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Originally posted by Akareyon
If twice the office space and half the cost means the whole thing comes down and flattens everything in it instead of one or two floors getting crushed, thousands of lives are saved and objects of value can be retrieved, an economic evaluation would most surely come get my skyscraper, not yours. No offense intended :-)
Oh, FEMA, NIST and those "debunkers" went to great lengths (examples abound in this thread, as in the parallel discussion between ANOK and GenRadek) to prove the opposite.
A simple office fire could have made the trusses of the floor slabs sag, pulling the outer columns inward (analogous to a built-in, heat-driven "screw clamp", so to speak).
At least that's what they say, not that you or I would buy that explanation for the initiation of the collapse sequence ;-)
Increasing F_c without increasing m proportionally is not all that hard, by the way. wmd_2008 raises a valuable point. If you look at a long steel column suspended horizontally by a crane, you can see how it bends visibly under its own weight - as if it were made of clay or paper. So what you want to do -- and has been done for centuries -- is to increase F_c not by making the columns stronger and much heavier, but by simply keeping them short. The shorter, the better. Because the strength of a column is inversely proportional to its length: the smaller u is, the greater F_c gets.
But you can't raise a high building then, you say, and just stacking a lot of short columns on top of each other doesn't really solve the problem?
You're completely right, and that's why you put horizontal beams in between them. The house I grew up in for example was made like that, just with oak beams, not steel beams (and, btw, it didn't have diagonal bracings in each rectangle between beams and columns either, just here and there). The horziontal beams make buckling for the columns harder, thus raise F_c -- at relatively little cost in m. The result is a steel grid called framework. Keeping F_c greater than m*g without much compromise in cost and office space is no problem anymore.
It's also somewhat easier to design then, because F_0 is hardly ever taken into consideration in engineering. The formula to calculate the critical force or maximum load (where F(u_c)=m*g, the point you never want to reach because a small nudge would be enough to bring it down) is
...
Check units: N=1 * N/mm² * m^4/ (1 * m)², that*s N*(1000*mm)²/m², that's N... yup, correct (Notice how Young's modulus is four-dimensional, therefor time and velocity come into the equation and a glimpse of the fabric of the universe is allowed? I love it!).
Of course not :-)
Except its not what "they" are saying.
I'm pretty sure the design I sketched here had it already implemented.
It wouldn't be possible with the design you proposed earlier.
No offense taken :-) I have clearly shown I know nothing about the subject at hand and that my dissent with the official explanations for the catastrophic failure of the twins is solely based on irrational paranoia and maybe my brain got a little hot under the tin foil hat, too...
No offence
Originally posted by Akareyon
Of course not :-)
This is of course assuming that any of the active fire suppression systems would either fail or be unable to control the development of the fire.
I'm pretty sure the design I sketched here had it already implemented.
No offense taken :-) I have clearly shown I know nothing about the subject at hand and that my dissent with the official explanations for the catastrophic failure of the twins is solely based on irrational paranoia and maybe my brain got a little hot under the tin foil hat, too...
Thank you anyways for the good time, it was a very nice discussion even if we had to agree to disagree on a few little details.
I still wonder what Feynman would have said, though :-)
My point is that I sense a sort of double-think, or I shall call it a "blind spot"; there is something you couldn't see even if you wanted to and if it were jumping up and down in front of you frantically waving a giant red flag.
Originally posted by -PLB-
So I don't really get your point.
And this one is really great. It's not about my opinion, I agree it holds little weight, no weight at all even -- and if I gave you my credentials, you'd question them because I'm not the most widely cited scientiest in the whole universe that Bazant is -- so I pretend I'm just a paranoid pauper and the last voice of reason in this debate: οἶδα οὐκ εἰδώς
you are no expert, so your opinion holds little weight.
Gloria Pall worked for the United Service Organization's headquarters on the 56th floor.
"I was at the file cabinet and all of a sudden the building felt like it was just going to topple over," Pall said. "It threw me across the room, and I landed against the wall. People were screaming and looking at each other. We didn't know what to do. We didn't know if it was a bomb or what happened. It was terrifying."
One engine was catapulted through the Empire State Building, emerging on the opposite side and crashing through the roof of a neighboring building. The second engine and part of the bomber’s landing gear fell through an elevator shaft
There was ONE reason for the global progressive collapse: an effective FoS < 1.
Originally posted by wmd_2008
There wasn't ONE reason for these buildings falling there was a lot of reasons.
Originally posted by Akareyon
My point is that I sense a sort of double-think, or I shall call it a "blind spot"; there is something you couldn't see even if you wanted to and if it were jumping up and down in front of you frantically waving a giant red flag.
Paranoid says "this never happened before" and "impossible!" and "laws of physics", Believer responds "well, Ronan Point" and "Vérinage!" and "cube-square law" and "there were planes" and "huge fire" and "huuuuge forces acting, you know, 58,000 tons falling through one floor" and "look, Bazant!". So Paranoid goes on to show that the proof for inevitability of global collapse relies on a mechanism that once triggered cannot be stopped, that such a mechanism doesn't happen to be there by accident and that triggering that mechanism is not all that hard -- even in a best case scenario. So Believer says "but fireproofing and sprinkler systems failed, and best case scenario never happened anyway" and even has the presumption to claim that that mechanism was a good thing -- because it prevented the even greater damage that a toppling of the towers would have caused (well, WTC 7 has a different story to tell) -- and that the conditions that triggered the collapse never happen anyway, because sprinkler systems always work, fireproofing never falls off and planes never fly into buildings and tube-in-tube architecture and steel framing was unique to the towers anyway.
And this one is really great. It's not about my opinion, I agree it holds little weight, no weight at all even -- and if I gave you my credentials, you'd question them because I'm not the most widely cited scientiest in the whole universe that Bazant is -- so I pretend I'm just a paranoid pauper and the last voice of reason in this debate: οἶδα οὐκ εἰδώς
It's about noone's opinion at all, it's about science, universal truths, the laws of nature and logical reasoning. And this isn't even rocket science or quantum physics, it's quite simple to understand and verify, it's the sort of stuff you learn at school -- force and counterforce, actio/reactio, conservation of energy -- and still you rely on an "expert" to do your thinking, to make up your mind and to tell you which opinion to have until the next best expert comes around, as if the cosmos somehow rearranged itself every few years according to the authority of the latest and loudest cognoscente.
Oh, blissful ignorance!
I know of some examples where several floors failed intentionally with the result of collapse arrest, here is one and another one, but I bet that doesn't count for some reason, so here is one more and the fourth one was unintended.
Originally posted by -PLB-
You still haven't come with a single example where a floor failed unintended with the result of collapse arrest. Its a scenario that as far as I know never happened.
What you do here is similar to saying "drug prescription is too complicated for laymen to understand, better believe the expert who proved that contact with water inevitably leads to instantaneous death" after somebody was found in the lake with cement shoes on his feet, so I rather use my own brain :-)
What you do here is similar to saying "every one can cut someone open or prescibe drugs, its quite easy". Still, I rather let surgeons and doctors do it.
Originally posted by -PLB-
Originally posted by Akareyon
My point is that I sense a sort of double-think, or I shall call it a "blind spot"; there is something you couldn't see even if you wanted to and if it were jumping up and down in front of you frantically waving a giant red flag.
Paranoid says "this never happened before" and "impossible!" and "laws of physics", Believer responds "well, Ronan Point" and "Vérinage!" and "cube-square law" and "there were planes" and "huge fire" and "huuuuge forces acting, you know, 58,000 tons falling through one floor" and "look, Bazant!". So Paranoid goes on to show that the proof for inevitability of global collapse relies on a mechanism that once triggered cannot be stopped, that such a mechanism doesn't happen to be there by accident and that triggering that mechanism is not all that hard -- even in a best case scenario. So Believer says "but fireproofing and sprinkler systems failed, and best case scenario never happened anyway" and even has the presumption to claim that that mechanism was a good thing -- because it prevented the even greater damage that a toppling of the towers would have caused (well, WTC 7 has a different story to tell) -- and that the conditions that triggered the collapse never happen anyway, because sprinkler systems always work, fireproofing never falls off and planes never fly into buildings and tube-in-tube architecture and steel framing was unique to the towers anyway.
Still don't get your point. There is no logical inconsistancy in my argument. You still haven't come with a single example where a floor failed unintended with the result of collapse arrest. Its a scenario that as far as I know never happened. I know of only one case where a floor failed which resulted in global collapse. Still you seem to argue its extremely important to design a building so that collapse arrests. My response to that is, ok, whatever, I disagree.
And this one is really great. It's not about my opinion, I agree it holds little weight, no weight at all even -- and if I gave you my credentials, you'd question them because I'm not the most widely cited scientiest in the whole universe that Bazant is -- so I pretend I'm just a paranoid pauper and the last voice of reason in this debate: οἶδα οὐκ εἰδώς
It's about noone's opinion at all, it's about science, universal truths, the laws of nature and logical reasoning. And this isn't even rocket science or quantum physics, it's quite simple to understand and verify, it's the sort of stuff you learn at school -- force and counterforce, actio/reactio, conservation of energy -- and still you rely on an "expert" to do your thinking, to make up your mind and to tell you which opinion to have until the next best expert comes around, as if the cosmos somehow rearranged itself every few years according to the authority of the latest and loudest cognoscente.
Oh, blissful ignorance!
If you think that creating building design codes to ensure safety is "quite simple", then I see a very bright future for your career. But my prediction is that you will never get further than making pretty much baseless claims on internet forums.
What you do here is similar to saying "every one can cut someone open or prescibe drugs, its quite easy". Still, I rather let surgeons and doctors do it.
Originally posted by Akareyon
I know of some examples where several floors failed intentionally with the result of collapse arrest, here is one and another one, but I bet that doesn't count for some reason, so here is one more and the fourth one was unintended.
What you do here is similar to saying "drug prescription is too complicated for laymen to understand, better believe the expert who proved that contact with water inevitably leads to instantaneous death" after somebody was found in the lake with cement shoes on his feet, so I rather use my own brain :-)
And still they don't collapse globally.
Originally posted by -PLB-
Of course they don't count because those examples are intentional.
And they didn't. That shows how hard it is to bring a building down. If, and only if its effective FoS = F_c/m*g > 1.
And by the way, for those structures it was expected they would collapse globally.
Half of it. That's what I said a badly built or severed building usually does - instead of falling into and out of itself.
And one of those buildings falls over.
Nah, those buildings were empty ;-)
Everyone is still dead.
Good, nor do I!
And with the forth I see nothing about full floor failure.
If you could get the most widely cited doctor to write a paper, it would surely become an accepted truth in a society that has externalized its thinking. Everybody would still be drinking water and taking showers, but not without mixing some vodka into the water so it isn't water anymore. There would even be a government agency making sure you never ever go the beach without pouring a bottle of vodka into the ocean first.
There is no medical expert in the world who would claim that.
What I think doesn't matter, Another_Nut. I don't hold a position because I don't want to end up having it ridiculed and fall into the trap of defending "my" theory instead of getting closer to the truth. I said a little earlier that I don't really have an opinion myself, I'm just dispersing weak and wrong arguments based on the findings of Archimedes, Galileo and Newton and hoping to get closer to the truth in a process of elimination of unlikelinesses. Video footage is all I have as evidence that the towers ever existed in the first place, I've never been to New York so it could be a huge Hollywood production to me, in a sense. But I've been on the Eiffel Tower so I guess not all famous Skylines ever are photoshop jobs.
I think 9/11 was a message from someone other than the u.s. Government to someone other than the u.s. People.
is that your thinking?
and I guess the biggest question is
do you think the towers fell do to a cd or natural collapse?
Originally posted by Akareyon
Buildings don't collapse progressively and globally and disproportionally if you don't want them to - and even then it's hard to make them so. Because they get erected so they don't. Normally.
If you could get the most widely cited doctor to write a paper, it would surely become an accepted truth in a society that has externalized its thinking. Everybody would still be drinking water and taking showers, but not without mixing some vodka into the water so it isn't water anymore. There would even be a government agency making sure you never ever go the beach without pouring a bottle of vodka into the ocean first.
Originally posted by -PLB-
That is because full floor failures almost never happen unintentionally in practice. Not because all buildings are build according to that rule of yours. There are plenty of demolition examples where an (intentional) floor failure does result in global collapse.
We indeed need experts for these kind of things. For instance, we found out how water can get infected with bacteria and parasites, and how to prevent that from happening. You would still be drinking that water because why believe those experts? You cant see anything wrong with the water right? (adding vodka might even kill some of those bacteria )
It seems to me that you would be the person arguing "Of course we can use lead for pluming, as a preservative for foods and use it to give the candy for our kids a nice yellow color. The heck what those experts say. I use my own mind."
See what I meant with "blind spot"? I show you that even if you try to make a building collapse intentionally, the easy way, by blowing its base away, it's hard to do and sometimes fails -- and you rationalize it by saying floor failure (almost) never happens unintentionally in practice. And even that is only half the truth (this is from this very discussion).
Originally posted by -PLB-
Originally posted by Akareyon
Buildings don't collapse progressively and globally and disproportionally if you don't want them to - and even then it's hard to make them so. Because they get erected so they don't. Normally.
That is because full floor failures almost never happen unintentionally in practice.
Rule of mine? I'll try to get the 1963 version of this (it might cost a penny or two) just to prove you wrong on this one as well.
Not because all buildings are build according to that rule of yours.
A single, intentional floor failure at the base leading to collapse? I wonder how that could happen.
There are plenty of demolition examples where an (intentional) floor failure does result in global collapse.
It seems to me that you are the person arguing "so you have doubts about blindly believing everything some expert says, that shows how dangerous you are because experts are saving our lives and health everyday".
It seems to me that you would be the person arguing "Of course we can use lead for pluming, as a preservative for foods and use it to give the candy for our kids a nice yellow color. The heck what those experts say. I use my own mind."
Bazant made many believe there's nothing wrong with 110-story towers that implode and explode at the same time from top to bottom after the failure of a single floor in each somewhere above the 70th.
Of course science works as it is supposed to work, and no single scientist can make anyone believe that water is bad for you.
Laws of physics and the universe don't give a single _ about "consensus".
It requires wide spread consensus.
Originally posted by Akareyon
And still they don't collapse globally.
Originally posted by -PLB-
Of course they don't count because those examples are intentional.And they didn't. That shows how hard it is to bring a building down. If, and only if its effective FoS = F_c/m*g > 1.
And by the way, for those structures it was expected they would collapse globally.Half of it. That's what I said a badly built or severed building usually does - instead of falling into and out of itself.
And one of those buildings falls over.Nah, those buildings were empty ;-)
Everyone is still dead.Good, nor do I!
And with the forth I see nothing about full floor failure.
Still not getting my point?
Buildings don't collapse progressively and globally and disproportionally if you don't want them to - and even then it's hard to make them so. Because they get erected so they don't. Normally.If you could get the most widely cited doctor to write a paper, it would surely become an accepted truth in a society that has externalized its thinking. Everybody would still be drinking water and taking showers, but not without mixing some vodka into the water so it isn't water anymore. There would even be a government agency making sure you never ever go the beach without pouring a bottle of vodka into the ocean first.
There is no medical expert in the world who would claim that.
²Another_Nut:What I think doesn't matter, Another_Nut. I don't hold a position because I don't want to end up having it ridiculed and fall into the trap of defending "my" theory instead of getting closer to the truth. I said a little earlier that I don't really have an opinion myself, I'm just dispersing weak and wrong arguments based on the findings of Archimedes, Galileo and Newton and hoping to get closer to the truth in a process of elimination of unlikelinesses. Video footage is all I have as evidence that the towers ever existed in the first place, I've never been to New York so it could be a huge Hollywood production to me, in a sense. But I've been on the Eiffel Tower so I guess not all famous Skylines ever are photoshop jobs.
I think 9/11 was a message from someone other than the u.s. Government to someone other than the u.s. People.
is that your thinking?
and I guess the biggest question is
do you think the towers fell do to a cd or natural collapse?
If you'd ask me official CT vs. slipshod architecture (ROOSD) vs. conventional CD (thermite) vs. mini nukes though, I'd lean more towards magic. My favourite theory is that Lord Voldemort avada kedavraed the Twins to kingdom come with the Death Star superlaser to reset the Matrix. If you think about it: everybody was distracted looking up at the smoke and fire -- in the meantime, a good magician could have rearranged the whole stage so it's in the back of the audience. If you like movies, you might want to see "The Prestige". It's not only a good movie, it explains a lot.edit on 29-5-2013 by Akareyon because: (no reason given)
Originally posted by Akareyon
See what I meant with "blind spot"? I show you that even if you try to make a building collapse intentionally, the easy way, by blowing its base away, it's hard to do and sometimes fails -- and you rationalize it by saying floor failure (almost) never happens unintentionally in practice. And even that is only half the truth (this is from this very discussion).
Rule of mine? I'll try to get the 1963 version of this (it might cost a penny or two) just to prove you wrong on this one as well.
A single, intentional floor failure at the base leading to collapse? I wonder how that could happen.
It seems to me that you are the person arguing "so you have doubts about blindly believing everything some expert says, that shows how dangerous you are because experts are saving our lives and health everyday".
Bazant made many believe there's nothing wrong with 110-story towers that implode and explode at the same time from top to bottom after the failure of a single floor in each somewhere above the 70th.
Laws of physics and the universe don't give a single _ about "consensus".
But you already know that so you know that your argument is total nonsense, except if you intend to endorse my magic did it theory called "Metaphysics of progressive collapse" which says the towers fell because... people wanted them to and thus brought them down with the pure energy of consent, thought and willpower. The planes were just catalysts helping to rationalize the impossible.
Factor of safety (FoS), also known as (and used interchangeably with) safety factor (SF), is a term describing the structural capacity of a system beyond the expected loads or actual loads. Essentially, how much stronger the system is than it usually needs to be for an intended load. Safety factors are often calculated using detailed analysis because comprehensive testing is impractical on many projects, such as bridges and buildings, but the structure's ability to carry load must be determined to a reasonable accuracy.
Many systems are purposefully built much stronger than needed for normal usage to allow for emergency situations, unexpected loads, misuse, or degradation.
Factors of Safety - FOS - are a part of engineering design. Typical overall Factors of Safety - FOSs - are indicated below:
Structural steelwork in buildings 4 - 6
Factor of Safety (FOS) for structural applications is the ratio of the allowable working unit stress, allowable stress or working stress. The term was originated for determining allowable stress. The ultimate strength of a given material divided by an arbitrary factor of safety, dependant on material and the use to which it is to be put, gives the allowable stress.
Where:
Sm = Allowable working unit stress
sw = Working stress (Allowable stress)
fs = Factor of Safety
FACTOR OF SAFETY
In the elastic design of steel structures, the factor of safety is applied on the yield stress of the material to obtain the working stress or permissible stress in the material.
The value of factor of safety is decided considering the followings:
The average strength of materials is determined after making tests on number of specimens. The strengths of different specimens of given structural material are not identical.
The values of design loads remain uncertain, but values of dead loads can be determined correctly. But live load, impact load, wind load, snow load, etc cannot be determined with certainty since these depend upon statistics available. The probable values of these loads are only determined.
The values of internal forces in many structures depend upon the methods of analysis. The degree of precision of different methods varies. The methods involving detailed analysis are more precise. In case, analysis of the structure is done precisely, a small value of factor of safety may be adopted.
During fabrication, structural steel is subjected to different operations. The punching of a hole in a structural element distorts the surrounding material and cause high residual stresses. The warping and buckling of elements may take place during welding. The welding leaves high residual stresses. Structural elements are subjected to uncertain stress.
The variations in temperatures and settlement of supports are uncertain. Many times, a well designed structure is damaged because of these effects. The strength of materials decreases because of corrosion. The extent of corrosion is more when a structure is located in industrial areas and exposed to chemical wastes.
The failure of some structures or some elements of a structure is less serious and less disastrous than the failure of large structures or a main element of a structure.
The factor of safety also known as Safety Factor, is used to provide a design margin over the theoretical design capacity to allow for uncertainty in the design process. The uncertainty could be any one of a number of the components of the design process including calculations, material strengths, duty, manufacture quality. The value of the safety factor is related to the lack of confidence in the design process.
Originally posted by -PLB-
I already challenged you to show any source that shows a similar definition of FoS as yours.
Yes, because it is not my proposal and has been in place for a long time. That is why full floor failure occurs rarely, except in controlled demolitions and alien attacks, and seldomly global progressive collapse ensues. Because structural systems are built with a FoS and with enough redundance so this sort of thing can not happen except if someone helps it along.
Originally posted by -PLB-
You completely derailed from the subject here. The subject is your proposal for increasing building safety for a scenario where full floor failure occurs. I am not even sure what you are getting at here. Are you still wearing your aluminum hat thinking that the WTC towers could not have collapsed?
4.2.4.1 Structural integrity is the ability of the structural system to absorb and contain local damage or failure without developing into a progressive collapse that involves the entire structure or a disproportionatelylarge part of it. [...] Compartmentation (subdivision of buildings/stories in a building) is an effective means of achieving resistance to progressive collapse as well as preventing fire spread, as a cellular arrangement of structural components that are well tied together provides stability and integrity to the structural system as well as insulation.
It is essential that the engineer of record take all necessary precautions to ascertain that the structure does not fail catastrophically during testing. A careful assessment of structural conditions before testing is a fundamental requirement.
See? Yet it happened in the Twins and led to global progressive collapse from top to bottom.
To summarize: unintentional full floor failure almost never happens in reality. Neither of your sources show it happening either.
Fine, then open the document I linked to and scroll down to page 68 of the PDF, start reading at C2 - Calculation of required strength, until you reach the definition of P_e1 (which you need for the formula that calculates B_1 which in turn determines the required flexural and axial strength in members of lateral load resisting systems M_r in second order analysis procedures) which is defined as (π²*E*I)/(K_2*L)² , where E = modulus of elasticity of steel = 29,000 ksi (200 000 MPa), I = moment of inertia in the plane of bending in m^4, L = story height in mm and K_2 = effective length factor in the plane of bending, calculated based on a sidesway buckling analysis. Since that formula has been known since Euler, I'm pretty sure it was in the 1963 version of the Specification for Structural Steel Buildings by the American Institute of Steel Construction too. Oh, wait, what does it say here:I already challenged you to show any source that shows a similar definition of FoS as yours. So by all means, prove me wrong, and I will gladly accept that you are right, and fully agree something fishy was going on in the WTC design.
Rule of mine? I'll try to get the 1963 version of this (it might cost a penny or two) just to prove you wrong on this one as well.
You may also want to read Appendix 6 - Stability Bracing for Columns and Beams. I challenge you to show that this is only in there because of the Twins and wasn't, in one form or another, in the 1963 edition.
The effective length method for assessing member axial compressive strength [...] has been used in various forms in the AISC Specification since 1961.
Bazants allegations are verifiable.
you can't verify everything so a lot of things I believe blindly.
I stopped accepting what I'm told just "because authority" a long time ago and am always glad to rearrange my world view when new information falsifies it.
Even though you wont admit it, so do you.
There was (expert!) consensus once that earth is the middle of the universe and everything revolves around it, that the indigenous people of America have no right to dwell upon the soil they inhabited for centuries, that people with darker skin are animals in human shape and fit for slavery, that Jews are guilty for the misery of the aryan race and deserve to be murdered on an industrial scale.
Unless you have some divine knowledge directly coming from a god, [consensus is] the best thing we have.