Loss Leader
I would save the receptionist., Moderator
I'm imagining a ... collapsing 110 story building.
Have you forgotten that the total milicochranes per foot pound at that moment was over 4.73 dB?
Debunk This
- Thread starter imstellar28
- Start date
I'm imagining a ... collapsing 110 story building.
Have you forgotten that the total milicochranes per foot pound at that moment was over 4.73 dB?
gumboot
lorcutus.tolere
- Joined
- Jun 18, 2006
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- 25,327
One thing that bugs me... and we should nip in the bud, is this talk of a single floor failing.
That's not what happened at all. The bowing was observed across the entire impact zone. The floors and core columns in this zone were all severely damaged. This section had very low structural integrity. When the exterior columns failed, they failed across not just one floor, but the entire impact zone. That's at least 5 floors for WTC1 and 7 for WTC2 (this is not allowing for a progression of structural failure in adjacent floors as the fire progressed).
The nature of the collapse also caused a violent twisting of the structure, in each case.
So. Let's apply imstellar28's scenario again...
Take a tower...
Remove 5 floors and their exterior columns part way down. Now twist the top half clockwise.
Will the core columns remain intact and hold up this enormous upper mass?
Of course not. The core columns are not huge (despite what CTers might claim). If the core columns are twisted into misalignment by only a matter of one or two feet, there is no longer ANYTHING holding that upper weight up. When it hits the first intact floor it will be travelling at about 60 MPH and again, none of the load bearing columns will match up. It will be entirely up to the first floor truss to bear over 12 GJ of energy bearing down on it, focused in the narrow footprint of the base of the columns.
Not going to happen. The upper section would punch through the first floor truss like paper.
-Gumboot
That's not what happened at all. The bowing was observed across the entire impact zone. The floors and core columns in this zone were all severely damaged. This section had very low structural integrity. When the exterior columns failed, they failed across not just one floor, but the entire impact zone. That's at least 5 floors for WTC1 and 7 for WTC2 (this is not allowing for a progression of structural failure in adjacent floors as the fire progressed).
The nature of the collapse also caused a violent twisting of the structure, in each case.
So. Let's apply imstellar28's scenario again...
Take a tower...
Remove 5 floors and their exterior columns part way down. Now twist the top half clockwise.
Will the core columns remain intact and hold up this enormous upper mass?
Of course not. The core columns are not huge (despite what CTers might claim). If the core columns are twisted into misalignment by only a matter of one or two feet, there is no longer ANYTHING holding that upper weight up. When it hits the first intact floor it will be travelling at about 60 MPH and again, none of the load bearing columns will match up. It will be entirely up to the first floor truss to bear over 12 GJ of energy bearing down on it, focused in the narrow footprint of the base of the columns.
Not going to happen. The upper section would punch through the first floor truss like paper.
-Gumboot
Gravy
Downsitting Citizen
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- 17,078
Since the exterior columns (including much of the weight of the floors) were not meant to hang from the hat truss, and enormous lateral and torsional forces would now be acting on the core, I'd say you'd have a building collapse there.
Do you understand what I meant about NIST not supporting the pancake collapse theory?
CurtC
Illuminator
No. If you take out one floor, the building sections above it and below it would be connected by the core, and the perimeter columns.
The perimeter columns bore a significant share of the weight of the towers, and if the only consideration was that the steel got hot and was weakened, the towers would likely not have fallen. But the sagging floors pulled inwards on the perimeter columns, causing their load-bearing capacity, already diminished by the heat, to fall drastically further.
You know, I never knew that.
That's what I love about this place, you get to learn so much from people who know so little.
I refer the OP to my response on page 1; where was I wrong? 
Dave Rogers
Bandaged ice that stampedes inexpensively through
Critiqueing Trumpman
In answer to the OP's original post, I thought I should take another look at Trumpman's paper - which I've read through before, by the way, so I already have a few comments to start with - and give it the same sort of critique I gave Jones's paper recently. I'll add to this as I have time, but here are some comments I would make for peer review on the first full section, "Fire Analysis".
Trumpman makes a series of assumptions to estimate how much area of each floor is on fire at any given time. This is very lengthy, and I won't go into the fine detail, mainly because Trumpman makes no real use of the results himself. Following this analysis, without making any calculations or invoking any mechanism, he then jumps directly to the statement that "What the data shows is that it is very unlikely that fires caused floor 97 to collapse." Without any justification, this statement is meaningless, and his arguments to back it up are nothing but handwaving. He then repeats the untrue assertion that UL's tests on the structure were capable of predicting the reaction of the structure to a real fire. Having failed to carry out any detailed modelling of fire initiated collapse initiation he then accuses NIST, who have modelled the collapse initiation in great detail, of not doing so.
The assertion that the bowing observed was only of the aluminium facade panels is geometrically absurd. As the facade was applied directly to the exterior girders, it could not have bowed inwards without occupying the same space as the girders.
Trumpman's repeated assertion throughout the paper that "Science says no way" is both unscientific and never justified by the minimal analysis he carries out.
Trumpman gives the weight of each tower as about 200,000 tons. It is well known to have been about 500,000 tons - see elsewhere in this thread for references.
Trumpman's description of the behaviour of steel under heating and cooling is entirely correct, and understanding this behaviour is in fact key to understanding the collapse mechanism hypothesised by NIST. This hypothesis is that the floor trusses initially sagged due to softening and thermal expansion, then as the fires burned out the floor trusses stiffened and cooled, retaining the sag. This pulled in the exterior girders, causing them to fail. While Greening has disputed this hypothesis, he has not refuted it, so at present it stands as the best model of the collapse we have. As the floor trusses covered the entire width of the building, Trumpman's argument that the fires did not cover enough area is invalid, as a large enough fire in any area of the building would cause this collapse mechanism. The assertion that some of the fires were weakening at the time of collapse is, of course, evidence not against but in favour of NIST's hypothesis, as this requires the fires to weaken to initiate collapse.
Trumpman's assertion that NIST's model predicted excessive fire temperatures is addressed elsewhere in this thread, but let me reiterate that: (1) Paint analysis, the technique used, is unable to determine maximum temperatures above 250C as paint is burned off at higher temperatures, so any steel that had experienced a higher temperature could not have been analysed by this technique, and (2) the points sampled by this method by NIST were fully in agreement with the results of their modelling. Trumpman's assertion that the structure could not have been damaged by fires of any temperature however high is, not to put too fine a point on it, utter stupidity.
Finally, Trumpan's assertions that more than 80% of the perimeter columns had to fail to cause collapse is based on the safety factor of single columns. Even if the figures used by Trumpman are correct, which is not established in the paper, for this to be valid for the structure as a whole is to make the assumption that the damage was roughly equally distributed about the structure, rather than localised as observed. Far more complex analysis is needed to make a realistic determination of the resistance of the structure to damage.
Dave
In answer to the OP's original post, I thought I should take another look at Trumpman's paper - which I've read through before, by the way, so I already have a few comments to start with - and give it the same sort of critique I gave Jones's paper recently. I'll add to this as I have time, but here are some comments I would make for peer review on the first full section, "Fire Analysis".
Trumpman makes a series of assumptions to estimate how much area of each floor is on fire at any given time. This is very lengthy, and I won't go into the fine detail, mainly because Trumpman makes no real use of the results himself. Following this analysis, without making any calculations or invoking any mechanism, he then jumps directly to the statement that "What the data shows is that it is very unlikely that fires caused floor 97 to collapse." Without any justification, this statement is meaningless, and his arguments to back it up are nothing but handwaving. He then repeats the untrue assertion that UL's tests on the structure were capable of predicting the reaction of the structure to a real fire. Having failed to carry out any detailed modelling of fire initiated collapse initiation he then accuses NIST, who have modelled the collapse initiation in great detail, of not doing so.
The assertion that the bowing observed was only of the aluminium facade panels is geometrically absurd. As the facade was applied directly to the exterior girders, it could not have bowed inwards without occupying the same space as the girders.
Trumpman's repeated assertion throughout the paper that "Science says no way" is both unscientific and never justified by the minimal analysis he carries out.
Trumpman gives the weight of each tower as about 200,000 tons. It is well known to have been about 500,000 tons - see elsewhere in this thread for references.
Trumpman's description of the behaviour of steel under heating and cooling is entirely correct, and understanding this behaviour is in fact key to understanding the collapse mechanism hypothesised by NIST. This hypothesis is that the floor trusses initially sagged due to softening and thermal expansion, then as the fires burned out the floor trusses stiffened and cooled, retaining the sag. This pulled in the exterior girders, causing them to fail. While Greening has disputed this hypothesis, he has not refuted it, so at present it stands as the best model of the collapse we have. As the floor trusses covered the entire width of the building, Trumpman's argument that the fires did not cover enough area is invalid, as a large enough fire in any area of the building would cause this collapse mechanism. The assertion that some of the fires were weakening at the time of collapse is, of course, evidence not against but in favour of NIST's hypothesis, as this requires the fires to weaken to initiate collapse.
Trumpman's assertion that NIST's model predicted excessive fire temperatures is addressed elsewhere in this thread, but let me reiterate that: (1) Paint analysis, the technique used, is unable to determine maximum temperatures above 250C as paint is burned off at higher temperatures, so any steel that had experienced a higher temperature could not have been analysed by this technique, and (2) the points sampled by this method by NIST were fully in agreement with the results of their modelling. Trumpman's assertion that the structure could not have been damaged by fires of any temperature however high is, not to put too fine a point on it, utter stupidity.
Finally, Trumpan's assertions that more than 80% of the perimeter columns had to fail to cause collapse is based on the safety factor of single columns. Even if the figures used by Trumpman are correct, which is not established in the paper, for this to be valid for the structure as a whole is to make the assumption that the damage was roughly equally distributed about the structure, rather than localised as observed. Far more complex analysis is needed to make a realistic determination of the resistance of the structure to damage.
Dave
Last edited:
westprog
Philosopher
- Joined
- Dec 1, 2006
- Messages
- 8,928
Just go to Google advanced search and put WTC and 911 in the without the words field.
However, if someone is really interested in how controlled demolition works then I'd suggest a visit to the local college bookstore and invest in a cellulose-based data retrieval system. And anticipate spending several months before really understanding very much.
This applies to structural engineering or architecture as well, but anticipate spending several years.
This involves a lot of effort, but it means that it's unlikely that you'll ever suggest that implosions work by creating a vacuum that sucks the building downwards.
A W Smith
Philosopher
Below we have a classic example of a wiki page being corrupted by the edit of a twoofer
http://en.wikipedia.org/w/index.php?title=Building_implosion&diff=next&oldid=94680837
An annonomous twoofer on jan 30th using RoadRunner as their isp.
defaultdotxbe
Drunken Shikigami
- Joined
- Jul 30, 2006
- Messages
- 7,474
i suppose one could argue that no building implosion in history has been properly designed, lol
CurtC
Illuminator
I just love it when True Believers edit Wikipedia. Whether it's creationists or 9/11 deniers. That one edit has it all, doesn't it? The explosions blowing the air out of the building, along with the support structures (!), leaving a vacuum, and the word vacuum even appears in quotes. Then it has the obligatory CT word "pull," again in quotes, and even manages to fit in the phrase "near freefall speeds." It's like the trifecta of idiocy, all in one sentence!
Dave Rogers
Bandaged ice that stampedes inexpensively through
Trumpman critique, part 2
Some comments on the second part of Trumpman's paper: Collapse Analysis.
Trumpman makes a number of assertions about the nature of the collapse which are based on observation of videos. These include the assertion that all four corners fell in near-unison, despite the undeniable fact that no single point of observation can possibly establish this (one corner must always be obscured), the contradictory assertion that the first point of collapse appears to be from the south side (suggesting that the corners did not fall in unison), and the assertion that no column bending was observed prior to collapse, which is flatly contradicted by photographic evidence available elsewhere (see, for example, http://www.debunking911.com/sag.htm, where inward bowing of the North tower is shown).
Timings of the collapse of individual floors are taken by manual stopwatch timing from an AVI video. No analysis of accuracy or precision other than the variance between readings is attempted. All timings are quoted to an accuracy of 0.01s. Since the AVI is presumably derived from a 25Hz refresh rate video, the frame refresh time is 0.04 seconds, and no timing can be measured to a higher precision than this. Notwithstanding this, Trumpman claims that a 0.02s discrepancy between the measured fall of the initial floor and a calculated freefall time indicates that the first floor collapse proceeded faster than freefall, and that the building was "pulled down". In fact, the difference between measured and calculated times is simply not significant. Assessment of random and systematic measurement errors is typically covered in high school physics courses, but Trumpman seems unaware of its significance.
Trumpman then goes on to argue that steel cannot fail suddenly in a fire, proposing some experiments using stacked books which have no relevance whatsoever to collapse mechanisms in steel. He asserts that progressive fatigue failure should have led to a slow collapse of the upper storeys. This might be the case if the building were supported by a single steel member or if the temperatures of all the columns were very carefully controlled to be equal, but these are not comparable with real world situations. In reality all columns would experience different loads and thermal conditions, and whenever the load on a single column exceeded its strength the column would fail. When the remaining columns had not enough strength combined to support the structure, very rapid progressive failure would then take place, leading to a sudden collapse of the type observed. This would be clear to anyone with training in structural engineering. He then asserts that columns with different load capacities would not give way at the same time, ignoring the fact that this is not necessary to explain a sudden collapse.
Trumpman asks why the upper part of the building did not continue to rotate southwards as it collapsed. There is no evidence advanced in the paper to show that it did not. He then conflates the NIST collapse theory with the earlier, superseded FEMA pancake collapse theory, and suggests that there is a contradiction in the requirement that floor attachment bolts be both strong enough to pull in exterior columns and weak enough to fail and initiate collapse. Since these are two different theories, and the FEMA theory has now been superseded, there is no contradiction.
Trumpman concludes by asserting that "WTC 1 did not collapse as science predicts it should have", and that "The government has been unable to reconcile the irrefutable data". This is deliberately misleading; there is a large body of work, including Bazant and Zhou's elastic dynamic analysis, Greening's studies of collapse progression and NIST's conclusions of collapse initiation by sagging of floor trusses, which, while possibly not correct in every last detail, presents a thorough, consistent and physically reasonable model of all features of the WTC1 collapse.
Dave
Some comments on the second part of Trumpman's paper: Collapse Analysis.
Trumpman makes a number of assertions about the nature of the collapse which are based on observation of videos. These include the assertion that all four corners fell in near-unison, despite the undeniable fact that no single point of observation can possibly establish this (one corner must always be obscured), the contradictory assertion that the first point of collapse appears to be from the south side (suggesting that the corners did not fall in unison), and the assertion that no column bending was observed prior to collapse, which is flatly contradicted by photographic evidence available elsewhere (see, for example, http://www.debunking911.com/sag.htm, where inward bowing of the North tower is shown).
Timings of the collapse of individual floors are taken by manual stopwatch timing from an AVI video. No analysis of accuracy or precision other than the variance between readings is attempted. All timings are quoted to an accuracy of 0.01s. Since the AVI is presumably derived from a 25Hz refresh rate video, the frame refresh time is 0.04 seconds, and no timing can be measured to a higher precision than this. Notwithstanding this, Trumpman claims that a 0.02s discrepancy between the measured fall of the initial floor and a calculated freefall time indicates that the first floor collapse proceeded faster than freefall, and that the building was "pulled down". In fact, the difference between measured and calculated times is simply not significant. Assessment of random and systematic measurement errors is typically covered in high school physics courses, but Trumpman seems unaware of its significance.
Trumpman then goes on to argue that steel cannot fail suddenly in a fire, proposing some experiments using stacked books which have no relevance whatsoever to collapse mechanisms in steel. He asserts that progressive fatigue failure should have led to a slow collapse of the upper storeys. This might be the case if the building were supported by a single steel member or if the temperatures of all the columns were very carefully controlled to be equal, but these are not comparable with real world situations. In reality all columns would experience different loads and thermal conditions, and whenever the load on a single column exceeded its strength the column would fail. When the remaining columns had not enough strength combined to support the structure, very rapid progressive failure would then take place, leading to a sudden collapse of the type observed. This would be clear to anyone with training in structural engineering. He then asserts that columns with different load capacities would not give way at the same time, ignoring the fact that this is not necessary to explain a sudden collapse.
Trumpman asks why the upper part of the building did not continue to rotate southwards as it collapsed. There is no evidence advanced in the paper to show that it did not. He then conflates the NIST collapse theory with the earlier, superseded FEMA pancake collapse theory, and suggests that there is a contradiction in the requirement that floor attachment bolts be both strong enough to pull in exterior columns and weak enough to fail and initiate collapse. Since these are two different theories, and the FEMA theory has now been superseded, there is no contradiction.
Trumpman concludes by asserting that "WTC 1 did not collapse as science predicts it should have", and that "The government has been unable to reconcile the irrefutable data". This is deliberately misleading; there is a large body of work, including Bazant and Zhou's elastic dynamic analysis, Greening's studies of collapse progression and NIST's conclusions of collapse initiation by sagging of floor trusses, which, while possibly not correct in every last detail, presents a thorough, consistent and physically reasonable model of all features of the WTC1 collapse.
Dave
Loss Leader
I would save the receptionist., Moderator
Here's my question: Wouldn't a vaccuum pull the floor up at the same time it's pulling the ceiling down? Whatever increase in speed of the ceiling that is caused by a vaccuum pulling it towards the ground would be offset by the decrease in speed of the floor caused by the vaccuum pulling it away from the ground, right?
I mean it's just so ... stupid.
I mean it's just so ... stupid.
Loss Leader
I would save the receptionist., Moderator
I think you can also add a minus sign in the regular google search window:
"controlled demolition" -WTC -"September 11"
Yup, it works.
Dave Rogers
Bandaged ice that stampedes inexpensively through
Errr... no. Wrong. The idea is that, if there's a vacuum below the falling part of the building, then 15psi air pressure above the falling part imparts an additional downward force. The floor won't accelerate upwards if there's no air space below it to provide the pressure to produce the force, plus it's still anchored to the ground so it can't move anyway. Whether 15psi would produce enough additional acceleration to be measurable is a different question.
Dave
defaultdotxbe
Drunken Shikigami
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- 7,474
well it wouldnt so much being the vacuum pulling the floor up, but rather the air pressure below the floor pushing it up, so explosives would have to create a vacuum throughout the entire building, and maintain that vacuum during the entire collapse
Z
Variable Constant
You DO realize, don't you, that the aluminum-clad outer structure supported a large portion of the building's weight, don't you?
It's hardly 'facade'.
CurtC
Illuminator
Yes, good point. Except for one thing - at the lowest floor, the vacuum wouldn't accomplish anything there, but it still would at the very top ceiling. So you'd get the speed benefit of one floor's worth.
On the other hand, you have to assume that blowing out all that air from the collapsing building takes a lot of energy, and that energy will come out of the speed of the collapse. I think the energy is completely negligible compared to the energy of the falling heavy building. A vacuum wouldn't make it pull down faster than gravity's 9.8 m/s2, but would make a theoretical difference in speed compared to the same building with air in it.
Also, concrete makes a lot of dust when it fractures, and so does wallboard and ceiling tile. Having a vacuum in the building would prevent all that dust from being blown outwards as it collapsed, which would be a benefit. The trouble is, there's no way to get a vacuum in a big structure like that, and the large billowing dust clouds from every building as it falls is proof that there was no vacuum in it.
CurtC
Illuminator
kookbreaker
Evil Fokker
- Joined
- Aug 23, 2001
- Messages
- 15,920
I just wanted to say: Good workin' Dave Rogers.