What are your favorite 9/11 debunking tactics?

Originally posted by psikeyhackr
Talk about desperate.

Could it be that steel is expensive and it does not make sense to use it in short buildings.

Skyscrapers were not possible until the late 19th century when the Bessemer process enabled relatively inexpensive and large steel production.

Nobody's arguing that steel is not superior in any way to concrete. My point is that steel is not some invulnerable metal. Trying to make even such a simple point is fraught with difficulty when people disagree for no apparent reason.

It looks like the Bazant defence has turned into verbal BS.

psik

Because you're refusing to answer my questions and pretending like they don't exist. For the seventh time: How can a model which accelerates all of the mass of the towers be considered a minimum?

If you truly had faith in your model, you'd answer this. You've brushed it off so many times now I can only think that you have no good answer.

Originally posted by exponent
Because you're refusing to answer my questions and pretending like they don't exist. For the seventh time: How can a model which accelerates all of the mass of the towers be considered a minimum?

If you truly had faith in your model, you'd answer this. You've brushed it off so many times now I can only think that you have no good answer.

Because you LEAVE OUT what you want to LEAVE OUT and pretend it is irrelevant.

The question should be this:

How can a model which is MAGICAL in that it has no REAL SUPPORTS which would have to be broken and destroyed by the mass falling from above be considered the minimum?

Because the destruction of those supports would absorb the energy from the falling mass and the Conservation of Momentum would not be the only factor involved in increasing the collapse time.

On the one hand you want to say you know physics but then you turn around and deny physics if it does not serve your conclusion. But then I am supposed to take you seriously and respond to absurd questions at the drop of a hat. I already took the time to conceive, design, build, test, video a physical model and upload it to YouTube and provide sufficient data for anyone to duplicate. A model which cannot possible defy the Laws of Physics but you can refuse to conclude the obvious influence of real physical supports but I am supposed to give a damn about your silly questions.

The fact that this issue, which should have been resolved in 2002, has dragged on for TEN YEARS is proof of massive stupidity on many people's part. And it has to be more than stupidity.

You have already decided what you want to BELIEVE for whatever reason so I will respond when and if I feel like it. Go study the DRAMATIC DIFFERENCES between the results of your program and mine and write a report on the lack of elegance of my code even though I admitted it was a kludge. It just works with results quite similar to yours. So why does Dr. Sunder say the north tower came down in less time than both of our programs? But everyone acknowledges that the entire building came down in less than 26 seconds.

But I say if the effect of real supports and accurate mass distributions are taken into account there is no way it could come down in less than 26 seconds. So something else had to be involved and that is what my physical model portrays. So why hasn't any engineering school built a bigger physical model than mine?

But after TEN YEARS if the schools had to admit the collapse was impossible then they would have to explain why they did not tell everyone that long ago. So how long do we go into the future with this contradictory physics crap?

psik

Originally posted by psikeyhackr
Because you LEAVE OUT what you want to LEAVE OUT and pretend it is irrelevant.

The question should be this:

How can a model which is MAGICAL in that it has no REAL SUPPORTS which would have to be broken and destroyed by the mass falling from above be considered the minimum?

Because the destruction of those supports would absorb the energy from the falling mass and the Conservation of Momentum would not be the only factor involved in increasing the collapse time.

Right, I agree. You've neglected the fact though that you have maximised the momentum transfer. This isn't what you do to get a minimum bound. If we want to talk about the absolute minimum time for rubble to start hitting the ground inside the tower then we have to minimise the momentum transfer. That means destroying floors only. Do you want to work together on the values for this? I'd be more than happy to do the work and present it if you agreed on initial conditions.

But I say if the effect of real supports and accurate mass distributions are taken into account there is no way it could come down in less than 26 seconds. So something else had to be involved and that is what my physical model portrays. So why hasn't any engineering school built a bigger physical model than mine?

We've already been over this. You don't have any data that says 26 seconds, we don't have any good or agreed upon method to model the energy consumption. If you propose something then I am interested, but reconstructing a huge model just to satisfy something the engineering community considers solved? I just don't have the time or energy (or the facility unless I want to confuse my neighbours!)

Originally posted by exponent
So it means nothing then, that's not a surprise, I am used to reading through hyperbole and waiting for you to actually bother to go read the paper you requested and I provided.

No it means what it said, you are just playing dumb now in order to ignore it.

I love this desperate scrabble to pick a preferable metric and then insist that's what is most important. If we believed your logic we'd have to ask why every single building isn't made out of steel. The answer of course is that concrete in compression is often far superior to steel as the 'failed demolition' videos show.

What? You claimed concrete was stronger than steel in compression, I showed you that is not even close to being true and you claim I'm desperate?

Concrete is not stronger in compression. How does the failed demolition video prove that it is? Circular logic unless you can show an equivalent steel framed building actually collapsing under the same circumstances.

Gee lets see how honest you're going to be:

What a shock, you won't even read a paper you demanded. Why are you so afraid of being shown to be wrong?

No why should I wade through a web site trying to find what you're talking about, when you can simply quote the point you want to make? How hard is that? You OSers have a habit of throwing up links without any explanation.
The idea in a debate is you debate, you don't just send people off to read other peoples opinions.

Notice I don't do that? I make my point and back it up with links and quotes. So make your point exponent and we can discuss it. I am here to debate you, and I like to know if the person I am debating knows what they are talking about and are not just blindly using other peoples opinion without understanding it.

Afraid of being wrong? You won't even address the video I presented. You hand wave away the fact you are wrong about concrete compression. That is where you are being intellectually dishonest, you will not accept anything if it contradicts your claims. You have no valid argument against what I have said.

Admit you are wrong about concrete being better in compression than steel. If you can't even get that simple fact right, how can anyone take anything else you claim seriously? You can check for yourself ANYTHING I say. If I am wrong you would be able to show me where I am wrong, but all you do is make excuses.

reply to post by exponent

Except it totally doesn't. Bazant's paper was a best case scenario for the building

Ahhh haaaa I know where i have heard those words before.......PLB.

So whats the game here.....are you good friends with PLB.....Or are you using both accounts.....your compartmentalization is the very similar.

Originally posted by exponent
Bazant's paper is peer reviewed, and is authored by a total of 5-6 researchers and cited by many more. Claiming it's just a single person is silly, especially as I quoted Newtons Bit for truss sagging beforehand.

So what? Jones paper on thermite was peer reviewed also. Newtons Bit for truss sagging?

What alternative are you offering? Before now the only excuse I've seen you use is 'it was the cladding bowing' which has been repeatedly demonstrated to not be geometrically possible.

Alternatives to the collapse mechanism offered by NIST is what I meant, not the cladding. Yes I did say it could have been the cladding bowing inwards and I still think that is a possibility. It doesn't matter, you don't have to know what it was to know what it couldn't have been.

I handwaved nothing, you literally just ignored where I explained the position as clearly as possible. Please go back and read my replies.

But you didn't.

How does sagging take up force? Please give me a detailed answer.

Because the truss would simply sag more. It wouldn't impart that force to the columns.

I already went through this in this very thread. This is true, but concrete exceeds steel in many ways too. In the WTC, weight was a dominant factor.

How? You're not making any sense. Steel is superior to concrete in every way, as you know now as I showed you.

You showed a demonstration of a completely different construction of building and floor, with no similar conditions. Here is a university paper from the UK on truss sagging: www.sciencedirect.com...

Again that link does not show sagging trusses can pull in columns. If it does point it out.

In fact it contradicts the OS...

The results and analysis indicate that composite truss flooring systems may not fail suddenly. Individual member buckling seems to be a much more gradual occurrence linked to material failure and expansion based geometry change rather than sudden “failure”.

Again you fail to understand the connections. If concrete by itself weighted down and sagging, but still rigid, after supports have failed does not pull in columns and collapse, then steel being much stronger and robust, sagging from heat and no columns removed will also not fail. Funny how you want to make that excuse but then you will try to use the verinage collapse method, of concrete buildings, as a valid comparison. Again intellectually dishonest.

It confirms that there are pull-in and push-out forces with a composite steel truss and concrete deck system matching the construction in the towers. It uses FEA as you agreed to and is from a reputable source in a reputable journal.

What does?

Originally posted by ANOK
No it means what it said, you are just playing dumb now in order to ignore it.

You refused to elaborate on a completely meaningless phrase. I don't need to play dumb to make light of that.

What? You claimed concrete was stronger than steel in compression, I showed you that is not even close to being true and you claim I'm desperate?

Concrete is not stronger in compression. How does the failed demolition video prove that it is? Circular logic unless you can show an equivalent steel framed building actually collapsing under the same circumstances.

It's not quite 'circular logic' but at least you're having a go at actually discussing what I post. Are you willing to have a discussion about the design of a steel framed building and whether it would collapse or not?

No why should I wade through a web site trying to find what you're talking about, when you can simply quote the point you want to make? How hard is that? You OSers have a habit of throwing up links without any explanation.
The idea in a debate is you debate, you don't just send people off to read other peoples opinions.

What are you talking about? Firstly, it's not a website, it's a scientific paper. Secondly, I asked you what sort of test you'd accept to prove that sagging trusses can exert pulling forces. You said that an FEA simulation would be acceptable, and so I have pointed you towards a paper with an FEA simulation of WTC representative trusses and their results.

I can tell you what their results are, but unless you actually read the paper then you're never going to believe my opinion.

Afraid of being wrong? You won't even address the video I presented. You hand wave away the fact you are wrong about concrete compression. That is where you are being intellectually dishonest, you will not accept anything if it contradicts your claims. You have no valid argument against what I have said.

What you have said is that people other than you have ignored 'newtons third law'. You haven't been able to explain how they've ignored it, or even how they would correct their equations to account for it. You made a naked assumption and I dismissed it with more evidence than you used to support it. At least I made an attempt to explain why. If you want to have a serious discussion, you must put forward serious points. I gave you an explanation and as with a lot of things, it gets completely ignored.

Admit you are wrong about concrete being better in compression than steel. If you can't even get that simple fact right, how can anyone take anything else you claim seriously? You can check for yourself ANYTHING I say. If I am wrong you would be able to show me where I am wrong, but all you do is make excuses.

What I actually said was concrete will almost always do very much better in compression, you then posted this amazingly authoritative source: encyclopedia2.thefreedictionary.com...

If you'd given me half a chance to explain without veering off into trying to prove you know better, concrete will better in compression because of the design of the building and the steel reinforcement used. High strength concretes do in fact compete well against steel because of their lower density. However the majority of concrete buildings are those with large continuously poured walls, forming their own structural framing. On the other hand steel buildings tend to be built of superframes or skeletons.

This is why concrete buildings like some of the examples of failed demolitions do so very well. They're essentially a giant connected frame, often with steel reinforcements to add tensile strength to the concrete. They don't have individual elements to break and deform, and concrete spalling doesn't result in the sort of large deformations a steel column buckling can.

Of course, I'm sure you don't want to hear this, and want to keep quoting the free dictionary for all your facts, without even considering what I was talking about. Enjoy.

Originally posted by plube
Ahhh haaaa I know where i have heard those words before.......PLB.

So whats the game here.....are you good friends with PLB.....Or are you using both accounts.....your compartmentalization is the very similar.

edit on 013030p://f46Saturday by plube because: (no reason given)

It's a pretty common phrase, and it accurately represents Bazant's model. I don't know PLB outside of the forums as far as I know, and if you want to ask the mods I'm sure they'll tell you that we don't share accounts.

Rest of the replies are to ANOK

Originally posted by ANOK
So what? Jones paper on thermite was peer reviewed also.

It's fairly doubtful it was. The editor resigned after its publication. Even if it were the case, it's hardly proof of this paper being incorrect. This paper was published in a much higher volume and prestigious journal and doesn't seem to have attracted serious criticism.

You're claiming that it violates a fundamental law of physics but somehow the Journal of Engineering Mechanics or whichever other journal you like missed this? That's just unbelievable.

Newtons Bit is a poster occasionally here and on JREF. He helped me understand some things I was not sure about. He posted a blog with a fairly good description of truss sagging, but it got read and ignored by you if I remember correctly.

Alternatives to the collapse mechanism offered by NIST is what I meant, not the cladding. Yes I did say it could have been the cladding bowing inwards and I still think that is a possibility.

I don't want to get diverted but really? It's been years and you still think somehow cladding can bow 50" inwards despite the fact it was a couple of inches away from the steel and surrounding it on 3 sides? How?!

I handwaved nothing, you literally just ignored where I explained the position as clearly as possible. Please go back and read my replies.

But you didn't.

But I did:

Originally posted by exponent
Certainly. Using the model me + psikey are using means there are suspended floating masses representing the floors. We drop one group on another from say the 90th floor. When the two meet, they will destroy each other and the supports holding the floor up. This turns them into rubble (essentially using up Kinetic Energy) and expels some of the debris.

At this point we have a lower block 'A' made of 88 intact floors. We have a rubble block 'B' made of 2 'rubbleised' floors. We have an intact upper block 'C'. From this point, the behaviour depends on how much KE was lost in the initial collision. Either the upper block will hit the rubble block first, or the lower block will hit the rubble block.

If the upper block impacts the rubble block, it is doing so while the rubble block moves away from it. If the rubble block impacts the lower block, then it is doing so at rest. The resulting velocities result in a difference in the impact force.

As a natural consequence, the upper block will experience significantly lower impact forces as soon as a rubble block has formed.

Because the truss would simply sag more. It wouldn't impart that force to the columns.

Sagging is caused by tension is it not? How is that tension force balanced if not by an equal and opposite force from the column? Were does this tensile force go if not into the columns?

How? You're not making any sense. Steel is superior to concrete in every way, as you know now as I showed you.

The Burj Khalifa uses primarily concrete. You better get on to them as you apparently know better than their structural engineers! The WTC engineers even finished their floors in concrete, it's almost like it had superior properties!

If concrete by itself weighted down and sagging, but still rigid, after supports have failed does not pull in columns and collapse, then steel being much stronger and robust, sagging from heat and no columns removed will also not fail.

Wait you genuinely think that because you have one example of something not happening, that means in a different material, configuration and in a fire it won't behave differently? I don't know what to tell you, but you're wrong in every important respect.

What does?

The paper I linked you to.

Originally posted by exponent
Right, I agree. You've neglected the fact though that you have maximised the momentum transfer. This isn't what you do to get a minimum bound. If we want to talk about the absolute minimum time for rubble to start hitting the ground inside the tower then we have to minimise the momentum transfer. That means destroying floors only. Do you want to work together on the values for this? I'd be more than happy to do the work and present it if you agreed on initial conditions.

Since I think it is obvious that breaking supports would have much more effect than momentum I am content to leave the momentum transfer as it is. But isn't a less than maximum momentum transfer going to be even slower and therefore take more time? Does what you are suggesting make sense?

We've already been over this. You don't have any data that says 26 seconds,

The collapse time for the Spire is universally regarded as 25 seconds from the start as far as I have seen.

The first fragments of the outer walls of the collapsed North Tower struck the ground 11 seconds after the collapse started, and parts of the South Tower after 9 seconds. The lower portions of both buildings' cores (60 stories of WTC 1 and 40 stories of WTC 2) remained standing for up to 25 seconds after the start of the initial collapse before they too collapsed.

en.wikipedia.org...

Suppose we had the north tower intact and then removed 5 stories, 91 through 95. That would leave a 60 foot gap with 15 stories in the air without support. They would fall. They would take 1.9 seconds to hit the top of the lower 90 stories and be traveling at 42 mph or 62 ft/sec.

Those 90 stories would be about 1080 feet tall. If the falling 15 stories could maintain a constant velocity while crushing six times as many stories as themselves even though they had to be stronger and heavier then the falling 15 stories then it would take 17.4 seconds to destroy 90 stories. This would yield a total of 19.3 seconds to destroy the north tower.

But we know the top 15 stories did not have 60 feet of free space to fall through. So even the 25 seconds is ridiculous.

So we end up with endless pseudo-scientifc crap with complex math that ignores things like Newton's Third Law to supposedly explain what couldn't happen and people condescendingly insult anyone who can't do the math or does not have elegant code. But they can't, or at least haven't, built a physical model that can actually collapse completely.

psik

reply to post by exponent


Address the fact that your link did not show sagging trusses can pull in columns, or quote where it does.

How do sagging trusses pull in columns? You haven't answered that question yet. All you can do is keep repeating that trusses can sag, we know that already, you are avoiding the actual point of this.

I have shown you an actual real life demonstration that shows that a much weaker structure, with added weigth and load beating columns removed, did not demonstrate the claim NIST makes.

If it could not happen in that scenario, it is not going to happen to a much stronger steel structure, that did not have missing load bearing columns, and did not have weight added to it, and it was sagging because it had expanded from heat, and thus was not rigid anymore, as it would need to be put any force on the columns.

Otherwise IF there was any more force on the trusses it would be absorbed by sagging more.

The whole NIST hypothesis is based on IF's.

You are simply ignoring this explanation and pretending I am not talking about the collapses. This is the main hypothesis for the whole collapse initiation according to NIST. I am trying to get to the crux of the issue, instead of arguing irrelevant points that make no difference in the grand scheme of things.

Originally posted by psikeyhackr
Since I think it is obvious that breaking supports would have much more effect than momentum I am content to leave the momentum transfer as it is. But isn't a less than maximum momentum transfer going to be even slower and therefore take more time? Does what you are suggesting make sense?

It does make sense. If you leave the upper block intact, and make it affect only the floors, they have very little in the way of resistive force and less in the way of mass. It makes the collapse quicker.

Of course, in reality the upper block did crack and disintegrate somewhat, for example we know that only a few tenths of seconds into WTC2s collapse one of the outer walls of WTC2s upper block failed, this would have severely compromised it. However, the method of compromise is to 'rubbleise' the interior floor sections. This then rains down directly on floor sections below.

Any way you put it, the real collapse was much more dangerous to the building than our ideal models.

The collapse time for the Spire is universally regarded as 25 seconds from the start as far as I have seen.

If we're approximating 'collapse complete' times then I'm cool with that, I think probably closer to 20 seconds as the spire was not really a major contributor once the floors had passed it. I thought you were saying "A real collapse should have taken more than this long because i say so", but you are not.

The first fragments of the outer walls of the collapsed North Tower struck the ground 11 seconds after the collapse started, and parts of the South Tower after 9 seconds. The lower portions of both buildings' cores (60 stories of WTC 1 and 40 stories of WTC 2) remained standing for up to 25 seconds after the start of the initial collapse before they too collapsed.

en.wikipedia.org...

Those 90 stories would be about 1080 feet tall. If the falling 15 stories could maintain a constant velocity while crushing six times as many stories as themselves even though they had to be stronger and heavier then the falling 15 stories then it would take 17.4 seconds to destroy 90 stories. This would yield a total of 19.3 seconds to destroy the north tower.

But we know the top 15 stories did not have 60 feet of free space to fall through. So even the 25 seconds is ridiculous.

You mistook 'constant velocity' with 'constant acceleration'. With a constant resistive force the acceleration remains constant, not the velocity.

So we end up with endless pseudo-scientifc crap with complex math that ignores things like Newton's Third Law to supposedly explain what couldn't happen and people condescendingly insult anyone who can't do the math or does not have elegant code. But they can't, or at least haven't, built a physical model that can actually collapse completely.

Show me a single bit of maths by anyone anywhere ever on this subject that ignores 'Newtons Third Law', and then show me how you'd make it obey the third law. Please.

Originally posted by ANOK
Address the fact that your link did not show sagging trusses can pull in columns, or quote where it does.

How do sagging trusses pull in columns? You haven't answered that question yet. All you can do is keep repeating that trusses can sag, we know that already, you are avoiding the actual point of this.

ANOK I don't know how to say this any simpler, but I'll have a go!

I linked you to this: www.sciencedirect.com...

This is a website of an article publishing company, it links you directly to the information page for a scientific paper published in the Journal of Constructional Steel Research. From this page you can then purchase or download the paper depending on if your university/company has any mass subscription.

This paper presents and then simulates a structure similar to the WTC, and explores the development of forces pushing/pulling on columns and their association with truss element failure / truss sagging.

It concludes that indeed trusses can and do exert significant forces against their restrining members.

I have shown you an actual real life demonstration that shows that a much weaker structure, with added weigth and load beating columns removed, did not demonstrate the claim NIST makes.

What you've shown is that when a column was removed, we didn't have any immediate evidence of bowing. You've carefully ignored the fact that the whole thing was a tiny construction with a braced frame, wheras we're talking about two or three storeys of 65ft long trusses, not reinforced concrete beams.

You are simply ignoring this explanation and pretending I am not talking about the collapses. This is the main hypothesis for the whole collapse initiation according to NIST. I am trying to get to the crux of the issue, instead of arguing irrelevant points that make no difference in the grand scheme of things.

You've spent something like a day and a half and 10-15 posts ignoring the article I linked you to. It would be a simple matter to download it and read it, it's a massive 13 pages long! (oh no!)

Seriously ANOK, you can't complain that i've linked you to a paper that explains exactly what you want, using a method you agreed upon, because you can't be bothered to read 13 pages. Surely?

reply to post by exponent


i just read the abstract from the site you provided a link from....

The results and analysis indicate that composite truss flooring systems may not fail suddenly. Individual member buckling seems to be a much more gradual occurrence linked to material failure and expansion based geometry change rather than sudden “failure”.

I am not sure...i will play dumb here for a second...but could you please tell me what this means and how it might affect what is contained in Bazants paper....in your own words please....

I want to know if your are parroting or if your actually understanding what is being presented...because i Never see you actually putting forth your own work.

Also you said ASK the mods about your connections to PLB....what could they tell me...I mean really...you could use a machine at one place and sign on another time from another machine .....there fore differing IP's.

Also i mean come on....this is a conspiracy site.....get a grip...i would of course be suspicious.....but i will say something that does not change....is verbiage and writing styles.....i am noticing some similarities in word usage and styling.....makes me curious as to why.

Could all be coincidence couldn't it.

now there is a key word in there......Composite......

i will ask you this also....was the floor and truss system in the towers a composite....Or were the trusses a separate entity ..... think hard about this...because it affects the apparent behavior of the trusses completely....and also any results of the NIST testing.....should the trusses alone be subjected to a fire test....or would the whole floor truss system together have to be tested to achieve viable results.

Originally posted by plube
I am not sure...i will play dumb here for a second...but could you please tell me what this means and how it might affect what is contained in Bazants paper....in your own words please....

I want to know if your are parroting or if your actually understanding what is being presented...because i Never see you actually putting forth your own work.

I could take this with great offence and rabbit on about how you have no right to blah blah. Honestly though I don't mind, I genuinely think that you're deluding yourself on this topic and so it's only good manners to give some concessions.

I should also mention that I have actually read the paper and so I'm cheating a little bit because I already know what they wrote about it, but here goes.

The abstract you quoted talks about the nature of fire-induced failure of floor trusses. They work by composite action of tension and compression in order to carry a greater load with reduced weight. What is shown in the paper is that as they are heated, a series of smaller gradual failures occurs (concrete cracking, web buckling, the transfer of stress between the top chord and the concrete deck etc). This is in contrast to the idea that internal stresses would build up and suddenly exceed an ultimate load here or there. The result of the paper is the conclusion that in a fire, a truss structure will slowly deform and transfer load between elements, until entering a final tension phase where all structural capacity is exhausted.

I hope that's a decent enough summary, and I can rewrite it any number of ways or explain my understanding of any bit of it, if you want to check that it's my own work

Also you said ASK the mods about your connections to PLB....what could they tell me...I mean really...you could use a machine at one place and sign on another time from another machine .....there fore differing IP's.

I have no idea about PLB, but I've probably accessed this forum through a total of about 3 IPs in my entire time. I appreciate that there's no real way to prove it, but I imagine if you were to graph our word use and post characteristics, our timing etc there'd be many differences. I don't work regular hours or have consistent times that I am around, which is pretty uncommon.

Could all be coincidence couldn't it.

Yup

now there is a key word in there......Composite......

i will ask you this also....was the floor and truss system in the towers a composite....Or were the trusses a separate entity ..... think hard about this...because it affects the apparent behavior of the trusses completely....and also any results of the NIST testing.....should the trusses alone be subjected to a fire test....or would the whole floor truss system together have to be tested to achieve viable results.

The trusses were 'composite elements' in that they have internal composite action, but their connection to the towers was very limited. They basically sat on a series of seats on the internal and external columns, the connection was fairly trivial:


The dampers were elastic, there were also some restraining straps but they were of no significant structural strength. As you can see, there was surprisingly little moment capacity on these individual elements. This is because moment action in the towers was achieved by a complex combination of the truss framing over multiple floors, the spandrel connections on exterior walls, a hat truss and some additional minor reinforcements in strategic places.

It's a complex subject, but if people are asking intelligent questions I don't mind writing out big replies, let me know if there's anything I've missed or that you want more detail on.

Cheers!

reply to post by exponent


Thank you for the excellent reply and it was well worded....and quite eloquent and i do appreciate it....the next question...would the composite components need to be tested as a whole?..to test any deflection or expansion due to the fires or would it be ok to just test the individual components and say this is how the entire composite piece is going to respond under the conditions they were exposed to on the day?

also the truss seats were fine for the design and they were fine for the loads they were required to carry loads pre collapse we will get to the loads later....try not to inject opinion as i can see the seats are of a common design and have perfectly held up in designs of steel structures throughout the world to this very day....so can you please not try to make out how weak they may appear to you.

for 40 years they did exactly the job they were designed to do without fail....during a 1993 truck bomb...and a fire in 1975. which pushed them then to their limits i am sure.

try to do this without putting in personal opinion.....also truss seat designs since 911 have not had a required design change in construction....at least not in this country.

I am sure you can see where this is leading to....

Also i am trying to get somewhere on this...and trying a different approach to see if anything can be learned.

I get tired of the repetitive rabble....

now you asked psik to try to come to some sort of consensus...because if there isn't any consensus on design and terminology then we are all just pissing in the wind.....

So are you in agreement the truss seats carried the loads they were designed to carry for the last forty years or not?

Note: also don't make it out to be more complex than it really is....it is a structure with design parameters....for some reason these parameters failed...the thing is trying to come up with why these parameters failed....nothing more nothing less.

Originally posted by plube
Thank you for the excellent reply and it was well worded....and quite eloquent and i do appreciate it

Thank you, compliments are rare here and so I take them to heart. I'm really happy with this sort of discussion, where we approach our differences by looking at where we agree. I hope it continues.

the next question...would the composite components need to be tested as a whole?..to test any deflection or expansion due to the fires or would it be ok to just test the individual components and say this is how the entire composite piece is going to respond under the conditions they were exposed to on the day?

That is a very tricky question! I guess my answer is: it depends on how you plan to test it. If you wanted to reproduce the actual structural conditions of the day then I'd say you'd need to carry out a full scale test. I haven't done the calculations in my head but in order to scale it down you'd have to take appropriate considerations. For example, the final geometry will be different unless you account for massively increased load, and then you have restraining conditions to think about.

So my answer to this question is: If you are going to use FEA, then you need only conduct tests on steel assemblies, so reduced scale can be ok. If you're aiming to reproduce realistic conditions, then you would need to conduct a full scale test.

also the truss seats were fine for the design and they were fine for the loads they were required to carry loads pre collapse we will get to the loads later....try not to inject opinion as i can see the seats are of a common design and have perfectly held up in designs of steel structures throughout the world to this very day....so can you please not try to make out how weak they may appear to you.

You're soliciting my opinion as well as facts, but I'll try and make it clear if needed. With regard to other common flooring solutions though, the WTC trusses were weaker. However:

for 40 years they did exactly the job they were designed to do without fail....during a 1993 truck bomb...and a fire in 1975. which pushed them then to their limits i am sure.
...
So are you in agreement the truss seats carried the loads they were designed to carry for the last forty years or not?

The 1993 attack didn't affect the trusses, and the 1975 fire was minimal and did no real damage. Despite this, I am in agreement with you. The truss design was definitely sufficient to carry the dead + live load and more, and was only modified when extra heavy items (safes, UPS batteries etc) were placed.

Note: also don't make it out to be more complex than it really is....it is a structure with design parameters....for some reason these parameters failed...the thing is trying to come up with why these parameters failed....nothing more nothing less.

I don't think I have made it any more complex than the design made it. If you want me to simplify bits or call me out on them, please do. Honestly I don't take any offence to being told I'm wrong, just told that i'm wrong without a reason

Originally posted by exponent

Originally posted by psikeyhackr
Since I think it is obvious that breaking supports would have much more effect than momentum I am content to leave the momentum transfer as it is. But isn't a less than maximum momentum transfer going to be even slower and therefore take more time? Does what you are suggesting make sense?

It does make sense. If you leave the upper block intact, and make it affect only the floors, they have very little in the way of resistive force and less in the way of mass. It makes the collapse quicker.

That is a contradiction!!!

An intact upper block is going to include THE CORE.

So the falling core would impact the stationary core which would involve the HORIZONTAL BEAMS in the Core.

The concrete slabs of the floors outside the core were SIX HUNDRED TONS. We don't hear that much but it is easy to calculate. Of course we never hear and I don't know how to calculate the weight of the pans and trusses. So the approximately 200 connections holding that weight and the live load on the floors were not exactly WEAK. So breaking those connections would take energy and...

SLOW THE COLLAPSE DOWN to more than TWELVE SECONDS.

GET REAL!

My magical collapse is an artificial creation for thought experiment purposes. You want to make something even more artificial for what purpose?

So regardless of what happened we should have all been demanding accurate data on the buildings years ago to eliminate this stupid speculation to rationalize preferred beliefs. Skyscrapers must hold themselves up and withstand the wind. There are 200 of them around the world over 800 feet tall. The physics cannot be that complicated and mysterious. But I can't find the distributions of steel and concrete on any of them. So it looks like there is a conspiracy of silence in the skyscraper industry.

psik

Originally posted by exponent

Originally posted by psikeyhackr
Since I think it is obvious that breaking supports would have much more effect than momentum I am content to leave the momentum transfer as it is. But isn't a less than maximum momentum transfer going to be even slower and therefore take more time? Does what you are suggesting make sense?

It does make sense. If you leave the upper block intact, and make it affect only the floors, they have very little in the way of resistive force and less in the way of mass. It makes the collapse quicker.

Of course, in reality the upper block did crack and disintegrate somewhat, for example we know that only a few tenths of seconds into WTC2s collapse one of the outer walls of WTC2s upper block failed, this would have severely compromised it. However, the method of compromise is to 'rubbleise' the interior floor sections. This then rains down directly on floor sections below.

Any way you put it, the real collapse was much more dangerous to the building than our ideal models.

The collapse time for the Spire is universally regarded as 25 seconds from the start as far as I have seen.

If we're approximating 'collapse complete' times then I'm cool with that, I think probably closer to 20 seconds as the spire was not really a major contributor once the floors had passed it. I thought you were saying "A real collapse should have taken more than this long because i say so", but you are not.

The first fragments of the outer walls of the collapsed North Tower struck the ground 11 seconds after the collapse started, and parts of the South Tower after 9 seconds. The lower portions of both buildings' cores (60 stories of WTC 1 and 40 stories of WTC 2) remained standing for up to 25 seconds after the start of the initial collapse before they too collapsed.

en.wikipedia.org...

Those 90 stories would be about 1080 feet tall. If the falling 15 stories could maintain a constant velocity while crushing six times as many stories as themselves even though they had to be stronger and heavier then the falling 15 stories then it would take 17.4 seconds to destroy 90 stories. This would yield a total of 19.3 seconds to destroy the north tower.

But we know the top 15 stories did not have 60 feet of free space to fall through. So even the 25 seconds is ridiculous.

You mistook 'constant velocity' with 'constant acceleration'. With a constant resistive force the acceleration remains constant, not the velocity.

So we end up with endless pseudo-scientifc crap with complex math that ignores things like Newton's Third Law to supposedly explain what couldn't happen and people condescendingly insult anyone who can't do the math or does not have elegant code. But they can't, or at least haven't, built a physical model that can actually collapse completely.

Show me a single bit of maths by anyone anywhere ever on this subject that ignores 'Newtons Third Law', and then show me how you'd make it obey the third law. Please.

I don't discuss the collapse of the south tower because no one explains the 22 degree tilt and where the center of mass of those 29 stories was. The north tower is simpler.

You have already been shown videos demonstrating that the top of the north tower mostly collapsed on itself before the lower portion even began being destroyed but you want to talk as though math is more important than reality. Some science. This is just endless BS.

psik

Originally posted by psikeyhackr
An intact upper block is going to include THE CORE.

So the falling core would impact the stationary core which would involve the HORIZONTAL BEAMS in the Core.

Certainly. This is likely the reason why the core spire that remained was 'stripped' of its outer elements. Only the very strongest and best connected sections of the core could possibly survive. The fact that the exterior rows were stripped off gives us a good indication that the collapse overloaded all but the strongest sections of the core.

I don't know why you think it is a contradiction.

The concrete slabs of the floors outside the core were SIX HUNDRED TONS. We don't hear that much but it is easy to calculate. Of course we never hear and I don't know how to calculate the weight of the pans and trusses. So the approximately 200 connections holding that weight and the live load on the floors were not exactly WEAK.

The average weight varies, but around a thousand tons. It is on average about half the weight of a particular floor. The problem is though that in no way is it comparable to the strength of upright core sections. I agree with posters who emphasise the size of core structures in that they were not slight or weak, but in every way individual truss sections and their connections were comparatively much weaker. This is the issue if we are discussing the actual collapse. How would you model the strength of the floors and their connections?

So breaking those connections would take energy and...

SLOW THE COLLAPSE DOWN to more than TWELVE SECONDS.

GET REAL!

How much more? Do you have any way to calculate it? Bazant included both large amounts of energy going into concrete communition and huge amounts in bending columns and even then the overload is far too significant. What evidence do you have that his numbers are wrong? You also seem to be implicitly accepting that what I said about momentum transfer is correct, but I expect you will deny it.

My magical collapse is an artificial creation for thought experiment purposes. You want to make something even more artificial for what purpose?

The purpose is simplified modelling. Your model didn't set a limiting case, and so we can either choose to discuss a limiting case (Bazant for tower survival, our model for minimum collapse time) or we can discuss reality, where we don't have anywhere like the detail required to model the effects.

So regardless of what happened we should have all been demanding accurate data on the buildings years ago to eliminate this stupid speculation to rationalize preferred beliefs. Skyscrapers must hold themselves up and withstand the wind. There are 200 of them around the world over 800 feet tall. The physics cannot be that complicated and mysterious. But I can't find the distributions of steel and concrete on any of them. So it looks like there is a conspiracy of silence in the skyscraper industry.

The physics are not that complicated and mysterious, that's why you don't hear any huge uproar. The answers NIST gave have been explicitly accepted by CTBUH for example, and a public statement to that effect exists. You'll have to realise at some point that people at least as smart as you have looked into this and been satisfied with the results.

You have already been shown videos demonstrating that the top of the north tower mostly collapsed on itself before the lower portion even began being destroyed but you want to talk as though math is more important than reality. Some science. This is just endless BS.

Even if I accept that the entirety of the upper section disintegrated into small rubble chunks, how would that change the result?. Other than mass which escaped outside the footprint (of which there was a fairly low amount) then the rest of the mass is being accelerated under gravity and essentially poured onto the floors below.

How do you expect this to fare any better at all? It's akin to saying that ten tons of boulders would kill someone, but that ten tons of bricks wouldn't because they're in smaller pieces. The ability to destroy the lower tower doesn't come from the structural strength of the upper block. It comes purely from the insane amount of potential energy that gets very rapidly converted into momentum whether it's as rubble or as intact floors.

It's not BS, and to be fair this is hardly science, we're discussing things. None of us are invoking our own authority, just simple facts and logic. At least you answered my question though so I thank you for actually doing that. My next question is in bold above, please explicitly answer that for me.

Originally posted by exponent
The average weight varies, but around a thousand tons. It is on average about half the weight of a particular floor. The problem is though that in no way is it comparable to the strength of upright core sections. I agree with posters who emphasise the size of core structures in that they were not slight or weak, but in every way individual truss sections and their connections were comparatively much weaker. This is the issue if we are discussing the actual collapse. How would you model the strength of the floors and their connections?

The average weight of what varies?

I hardly talk about the FLOORS I refer to entire LEVELS.

By that I mean a 12 foot height including one floor assembly and 12 feet high of core plus the horizontal beams and the perimeter columns and spandrels. That is the mass I refer to as a LEVEL. But until someone does a test on one of those floor connection and provides some DATA on what it takes to break one loose I am not modeling anything about it. That is what I like about my Conservation of Momentum collapse.

IT IS SIMPLE AND EASY TO UNDERSTAND WITH A MINIMUM OF ASSUMPTIONS even though we all agree it is impossible. But it does give a minimum collapse time which is more than some estimates for the real building. Breaking connections could only INCREASE THAT TIME. no modeling required.

psik