Building Collapses in Rio

Again, this is par for the course. Lay-people present themselves as experts on physics in forum after forum, claiming whatever they personally believe to be some immutable law of physics. When called on it, the response is spin, misdirection, evasion, painful parsing of off-the-cuff remarks, repetition of mantras, and failure to address specific questions and arguments. Rinse and repeat.

Which is why the hamster wheel spins furiously after more than a decade. Enjoy the ride.

I've said it before, I'll say it again. There's a reason very few people enter the study of physics in university, and even fewer stick with it. If all the thousands of armchair 'physicists' in forums who've never taken a single class in high school are any indication, it isn't for lack of interest.

It's for lack of ability.

No shame in that. The shame is in pretending you have the knowledge and skills when you don't, and not lifting a finger to remedy the situation. Even after years. Plenty of time for talk, but no time to walk the walk.

I'd find it amusing if it weren't so offensive and loathsome.

Originally posted by IrishWristwatch

Originally posted by ANOK

Originally posted by IrishWristwatch
momentum counts for nothing

That is the most relevant thing you said and needs addressing because it shows your confusion of the argument.

No one has EVER said momentum counts for nothing.

For you to seize on that one thing out of all I've said to you is very telling in itself.

For all the discussion about collapse progression, NO ONE here is talking about the necessary condition of arrest being net momentum of zero, no one is including momentum in the dynamical considerations (except psikeyhackr, who only emphasized the resistive aspect, not the overload aspect) - in short, no one is counting momentum, which is to say momentum counts for nothing.

I don't know what you mean by that. The whole purpose of the physical model is to show the effect of overload and the dynamic energy being consumed in the process of overload.

It takes 0.118 joules of energy to crush a single paper loop flat. I computed how much potential energy my falling mass had. Enough to flatten 8 loops. The result was 9 damaged loops but not all flattened. So the kinetic energy gets absorbed and that slows the falling mass until it stops. The total structure comes nowhere near being completely destroyed.

But then people come up with various excuses for why the model is irrelevant.

Now I have not seen anyone show how the amount of energy required ot collapse a level of the core must increase down the building.

psik

Correction: Earlier I gave the catenary sag angle as approximately 15 degrees; that was in error. It didn't seem right so I went back and checked, apparently I'd confused it with the number for core-driven pull in, which is twice the distance to the low point (the full long span truss distance).

The correct figure is over 30 degrees, which is twice as bad and 10x the average rotational limit for connections.

This mass-spring system is set to a (flat) length of 18m, approximately the long span truss distance. The endpoints are constrained to be 1.3m less to reflect the inward bowing distance. There are both linear and rotational springs in the model but the rotational spring constant is set to zero for free (limp) hang. The translational spring constant is stiff compared to masses so there is negligible stretch.

The resulting catenary is:



and showing angle measurement, is:



There is over 2.9m of vertical displacement at the vertex. Trusses tend to mangle spectacularly at those deflections. Concrete would be fractured. The only things left to supply the needed tension are the pans, a modest weld, and magic lawnmower bolts.(edit: and rebar mesh, I believe)

Originally posted by psikeyhackr
I don't know what you mean by that.

I meant that you're the only one around here who has explicitly included momentum in your calculations, but that your emphasis has been the effect of momentum transfer slowing the descent.

reply to post by IrishWristwatch

Again, this is par for the course. Lay-people present themselves as experts on physics in forum after forum, claiming whatever they personally believe to be some immutable law of physics.

I'm sorry Irish, a person with a Bachelor's degree in a subject does not get to call themselves an "Expert".

If you think that your experience makes you an expert then the experience must talk for itself, lots of people who have experience in sundry disciplines are not "experts" and have no hope of becoming experts. Being an astronaut who has never driven a car is more like being Michael Schumacher than someone who commutes every day for fifty years.

You don't get to call yourself an expert just because you have an undergrad degree, especially when your brand of "expertise" explicitly denies the scientific method and the universal applicability of natural law.

You can penetrate steel with air. (High explosives) Penetrate steel with water (Water jet cutters)

It is not the air that is penetrating the steel, it is pressure pulse moving through the medium of air that causes a deformation in the steel. You try and blow a whole through steel with low pressure air pulses and get back to me when you succeed.

Water cutters use grit, it is not the water doing the cutting. If no abrasives are used I am willing to bet that it is shear we are talking about and not cutting in the sense of something hard like diamond.

It is always a matter of pressure and surface area, not about relative sizes. It is about the amount of MASS concentrated at a given point by the objects in question. That is why we use soft lead bullets which only have steel points to minimize deformation, which increases the surface area of the bullet which in turn reduces the PRESSURE exerted on a given area of the target.

Are you picking up the theme here?

reply to post by Darkwing01


I don't see IrishWristwatch claiming he is an expert. I can understand where you got that idea, as his understanding of physics seems to be pretty ok, at least compared to the average truther. See how hat goes? People are looked upon as expert because they demonstrate a good understanding on a subject, not because of claims about their education.

reply to post by -PLB-


So do you agree with IrishWristwatch and me, that the sagging trusses could not have pulled in the columns?

Just curious because you never agree with that when a 'truther' says it, but because IrishWristwatch is supporting the OS you do?

If you don't agree with him either then why is his physics knowledge good according to you and 'truthers' not?

Another question seeing as no one has yet taken a stab at this that I keep asking...

Do you think the 5/8" and 1" bolts connecting the trusses to the columns were stronger than the columns? Or are they weak points that allowed the floor assemblies to not resist the collapse?

Originally posted by ANOK
So do you agree with IrishWristwatch and me, that the sagging trusses could not have pulled in the columns?

No I don't. In fact, I just don't know (neither do you or IrishWristwatch)

Just curious because you never agree with that when a 'truther' says it, but because IrishWristwatch is supporting the OS you do?

I have already previously discussed this matter with IrishWristwatch. And he could not convince me its impossible.

If you don't agree with him either then why is his physics knowledge good according to you and 'truthers' not?

Because his arguments make sense, while yours, or Darkwings don't. Stephen Hawking also turned out to be wrong about the black hole information paradox. Does that mean his understanding of physics is on par with yours or mine, who without a doubt are also wrong about it?

You see, this whole line of reasoning of yours is totally flawed. As always.

Another question seeing as no one has yet taken a stab at this that I keep asking...

Do you think the 5/8" and 1" bolts connecting the trusses to the columns were stronger than the columns? Or are they weak points that allowed the floor assemblies to not resist the collapse?

Of course I don't think that. But even NIST doesn't say it is sagging trusses alone. Its most likely a combination of redistribution of load (via hat truss), damaged lateral support (resulting in Euler buckling), weakening of steel in the columns from the fire, and pull in force from the trusses.

When steel is heated, it starts to behave differently. It bends much easier and breaking it becomes harder. When heated enough, a steel frame will collapse like it is made of cooked spaghetti. (which is of course not meant literally but metaphorically).

reply to post by ANOK


And I will again confront you with your miserable understanding of physics and your dishonest behavior.

Until yesterday, your argument was that it is impossible for sagging trusses have a pull-in force. You argued that there was only expansion resulting in a push force, but that there was no mechanism for pull-in.

That was your argument, and that shows your miserable understanding of physics.

And since yesterday, you have disingenuously changed your argument from "the physics make any pull-in force impossible" to "the force would make the bolds break and not the columns". So you went from denying the force, to claiming the force would break the bolts.

In fact, your new argument does make sense. You haven't seen me attacking it (yet). Your problem however is, you now need to support your assertion. Either do so by showing the physics (math) which made you come to this conclusion (which we both know does not exist, as it is a baseless assertion), or you will have to demonstrate it by experiment. And we both know that truthers can't get anything done, so that won't happen either. And we are left with baseless assertions and speculation.

reply to post by IrishWristwatch


Well, thank you for the prompt reply.

I'm having a bit of a hard time understanding what you're saying. Allow me to attempt a summary:

Due to earlier damage, and ongoing fire, core columns were undergoing a 'slow motion' buckling, as evidenced by some visible drop in the antenna on the roof. This necessarily transferred some of the weight of the upper (above impact) floors from the core to the perimeter columns, via the hat truss... In turn, the perimeter columns now begin to buckle on the floors nearest the impact zone.

Is that right?
I've not yet been able to find Dr. Vlassis' work in an accessible "webzone", but I will continue to try.

When you speak of "seismically qualified connnections," I'm not quite sure I take your meaning. Are you speaking of moment resisting connections in steel? this is the implication of what I'm finding online, as well as my own understandiing. I assume that qualified refers to meeting code or standard. These Jargons can differ internationally, even in the english language, so I thought I'd ask for clarification.

I'm thinking about your argument above about the implied damage to the trusses at the implied nearly 10 feet of vertical sag. I need to look at some drawings to make good sense of these arguments.

Thanks for raising the quality of the discussion here.

Please don't get too angry at ANOK. He does learn, gradually. It's only this past October that he was telling us that potential energy (due to gravity) pushes up! He is apparently trying to learn physics by argument.

reply to post by IrishWristwatch

To disagree with my argument is the same as claiming:

- the floor slabs have the same psf rating as the columns (they don't)
- the upper block would be supported if it were set on a floor assembly (it wouldn't)

If you feel both of those are statements are true, then you do understand the context.

No.

A column does not require an equal or higher psf rating than another material to exert its axial capacity on said material.

Do you:

-Disagree that floor slabs and debris would be compacted into a stack which is crushing the rest of the tower?

-Feel that a column could punch through a stack of several floor slabs (whist not even getting close to applying its axial capacity)?

The unit kips refers to kilopounds, ksi to kilopounds per square inch (units of pressure). Let's take the

It's ok, I have a degree in structural engineering, I know how that stuff works.

Now the floors. I've seen figures for the floor between 80-150 psf, I'll use 200 to be safe. The maximum live load before theoretical yield on an area equal to a column end is then 200 x 1.6 = 320 pounds. By comparison, a column can exert a force of 518,400 pounds, an overload ratio for the floor of over 1600x. To be extremely generous to this already lopsided estimate, call it 1000x.

Yes, the tiny area of the section of the column would obviously crush, but as it does so and the column is driven into the stack of floors the effective area the column applies its axial load to increases. I can go into more detail here if you persist that a column can effortlessly drive through a stack of floors.

I noticed you used the words "proportional" and "axial", and I applaud you for your precision. In doing so, you seem to be aware of two things: some proportionality is involved in out-of-spec conditions, and out-of-spec geometry is also involved.

Yes, but I believe the overwhelming difference would be in the unrestrained length of column.

I'm only guessing, but I'd bet if a single column impacted an intact floor at a severe enough off-axial angle, it would bend instead of punching through.

Agreed, and a lot of energy would be exerted in doing so.

What if the impact is not axial, regardless of what the column impacts? Then the FOS rating of the column does not apply. More than a few degrees off axial, and the failure mode shifts from hinge buckling under axial compression to bending under applied moment.

Axial capacity of columns are determined with this in mind. In real conditions the column is not braced for its entire length and deformations under capacity axial load generate moments in addition to any other moments it may be designed to carry. The in-situ axial capacity is closely related to its moment capacity. For the column to fail in bending while its unrestrained length is close to original configuration will require almost the same amount of force as its design capacity.

Fair enough; the context I described would apply mostly if not exclusively in the initial impacts between upper and lower, and is therefore quite a limited context.

The context was collapse progression which I always assumed meant undamaged structure being impacted. By this point a compacted stack of floors and debris must have accumulated.

Why? Why can't it be loose (uncompacted) rubble?

How would loose rubble crush (and completely decimate) 80 or so undamaged levels of structure at ~2/3rds free fall? Uncompacted rubble can't apply much force without compacting itself.

Arrest is possible, assuming the momentum of the integral pancake mass doesn't overload the columns.

I'm not saying it should necessarily arrest, just that it is suspicious the undamaged structure only applied an average force to the falling top section of about one third of the force it applied to it as it held it stationary.

Originally posted by DrinkYourDrug
I'm not saying it should necessarily arrest, just that it is suspicious the undamaged structure only applied an average force to the falling top section of about one third of the force it applied to it as it held it stationary.

I don't see how this is suspicious, and I can think of 2 reasons why it isn't.

1) The force in the stationary situation is only valid for a very specific configuration of the structural members. Mess up that configuration and you end up with different forces.

2) The average force is the integral of the force over distance (energy) divided over that distance. One moment you can have a large force, where an intact column is resisting, the next moment you can have a small force where a bent column is resisting. An intact column has a much larger load capacity than a bent column.

The second point only kinda makes sense in column on column collision, as was used in Bazants model. In his paper you can see diagrams of this force. In the actual collapse this hardly played a role, as the would be column on floor and floor on floor collisions instead. Both the load capacity as well as the strength of the floors was of course much lower than that of the columns, so point 1 applies there.

reply to post by -PLB-

1) The force in the stationary situation is only valid for a very specific configuration of the structural members. Mess up that configuration and you end up with different forces.

I contend that floor stack to column impacts would allow the columns to exert larger axial forces than they did pre-collapse.

2) The average force is the integral of the force over distance (energy) divided over that distance. One moment you can have a large force, where an intact column is resisting, the next moment you can have a small force where a bent column is resisting. An intact column has a much larger load capacity than a bent column.

Failing columns through bending requires a lot more force than you portray, and this force would have to be exerted over a fairly large inter-floor distance.

reply to post by -PLB-

I don't see IrishWristwatch claiming he is an expert. I can understand where you got that idea, as his understanding of physics seems to be pretty ok, at least compared to the average truther. See how hat goes? People are looked upon as expert because they demonstrate a good understanding on a subject, not because of claims about their education.

I don't doubt that Irish has a good grasp of the engineering disciplines he practices regularly or basic physics.

And yes he does present himself as an expert, even if only implicitly by ample use of jargon-filled quasi-considered posts. He certainly does present himself as some sort of knowing godfather.

But there is quite a large difference between knowing a lot about a subject and being able to integrate that knowledge into something resembling coherent understanding. He is as much an expert as your average G.P. is an expert of medicine. I have gotten lots of bad advice from G.P.'s with more years of study and more experience than he has.

That doesn't mean he is wrong, but it does cast the fact that Irish returns to the ROOSD hypothesis again and again despite an admitted inability to reconcile the idea with anything resembling the scientific method into a rather different light.

Originally posted by Darkwing01
I don't doubt that Irish has a good grasp of the engineering disciplines he practices regularly or basic physics.

As a habitual poseur, that's not for you to evaluate. Hell, you couldn't even construct an argument using formal logic without affirming the consequent. Done any "computer simulations" involving musical notes recently?

I find it highly amusing to the point of Monty Python-like absurdity to see you attempt to puff up your own stature not by engaging in scientific dialogue but by a constant barrage of arrogant quasi-philosophical meta-discussion.

You mentioned something about qualifications... what are your qualifications again?

And when putting that aside, since in the end, as many of us realize this past decade, anyone can put an expert to shame given enough focused auto-didactic study, what can you demonstrate in terms of technical, analytic work done on those building collapses, other than incessant carpet bombing of forum threads with sophistry and sciolism? It's the ultimate affront to see someone so wary of hardcore technical analysis, never getting his hands dirty, lecture about the "scientific method". What you're doing is armchair, committal-free beard scratching, not participating in technical discussion.

Asserting you don't believe IWW's analysis or challenging arguments with "ipse dixit" won't give you much to go on.

For once, point out exactly what is technically wrong with IWW's arguments, then stick with it until the issue has been resolved one way or the other, don't retreat again into glittering generalities and vague philosophical abstractions immune to direct factual scrutiny. And please, don't position yourself as a judge and jury of 'science', because you haven't earned it.

Point out the technical flaws. Prove it. Your opinion on what science is and who qualifies to do it by your standard is irrelevant and useless. Point out the technical flaws. Prove it. Commit to a technical argument and defend it.

Originally posted by IrishWristwatch

Originally posted by psikeyhackr
I don't know what you mean by that.

I meant that you're the only one around here who has explicitly included momentum in your calculations, but that your emphasis has been the effect of momentum transfer slowing the descent.

It is not just momentum that slows it down. That is why my model is important. Crushing the paper loops slows the falling mass down more than momentum transfer. But I have no idea how to calculate that for the WTC. Trying to do it for my model has been really difficult and I have not gotten it right. Too many things happen simultaneously. The paper loops in the falling mass get crushed along with the ones in the impacted mass due to Newton's 3rd Law but that depends on the inertia of the mass above them. In fact since I don't even have accurate data on the distributions of steel and concrete in the towers any momentum calculations will be wrong. That is why this TEN YEAR farce is so ridiculous.

Any honest people on both sides should be demanding that data.

So why isn't Richard Gage screaming bloody murder about it?

psik

Originally posted by DrinkYourDrug
I contend that floor stack to column impacts would allow the columns to exert larger axial forces than they did pre-collapse.

I agree that it is possible, but only momentarily. You won't end up with a stable new static situation.

Failing columns through bending requires a lot more force than you portray, and this force would have to be exerted over a fairly large inter-floor distance.

An assertion that either requires calculations or experiment to back it up. Bazant concluded that the force (and energy) was well withing the limits for the collapse to progress. If you can somehow show this to be wrong, you would, as far as I know, be the first.

Originally posted by IrishWristwatch
Correction: Earlier I gave the catenary sag angle as approximately 15 degrees; that was in error. It didn't seem right so I went back and checked, apparently I'd confused it with the number for core-driven pull in, which is twice the distance to the low point (the full long span truss distance).

The correct figure is over 30 degrees, which is twice as bad and 10x the average rotational limit for connections.

This mass-spring system is set to a (flat) length of 18m, approximately the long span truss distance. The endpoints are constrained to be 1.3m less to reflect the inward bowing distance. There are both linear and rotational springs in the model but the rotational spring constant is set to zero for free (limp) hang. The translational spring constant is stiff compared to masses so there is negligible stretch.

The resulting catenary is:

and showing angle measurement, is:

There is over 2.9m of vertical displacement at the vertex. Trusses tend to mangle spectacularly at those deflections. Concrete would be fractured. The only things left to supply the needed tension are the pans, a modest weld, and magic lawnmower bolts.(edit: and rebar mesh, I believe)

edit on 30-1-2012 by IrishWristwatch because: (no reason given)

edit on 30-1-2012 by IrishWristwatch because: (no reason given)

That is all very nice but why don't we just demand that floor assemblies be tested in furnaces to see if that phenomenon can be produced in TWO HOURS of heating. Because if it can't then all of this talk is meaningless.

psik

reply to post by psikeyhackr

Any honest people on both sides should be demanding that data.

And yet they're not. So, we may then conclude that either:

A) Everybody in the world is dishonest.
B) You're wrong.

So, from a scientific standpoint, what do you think the odds are for "A" vs. "B"?

Originally posted by DrEugeneFixer
Well, thank you for the prompt reply.

You're welcome. As -PLB- mentioned, I haven't convinced him, nor do I expect to convince you or anyone. I'm not entirely convinced myself! It's just that I do see problems. I'm more inclined to accept a combination scenario, where pull in is only a part of the equation, rather than the primary driver.

I'm having a bit of a hard time understanding what you're saying. Allow me to attempt a summary:

Due to earlier damage, and ongoing fire, core columns were undergoing a 'slow motion' buckling, as evidenced by some visible drop in the antenna on the roof. This necessarily transferred some of the weight of the upper (above impact) floors from the core to the perimeter columns, via the hat truss... In turn, the perimeter columns now begin to buckle on the floors nearest the impact zone.

Is that right?

That's pretty much it.

I've not yet been able to find Dr. Vlassis' work in an accessible "webzone", but I will continue to try.

Unfortunately, the paper I referenced used to be available for free. I understand Vlassis is amenable to sending a copy on email request. Let me dig up the citation and quotes I have.

I don't think Vlassis is the be-all, end-all on this subject, but he's the only one* I know of to research residual capacity in REAL collapsing buildings which have been instrumented. Not a very popular field.

When you speak of "seismically qualified connnections," I'm not quite sure I take your meaning. Are you speaking of moment resisting connections in steel?

All connections. Bolts, welds, fasteners of all types. I use the term in the same manner as Vlassis, which is in a general sense of connections which must conform to code in seismically active regions. Obviously, not all codes are identical, so this is a general term.

this is the implication of what I'm finding online, as well as my own understandiing. I assume that qualified refers to meeting code or standard. These Jargons can differ internationally, even in the english language, so I thought I'd ask for clarification.

Meeting code, primarily.

I'm thinking about your argument above about the implied damage to the trusses at the implied nearly 10 feet of vertical sag. I need to look at some drawings to make good sense of these arguments.

That's a true catenary, obviously an approximation to how mangled truss assemblies and broken concrete might hang. In this case, though, the approximation of true catenary establishes an upper bound for the horizontal force possible. Deviations from ideal all produce shallower angles and necessarily less pull in force.

Thanks for raising the quality of the discussion here.

Thank you. And thanks for being there to respond in kind.

Please don't get too angry at ANOK. He does learn, gradually. It's only this past October that he was telling us that potential energy (due to gravity) pushes up! He is apparently trying to learn physics by argument.

Okay.



* actually, there's also Yarimer and Brown, and I honestly mix up the three all the time. Don't be surprised if I come back with a correction that the citation is actually to Yarimer. I'm not perfect! But I catch my own mistakes more frequently than others do.