Moderated Steel structures cannot globally collapse due to gravity alone

[Dave Rogers]

Your off-the-cuff math for 300, 4 ton pieces traveling 600' after being ejected from the top of the building is silly.

Congratulations, you just joined Homeland Insurgency and KreeL in the "La la la la, I can't hear you" truther action group. If your comment on the argument ranged against you is no more than "That's silly", then you're exposing your own intellectual bankruptcy.

Most of the debris fell outside the footprint.

^{[citation needed]} A graph of debris distribution by weight against distance would be nice. Even a vague estimate would help. If you don't have that, then you're making things up.

Your off-the-cuff math does not give a reasonable estimate of how much energy it would take.

Bare assertion fallacy, one of your favourites. Please feel free to substitute a reasonable estimate of your own. Extra credit will be given for demonstrating how much energy would be required to move the upper section laterally by 208 feet, which you insist would have happened had the lower block not been destroyed by explosives, and showing that this is less than the energy required to eject 4-ton sections up to 600 feet.

Dave

 

[Dave Rogers]

The top was not being pushed to the side, it was falling to the side. That doesn't require any energy.

Sideways motion doesn't require any energy? Well, in that case, the 4-ton sections could have fallen to the side without requiring any energy, couldn't they? Or maybe it takes energy to move a 4-ton object, but not a 30,000 ton object? Which is it, Chris? Because you seem to be claiming that it required energy to move 4 tons 600 feet, but none to move 30,000 tons 200 feet.

Dave

 

[Furcifer]

Sorry, gravity is one important load to consider both for structural design and structural damage analysis.

The difference between, e.g. a tall building structure designer and a naval architect is that the tall building designer mainly considers static loads (incl. e.g. snow on the roof) and some wind loads.
In naval architecture you have to consider much more loads, incl. impacts, e.g. when big waves smash into the structure. So at least I am quite familiar with the latter subject.
So when part C - upper part of WTC 1 - is alleged to smash into part A - lower structure of WTC 1 - I have a quite good feeling for it.

And in my simple view it is part C that shall be destroyed first and not part A in some funny crush down ... due to gravity alone.

I have great respect for the forces of nature and sea ... incl. gravity.

You say this and yet it eludes you how a crushing front can exsist as part of the collapse mechanism in a building and not a fender bender? Either you don't understand the function of gravity in this equation or you remain woefully ignorant.

I've made my personal views know as to the validity of the upper section remaining intact for the duration of the collapse. In fact, I've expressed my views to 2 or 3 of the authors. If I remember correctly, they don't stand behind this assumption as anything more than a necessary simplification. Necessary but more importantly justified, mathmatically. Unless you can provide evidence (ie. some calculations) to the contrary, you're simply handwaving. I would encourage you do this if you have the faculties to do so. Present some actual calculations to make the assumption of a rigid upper block appear flawed. I am sure they, and many here, would be more than willing to review your findings.

 

[Heiwa]

1. So why are you trying to compare it to a lemon? Is a lemon 95 % air?



2. Also what happens if the massive dynamic weight misses the 5% of the structure below? What happens if this massive dynamic weight misses all the supporting structure and actually hits something that cannot support it?



3. Also why are you trying to make out that the volume of the upper block in anyway represents the actual weight of it and try to dismiss it as weak and it cannot destroy anything? What did this mass weigh ? Produce some maths to support your case that this weight can be stopped by the structure below, that by your own admission "is quite weak and volum wise 95% air".



4. If a massive weight is dropped onto something that by volume is 95 % air and very weak, what is going to stop it dropping?

1. It is an analogy. Everyone understands that lemons do not crush by themselves due to gravity alone. Same for WTC 1.

2. The upper dynamic weight is not massive - is is 95% air. A thin bottom floor with broken columns (and more floors and a hat truss on top with air between). The bottom floor will hardly miss the columns sticking up below. So the bottom floor of the upper part is destroyed first!

3. Total weight of upper part does not matter. It is the local strength of the part that contacts first e.g. the bottom floor of the upper part contacting the columns below. That floor cannot withstand the forces applied by the columns. But NIST assumes it remains intact and acts as a snow plough compressing everything below - compare 1.

4. In this imaginary example - a massive weight dropping on something 95% full of air - what is the other 5%? Anyway - this is what NIST wants you to believe - WTC 1 upper part was a massive weight (rigid!) so it compressed the structure below - crush down. Just ignorant people believe such rubbish - like this Gravy charachter.

 

[Heiwa]

You say this and yet it eludes you how a crushing front can exsist as part of the collapse mechanism in a building and not a fender bender? Either you don't understand the function of gravity in this equation or you remain woefully ignorant.

I've made my personal views know as to the validity of the upper section remaining intact for the duration of the collapse. In fact, I've expressed my views to 2 or 3 of the authors. If I remember correctly, they don't stand behind this assumption as anything more than a necessary simplification. Necessary but more importantly justified, mathmatically. Unless you can provide evidence (ie. some calculations) to the contrary, you're simply handwaving. I would encourage you do this if you have the faculties to do so. Present some actual calculations to make the assumption of a rigid upper block appear flawed. I am sure they, and many here, would be more than willing to review your findings.

Right - a weak floor of upper part C cannot produce a crushing front.

Yes, I know Benson and Greening, the last two of the BLGB authors' paper; they do not stand behind the assumption that part C remains intact during the complete crush down - it is just a necessary simplification in a one-dimensional model that is not valid for anything. So The BLGB paper is only useful in the WC room (not drying your hands, though).

And they have reviewed my findings - read http://heiwaco.tripod.com/nist3.htm . I quote them, they comment, I add their comments, etc.

I feel sorry for them. Benson has not seen any videos, and Greening ask me to tell him what I see on the videos, etc, etc. These guys are gaga!

 

[stateofgrace]

1. It is an analogy. Everyone understands that lemons do not crush by themselves due to gravity alone. Same for WTC 1.

Your analogy is worthless then,because it in no way shape of form represents the towers, correct?

2. The upper dynamic weight is not massive - is is 95% air. A thin bottom floor with broken columns (and more floors and a hat truss on top with air between). The bottom floor will hardly miss the columns sticking up below. So the bottom floor of the upper part is destroyed first!

How much did it weigh? I am not interested in your volume, I asked you how much it weighed, please answer. Are you seriously suggesting that the top hat did not contribute to the weight of this falling mass? Are you being serious here? Volume and weight are NOT the same thing.

3. Total weight of upper part does not matter. It is the local strength of the part that contacts first e.g. the bottom floor of the upper part contacting the columns below. That floor cannot withstand the forces applied by the columns. But NIST assumes it remains intact and acts as a snow plough compressing everything below - compare 1.

Yes it does matter, now what was the weight of the falling mass? If the columns hit the lower floor trusses, what happens, explain, with maths why the lower section, which you describe as weak and 95% air will stop the massive falling weight.

4. In this imaginary example - a massive weight dropping on something 95% full of air - what is the other 5%? Anyway - this is what NIST wants you to believe - WTC 1 upper part was a massive weight (rigid!) so it compressed the structure below - crush down. Just ignorant people believe such rubbish - like this Gravy charachter.

The other 5% is the steel structure of the towers. Stop your pathetic attempts at character assination, if you do so again I will report you. Now, again produce your maths that shows that the lower section will stop the massive dynamic weight. Man up and stop with your silly, worthless analogies and produce you maths that shows the upper massive dynamic weight can be stopped by the floor trusses.

I want you to explain precisely how a steel structure that by your own words is “weak and by volume 95% air” can stop the massive falling weight, hand waving it away with your silly assertion that it was 95% air is as absurd as it gets. Produce some maths, show everybody what this weight was and how it can be stopped by the lower floor trusses,show everybody how the lower section , that was also 95% air and weak could stop this massive dynamic weight.

If you fail to produce your maths to back your claims in the next post, consider this conversation over.

 

[Furcifer]

Right - a weak floor of upper part C cannot produce a crushing front.

Right- the weak floor of the bottom part produces the crushing front, assisted by the "explosive" lateral forces of the descending upper part peeling the floors from the exterior like a banana. You can see this here http://heiwaco.tripod.com/nist3.htm

 

[Architect]

2. The upper dynamic weight is not massive - is is 95% air. A thin bottom floor with broken columns (and more floors and a hat truss on top with air between). The bottom floor will hardly miss the columns sticking up below. So the bottom floor of the upper part is destroyed first!

3. Total weight of upper part does not matter. It is the local strength of the part that contacts first e.g. the bottom floor of the upper part contacting the columns below. That floor cannot withstand the forces applied by the columns. But NIST assumes it remains intact and acts as a snow plough compressing everything below - compare 1.

Bill - assuming that you're still reading - I'm hoping that you can see the problems with this kind of argument. Firstly, Heiwa is now (for the first time) moving to a recognition that the floors could not accommodate the new imposed loadings posed by the collapse. However he seems to be arguing (it's not entirely clear) that because the upper mass would not be intact it would in some way not cause sufficient increased loadings to explain global failure. This doesn't make sense, of course; the mass is still falling, and still hitting, whether as one or a series of ones.

Moreover Heiwa still ignores the impact (no pun intended) of the lost floors on overall structural stability and hence the possibility that resistance to the failure will be further compromised.

Just ignorant people believe such rubbish - like this Gravy charachter.

Just pretty much the entire structural engineering community, eh?

 

[Gravy]

Sideways motion doesn't require any energy? Well, in that case, the 4-ton sections could have fallen to the side without requiring any energy, couldn't they? Or maybe it takes energy to move a 4-ton object, but not a 30,000 ton object? Which is it, Chris? Because you seem to be claiming that it required energy to move 4 tons 600 feet, but none to move 30,000 tons 200 feet.

Dave

Well, you've hit on Christopher7's magic, after a couple of years . It's been that long, and he cannot explain the first thing about why he thinks the structural steel falling where it did is correct.

 

[Heiwa]

Heiwa is now (for the first time) moving to a recognition that the floors could not accommodate the new imposed loadings posed by the collapse. However he seems to be arguing (it's not entirely clear) that because the upper mass would not be intact it would in some way not cause sufficient increased loadings to explain global failure. This doesn't make sense, of course; the mass is still falling, and still hitting, whether as one or a series of ones.

Moreover Heiwa still ignores the impact (no pun intended) of the lost floors on overall structural stability and hence the possibility that resistance to the failure will be further compromised.

Actually I have always from the beginning pointed out that the floors in the upper part C could never accommodate the imposed forces by the static lower part A columns.
Yes, I ignore the impact as a load (the upper part C) carried by 287 alleged kneeling columns cannot free fall and thus not impact anything. The kneeling columns will just dispose upper part C sideways, etc. No mass is falling anywhere - particularly not upper part C. It is the first to be destroyed by some mysterious energy applied inside it. Wonder what it can be?

 

[Heiwa]

Right- the weak floor of the bottom part produces the crushing front, assisted by the "explosive" lateral forces of the descending upper part peeling the floors from the exterior like a banana. You can see this here http://heiwaco.tripod.com/nist3.htm

Not really - as anyone checking the link sees.

 

[Heiwa]

Yes it does matter, now what was the weight of the falling mass? If the columns hit the lower floor trusses, what happens, explain, with maths why the lower section, which you describe as weak and 95% air will stop the massive falling weight.



If you fail to produce your maths to back your claims in the next post, consider this conversation over.

I have already done this previously several times. Check posts above. The strain energy, SE, associated with columns slicing two floors far exceeds the potential energy, PE, any upper part can apply.

Thus SE>PE = crush down is arrested. It is not difficult to do this calculation.

Thanks for the questions and interesting conversation that is now ended.

 

[Gravy]

I have already done this previously several times.

Yes, I see.

 

[Architect]

Actually I have always from the beginning pointed out that the floors in the upper part C could never accommodate the imposed forces by the static lower part A columns.
Yes, I ignore the impact as a load (the upper part C) carried by 287 alleged kneeling columns cannot free fall and thus not impact anything. The kneeling columns will just dispose upper part C sideways, etc. No mass is falling anywhere - particularly not upper part C. It is the first to be destroyed by some mysterious energy applied inside it. Wonder what it can be?

Bill et al

Although perhaps initially compelling, there are a number of problems with this kind of analysis. Firstly, and at the risk of repeating my earlier comments, it completely ignores the issue of overall structural stability - or bearing capacity - following removal of the key elements. However we see other areas of concern too. For example, there is an underlying assumption that the buckled columns fail gradually and do not "impact" on anything. But we don't see any calculations to support this rather unorthodox view.

Instead there is merely the suggestion (if I understand Heiwa correctly) that they will cause a significant degree of lateral movement. This in itself is even more puzzling, as there is no suggestion that the upper structure in isolation would have sufficient rigidity to topple monolitically. Rather, we would expect the joints to fail almost immediately under the lateral loads and thereafter a more or less vertical path to occur.

Baazant, Greening and others undoubtedly simplify some aspects of the collapse in order to show that there is sufficient energy to support the progressive collapse case. These assumptions are, however, well stated and not unreasonable. Compare and contrast them with the incomplete summaries and rather peculiar analogies which Heiwa uses.

 

[stateofgrace]

Edit, never mind, this really is not worth it.

 

[ElMondoHummus]

Bill et al

Although perhaps initially compelling, there are a number of problems with this kind of analysis. Firstly, and at the risk of repeating my earlier comments, it completely ignores the issue of overall structural stability - or bearing capacity - following removal of the key elements. However we see other areas of concern too. For example, there is an underlying assumption that the buckled columns fail gradually and do not "impact" on anything. But we don't see any calculations to support this rather unorthodox view.

Instead there is merely the suggestion (if I understand Heiwa correctly) that they will cause a significant degree of lateral movement. This in itself is even more puzzling, as there is no suggestion that the upper structure in isolation would have sufficient rigidity to topple monolitically. Rather, we would expect the joints to fail almost immediately under the lateral loads and thereafter a more or less vertical path to occur.

Baazant, Greening and others undoubtedly simplify some aspects of the collapse in order to show that there is sufficient energy to support the progressive collapse case. These assumptions are, however, well stated and not unreasonable. Compare and contrast them with the incomplete summaries and rather peculiar analogies which Heiwa uses.

Architect, let me see if I got this right. Heiwa says this:

The kneeling columns will just dispose upper part C sideways, etc.

Which means that he's saying "kneeling" columns will still be able to resist a dynamic (i.e. moving, and in fact accelerating) load in the midst of failure? Rather than continue to "kneel" (by that, I presume he and Bill means "buckle") until it's either basically horizontal or until the connection points to the lower column fail? And while it's resisting, it will be able to deflect mass from a vertical path into a partially horizontal one? Do I understand his misunderstanding correctly?

And would it be fair to ask how the buckled columns are supposed to do this when their connections to lower columns have failed? This question of course presumes that I understand both the initial misapprehension and the correct failure mode to begin with.

Thanks.

 

[Architect]

Yes, that's my understanding of his contention however he also assumes that the buckling action is sufficiently uniform to lead to a toppling movement.

Amazing, isn't it?

 

[Heiwa]

(Heiwa) completely ignores the issue of overall structural stability - or bearing capacity - following removal of the key elements. However we see other areas of concern too. For example, there is an underlying assumption that the buckled columns fail gradually and do not "impact" on anything. But we don't see any calculations to support this rather unorthodox view.

Instead there is merely the suggestion (if I understand Heiwa correctly) that they will cause a significant degree of lateral movement. This in itself is even more puzzling, as there is no suggestion that the upper structure in isolation would have sufficient rigidity to topple monolitically. Rather, we would expect the joints to fail almost immediately under the lateral loads and thereafter a more or less vertical path to occur.

Baazant, Greening and others undoubtedly simplify some aspects of the collapse in order to show that there is sufficient energy to support the progressive collapse case. These assumptions are, however, well stated and not unreasonable. Compare and contrast them with the incomplete summaries and rather peculiar analogies which Heiwa uses.

Overall structural stability, whatever that can be, is not affected by local failures, e.g. 287 columns simultaneously kneeling in the initiation zone - not seen of course - due to being weakened by heat in or overloaded due to load transfers above the initiation zone. This situation can be analysed by proper structural damage analysis to find the energy used, if any rubble is produced and to see the new interface between upper part C and lower structure, part A.

So what is the new interface and what local failures may occur there? The affected columns punching holes in the top floor of part A or the affected columns fracturing leaving two free ends of each column that may contact something? And where is part C with regard to part A at this new interface? Part C is probably shifted laterally. What does it mean?

Proper structural damage analysis provide the answers to these questions.

Bazant had all the answers ready two days after 911. Part C free fell on part A (not seen of course) - perfect impact - shock wave - and part A columns broke like spaghetti. Not seen any videos, of course. Bazant has since, with new co-authors - tried to refine this simple model, latest, the BLGB paper, with a one-dimensional model based on unreasonable assumptions; upper line C having constant length/mass, lower line A being transformed bit by bit into a line B with 4 times greater one-dimensional density (kg/m!), etc. That model is a joke. Line C is driven by gravity and accelerates all the time while line B grows and line A is shortened At the end of crush down line A is replaced by a line B that is 1/4 of the original line A and 4 times greater density??? The whole is described by a differential equation that is supposed to describe the three lines.

The interface between lines A and B is supposed to be a crush front where air is compressed - air in the line??? - and ejected from this one-dimensional model - how?

When line A becomes 0 and line B is 1/4 of original line A, then POUFF, line B becomes even shorter (and denser) and then line C suddenly disappears - POUFF UP! Nothing then remains of lines A, B and C. This is described with a new differential equation. Absolut nonsense - all of it

Asking Benson and Greening what the paper is all about you just get funny excuses.

Anyone reading the article at http://heiwaco.tripod.com/nist3.htm evidently reads the title and knows what it is all about. Then, to be helpful, the author presents another, more realistic scenario what could happen if part C contacts part A - collapse arrest; part C gets stuck on part A with some local failures as result. Evidently collapse arrest didn't take place because, as the author points out, part C disappeared completely very early
in the destruction, so it can not be arrested. Part C was gone before part B even started to get formed!

Asking Benson and Greening about this, Benson said he had never seen a video of the crush down. His PC is to slow, etc.

Anyway, topic was the fact that steel structures cannot globally collapse due to gravity alone, later refined to be that a steel structure cannot be crushed down by dropping a part of it on itself. This should be quite clear by now so I suggest the thread is closed!

I am leaving for ski vaccation, anyway. See you in March at some other thread.

 

[Architect]

Overall structural stability, whatever that can be, is not affected by local failures, e.g. 287 columns simultaneously kneeling in the initiation zone - not seen of course - due to being weakened by heat in or overloaded due to load transfers above the initiation zone. This situation can be analysed by proper structural damage analysis to find the energy used, if any rubble is produced and to see the new interface between upper part C and lower structure, part A.

Two problems with this:

1. The first sentence assumes that the individual failures within a composite structure do not lead to failure because, one assumes, of redundant capacity. To come to this position one would need to do the necessary calculations, as NIST have done. If Heiwa is unhappy with their findings then he simply needs to post his own detailed structural calculations.

2. One cannot do a damage analysis until one understands the structure. So far we have seen no such rigorous assessment from Heiwa and the rather peculiar analogies do nothin to convince me that such a paper exists.

 

[twinstead]

Anyway, topic was the fact that steel structures cannot globally collapse due to gravity alone, later refined to be that a steel structure cannot be crushed down by dropping a part of it on itself. This should be quite clear by now so I suggest the thread is closed!

What is quite clear is that every single qualified person I've talked to, both on this forum and in my personal life, thinks you are wrong. So, pardon me if I decide to get a second opinion when you insist that the WTC collapses were impossible.

Have fun on your vacation, though. Everybody needs those once in a while.