Video Nullfies Pancake/CD Theory

Originally posted by exponent

Originally posted by Another_Nut
My name is Jeremiah . Im an electrician in Oklahoma city.

I come home from work weekly covered in sheetrock and various other stuff.

I can with authority say that if you want to get sheetrock dust off of you the best way is to

Go outside into a stiff wind (not hard this is Oklahoma. You know "wind comes sweeping down the plains")

And shake.( a little more disturbing than it sounds)

Wow that just so happens to be what happened to the spire.

Ah of course! Thanks for the amazing science there. If only real scientists could understand the 'well it seems to come off me therefore i can predict conditions hundreds of feet in the air in the middle of the two largest collapses known to man'.

Wait no once again total nonsense, you've convinced yourself that you're right, and so you've picked a ridiculous fantasy theory to explain what is trivial.

Is that how dust behaves in your mind?

How many building collapses have you been in the middle of? How many times have you taken your entire stack of sheetrock and dropped it hundreds of feet?

Oh wait no you actually have zero experience of these conditions. Seriously, your logical chain is this:

• Dust comes off me quite easily
  
• Therefore it came completely off all the spire
  
• Therefore the dust we clearly see can't actually be dust
  
• Therefore it's steel particles
  
• Therefore some technology exists that violates fundamental laws

That is a chain of inference that a child would be embarrassed about.

edit on 19/5/13 by exponent because: (no reason given)

Am I really going to have to model this when I get home home so you will quit avoiding the question.

The fact it takes a 3rd grade experiment to prove you dust falls off of shaking things in the wind is incredible.

Man let me see what I can do we got a hell of storms brewin.

Ill show you what wind and shaking do to dust .lol

Originally posted by exponent
But yes, superior fireproofing would certainly have helped, the core would have resulted in more survival though regardless of fireproofing.

So you mean if there was fireproofing on the trusses, they would not have sagged and pulled in columns?

How did the fireproofing get knocked off the truss that sagged? Did lack of fire proofing give it more pulling power, or weaken the columns?

From a structural engineer’s point of view, the most common forms of steel framed construction are considered structurally restrained to some degree, and certainly at ambient temperatures, this is correct. The main question, however, is whether the same assembly is Thermally Restrained at elevated temperatures as defined by Underwriters Laboratories Inc (UL). In other words, will the structure remain restrained and be able to support the design loads as the steel temperature approaches 1100°F [593c]. When worded in this fashion, few architects or engineers are able to answer this question with an affirmative yes.

www.structuremag.org...



Temperatures in the WTC didn't even get high to get into the range that could start to cause deformation of the steel, let alone fail suddenly and completely. Collapses due to fire simply don't happen that way. Steel loses it's strength gradually, not instantly.

The only steel that would even start to get hot would that which was in direct contact with fire, which would have been very little of it, seeing as there are walls between rooms and the steel, that first had to be burned away.

First tower collapses in an hour.

Temperatures of objects

It is common to find that investigators assume that an object next to a flame of a certain temperature will also be of that same temperature. This is, of course, untrue. If a flame is exchanging heat with a object which was initially at room temperature, it will take a finite amount of time for that object to rise to a temperature which is 'close' to that of the flame. Exactly how long it will take for it to rise to a certain value is the subject for the study of heat transfer. Heat transfer is usually presented to engineering students over several semesters of university classes, so it should be clear that simple rules-of-thumb would not be expected. Here, we will merely point out that the rate at which target objects heat up is largely governed by their thermal conductivity, density, and size. Small, low-density, low-conductivity objects will heat up much faster than massive, heavy-weight ones.

Of interest is the maximum value which is fairly regularly found. This value turns out to be around 1200°C, although a typical post-flashover room fire will more commonly be 900~1000°C. The time-temperature curve for the standard fire endurance test, ASTM E 119 [13] goes up to 1260°C, but this is reached only in 8 hr. In actual fact, no jurisdiction demands fire endurance periods for over 4 hr, at which point the curve only reaches 1093°C.

Temperatures in flames and fires by Dr. Vytenis Babrauskas, Fire Science and Technology Inc.

Your arguments are based on assumptions, mine are based on known science.

Originally posted by Another_Nut
Am I really going to have to model this when I get home home so you will quit avoiding the question.

The fact it takes a 3rd grade experiment to prove you dust falls off of shaking things in the wind is incredible.

Man let me see what I can do we got a hell of storms brewin.

Ill show you what wind and shaking do to dust .lol

I fail to see how you can model this without wasting a couple hundred bux of sheetrock and getting some pretty large steel sections (they weren't your average box column). If you think you can though please feel free, I would be extremely impressed.

It's not that i'm avoiding a question though, it's that you are making a statement, 'all the dust would have fallen off' that is patently absurd. Dust covered everything after the collapses, and while I'm sure plenty did fall off, a little remaining and hanging in the air as the spire falls is far more likely than some magical technology that can disintegrate steel but that you can't explain or name or give any information about at all.

Sorry man, that's just how things go, you need evidence to make these claims and the only thing we have evidence for is dust. Lots of dust. More dust than anyone will ever see in their life again most likely.

Originally posted by ANOK

Originally posted by exponent
But yes, superior fireproofing would certainly have helped, the core would have resulted in more survival though regardless of fireproofing.

So you mean if there was fireproofing on the trusses, they would not have sagged and pulled in columns?

Correct, fireproofed trusses resist fire for longer, potentially enough for the fire to burn out the local fuel supply.

How did the fireproofing get knocked off the truss that sagged?

The impact of a commercial jetliner.

Did lack of fire proofing give it more pulling power, or weaken the columns?

Columns also lost fireproofing, but the key is the failure of the composite truss action, which degrades to a catenary as you well know.

Temperatures in the WTC didn't even get high to even get into the range that could start to cause deformation of the steel, let alone fail suddenly and completely. Collapses due to fire simply don't happen that way. Steel loses it's strength gradually, not instantly.

A complete lie from start to finish ANOK. You are well aware that NIST recreated the fires in the WTC and measured upper layer temperatures above 1000C. Every single other test of this system including real world tests like Cardington agree. None measure temperatures below 800C in the upper layer.

The only steel that would even start to get hot would that which was in direct contact with fire, which would have been very little of it, seeing as there are walls between rooms and the steel, that first had to be burned away.

There are no walls between 'rooms and the steel'. There are in fact ceiling tiles which don't survive aircraft impacts well.

It is common to find that investigators assume that an object next to a flame of a certain temperature will also be of that same temperature. This is, of course, untrue. If a flame is exchanging heat with a object which was initially at room temperature, it will take a finite amount of time for that object to rise to a temperature which is 'close' to that of the flame. Exactly how long it will take for it to rise to a certain value is the subject for the study of heat transfer. Heat transfer is usually presented to engineering students over several semesters of university classes, so it should be clear that simple rules-of-thumb would not be expected. Here, we will merely point out that the rate at which target objects heat up is largely governed by their thermal conductivity, density, and size. Small, low-density, low-conductivity objects will heat up much faster than massive, heavy-weight ones.

The available area for thermal conductivity in trusses represents less than 10% of the surface area exposed to fire. Thermal conductivity is not going to save them.

You then quote temperatures of 1000C, after also saying that this wouldn't be enough to deform steel. Why are you posting this dishonestly? You know perfectly well that 1000C will reduce steel to a soft mess, holding a fraction of its cold strength.

reply to post by exponent


So both planes knocked off fireproofing, in both impacts in exactly the same way, resulting in exactly the same conclusion?

Really?

So why, when these planes were knocking off the fire proofing, did they not destroy the lightweight truss causing the collapse to happen sooner? If the truss sagged and pulled in columns then that requires the truss to be sound, undamaged. Right?

And if they did destroy the truss, then how did the planes have enough energy left to destroy the core columns?

Now think about this, the planes hit the outer columns, according to accepted Newtonian physics the forces during the collision would be the same, equal and opposite in direction. In other words the amount of force taken to break the columns would be lost from the force of the aircraft. The force is transferred and can not be regained. So how did the plane then continue to destroy even larger core columns, especially if it also hit the trusses edge on?

Sorry but that does not make any scientific sense, none at all. Not logical in any language or dimension, that we know of.

Originally posted by exponent

Originally posted by Another_Nut
Am I really going to have to model this when I get home home so you will quit avoiding the question.

The fact it takes a 3rd grade experiment to prove you dust falls off of shaking things in the wind is incredible.

Man let me see what I can do we got a hell of storms brewin.

Ill show you what wind and shaking do to dust .lol

I fail to see how you can model this without wasting a couple hundred bux of sheetrock and getting some pretty large steel sections (they weren't your average box column). If you think you can though please feel free, I would be extremely impressed.

It's not that i'm avoiding a question though, it's that you are making a statement, 'all the dust would have fallen off' that is patently absurd. Dust covered everything after the collapses, and while I'm sure plenty did fall off, a little remaining and hanging in the air as the spire falls is far more likely than some magical technology that can disintegrate steel but that you can't explain or name or give any information about at all.

Sorry man, that's just how things go, you need evidence to make these claims and the only thing we have evidence for is dust. Lots of dust. More dust than anyone will ever see in their life again most likely.

So now you will only accept fullsized replica steel beams and dust? I can MODEL dust falling off things ( including steel ) so u will see.

But u will now not accept anything short of a fullsized replica.

Because you know your argument is silly.

you know you dont need a replica to model dust falling.

And I have asked you multiple time.

Pleas explain how dust sticks to a swaying beam in the wind? Without falling off at any point other that when it falls.

See I use science

Hypothisis- dust cant stick to swaying steel beams in the wind.

Test hypothisis.- apply dust to steep beam . Step into wind and shake.

Observe results.

If it sticks you are right. If it falls off I am

That is the scientific method.

Not

" I've never seen it. So I don't believe it. So it cant exist."

So have I still not asked a question?

Eta I can explain dust falling off of swaying steel in the wind using Newton..

Can u explain how it would stick using Newton.

( PS ill give you a hint. It has to do with bodies in motion when the thing they are resting on STOPS and/or suddenly reverses motion . Think unbuckled person in a car when it hits a tree. Does the person stick to the seat ? Or does that person continue forward?)

Now argue with Newton. Because I've proven your shame argument for what it is.

Obvious is obvious.

Originally posted by ANOK
reply to post by exponent

 

So both planes knocked off fireproofing, in both impacts in exactly the same way, resulting in exactly the same conclusion?

Really?

Not exactly the same, obviously both impacts were slightly different. However in general yes, both were large commercial airliners impacting nearly identical buildings at cruising speed. Both cause significant debris impact and structural vibration, both of which are confirmed to cause fireproofing to be disloged.

So why, when these planes were knocking off the fire proofing, did they not destroy the lightweight truss causing the collapse to happen sooner? If the truss sagged and pulled in columns then that requires the truss to be sound, undamaged. Right?

It's not quite as simple as that. Obviously the planes did destroy many trusses, primarily on the impact side but damage also continued through the structures. Further to that we know that whole floor sections became disconnected due to bolt or seat failure during the fires. What you might consider 'diagnostic' is that both towers collapses started opposite to the impact, where truss damage would be lesser, but debris loading would be higher. Fires also did not become as intense in these areas until a period after impact.

And if they did destroy the truss, then how did the planes have enough energy left to destroy the core columns?

Most core columns survived in both impacts, otherwise it's likely collapse would have been immediate.

Now think about this, the planes hit the outer columns, according to accepted Newtonian physics the forces during the collision would be the same, equal and opposite in direction. In other words the amount of force taken to break the columns would be lost from the force of the aircraft. The force is transferred and can not be regained.

This is kinda misworded. What you want to say is that the kinetic energy of the plane is transferred and absorbed by material deformation, acceleration etc. Force is applied, Energy is transferred.

So how did the plane then continue to destroy even larger core columns, especially if it also hit the trusses edge on?

The likely answer and the result of NISTs simulations is that the trusses on the impact side primarily stopped that debris, but the 12 feet of space between the trusses allowed some debris to break through and impact internal structures, destroy fireproofing and gypsum walls, destroy furniture and push it into the building etc. Where the trusses were impacted, damage does not extend to the core columns.

Sorry but that does not make any scientific sense, none at all. Not logical in any language or dimension, that we know of.

Then why is there not a huge uproar from building professionals? Why is, for example, CTBUH not only not arguing against these conclusions but actively endorsing them?

Honestly ANOK I have nothing against you as a person, but you really need to sit down and learn a lot more about how the mechanics of the collapse and the physics of the impact work. I can recommend you a lot of reading but so far everything I have presented you have skimmed and used to reinforce your preexisting belief. This is Confirmation Bias and endemic in the truth movement.

I don't believe I'm uniquely gifted, or exceptionally smart, or in any way superior to other posters here except in one respect. When I first heard about these theories I researched both sides of the argument equally. For example, Loose Change and some online websites convinced me early on that something weird was going on with The Pentagon. It wasn't until significantly later, probably 18 months or so that I had done enough research that my mind changed. Since that time the evidence for the 'official story' just gets stronger and stronger, wheras the truth movement has fractured more and more into smaller and smaller camps that cannot even agree on basic elements. It doesn't speak well that in the last 5 days I have seen theories that range from unknown semi magical steel disintegration technology, to micronukes, to thermite, to high explosives and everything inbetween.

This is not how discovery works, it's politics more than anything else.

reply to post by exponent


The goal posts just keep getting wider, eh?

You guys drop and pick up "arguments" faster than a NYC bike messenger.

Let me remind you of what the professionals say about catenary action again, shall we?

In the initial stages of heating the restraint from the surrounding structure tends to resist the expansion of a beam...

So how do trusses pull in exactly?

Sagging, deflection, is a result of expansion, not loading. The truss could still hold the load even when sagging.
FoS makes sure of that. I notice you trying to dismiss FoS based on some arbitrary claim it would cost too much?
Wow any excuse you can come up with eh? Do you actually expect that we night accept what you're saying as you type it? Just denying everything that contradicts your claims is not helping your argument, in fact it is only dong the opposite.

...The initial deflection is increased by this restrained expansion together with the thermal bowing caused by the temperature variation across the beam’s cross-section...

...Fig. 5 illustrates the main influence of the catenary action which is apparent in the deflection temperature curves when the beams survive up to large deflection. The fact that the axial compression force in the beam changes to tension force tends to stop the run-away caused by the applied load and material degradation. Depending on the temperature history during the fire scenario, the remaining material strength helps the heated beam to act in catenary to support the load, and tends to prevent run-away. The analysis was carried out using end-plate connections and a 50% load ratio...

...In this study, the case has been made that catenary action can enhance survival times for steel beams in fire, suggesting that such methods should be extended to include its effect where support conditions are appropriate....

...Catenary action certainly occurs, and has been seen to affect a heated beam’s behaviour by preventing run-away deflection at high temperature plus applied load. The tensile axial force grows progressively as the deflection grows provided that some horizontal reaction stiffness exists. A change of the horizontal restraint stiffness can have a large effect on the behaviour of the beam at high deflection, and the loading on the beam can be carried very effectively as catenary tension replaces bending...

Source? Ask PLB...

When design engineering structures using structural steel section a useful standard is..

BS 5950-1:2000-Structural use of steelwork in building. Code of practice for design. Rolled and welded sections.

This standard together with BS 5950-Part 2,3-1,4,5,6,7,8 & 9 provide service factors and design stresses relevant to structural design.

This one costs $307.20

BS 5950-1:2000-Structural use of steelwork in building

So this will have to do....

Factors of Safety - FOS - are a part of engineering design. Typical overall Factors of Safety - FOSs - are indicated below:

Structural steelwork in buildings FoS 4 - 6

www.engineeringtoolbox.com...

It has NOTHING to do with cost.

Originally posted by Another_Nut
So now you will only accept fullsized replica steel beams and dust? I can MODEL dust falling off things ( including steel ) so u will see.

But u will now not accept anything short of a fullsized replica.

Because you know your argument is silly.

Actually no, assuming you intend to use a representative model then I have absolutely no problem with a reduced scale test. My concern is that the larger relative particle size could result in it being easier to dislodge from a small platform, but you could easily use something like flour to mitigate that.

you know you dont need a replica to model dust falling.

I would have thought that this would be a self evident truth for anyone but it's hard to say. Lets restate the issue clearly though.

The effect in contention is this:


I believe the trails seen coming off the collapsing sections is dust made up of concrete and gypsum, you believe that it is some sort of powdered steel caused by an unknown mechanism. Is that a reasonable summary?

See I use science
Hypothisis- dust cant stick to swaying steel beams in the wind.
Test hypothisis.- apply dust to steep beam . Step into wind and shake.
Observe results.
If it sticks you are right. If it falls off I am
That is the scientific method.

The scientific method is a bit more complex than that, there's a requirement called rigour which means that you need to ensure your experiments and investigations are thorough. For example, how fast is the wind? On 911 it was relatively light. How much do you shake the column? In the WTC the columns seemed to sway more than shake. How much debris is there on the columns? Is anything attached? How much was deposited by the collapse.

These are not just simple questions, they are requirements of the scientific method in order to properly evaluate what happened to the towers. I think that you are probably thinking of a completely flat, clean steel I beam or similar with something like sand placed on top. In that sort of condition I think yes it's entirely possible that even brief wind could almost entirely clean the surface.

However, the spire at the WTC was a jagged mess of hollow columns, beam sections, very thick (2") gypsum panels attached to the steel, concrete flooring and it had all not 10 seconds earlier been coated in a gigantic amount of extremely diverse debris, from the finest powder to the largest chunks.

You may find it a simple matter to decide what you believe, but rigour insists that I cannot make those assumptions and so without the assumption that the dust would have been blown off, your case collapses. There is no need to hypothesize unknown, law violating technology if dust is a reasonable explanation.

Dust is a reasonable explanation.

Originally posted by ANOK
reply to post by exponent

 

The goal posts just keep getting wider, eh?

The phrase is 'moving the goal posts'. If I am making my goal posts wider, I am making it easier for you. Considering you can't even get a simple burn right please stop to think a little.

Let me remind you of what the professionals say about catenary action again, shall we?

What you are quoting is a discussion of thermal expansion in a beam, not catenary action in a truss. I know because I have repeatedly shown you sections from a paper by the same authors which does discuss catenary action in trusses and it confirms they apply inward pulling forces that can displace columns.

Sagging, deflection, is a result of expansion, not loading. The truss could still hold the load even when sagging.
FoS makes sure of that. I notice you trying to dismiss FoS based on some arbitrary claim it would cost too much?

I'm not dismissing factors of safety, but they are not a magic bullet. The size of the steel in the WTC is pretty open knowledge and the masses have all been well calculated. From this there is no mystery, the strength of the steel is known and the loads applied are known. Why do you want to deny this?

This one costs $307.20
So this will have to do....
www.engineeringtoolbox.com...

Or... you could just read the NIST report, which has the actual details of the construction, rather than a generic not even specific amount.

It has NOTHING to do with cost.

Primarily it has to do with safety, building codes dictate that like they dictate truss deflection which determines the size of the elements used. However, once building codes are met it is all about cost. How could you possibly justify putting in 5x more steel than is safe? What would you say to your client?

Do you care to respond to anything else I have said? You don't seem to be capable of reading a full post and then answering it. Are you just skimming through without even considering what I say?

reply to post by exponent


My reply is right here...

www.abovetopsecret.com...

It hasn't change since yesterday. I don't have to keep changing my point in order to keep arguing.

reply to post by exponent
You are obviously trying to make this a you vs. me argument, I'm not going with that.

the fires were the cause of collapse,

Other supporters of the official conspiracy theory argue (in this very thread) that it was a combination of things, not just one thing. The fires were not the cause of collapse. The towers were burning before 9/11. Other skyscrapers have burned before and after 9/11. And never collapsed.

So it turns out you have no actual arguments against Bazant, you just don't understand the physics therefore you feel confident in slandering him.

I do have actual arguments against Bazant and put them forward in this thread which discusses my Open letter to Professor Zdeněk Pavel Bažant where I show that the only thing all uf us can agree upon is that "Columns were overstressed before impact" (you), Fig. 4a of B/V('07) applies for the complete structure (Bazant), progressive collapse is possible (-PLB-). "The 'spring' [...] was broken into a million pieces long before [compression]" (Greening), the towers were hanging instead of standing (me). We differ in this little aspect: some think this is the way all towers are built like, progressive collapse from top to bottom is inevitable in ANY skyscraper and that this is the most natural thing to occur -- whereas others argue that even if towers were built like card houses, they would not collapse progressively from top to bottom (because card houses don't either), that the failure of one floor's height would have resulted in the crushing of a few more floors before the progression would stop, that slipshod architecture leads to leaning and toppling instead, and that a study-book worthy progressive collapse as seen on TV would require massive amounts of energy hidden in the towers - be it "black tech", cutter charges, a rope or intelligently placed springs and levers.

That is how all conspiratorial theories work, by generalising to the point that they can speculate freely without evidence.

Including the official conspiracy theories.

Better to prevent collapse at all, than accept the deaths of hundreds or thousands.

I agree unconditionally. However, the worst case scenario should be the crushing of two or three floors, as in a card house or my Jenga block towers, not progressive collapse, that's what I was trying to convey.

So because some high tech stuff exists, you feel you can just imagine whatever you want to exist and assume it does?

Did I? I think I'm on the safe side interpolating from stuff that is widely known (micro wave ovens and CRT) and the lesser known stuff (Active Denial System, LaWS, directed energy weapons) to the stuff that only few are supposed to know - at least until the next best thing is ready for deployment. That's not evidence for their existance, but their not being displayed on your favourite newspaper's frontpage or advertised during Super Bowl commercial breaks is not evidence against their existance either.

If you're willing to discuss things from a scientific perspective then I have no complaints, but so far you've dismissed one of the most cited scientists you'll ever find

[...] sì perché l'autorità dell'opinione di mille nelle scienze non val per una scintilla di ragione di un solo [...]

- Galileo Galilei in his December 1612 letter to Mark Wesler

I don't have too much time at the moment to respond in detail, so I will give a quick response.

I don't see how in your design you prevent your "light-weight floors, barely consisting of much more than steel rod lattice" from collapsing all the way down once one of the floors get overloaded and fails.

Originally posted by Akareyon
Just like my Jenga towers and card houses prevent progressive collapse :-)

But that is the point really. The floors in your jenga tower were very strong, much stronger compared to the floors in the WTC. Achieving this with "light-weight floors, barely consisting of much more than steel rod lattice" seems impossible to me. How do you plan to do this?

Lets go through the numbers. You talk about safety factors of 2 to 10. The overload ratio of the top section coming down is more in the range of 31 to 64, on the columns (that is from Bazants work). If you disagree with that value, then show your own, including calculations. How are your floors going to cope with that kind of force?

So Bazant calculated that value for the columns, even they would fail in case of the WTC. Even if you made your floors so strong they would resist, then still, the columns would fail. Ok, your core is already stronger, but still, an overload of 31 to 64? Isn't that just way extreme?

If you want a building that can cope with these kind of forces, you would not end up with a skyscraper, but with a structure more like a pyramid.

And then on a final note, how do you prevent your top section from toppling over or falling down on the side in your design idea? That seems to be causing even more damage and deaths.

Originally posted by Akareyon
reply to post by exponent

 

You are obviously trying to make this a you vs. me argument, I'm not going with that.

Well you clearly are as you're replying to me. That's what a debate is.

Other supporters of the official conspiracy theory argue (in this very thread) that it was a combination of things, not just one thing. The fires were not the cause of collapse. The towers were burning before 9/11. Other skyscrapers have burned before and after 9/11. And never collapsed.

You've taken my reply out of context completely. Obviously debris impact has bearing on the collapse but with no fire, there would have been no collapse. Hence my point about sprinklers.

I do have actual arguments against Bazant and put them forward in this thread which discusses my Open letter to Professor Zdeněk Pavel Bažant where I show that the only thing all uf us can agree upon is that

I find it hard to see much agreement in this list of seemingly unconnected fragments. I read your blog and it appears both Bazant and Greening have explained briefly why you are wrong, but you have brushed aside their criticism.

Including the official conspiracy theories.

A mindless retort, not based in reality. The 'official theory' has the benefit of experimental backing, rigorous modelling and acceptance by the wider engineering community.

I agree unconditionally. However, the worst case scenario should be the crushing of two or three floors, as in a card house or my Jenga block towers, not progressive collapse, that's what I was trying to convey.

Building professionals disagree. Designing for an arrest of a progressive collapse should inherently be designing for the prevention of progressive collapse. Whether you or I like this or not, that is the reality of the view in the SE world.

I'm not even going to bother finding a pithy quote to reply to your Galileo comment. You have no authority, nor publications, nor evidence to promote your position, yet you quote a man who is discussing observations, evidence.

Originally posted by -PLB-
Lets go through the numbers. You talk about safety factors of 2 to 10. The overload ratio of the top section coming down is more in the range of 31 to 64, on the columns (that is from Bazants work). If you disagree with that value, then show your own, including calculations. How are your floors going to cope with that kind of force?

I don't disagree with the overload number, pick any which one you like. That's from his model where there is a free fall for one floor, I believe, 58.000 tons and 3.7 meters, insert for E=m*h²/t²=m*a*h where a=9.8 m/s².

That force is counteracted by the whole structure underneath, so in the real world, it acts only momentarily. Kinetic energy is converted to internal energy (deformation), in other words, the impacting mass is decelerated and has less force, the energy is not avaliable for further destruction anymore. And there is no more freefall to pick up another 31-to-64-fold force. We've had this discussion before, -PLB-. Fill a long tube with 10 eggs and drop 10 eggs on them and tell me from how high above you have to drop the 10 eggs to smash the other 10 eggs (hmmm, omelette). Of course, at the moment of impact, the impact force will exceed what an egg can take. And probably will be distributed to the eggs from above and beneath, crushing a few more of them. But then that's it. All kinetic energy has been converted to internal energy and a lot of eggs will remain whole. Bazant basically just takes a heavy rock and puts it on top of the eggs so it squeezes them flat. He never explains how the 31-to-64-fold force can be maintained through the complete structure.

So Bazant calculated that value for the columns, even they would fail in case of the WTC. Even if you made your floors so strong they would resist, then still, the columns would fail.

That's the point. Bazant argues neither strength nor stiffness would make a difference. There's no way a tower would not collapse progressively from top to bottom. Each and every tower is bound to progress through itself the way the twins did once collapse is initiated.

You and I have proven otherwise. It is highly unusual for a tower to collapse that way, you have to make it so it does.

If you want a building that can cope with these kind of forces, you would not end up with a skyscraper, but with a structure more like a pyramid.

Yes, that's why I said my tower would resemble a pyramid structurally, integrally, statically, just not visibly. The bottom columns would have to keep 110 floors up, the 90th floor only 20 floors so no need to make them as strong (and therefor heavy) as those on ground level. Basically most tall buildings are pyramids, in a sense.

²exponent:

Well you clearly are as you're replying to me.

Not anymore if you insist all skyscrapers collapse progressively once collapse is initiated just because "the experts say so".

Originally posted by Akareyon

That force is counteracted by the whole structure underneath, so in the real world, it acts only momentarily.

What has the structure below have to do with the floor with something impacting it? That floor does not mind at all if there is a whole structure below consisting of 100 floors, or if it is the 2st floor with just floor with ground level below it. It will be just as strong, and be able to hold just as much weight.

And yes that force is only momentarily. In that moment the floor fails, and whatever it was that was falling on it, will continue to fall to the next floor, including the mass of your failed floor. And so on.

I don't see in any way how your structure is going to prevent this from happening.

Kinetic energy is converted to internal energy (deformation), in other words, the impacting mass is decelerated and has less force, the energy is not avaliable for further destruction anymore. And there is no more freefall to pick up another 31-to-64-fold force.

That is only true if your floor is going to stop whatever is falling on it. Your floor can't even hold the mass of a top section in static situation. How is it going to stop the falling mass? How is it going to prevent the falling mass to accelerate for the length of another story, just to drop on the next floor?

We've had this discussion before, -PLB-. Fill a long tube with 10 eggs and drop 10 eggs on them and tell me from how high above you have to drop the 10 eggs to smash the other 10 eggs (hmmm, omelette). Of course, at the moment of impact, the impact force will exceed what an egg can take. And probably will be distributed to the eggs from above and beneath, crushing a few more of them. But then that's it.

Completely incorrect analogy. Eggs are filled. There is no room for acceleration after first impact. What you describe here would be analog to a solid block impacting a stack of solid blocks.

All kinetic energy has been converted to internal energy and a lot of eggs will remain whole. Bazant basically just takes a heavy rock and puts it on top of the eggs so it squeezes them flat. He never explains how the 31-to-64-fold force can be maintained through the complete structure.

Not at all. You grossly misunderstand Bazants model. What happens in his model is a small length of resistance (where columns fail/buckle) and then a large length of acceleration (the buckled columns are not going to give much resistance).

That's the point. Bazant argues neither strength nor stiffness would make a difference. There's no way a tower would not collapse progressively from top to bottom. Each and every tower is bound to progress through itself the way the twins did once collapse is initiated.

Given certain conditions. But I agree that most buildings would at least partly collapse when you rip out 2 floors along the middle, maybe most will even completely collapse. We don't have that much material to go with though.

You and I have proven otherwise. It is highly unusual for a tower to collapse that way, you have to make it so it does.

Huh? It took me very little effort to come to the desired effect. You seem to miss the fact that your Jenga blocks are 1000 times stronger when compared to the columns in an average building. You can probably place the weigh of 50 complete towers on a single block and it wont buckle.

Yes, that's why I said my tower would resemble a pyramid structurally, integrally, statically, just not visibly. The bottom columns would have to keep 110 floors up, the 90th floor only 20 floors so no need to make them as strong (and therefor heavy) as those on ground level. Basically most tall buildings are pyramids, in a sense.

That is complete nonsense. Buildings are design to handle static loads, not the load of the top of the building crashing down.

Originally posted by -PLB-
And yes that force is only momentarily. In that moment the floor fails, and whatever it was that was falling on it, will continue to fall to the next floor, including the mass of your failed floor. And so on.

I will keep this short, as I get the impression you're misinterpreting what I'm saying on purpose, we're getting off-topic and the arguments are getting circular all over again.

Completely incorrect analogy. Eggs are filled. There is no room for acceleration after first impact.

Fine, use lightbulbs, paper boxes, empty egg shells, whatever you like, anything stable enough to support the weight of its own mass times 20 (or hundred, if you want to let 50 drop on 50). You're completely missing the point I'm trying to make. And you know what I'm talking about, there is no fundamental difference between the eggs and the floors. The floors weren't hollow either. There was stuff in between, or are you going to argue the columns away as well now that you've gotten rid of vertical and diagonal beams and everything else that doesn't fit into your vision of how a tower must be designed so it collapses straight down? And no, even if you take Fig. 4a from B/V'07, you'll see that there is at least some deceleration due to the force that must be exerted to push the columns away. No more free fall energy for you, hollow or not. Only one free fall. After that: progressive deceleration until stop. As in every other collision.

You grossly misunderstand Bazants model. What happens in his model is a small length of resistance (where columns fail/buckle) and then a large length of acceleration (the buckled columns are not going to give much resistance).

What happens in his model is that each and every floor is being crushed with the same freefall force multiplicator of the impact after the first one story free fall. Do the math.

Bazant argues neither strength nor stiffness would make a difference. There's no way a tower would not collapse progressively from top to bottom. Each and every tower is bound to progress through itself the way the twins did once collapse is initiated.

Given certain conditions.

No, not given certain conditions. The only condition is that of a one story free fall of one floor. There is no mention about anything being special about the Twins, his model applies to all skyscrapers and upright structures in general. Card houses prove him wrong.

But I agree that most buildings would at least partly collapse

No, not most, all of them. Not partly, but completely. That's what Bazant says. Read it up.

Yes, that's why I said my tower would resemble a pyramid structurally, integrally, statically, just not visibly. The bottom columns would have to keep 110 floors up, the 90th floor only 20 floors so no need to make them as strong (and therefor heavy) as those on ground level. Basically most tall buildings are pyramids, in a sense.

That is complete nonsense.

Oh, sure it is.

Originally posted by Akareyon
Fine, use lightbulbs, paper boxes, empty egg shells, whatever you like, anything stable enough to support the weight of its own mass times 20 (or hundred, if you want to let 50 drop on 50).

Fine, but this still isn't anything like your floors. Your floors are not holding the weight of the stories above. Your light bulbs. paper boxes, empty egg shells are. That is where your analogy fails.

You're completely missing the point I'm trying to make. And you know what I'm talking about, there is no fundamental difference between the eggs and the floors.

There is a very big huge fundamental difference. Again, your egg shells would be carrying all that weight above it. The floors won't and can't.

What happens in his model is that each and every floor is being crushed with the same freefall force multiplicator of the impact after the first one story free fall. Do the math.

He models failed columns, not floors (which makes his model completely unrealistic to begin with). The rest of your sentence does not make too much sense to me. What exactly is free fall force multiplicator?

No, not given certain conditions. The only condition is that of a one story free fall of one floor. There is no mention about anything being special about the Twins, his model applies to all skyscrapers and upright structures in general. Card houses prove him wrong.

No, not most, all of them. Not partly, but completely. That's what Bazant says. Read it up.

You are completely wrong. Bazants clearly makes a distinction between global collapse and collapse arresting.

He clearly identifies the conditions for each scenario:

Global collapse: The next story will be impacted with higher kinetic energy if and only if Wg > Wp

Arrest: So, the crushing of columns within one story will get arrested before completion (Fig. 4c) if and only if K < Wc

This is from the paper "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions". Look it up.

Originally posted by -PLB-
Fine, but this still isn't anything like your floors. Your floors are not holding the weight of the stories above. Your light bulbs. paper boxes, empty egg shells are. That is where your analogy fails.

The floor slabs don't have to hold any weight other than a few file cabinets and office desks. It's the core and the perimeter that is holding the floors up. What is it with you?

You're completely missing the point I'm trying to make. And you know what I'm talking about, there is no fundamental difference between the eggs and the floors.

There is a very big huge fundamental difference. Again, your egg shells would be carrying all that weight above it. The floors won't and can't.

And don't have to either.

What happens in his model is that each and every floor is being crushed with the same freefall force multiplicator of the impact after the first one story free fall. Do the math.

He models failed columns, not floors (which makes his model completely unrealistic to begin with).

It is totally realistic because it successfully models the collapse. He's an expert at what he's doing, after all.

The rest of your sentence does not make too much sense to me. What exactly is free fall force multiplicator?

That 31-64 number you mentioned. Explanation as follow.

No, not given certain conditions. The only condition is that of a one story free fall of one floor. There is no mention about anything being special about the Twins, his model applies to all skyscrapers and upright structures in general. Card houses prove him wrong.

No, not most, all of them. Not partly, but completely. That's what Bazant says. Read it up.

You are completely wrong. Bazants clearly makes a distinction between global collapse and collapse arresting.

He clearly identifies the conditions for each scenario:

Global collapse: The next story will be impacted with higher kinetic energy if and only if Wg > Wp

Arrest: So, the crushing of columns within one story will get arrested before completion (Fig. 4c) if and only if K < Wc

This is from the paper "Mechanics of Progressive Collapse: Learning from World Trade Center and Building Demolitions". Look it up.

I don't have to because I know it by heart. He's talking about "loss of gravity", incosistently mixing in K and Wg and Wc and Wp until noone knows what's up or down anymore.

He never substracts Φ(u) from K for the K of the next story (K').

In his words:

As Wg was, for the WTC, greater than Wp by an order of magnitude, acceleration of collapse from one story to the next was ensured.

He just assumes that Wg was >> Wp. Obviously it was, otherwise, progress would have stopped. He never bothers to explain why he comes to the conclusion that Wg >> Wp other than that the towers collapsed. "The towers collapsed, therefor, collapse was inevitable."

Good he's the expert and I am not.

And here our discussion comes full circle again, just in other words: is Wg always greater than Wp in skyscrapers? Was it a feature unique to the Twins? If so, for what reason? Because it surely is not in card houses because Wc can only be smaller than Wb (Fig. 3) when it is already under tension (Fc < m*g) - and just waiting for an excuse to be triggered and snap together like a trap. Like your dishwasher tablet tower, for example.

It's amazing how the same few people can argue for so long on an issue the experts have setteled long ago.