Video Nullfies Pancake/CD Theory

Originally posted by Akareyon
I'm fine with any explanation for the initiation of the collapse, I'll go along with Bazant and pretend one floor was removed and there was a one story freefall.

That's really a simplifying assumption but I guess it depends what you want to investigate.

So, the collapsing stucture then stripped the columns as it descended, which in turn caused the columns to buckle under their own weight, right?

No. If we're talking about the actual collapse mechanism then the majority of columns in the WTC were not buckled, certainly not under their own weight. They were disconnected from the structure and thrown outwards. The whole point of this sort of collapse is that the collapses aren't perfect column-on-column impacts. That's why Bazant used that as his limiting case, as it's the best the building could possibly hope for.

Sounds like the engineers made some big, big, big mistake, doesn't it? Maybe not and all skyscrapers have this flaw built in, I'm no expert, I just wonder.

This is exactly why the NIST report recommended that buildings be studied prior to construction to understand the risk of progressive collapse. IE the risk of one failure cascading. As I mentioned before, modern buildings have much more strongly armoured cores, making sprinkler activation much more likely and making evacuation that much safer. That's the biggest change after 911.

Because if it was an engineering failure unique to the Twins, I would find it strange that none of the white-collar victim's families sued the hell out of those engineers for compensation of their loss in a legal system where you can sue McDonald's for serving hot coffee.

The McDonalds Coffee has never been a particularly good example because the woman involved never wanted to sue and suffered horrific injuries that McDonalds had been warned about before. Still I would not be surprised to see Silverstein or Robertson sued over this. Don't think I've seen anything so far though.

Originally posted by Akareyon

Originally posted by -PLB-
The rest of the building is no longer attached to the floors once they fail. How is the load going to be transfered to the columns in your design?

When it is not transferred, the columns cannot fail because the whole mass - if you somehow manage to move it over the floor slabs - just crashes into the basement without its force acting on the columns in any way. Perimeter and core remain standing, because they are stable on their own by design and definition.

They are? The engineers who designed and built the WTC did not think so. They built the core and the outer wall together as they both required each other connected via the floor trusses in order to mitigate wind forces. If all floors were removed the outer frames have little to no moment resistance in their normal direction. They would buckle and collapse almost immediately.

In reality, they did, helped of course by a couple hundred thousand tons of debris pushing out on them too.

88kg of explosives, intelligently placed. Just throwing them through an open window would hardly have the same effect. Intelligence, planning and intention are a form of energy, as it seems. You're getting very close to what I'm trying to say here...

Just like a bunch of domino randomly set up on a given area will not completely collapse progressively, only if you set them up intelligently so they do.

To some extent yes, but if you're talking buildings of similar geometry to the WTC then just dropping one half on the other half is often good enough:


There's no doubt that the design of the WTC contributed to its collapse. This should be plainly obvious to anyone with a little structural knowledge, it should also be clear to any conspirators. The idea that they'd plant hundreds of explosives on every floor as others are implying is ridiculous.

Originally posted by -PLB-
So you still have progressive floor collapse,

Wait. My floor slabs are designed for little load except for some office furniture so if you go ahead and rip them down by somehow moving all the weight of the columns of the top part of the building on the topmost floor slab and these get ripped out, depending on the mass probably all the way to the bottom, it's hardly a progressive collapse, it's just being smashed by overload.

Let me put it another way. What exactly is the benefit that after collapse your columns are still standing, compared to a situation where the columns collapsed along with the floors?

Describe a scenario where all the weight of the top is being dislocated to come down over the floors only, and I might think about going back to the drawing board.

But then it would not have the same potential energy, would it?

Nope. What is your point exactly?

So if you put it up, storing potential energy in the structure, you may want to make sure it is properly contained, wouldn't you? I mean, how many shades of grey are there between "stable", "metastable" and "unstable"?

Sure it is. But that energy is like ten gallons of diesel packed in a plastic bag instead of a steel tank - not very well contained, obviously.

I haven't noticed skyscrapers collapsing all over the world, so its pretty well contained.

Obviously, the potential energies of other skyscrapers that were burning extensively or got a hole punched in their structure by a plane were much better contained, so please excuse my asking so ignorantly if containing 981 GJ of potential energy in 55 GJ of tensile energy is the school-book of engineering way to go.

Either intelligent placing, or just overkill. Either is possible. A plane impact with subsequent fires obviously was a massive energy release compared to explosives. At least it was enough to make 1 or 2 floors of that building fail. The energy that was released when the top started falling completely dwarfed any kind of explosives,

2.1 GJ... pfff.... even the planes had more kinetic energy (E_kin_planeimpact = 1/2 * 124.000kg * (225 m/s)² ≈ 3,14 GJ) when they impacted - from the side, I may add - than the top dropping free-fall (in the most optimistic scenario towards collapse) on the rest of the building. Add another few GJ for half of the kerose exploding instantly, creating a huge fireball, and another half burning away in a matter of minutes (according to NIST at least, if I remember correctly), igniting fire-retardant office furniture. All this left 2/3 of the building structurally completely intact (according to NIST at least, if I remember correctly). Overkill, really?

²exponent:

If we're talking about the actual collapse mechanism then the majority of columns in the WTC were not buckled, certainly not under their own weight. They were disconnected from the structure and thrown outwards.

I'm sorry, it's hard to keep track of all the different explanations that endorse the official conspiracy theory. I'm not even going to post the photos of all the bent and crippled beams and columns here. Certainly, the debris field shows a lot of colums that were not bent.

So when the weight slammed on the floor slabs, these ripped the columns out of their bolts and weldseams and pushed them outward, is that right? That in turn would require the floor slabs to be stable enough to transfer the forces to the columns!

The whole point of this sort of collapse is that the collapses aren't perfect column-on-column impacts. That's why Bazant used that as his limiting case, as it's the best the building could possibly hope for.

He assumed the best case scenario and still the towers were doomed! Poor architects, he's literally destroying them.

Still I would not be surprised to see Silverstein or Robertson sued over this. Don't think I've seen anything so far though.

Nor have I. Strange, isn't it? I know this is completely off-topic, but it really bugs me how all the victims' families obviously don't mind that their beloved ones were smashed by the buildings they were working in and that collapsed without any resistance worth mentioning. Some of them were well-off people, I would think - bankers, insurance agents and so on.

When that garment factory collapsed in Savar, Bangladesh, however, reactions were different. Nine people were detained and might be facing a life in prison:

"We asked the government to give the highest punishment to all the accused as it was nothing but gross negligence of responsibilities for which 1,130 innocent workers were killed," Mainuddin Khandaker, a senior interior ministry official, told Reuters.

Source

Originally posted by Akareyon
²exponent:
I'm sorry, it's hard to keep track of all the different explanations that endorse the official conspiracy theory.

That's fine. Bazant's mechanism was designed to be the best possible case for bulding survival, but the actual collapse was nowhere near as simple and obviously once the columns and debris are impacting the floors the building is doomed.

I'm not even going to post the photos of all the bent and crippled beams and columns here. Certainly, the debris field shows a lot of colums that were not bent.

Indeed there are both bent and straight columns, I'm not claiming that all columns were broken away, just that it was a dominant mechanism.

So when the weight slammed on the floor slabs, these ripped the columns out of their bolts and weldseams and pushed them outward, is that right? That in turn would require the floor slabs to be stable enough to transfer the forces to the columns!

That is probably not correct. We know that at the impact levels the floors did pull inward on columns and truss seats were found where the bolts had 'torn out'. However, once the destruction begins there's not going to be much of a chance for floors to be applying any force. What happens then is the debris simply strips the floors from the columns, bending the truss seat downwards or shearing it off entirely. The static pressure from debris then causes the columns to be pushed outwards.

Some other commentators have described this as 'ROOSD'. 'Runaway Open Office Space Destruction'. Where the debris is essentially funneled onto the floors by the outer walls and so both elements end up being destroyed.

The whole point of this sort of collapse is that the collapses aren't perfect column-on-column impacts. That's why Bazant used that as his limiting case, as it's the best the building could possibly hope for.

He assumed the best case scenario and still the towers were doomed! Poor architects, he's literally destroying them.

Indeed Bazant's analysis is a fairly scathing critique of 'lightweight' buildings with large open spaces. I haven't seen many new buildings of this sort of scale take a similar approach after 911. Now it seems to be mostly reinforced concrete for this sort of thing as it inherently resists fire an awful lot better than steel. Do you know of any examples?

Nor have I. Strange, isn't it? I know this is completely off-topic, but it really bugs me how all the victims' families obviously don't mind that their beloved ones were smashed by the buildings they were working in and that collapsed without any resistance worth mentioning. Some of them were well-off people, I would think - bankers, insurance agents and so on.

When that garment factory collapsed in Savar, Bangladesh, however, reactions were different. Nine people were detained and might be facing a life in prison:

There is one major difference between these two examples, and that is the rather large jet airliners which struck both buildings. If the WTCs sprinkler systems had failed and it had fallen due to a regular office fire (which some believe to be possible) then I think you would see a giant outrage. Once an aircraft hits your building though? I think your responsibility is diminished significantly.

Originally posted by Akareyon
Wait. My floor slabs are designed for little load except for some office furniture so if you go ahead and rip them down by somehow moving all the weight of the columns of the top part of the building on the topmost floor slab and these get ripped out, depending on the mass probably all the way to the bottom, it's hardly a progressive collapse, it's just being smashed by overload.

Alright, lets call it floor collapse in which everyone who happens to be on a floor dies. The end result is the same, everyone is dead, except you still have columns standing.

Describe a scenario where all the weight of the top is being dislocated to come down over the floors only, and I might think about going back to the drawing board.

Why all the weight of the top? Terrorists can simply use explosive to make 1 or 2 floors in the top fail. And easy feat if you believe those buildings were rigged all over the place on 911. Another way of achieving floor overload is by parking a Boeing on them.

So if you put it up, storing potential energy in the structure, you may want to make sure it is properly contained, wouldn't you? I mean, how many shades of grey are there between "stable", "metastable" and "unstable"?

You want it to be safely contained. I don't see how this proportion is important.

Obviously, the potential energies of other skyscrapers that were burning extensively or got a hole punched in their structure by a plane were much better contained, so please excuse my asking so ignorantly if containing 981 GJ of potential energy in 55 GJ of tensile energy is the school-book of engineering way to go.

I would say yes. But you can do these kind of calculations for other buildings too, so we don't really need to guess if you really want to know.

2.1 GJ... pfff.... even the planes had more kinetic energy (E_kin_planeimpact = 1/2 * 124.000kg * (225 m/s)² ≈ 3,14 GJ) when they impacted - from the side, I may add - than the top dropping free-fall (in the most optimistic scenario towards collapse) on the rest of the building.

Where did you get 2.1 GJ? Thats completely wrong. Even the calculation in your post shows this.

Add another few GJ for half of the kerose exploding instantly, creating a huge fireball, and another half burning away in a matter of minutes (according to NIST at least, if I remember correctly), igniting fire-retardant office furniture. All this left 2/3 of the building structurally completely intact (according to NIST at least, if I remember correctly). Overkill, really?

Are you arguing that explosives would release more energy? By all means, make an estimate.

Originally posted by exponent
We know that at the impact levels the floors did pull inward on columns and truss seats were found where the bolts had 'torn out'. However, once the destruction begins there's not going to be much of a chance for floors to be applying any force. What happens then is the debris simply strips the floors from the columns, bending the truss seat downwards or shearing it off entirely. The static pressure from debris then causes the columns to be pushed outwards.

Some other commentators have described this as 'ROOSD'. 'Runaway Open Office Space Destruction'. Where the debris is essentially funneled onto the floors by the outer walls and so both elements end up being destroyed.

We're slowly getting to the meat. The mass from above manages to rip down the floors and push the columns out of their joints at the same time - without considerable deceleration so enough energy is left to do the same thing again. And again. And again.

Indeed Bazant's analysis is a fairly scathing critique of 'lightweight' buildings with large open spaces. I haven't seen many new buildings of this sort of scale take a similar approach after 911. Now it seems to be mostly reinforced concrete for this sort of thing as it inherently resists fire an awful lot better than steel. Do you know of any examples?

What's wrong with the examples I have already posted, except that they are no exact replicas of the Twins?

There is one major difference between these two examples, and that is the rather large jet airliners which struck both buildings.

I thought we had agreed that it was not really the planes. Truly, they caused considerable damage, however NIST concludes (if I remember correctly) that the redundant design of the towers easily made up for that.

Once an aircraft hits your building though? I think your responsibility is diminished significantly.

So all you have to do if you want to get rid of your building, just slam an aircraft in the top and nobody's gonna ask any questions...

²-PLB-:

Terrorists can simply use explosive to make 1 or 2 floors in the top fail.

That would not result in progressive collapse in my building, because it will act like my Jenga tower or a card house by definition.

And easy feat if you believe those buildings were rigged all over the place on 911.

If. I haven't stated yet what I believe, I don't even know myself and it's not all that important. I explicitly stated I have no agenda of my own and am not trying to convince you of this theory or that. All I do is question the logic of all the conspiracy theories (including progressive collapse, slipshod architecture/ROOSD, CD, thermite, mini nukes, black tech and alien death rays) because I do not believe Newtons laws and the fabric of the universe were suspended on September 11th, 2001, for a few cubic meters in Manhattan.

Another way of achieving floor overload is by parking a Boeing on them.

See my Jenga tower. 10 blocks smash one floor, not more. Even with cube-square law and cost/FoS-compromises, I think you will have a hard time smuggling enough mass into the building to achieve an overload that shoots its way through all the floor slabs.

You want it to be safely contained. I don't see how this proportion is important.

You said so yourself when you quoted Bazant. Wp = potential energy; Wg = "containing" energy; IF Wg > Wp THEN GOSUB(progressive.collapse) ELSE GOSUB(collapse.arrest).

Obviously, the potential energies of other skyscrapers that were burning extensively or got a hole punched in their structure by a plane were much better contained, so please excuse my asking so ignorantly if containing 981 GJ of potential energy in 55 GJ of tensile energy is the school-book of engineering way to go.

I would say yes.

Get everbody out of those buildings, now!

Where did you get 2.1 GJ? Thats completely wrong.

Not so completely. Ekin = m * g * h = 58,000,000 kg * 9.81m/s² * 3.7m = 2,105,226,000 J = 2.1 GJ. I know Bazant gives another number, but only because he's going for the potential difference to the next floor (m·g·h != m·g·h·2):

the total release of gravitational potential energy is Wg = mg·2h = 2×2.1 GN m = 4.2 GN m

Bazant/Zhou - Why did the World Trade Center collapse? - Simple Analysis

Originally posted by Akareyon
We're slowly getting to the meat. The mass from above manages to rip down the floors and push the columns out of their joints at the same time - without considerable deceleration so enough energy is left to do the same thing again. And again. And again.

This is pretty accurate. Once the first floor has been ripped away, there's another 12 feet to fall and that little bit more mass to hit the next floor down.

What's wrong with the examples I have already posted, except that they are no exact replicas of the Twins?

I apologise, I came into this conversation quite late, I've gone over your older posts and quickly picked out each example I see and my comments:

• Petronas Towers - Concrete cored, set a record at the time
  
• Jin Mao Tower - Primarily concrete, concrete core
  
• Burj Khalifa - Uses a very interesting 'buttressed core'. I actually am not too happy with its structural design but it's such a beautiful building.
  
• Aon Center - A good example, I wasn't able to find information on any post 911 modifications. Depending on the floor structure, this building could potentially progressively collapse in a similar manner to the WTC
  
• Minsheng Bank Building - Seems to be no available information on its construction. I would bet it has a concrete reinforced core for safety.
  
• China World Trade Center III - Steel and reinforced concrete with a concrete core.
  
• NYT Tower - Steel and reinforced concrete, regular beam floored.

The problem with most of these buildings is that they were built after 911 and so have the lessons learned, or they are built in concrete. The only one built in steel beforehand which is substantially similar is the Aon Center. So, if a plane hits that building I'd be pretty worried. Frankly some of the others are quite vulnerable, if a plane managed to breach the core of the Burj Khalifa the damage done would be insane. No building can be invulnerable to these attacks, but all of the above should survive an intense fire, something the WTC might not have been able to do.

I thought we had agreed that it was not really the planes. Truly, they caused considerable damage, however NIST concludes (if I remember correctly) that the redundant design of the towers easily made up for that.

On the contrary, NIST concludes that both plane impact (to dislodge fireproofing and sever stairwells) and large scale fire (to deform trusses and weaken columns) are required for the events of that day to occur. Either / or probably wouldn't cut it, although there are some dissenters who believe the fireproofing quality was so low that a big fire might have done it. It likely wouldn't have been able to sever stairwells though so we wouldn't see anywhere near the same number of fatalities.

So all you have to do if you want to get rid of your building, just slam an aircraft in the top and nobody's gonna ask any questions...

Well I mean you're not far off. It's not unheard of for someone to set their car on fire or deliberately crash it to get an insurance payout. If you can really arrange to have a suicide bomber fly into your building and you have great coverage and you can just let it sit destroyed and you don't get caught, then it might be at least a semi rational idea. I don't think it's ever going to be a 'good' idea.

Originally posted by exponent

I didn't mean to ignore it, but I feel this argument has been discussed enough already as well. Please allow me to point you to the patent specification of the European Patent Office for EP 1 082 505 B1, commonly known as "vérinage". Let me know if you really think that the towers were brought down by the thoughtful removal of walls and the usage of ropes, pulleys and hydraulics. It's called "vérinage" for a reason, you know, because a vérin is a hydraulic cylinder in french.

La présente invention concerne un procédé de démolition d'un immeuble de plusieurs étages constitué d'un ensemble de murs porteurs sensiblement parallèles entre eux appelés couramment des voiles et d'un ensemble de dalles délimitant les étages, les dalles étant sensiblement parallèles entre elles et sensiblement perpendiculaires auxdits murs porteurs.

A method for the demolition of a building comprising several storeys and formed from an assembly of substantially mutually parallel load-bearing walls, generally called shear walls, and an assembly of flags delimiting the storeys, the flags being substantially mutually parallel and substantially perpendicular to the said load-bearing walls...

(emphasis mine)

The nice thing about the European Union is that the important stuff is always explained in German and English as well :-) Although I'm not sure why they translated "dalle" with "flag" (I couldn't find a source that mentions that a flag is a concrete floor); it should be concrete slab or so.

reply to post by exponent

Fair enough :-)

Yes, those are the buildings I mentioned when the other examples I've given for tubular design were criticized for being built before 9/11 - the Twin's little sibling, the BOK Tower, for example ;-) The next set of three was criticized for being a bad example because they have concrete structures, so I queried for steel frame skyscrapers and so the AON Center, China World Trade Center III and the NYT Tower are on the list now.

The only one built in steel beforehand which is substantially similar is the Aon Center. So, if a plane hits that building I'd be pretty worried.

Nothing to worry about, it will be fine. It will have a hole, burn a lot (because the CFD will not dare to enter probably, due to the FDNY experience with other burning towers ) and that's it.

Except if it also has that strange WTC mechanism built in, in other words, its potential energy is harnessed by a fraction in tensile energy, in other words, it is hanging in itself like -PLB-s dishwasher tablet model instead of standing like my Jenga model, in other words, a greater sum of forces is latently pulling downwards than the sum of forces pushing upwards (with "sum of all (latent) forces" I refer to Newtons so-called "lex quarta" or superposition principle, refined in the d'Alembert principle Professor Bazant was so kind to point me to).

But I don't think so. It will be fine. I hope the day never comes that proves my confidence right, though.

If you can really arrange to have a suicide bomber fly into your building

In the case we're talking about, a remote controlled plane will surely do :-)

Originally posted by Akareyon
I didn't mean to ignore it, but I feel this argument has been discussed enough already as well. Please allow me to point you to the patent specification of the European Patent Office for EP 1 082 505 B1, commonly known as "vérinage". Let me know if you really think that the towers were brought down by the thoughtful removal of walls and the usage of ropes, pulleys and hydraulics.

Oh no of course I don't. I posted the video to illustrate that if set up to shear floors from columns, buildings can be demolished progressively and seemingly in greater proportion than the energy input.

It's called "vérinage" for a reason, you know, because a vérin is a hydraulic cylinder in french.

Ah tres bon! I am actually trying to learn French but gendered languages can kiss my butt!

I couldn't find a source that mentions that a flag is a concrete floor

A 'flag' is generally a portion of an exterior concrete floor / footing here, so it is a strange translation.

Except if it also has that strange WTC mechanism built in, in other words, its potential energy is harnessed by a fraction in tensile energy, in other words, it is hanging in itself like -PLB-s dishwasher tablet model instead of standing like my Jenga model, in other words, a greater sum of forces is latently pulling downwards than the sum of forces pushing upwards

This is the balance of forces in anything accelerating downwards, but the forces were balanced before 911. In this case we're looking more at Unstable Equilibrium.

The WTC could survive substantial perturbation, most notably from the wind. It had tens of thousands of viscoelastic dampeners and a well designed load transfer system and exterior moment frame. As a design I can genuinely see where the innovation is, especially when I consider it was designed before I was born.

But I don't think so. It will be fine. I hope the day never comes that proves my confidence right, though.

Agreed. Considering the WTC was built before modern simulation and they self admit they had no real ability to assess fire behaviour, I'm surprised its design actually holds up as well as it does. Slightly more robust trusses, a concrete protected core and inspected and verified fireproofing would put it on a par with any of the modern buildings listed.

In the case we're talking about, a remote controlled plane will surely do :-)

Have you ever tried this though? The only ones that tend to work well are those designed for it and with substantial onboard equipment. If you can get your hands on an untraceable remote controlled commercial airliner you're talking $250m+ of value. Really just crash that and its insurance will outstrip your building!

Originally posted by exponent
Oh no of course I don't. I posted the video to illustrate that if set up to shear floors from columns, buildings can be demolished progressively and seemingly in greater proportion than the energy input.

...if set up!

Post by post, we agree on more things than in the beginning of the discussion.

Ah tres bon! I am actually trying to learn French but gendered languages can kiss my butt!

Je te souhaite bonne chance! And when you're good at French, try German next, it has three sexes and four cases and... umlauts + ß :-)

A 'flag' is generally a portion of an exterior concrete floor / footing here, so it is a strange translation.

The German translation says "Schale" ("shell" or "tray"), which I believe refers to any concrete segment poured into a basin made of wood which is removed when the concrete has hardened.

This is the balance of forces in anything accelerating downwards, but the forces were balanced before 911. In this case we're looking more at Unstable Equilibrium.

Now we're talking! :-)

The WTC could survive substantial perturbation, most notably from the wind. It had tens of thousands of viscoelastic dampeners and a well designed load transfer system and exterior moment frame. As a design I can genuinely see where the innovation is, especially when I consider it was designed before I was born.

Same with me.

Considering the WTC was built before modern simulation and they self admit they had no real ability to assess fire behaviour, I'm surprised its design actually holds up as well as it does. Slightly more robust trusses, a concrete protected core and inspected and verified fireproofing would put it on a par with any of the modern buildings listed.

Well, they may not have had access to supercomputers for FEMs and simulations, but they surely had the experience of decades of skyscraper construction.

I've read somewhere they had other unforeseen problems to cope with, like galvanic reactions between the steel, the aluminium claddings and salty seawater droplets

But it would be unfair to insinuate that if they had to choose between being on the safer side of the equation and saving a few bucks, they'd go for the money and let that thing come down as soon as it can.

I mean, with all these dampeners and other load transfer systems that were in place to stabilize the towers against subtropical hurricanes (really, the dampeners just convert kinetic energy into "heat"/internal energy just like the rockwool in a speaker box converts pressure into heat), how could the force of the upper part of the building possibly be transferred to the columns? Of course they were in place for lateral forces, but the forces acting during collapse weren't strictly of the vertical kind either, were they?

In the case we're talking about, a remote controlled plane will surely do :-)

Have you ever tried this though? The only ones that tend to work well are those designed for it and with substantial onboard equipment. If you can get your hands on an untraceable remote controlled commercial airliner you're talking $250m+ of value. Really just crash that and its insurance will outstrip your building!

...and now imagine money wouldn't be an issue...

One thing EVERYONE should remember in regards to pancaking and the collapses of the WTC Towers:

The original FEMA hypothesis was based on the WTF floors detaching and pancaking down, which initiated the collapse causing the whole structure to crash down. The idea was that the floor truss ends snapped off as the trusses expanded and then sagged down. When the trusses snapped off, that left the floor unsupported and causing it to pancake down onto the floor below, which then overloaded and snapped those connections, and so on and so on. Once enough floors pancaked internally, the exterior columns began to give way because they lost their horizontal stability the trusses gave. This was given the term "pancake" collapse, but this just ended up muddying the waters a bit, since the floors DID in fact end up pancaking down but only AFTER collapse initiated.

NIST discovered that this was not the case, and after a more thorough investigation, it turns out the floors were still attached and caused the exterior columns to bend inward. This can be seen prior to collapse in a few videos, and we do not see any floors pancaking internally BEFORE any movement of the exterior structure. What is seen is the exterior columns beginning to bend inward and the interior floors sagging down. Then the exterior columns snapped, which left the whole side unsupported, and the building began its decent. The floors above came crashing down onto the floor below, and then, rapid progressive collapse ensued, which was the floors pancaking down onto each other.

Anok insists that there was no pancaking at all. He incorrectly points to the NIST FAQ and misuses a quote which said that pancaking was not the cause of collapse. It gets twisted into meaning no pancaking happened at all, which is false, as there is plenty of evidence of it happening in the debris afterward. He ignores the part about the trusses sagging and pulling in the exterior columns, which then failed, INITIATING collapse. I have never seen any evidence of the floors being ejected, and have asked ANOK numerous times to provide one iota of proof or evidence that the floors were magically ejected. Nothing has come forward.

Folks, you have to read everything and have some reading comprehension to understand what is being said.

I finally am finished with the rubbish I've been working on so I'm gonna vanish shortly, probably for a day or two but who knows. I've enjoyed this conversation though and I don't feel that you are being as unreasonable now as your criticism of Bazant seems. Hopefully we can continue it.

Je te souhaite bonne chance! And when you're good at French, try German next, it has three sexes and four cases and... umlauts + ß :-)

Ach mein gott! (I cringe that I used that)

Now we're talking! :-)
..
Well, they may not have had access to supercomputers for FEMs and simulations, but they surely had the experience of decades of skyscraper construction.

Indeed they did, but still knowing what I know now, trying to predict fire behaviour without significant FEM work is a fools errand.

I've read somewhere they had other unforeseen problems to cope with, like galvanic reactions between the steel, the aluminium claddings and salty seawater droplets

As far as I am aware this is a meme started by the truth movement. I started seeing it as a rumour back in 2004/5 and since then it's grown into a full blown factoid. Not aware of any significant kernel of truth in it though. The corrosion would be expected to be pretty minimal and there was no evidence of it in the debris studies that I saw.

But it would be unfair to insinuate that if they had to choose between being on the safer side of the equation and saving a few bucks, they'd go for the money and let that thing come down as soon as it can.

The idea that the collapses made anyone money is flawed, it's based on only adding up one side of the equation, the insurance income. Most people who do this forget that the whole site had to be cleared and redeveloped, a project taking over a decade and no rents or income could be collected in this time etc.

I mean, with all these dampeners and other load transfer systems that were in place to stabilize the towers against subtropical hurricanes (really, the dampeners just convert kinetic energy into "heat"/internal energy just like the rockwool in a speaker box converts pressure into heat), how could the force of the upper part of the building possibly be transferred to the columns? Of course they were in place for lateral forces, but the forces acting during collapse weren't strictly of the vertical kind either, were they?

I'm not sure what you're getting at here. You're correct about the dampeners but the forces are transferred into the floors, not the columns. It is the inability of the floors to transfer that load back that is the issue I'm trying to highlight.

...and now imagine money wouldn't be an issue...

edit on 22-5-2013 by Akareyon because: (no reason given)

edit on 22-5-2013 by Akareyon because: (no reason given)

Well if money's not an issue then you don't need the insurance payout in the first place, so problem solved! No impossible conspiracy to pull off and you still have a building.

Originally posted by Akareyon

That would not result in progressive collapse in my building, because it will act like my Jenga tower or a card house by definition.

See my Jenga tower. 10 blocks smash one floor, not more. Even with cube-square law and cost/FoS-compromises, I think you will have a hard time smuggling enough mass into the building to achieve an overload that shoots its way through all the floor slabs.

This is in strong conflict with what you said earlier "My floor slabs are designed for little load except for some office furniture".

Now you are saying your floors can hold the mass of a Boeing and the load of several floors.

You said so yourself when you quoted Bazant. Wp = potential energy; Wg = "containing" energy; IF Wg > Wp THEN GOSUB(progressive.collapse) ELSE GOSUB(collapse.arrest).

Now you are mixing up a lot of things. You are looking at total potential energy vs total resistance. These are not the conditions given by Bazant, and for good reason, as it is incorrect. Bazant looks at available kinetic energy after a fall of 2 stories, and compares it to the energy required to make another story fail. The available kinetic energy depends on the amount of mass that is falling. It is completely different when just 2 floors come down, vs 15 in the WTC. The collapse could have been arrested then, according to Bazant's model. In reality maybe not.

Get everbody out of those buildings, now!

When planes are about to crash into them, or when they are on fire, its top priority.

Not so completely. Ekin = m * g * h = 58,000,000 kg * 9.81m/s² * 3.7m = 2,105,226,000 J = 2.1 GJ. I know Bazant gives another number, but only because he's going for the potential difference to the next floor (m·g·h != m·g·h·2):

the total release of gravitational potential energy is Wg = mg·2h = 2×2.1 GN m = 4.2 GN m

You go completely wrong here again. You calculated the amount of potential energy that is transfered to kinetic energy after falling a single story. Of course this is useful to know if there is enough energy for progressive collapse (this is where you go wrong above, but the other way around), but this is of course not the total potential energy in the top section. For that you need to compare it to ground level. Lets do the calculation based on your values:

Ekin = m * g * h = 58,000,000 kg * 9.81m/s² * 3.7m * 80 = 168 GJ.

And thats just the top section. All that energy is available to destroy the building to ground level.

You are really making some fundamental mistakes here.

As far as I am aware this is a meme started by the truth movement. I started seeing it as a rumour back in 2004/5 and since then it's grown into a full blown factoid. Not aware of any significant kernel of truth in it though. The corrosion would be expected to be pretty minimal and there was no evidence of it in the debris studies that I saw.

Yes, maybe. Legends abound where facts are made state secrets. It was meant as an example, other rumors have it most of the floors were unoccupied.

But it would be unfair to insinuate that if they had to choose between being on the safer side of the equation and saving a few bucks, they'd go for the money and let that thing come down as soon as it can.

The idea that the collapses made anyone money is flawed, it's based on only adding up one side of the equation, the insurance income. Most people who do this forget that the whole site had to be cleared and redeveloped, a project taking over a decade and no rents or income could be collected in this time etc.

[...]

...and now imagine money wouldn't be an issue...

Well if money's not an issue then you don't need the insurance payout in the first place, so problem solved! No impossible conspiracy to pull off and you still have a building.

That's not what I meant, I see my formulation was misleading. I was playing at the explanation that a stable structure would be too costly and therefor architects end up building skyscrapers that are hardly strong enough to support their own weight.

I actually lean more to the conclusion that money really wasn't an issue at all, Whatever the destruction, cleanup, repair and rebuilding may have cost in $$, the actual yield was much, much higher and measured in a totally different and much stronger currency...

I finally am finished with the rubbish I've been working on so I'm gonna vanish shortly, probably for a day or two but who knows. I've enjoyed this conversation though and I don't feel that you are being as unreasonable now as your criticism of Bazant seems. Hopefully we can continue it.

It has been a pleasure! I'm looking forward to continue this fruitful debate. Enjoy your free time :-)

Try German next, it has three sexes and four cases and... umlauts + ß :-)

Ach mein gott!

...and all Nouns start with a Capital

I have been reading the last several replies on this posting and have, what to me is, a simple question.
Through out all the retoric and calculation, there seems to be no attention given to the amount of debris material which was ejected from the buildings as they collapsed. Not just the steel members buy also the concrete.
Would not the apparent loss of this mass need to be figured into the calculus of this event in order to define the true nature of how the collapes happened as it appeared?

reply to post by teamcommander


It is of course of some relevance, but the amount of mass that would need to be ejected for the collapse to arrest is rather large. The thing is, when a large amount of mass is being ejected, it means there must be quite large forces acting. And when there are large forces, you won't have an arrest any time soon. So it is a bit of a self contradicting argument.

Bazant took debris falling sideways in consideration his papers by the way.

Originally posted by teamcommander
I have been reading the last several replies on this posting and have, what to me is, a simple question.
Through out all the retoric and calculation, there seems to be no attention given to the amount of debris material which was ejected from the buildings as they collapsed. Not just the steel members buy also the concrete.
Would not the apparent loss of this mass need to be figured into the calculus of this event in order to define the true nature of how the collapes happened as it appeared?

You are on the right path.

Yes it should have been especially when you look at the amount.

Now the question is if the concrete was being turned to dust what was acually "pancaking"?

And how did all that pancaked concrete manage to make a pile of rubble less than the height of the lobbies?

Well that easy. Because the concrete was turned into dust that covered most everything in 2inches of dust

Therefore the concrete wouldn't/couldn't be used as a mass when calculating

But dont suggest that to the os side.

reply to post by Another_Nut


This is pretty much my thinking.
You know there is a lot of water in even a small cloud, and water is fairly dense and heavy, but you don't get much of a reading on a set of scales when you try to weigh one.

Originally posted by -PLB-
reply to post by teamcommander

 

It is of course of some relevance, but the amount of mass that would need to be ejected for the collapse to arrest is rather large. The thing is, when a large amount of mass is being ejected, it means there must be quite large forces acting. And when there are large forces, you won't have an arrest any time soon. So it is a bit of a self contradicting argument.

Bazant took debris falling sideways in consideration his papers by the way.

So the concrete floor slabs for 220 stories is negligible?

Than that is why noone takes the os side seriously.

Silly statements like that.