, so I can well be wrong here. But doesn't what you say here means that his model does not account for static loads? A debris layer laying on an intact floor increases the load of that floor. In fact, even without a debris layer, the load on the lower floor is greater by the weight of 2 floors during an impact.

reply to post by -PLB-


I think it does, which is why IWW said: "static weight plus force from change in momentum"

reply to post by snowcrash911


Then I do not understand how the model can ever predict arrest without initial debris layer. Even if the collapse starts with crush up, as debris piles up, crush down will happen as result of static load.

Originally posted by snowcrash911
Hmmm, I apologize if I was being a bit dense here, but, I humbly quote my favorite online free physics textbook:

This is the part you question:

From Newton's 3rd, we know that whatever force the man applies to the crank to turn it is matched by a force of the same magnitude and opposite direction applied by the crank to his hand. Two equal and opposing forces net to zero force!

At this point, I'm only talking about the action-reaction pair of forces - the force the hand applies to the crank and vice versa. The hand is in contact with the crank and vice versa. This conforms to the definition of bodies in contact according to Newton's 3rd law and constitutes and action-reaction pair. Therefore they are equal and opposite, and F + (-F) = 0. The net force due to these two forces alone is indeed zero.

Look closely at what I said: Two equal and opposing forces net to zero force. How can it be otherwise? It's just that, at this stage, I have not introduced any other forces on the bodies.

If those were the only forces acting, for example if both the man and machine were floating inside a space capsule, then the application of force would cause BOTH bodies to move away from each other on the push and towards on the pull. It might well be impossible to turn the crank, if it's sticky or provides significant resistance. The machine and man would just move instead.

In order to actually crank, another force would have to be introduced, and this is where we get into your quote:

To students, it often sounds as though Newton's third law implies nothing could ever change its motion, since the two equal and opposite forces would always cancel. The two forces, however, are always on two different objects, so it doesn't make sense to add them in the first place --- we only add forces that are acting on the same object.

I actually strenuously disagree with this interpretation, and recommend you find a new go-to source. In the scenario I describe above, there are only these two forces and they do indeed cancel. In order to resolve the horse-cart problem, additional, distinct forces must be introduced which do act on the bodies.

So far, in my space capsule example, there are but two very real forces acting in opposition. The man experience one force and goes one way, the machine experiences the other force and goes the other way, so there is motion. But the center of mass of the man-machine system remains in a constant location, as there is no net external force acting on the system.

Now, if I attach the machine rigidly to the space capsule, a new force has been introduced to act on the machine. By the third law, that means an equal and opposite force from machine to capsule. That doesn't make the other two prior forces go away, as the author of the quote implies. The author says there are only two forces, where clearly we now have two action-reaction pairs, the forces acting at the man-machine interface and those acting at the machine-capsule interface.

Once again, if the man (who is still floating) tries to crank, the center of mass location of the coupled man-machine-capsule system remains constant. But, if the capsule is very massive compared to the man, what an observer inside the capsule sees is man pushing and pulling crank, moving himself alternately closer and farther from the machine. Relative to the machine-capsule center of mass reference frame, the man('s center of mass) experiences acceleration.

The mistake the author makes is in confusing force with net force. The latter is the sum of all real forces acting on the system. It's easy to ignore those forces which do cancel each other, but that doesn't make them go away. Does the man still feel force on his hand once the machine is fixed to capsule? Of course. In fact, if the machine is lighter than he, he will experience MORE force in attempting to crank, because now he will be accelerating his own (greater) mass to accomplish a crank cycle.

Now let's let the man brace himself against the capsule, so he too is fixed. Another action-reaction pair is introduced, man-capsule, yet another pair of real forces. Now there are three pairs, all satisfying the third law. How does the crank move? It moves because the TWO action-reaction PAIRS acting on the machine/crank are not equal. This is what your author is trying to say, but says incorrectly.