Oystein
Penultimate Amazing
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CD = Free Fall?
- Thread starter Case
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alienentity
Illuminator
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I was in a hurry. Here's a link
http://archive.ifla.org/IV/ifla71/papers/009e-Coraggio.pdf
http://archive.ifla.org/IV/ifla71/papers/009e-Coraggio.pdf
Grizzly Bear
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http://www.cool-places.0catch.com/911/OpenLetterToRichardGage.pdf
Not sure if he's seen this already, but...
In case Zeuzz is interested, this was an open letter posted by Gregory Urich a few years back to Richard Gage. Considering his stance on the whole thing his comments are among the most competent I've read from people "supporting" the truth movement efforts, and someone who respectably followed the evidence despite where it took him. If I ever get sufficient time I'll write something up since everythings' kinda repetitious and I'm not always patient with on the fly exchanges, but he tackled most of the issues already that I would be concerned with in writing a critique of AE911's claims.
There's also a short write up done by Blanchard which answers some of the common questions at length: LINK... Of course there's plenty of options from others who've written on the issues as well.
Not sure if he's seen this already, but...
In case Zeuzz is interested, this was an open letter posted by Gregory Urich a few years back to Richard Gage. Considering his stance on the whole thing his comments are among the most competent I've read from people "supporting" the truth movement efforts, and someone who respectably followed the evidence despite where it took him. If I ever get sufficient time I'll write something up since everythings' kinda repetitious and I'm not always patient with on the fly exchanges, but he tackled most of the issues already that I would be concerned with in writing a critique of AE911's claims.
There's also a short write up done by Blanchard which answers some of the common questions at length: LINK... Of course there's plenty of options from others who've written on the issues as well.
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It wasn't an academic paper, but an official report by an agency of the US Gov't. It is open to criticism and reference by anyone, and has been criticized and referenced by many, including structural engineering courses.
Zeuzz,
A few first principles. If you know all of this, then I apologize for being pedantic. (Gotta do what I do best...)
Conservation of energy (conversion of potential energy (PE) to kinetic energy (KE). I assume you've got this.
Equivalence of work & energy: Work is defined as the product of an instantaneous force times the distance over which the force acts. For a component that breaks, in essence, the area under a "force vs. distance" curve from its initial position until fracture.
Both energy & work are scalar quantities, and you can simply subtract & add them, once expressed in the same units.
You can establish an "energy budget" as PE decreases & KE increases, giving a total PE + KE for the system. In the absence of other sinks of energy (i.e., work required to break things), then that total will remain a constant.
The work it takes to break something sucks away some energy from that total, and the KE won't rise as much as it would in the absence of this work.
As I said, the work to break something is the area under the force vs. deflection (or force vs. distance) curve for each element broken.
In gross terms:
"Weak" = low force to break
"Strong" = high force to break.
"Brittle" = low deflection to break.
"Ductile" = large deflection to break.
The size of the part obviously plays a significant role in "how far" it deforms. A 1" diameter bolt is not going to deform much before it snaps compared to a 36' tall column.
And all the work (energy) sinks add up as scalars. 10x as many fractures consumes 10x as much energy as one identical fracture.
You can see that weak/brittle, weak/ductile, and strong/brittle objects have small areas under their "load to failure curves", take small amounts of work to break, and therefore consume little of the kinetic energy.
The combination that absorbs lots of energy is strong/ductile. Which is exactly why they use structural steel in the first place, btw.
So you've got to consider, when thinking about this, what exactly are the parts that break, how much force it takes to break them, how much they have to deform before they break, and how many of them have to break.
For example, it would take a LOT of energy to crush down a column. But it would take a minuscule amount (in comparison) to snap the 8 or 12 or 20 bolts that connect it to adjacent columns. If the failure mechanism is crushing the columns, then you'd expect a lot of energy to be diverted to that process, and the downward acceleration to be smaller.
If the failure mechanism is fractured bolts, then only a (comparatively) tiny amount of that energy is going to be sapped away from the descending part's acceleration.
You can immediately tell, by looking at the columns in the debris piles, that very little energy was sapped away in crushing, deforming, bending columns. The vast majority of the columns were still pretty straight. Not grossly deformed or ripped apart. By far, the most common failure was the snapping of relatively small bolts & welds, or pull thru of those bolts thru thin angle plates.
Note that there are other sinks of energy, too. Moving air, throwing objects, etc.
___
Regarding your question about the acceleration vs. time curve for WTC7 …
This was the topic of much discussion here.
Here is my best take on "what really happened" vs. "the concept of 2.25 seconds of free fall acceleration". This is from data that was taken (by a crypto-truther poster named femr2). It looks at every frame of the videos, instead of every 5th, 10th, or 15th. The Chandler & NIST analyses did not look at each frame, and therefore lost a bunch of fine detail of the collapse motion.
BTW, you do realize, I hope, that by choosing to fit his velocity vs. time data to a linear regression, Chandler artificially FORCES the measured acceleration to be a constant over that time interval. A linear change in velocity over time is, BY DEFINITION, a constant acceleration.
The curve below does not impress this artificial constraint.
I wrote this, because I saw (but couldn't figure out what you were trying to say) a comment about "acceleration being small at first, and getting larger."
Just wanted to make sure that you didn't make a common mistake. For an object that suddenly enters free fall (say by having its legs taken out from underneath it by an explosive charge), its velocity starts out small & grows over time, but its acceleration does not.
Its acceleration is zero before the charge goes off, and then immediately jumps to the full value of "g". The acceleration does not build up gradually. I've shown that sudden "step function" in acceleration as the red line in the graph below.
The light green line (sorry its almost invisible) shows acceleration of the north west corner of WTC7 (the same point that Chandler, but not NIST, measured), using all the data frames.
The key point is that, if WTC7 really did fall "at free fall acceleration for 2.25 seconds", as Chandler claims, then there would be a 2.25 second long interval where the green line laid exactly on top of the red line. Clearly this is not true. Therefore the inescapable conclusion is that, in contradiction to what Chandler says, WTC7 did NOT fall "at free fall for 2.25 seconds."
Be warned that a complication hidden in this analysis is the proper filtering of the position vs. time & velocity vs. time graphs, in order that one may ultimately calculate acceleration vs. time. There are interminable, painful threads slicing this hair about 54 times.
I believe that the graph above addresses these complication appropriately. The integrated average acceleration that I get over Chandler's 2.25 seconds (between about 5.0 seconds & 7.25 seconds, in the graph above) is 0.94G. Not 1.0G.
If you believe my analysis, then you can see that acceleration profile that Chandler champions as "2.25 seconds of pure free fall" is nothing of the sort.
Other people here have done their own interpretations of the same data, come up with similar, but slightly different acceleration curves (it all depends on the data filtering), and reached essentially the same conclusion: Chandler's "constant G" is not accurate.
If you look carefully at Chandler (or NIST's) data, you can easily see these intervals of lower & higher accelerations, that Chandler (& then NIST) smooth out (i.e., "ignore") by taking the slope of the best fit linear curve.
You'll also note the curiosity of two brief periods of "greater than G" acceleration. Also the subject of much discussion. And, in my opinion, really happened.
Hope this wasn't too painful…
Welcome to the forum.
Tom
A few first principles. If you know all of this, then I apologize for being pedantic. (Gotta do what I do best...)
Conservation of energy (conversion of potential energy (PE) to kinetic energy (KE). I assume you've got this.
Equivalence of work & energy: Work is defined as the product of an instantaneous force times the distance over which the force acts. For a component that breaks, in essence, the area under a "force vs. distance" curve from its initial position until fracture.
Both energy & work are scalar quantities, and you can simply subtract & add them, once expressed in the same units.
You can establish an "energy budget" as PE decreases & KE increases, giving a total PE + KE for the system. In the absence of other sinks of energy (i.e., work required to break things), then that total will remain a constant.
The work it takes to break something sucks away some energy from that total, and the KE won't rise as much as it would in the absence of this work.
As I said, the work to break something is the area under the force vs. deflection (or force vs. distance) curve for each element broken.
In gross terms:
"Weak" = low force to break
"Strong" = high force to break.
"Brittle" = low deflection to break.
"Ductile" = large deflection to break.
The size of the part obviously plays a significant role in "how far" it deforms. A 1" diameter bolt is not going to deform much before it snaps compared to a 36' tall column.
And all the work (energy) sinks add up as scalars. 10x as many fractures consumes 10x as much energy as one identical fracture.
You can see that weak/brittle, weak/ductile, and strong/brittle objects have small areas under their "load to failure curves", take small amounts of work to break, and therefore consume little of the kinetic energy.
The combination that absorbs lots of energy is strong/ductile. Which is exactly why they use structural steel in the first place, btw.
So you've got to consider, when thinking about this, what exactly are the parts that break, how much force it takes to break them, how much they have to deform before they break, and how many of them have to break.
For example, it would take a LOT of energy to crush down a column. But it would take a minuscule amount (in comparison) to snap the 8 or 12 or 20 bolts that connect it to adjacent columns. If the failure mechanism is crushing the columns, then you'd expect a lot of energy to be diverted to that process, and the downward acceleration to be smaller.
If the failure mechanism is fractured bolts, then only a (comparatively) tiny amount of that energy is going to be sapped away from the descending part's acceleration.
You can immediately tell, by looking at the columns in the debris piles, that very little energy was sapped away in crushing, deforming, bending columns. The vast majority of the columns were still pretty straight. Not grossly deformed or ripped apart. By far, the most common failure was the snapping of relatively small bolts & welds, or pull thru of those bolts thru thin angle plates.
Note that there are other sinks of energy, too. Moving air, throwing objects, etc.
___
Regarding your question about the acceleration vs. time curve for WTC7 …
This was the topic of much discussion here.
Here is my best take on "what really happened" vs. "the concept of 2.25 seconds of free fall acceleration". This is from data that was taken (by a crypto-truther poster named femr2). It looks at every frame of the videos, instead of every 5th, 10th, or 15th. The Chandler & NIST analyses did not look at each frame, and therefore lost a bunch of fine detail of the collapse motion.
BTW, you do realize, I hope, that by choosing to fit his velocity vs. time data to a linear regression, Chandler artificially FORCES the measured acceleration to be a constant over that time interval. A linear change in velocity over time is, BY DEFINITION, a constant acceleration.
The curve below does not impress this artificial constraint.
I wrote this, because I saw (but couldn't figure out what you were trying to say) a comment about "acceleration being small at first, and getting larger."
Just wanted to make sure that you didn't make a common mistake. For an object that suddenly enters free fall (say by having its legs taken out from underneath it by an explosive charge), its velocity starts out small & grows over time, but its acceleration does not.
Its acceleration is zero before the charge goes off, and then immediately jumps to the full value of "g". The acceleration does not build up gradually. I've shown that sudden "step function" in acceleration as the red line in the graph below.
The light green line (sorry its almost invisible) shows acceleration of the north west corner of WTC7 (the same point that Chandler, but not NIST, measured), using all the data frames.
The key point is that, if WTC7 really did fall "at free fall acceleration for 2.25 seconds", as Chandler claims, then there would be a 2.25 second long interval where the green line laid exactly on top of the red line. Clearly this is not true. Therefore the inescapable conclusion is that, in contradiction to what Chandler says, WTC7 did NOT fall "at free fall for 2.25 seconds."
Be warned that a complication hidden in this analysis is the proper filtering of the position vs. time & velocity vs. time graphs, in order that one may ultimately calculate acceleration vs. time. There are interminable, painful threads slicing this hair about 54 times.
I believe that the graph above addresses these complication appropriately. The integrated average acceleration that I get over Chandler's 2.25 seconds (between about 5.0 seconds & 7.25 seconds, in the graph above) is 0.94G. Not 1.0G.
If you believe my analysis, then you can see that acceleration profile that Chandler champions as "2.25 seconds of pure free fall" is nothing of the sort.
Other people here have done their own interpretations of the same data, come up with similar, but slightly different acceleration curves (it all depends on the data filtering), and reached essentially the same conclusion: Chandler's "constant G" is not accurate.
If you look carefully at Chandler (or NIST's) data, you can easily see these intervals of lower & higher accelerations, that Chandler (& then NIST) smooth out (i.e., "ignore") by taking the slope of the best fit linear curve.
You'll also note the curiosity of two brief periods of "greater than G" acceleration. Also the subject of much discussion. And, in my opinion, really happened.
Hope this wasn't too painful…
Welcome to the forum.
Tom
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Zeuzzz
Banned
- Joined
- Dec 26, 2007
- Messages
- 5,211
Well thanks for the long reply. I did kind of know most of that maths/mechanics already 
but not so much some of the facts about chandler or specific data, so thanks anyway, will help other people here understand no doubt.
Why does that graph use ft/s2? My brain does not work in imperial it just confuses me!
So we seem to have an average acceleration for the time period 5.0 seconds to 7.25 of approximately 0.94*9.81 = 9.2m/s2.
So 0.61m/s2 short of free fall.
What was the weight of the section of the building above the collapse initiation floor?
but not so much some of the facts about chandler or specific data, so thanks anyway, will help other people here understand no doubt.Why does that graph use ft/s2? My brain does not work in imperial it just confuses me!
So we seem to have an average acceleration for the time period 5.0 seconds to 7.25 of approximately 0.94*9.81 = 9.2m/s2.
So 0.61m/s2 short of free fall.
What was the weight of the section of the building above the collapse initiation floor?
ozeco41
Philosopher
Possibly it is to avoid confusing some of us ancient engineers from the slide rule and imperial measurements era.....
Whilst I tend to think Imperial
BTW Top explanation tfk.
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Zeuzzz
Banned
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Anyone know this?
Trying to get an idea of the energies involved, and how much support the exterior columns might give.
Zeuzzz
Well, if it makes you feel more comfortable, you can multiply the ordinate axis by 2.217E9, and you will have the acceleration in "furlongs/fortnight2".
That's what I got when I did a numerical integration over that interval.
Search for "Greg Urich" wtc energetics.
Tom
Well, if it makes you feel more comfortable, you can multiply the ordinate axis by 2.217E9, and you will have the acceleration in "furlongs/fortnight2".
That's what I got when I did a numerical integration over that interval.
Search for "Greg Urich" wtc energetics.
Tom
Oystein
Penultimate Amazing
- Joined
- Dec 9, 2009
- Messages
- 18,903
a) I am not aware that Urich did meticulous tallying of the mass of all parts of WTC7, like he did for the twin towers.
b) Referencing Urich, I have a summary of the total mass and potential energy of the towers in my modest little blog: Twin towers and WTC7
c) Not sure if knowing the mass above the buckling region alone would help you much. You'd get large numbers in kg, N, P or psi, but what does it mean if the north wall perimeter columns carried 30000000kg, or 10000000 kg? How would such a number help you understand anything?
Greetings Re: WTC 7
Hello fellow skeptics. I'm the aforementioned person, Kurt Benshoof, who contacted the Seattle Weekly regarding their prior reporting on the subject of WTC 7.
Like many people, I accepted the US Government conspiracy theory regarding the events of 9/11 without question for about five years, at which time I was presented with a number of pieces of information that put the validity of the USG CT into question for myself.
Paul Case recommended this forum as a great place to get answers to my questions regarding the NIST report on the destruction of WTC 7.
I recognize at least one of the names of people who have posted comments on the Seattle Weekly blog page, and hope that we can all have a civil and informative discourse that will result in greater clarity and understanding of the subject matter. However, if any of you feel a compulsion to cast aspersions, I'm an ardent proponent of free speech, and will take no offense.
First of all, I'd like to clarify a few things before we delve into the NIST report. The challenge I made to journalist Curtis Cartier was an attempt to create a dialogue with, and research by, a Seattle writer who has spoken authoritatively on the subject of WTC 7---without actually having done much research. I'd already gone to my local congressman's office to get answers as to why NIST was refusing to release all of their modeling data, as that seemed of paramount importance to current and future building safety. Regardless of exactly what occurred with WTC 7, it seems logical that all NIST investigation data should be released to the public, in order to facilitate a better understanding of how a steel framed high rise building can be destroyed.
In the pursuit of keeping things as organized as possible---at least with regard to my points/questions---I'm going to number them for easier reference.
In no particular order of importance, here are some preliminary questions:
1) If, as the NIST report stated, there were only enough burnable materials to sustain a fire for 20-30 minutes in any given area, how is it that fires burned long enough to initiate collapse? According to their computer model, global collapse didn't manifest until the raging fires had burned continuously for 4 hours.
2) Regarding the thermal expansion that allegedly initiated the girder unseating from Column 79, did the NIST report exhibit scientific integrity by excluding thermal conductivity from their simulation?
3) Regarding the thermal expansion that allegedly initiated the girder unseating from Column 79, did the NIST report exhibit scientific integrity by only applying heat to Column 79---and not the connecting floor system---in their computer simulation?
4) Doesn't the NIST report acknowledge that steel and concrete have virtually the same coefficient of thermal expansion?
5) The NIST report stated that they tested no actual steel from WTC 7. Does this exhibit scientific integrity?
6) The NIST stated that they did not test for explosives. Does this exhibit scientific integrity in an impartial investigation into the collapse of WTC 7?
7) Does the verifiable evidence that the NIST report presents show that the fires burned long and hot enough to meet the four hire fire requirement exhibited by their computer model?
8) Do we know which way the 58 perimeter columns allegedly buckled, or is that an unknown?
9) What was the cause of the alleged buckling of the 58 perimeter columns? Were they significantly weakened by the fires?
10) If floors disconnected from the interior columns due to thermal expansion, what caused the interior columns collapse? Were the interior columns significantly weakened by fires?
Cheers,
Kurt
Hello fellow skeptics. I'm the aforementioned person, Kurt Benshoof, who contacted the Seattle Weekly regarding their prior reporting on the subject of WTC 7.
Like many people, I accepted the US Government conspiracy theory regarding the events of 9/11 without question for about five years, at which time I was presented with a number of pieces of information that put the validity of the USG CT into question for myself.
Paul Case recommended this forum as a great place to get answers to my questions regarding the NIST report on the destruction of WTC 7.
I recognize at least one of the names of people who have posted comments on the Seattle Weekly blog page, and hope that we can all have a civil and informative discourse that will result in greater clarity and understanding of the subject matter. However, if any of you feel a compulsion to cast aspersions, I'm an ardent proponent of free speech, and will take no offense.
First of all, I'd like to clarify a few things before we delve into the NIST report. The challenge I made to journalist Curtis Cartier was an attempt to create a dialogue with, and research by, a Seattle writer who has spoken authoritatively on the subject of WTC 7---without actually having done much research. I'd already gone to my local congressman's office to get answers as to why NIST was refusing to release all of their modeling data, as that seemed of paramount importance to current and future building safety. Regardless of exactly what occurred with WTC 7, it seems logical that all NIST investigation data should be released to the public, in order to facilitate a better understanding of how a steel framed high rise building can be destroyed.
In the pursuit of keeping things as organized as possible---at least with regard to my points/questions---I'm going to number them for easier reference.
In no particular order of importance, here are some preliminary questions:
1) If, as the NIST report stated, there were only enough burnable materials to sustain a fire for 20-30 minutes in any given area, how is it that fires burned long enough to initiate collapse? According to their computer model, global collapse didn't manifest until the raging fires had burned continuously for 4 hours.
2) Regarding the thermal expansion that allegedly initiated the girder unseating from Column 79, did the NIST report exhibit scientific integrity by excluding thermal conductivity from their simulation?
3) Regarding the thermal expansion that allegedly initiated the girder unseating from Column 79, did the NIST report exhibit scientific integrity by only applying heat to Column 79---and not the connecting floor system---in their computer simulation?
4) Doesn't the NIST report acknowledge that steel and concrete have virtually the same coefficient of thermal expansion?
5) The NIST report stated that they tested no actual steel from WTC 7. Does this exhibit scientific integrity?
6) The NIST stated that they did not test for explosives. Does this exhibit scientific integrity in an impartial investigation into the collapse of WTC 7?
7) Does the verifiable evidence that the NIST report presents show that the fires burned long and hot enough to meet the four hire fire requirement exhibited by their computer model?
8) Do we know which way the 58 perimeter columns allegedly buckled, or is that an unknown?
9) What was the cause of the alleged buckling of the 58 perimeter columns? Were they significantly weakened by the fires?
10) If floors disconnected from the interior columns due to thermal expansion, what caused the interior columns collapse? Were the interior columns significantly weakened by fires?
Cheers,
Kurt
A W Smith
Philosopher
Because there weren't any continuous columns 610 feet in length.. You are aware of course that columns are assembled end to end? In your opinion, what portion of a series of unsupported columns assembled end to end would be the least resistant to buckling?
Yes, I am aware that columns are assembled end to end.
It depends upon the structure of the columns and the attachments.
Was there evidence of unsupported columns?
LSSBB
Devilish Dictionarian
Kurt, my quick take regarding these 3 points:
There is a difference between heat transfer to concrete than to steel, so concrete and steel will heat differently.
There is a difference between heat transfer to concrete than to steel, so concrete and steel will heat differently.
Thanks for your input.
How substantive is the difference?
If the steel girder was connected to the support flange of Column 79, is there scientific integrity in not applying any heat to the composite floor system, of which the girder is a component, nor having any thermal conductivity to a connected floor system that is both metal and concrete?
A W Smith
Philosopher
to your first question in the previous post.
Was there evidence of column damage or shearing due to therm*te or explosive CD?
If the bolts (the weakest link) were sheared, The column ends wouldn't be significantly deformed nor show evidence of being ripped apart. Therefore very little energy would be sapped away in crushing, deforming, bending columns.
@ AW Smith: I didn't see an answer to my question, "Was there evidence of unsupported columns?", which was in reference to your statement.
According to FEMA, there was a WTC solid steel girder that had been turned into 'swiss cheese'. That is potentially evidence of some sort of incendiary or explosive involved in the collapse of WTC 7, as I'm not aware of a way in which burning papers and desks in WTC 7 would have cause that. Are you?
However, since the NIST investigation refused to test for any such materials, we have no way of knowing without a proper investigation---which is what I'm calling for. Do you have any objection to a new investigation with full public transparency and peer review of all data?
Are you certain that the shearing of bolts wouldn't leave evidence marks on the flanges of the columns in and/or around the holes? As long as the US Government refuses to actually examine any of the structural steel, we're left in the dark a bit.
AW Smith: "If the bolts (the weakest link) were sheared, The column ends wouldn't be significantly deformed nor show evidence of being ripped apart. Therefore very little energy would be sapped away in crushing, deforming, bending columns."
Do you know of any evidence regarding what force could have sheared column sections apart above Floor 13?
Do you know of any evidence regarding what force could have sheared column sections apart above Floor 13?