WCT1 Near-Freefall not Evidence of CD

[GregoryUrich]

My latest submission (http://www.cool-places.0catch.com/docs/FalaciousCdArguments2_14.pdf) to the Journal of 9/11 Studies.

...more truth from a "truther".

[einsteen]

You say near-freefall behaviour is no evidence of CD. Do you mean with this that only freefall is evidence of CD? If we look at wtc7 it was also no freefall, it was fast, more near g than wtc1,2 but no freefall. There is also no CD that goes with freefall. CDs are always near freefall, never freefall. I think that the point you are making is that the potential energy is sufficient, but we knew that already.

[Disbelief]

You say near-freefall behaviour is no evidence of CD. Do you mean with this that only freefall is evidence of CD? If we look at wtc7 it was also no freefall, it was fast, more near g than wtc1,2 but no freefall. There is also no CD that goes with freefall. CDs are always near freefall, never freefall. I think that the point you are making is that the potential energy is sufficient, but we knew that already.

What do you consider near freefall? Within 10%? 20%?

[Apollo20]

Gregory Urich:

I do not find your new JONES paper very convincing of anything!

You state WITHOUT PROOF (or any attempt at calculations) that 1.8 GJ per floor "can easily account for all energy requirements including breaking the structure, comminution of concrete, ejection of debris, air expulsion, adiabatic heating, and other less significant factors."

Well, it is precisely these energy requirements that have been called into question by many "truthers" - including you! Did you not recently claim you had a problem with concrete comminution at 8.5 m/s -the velocity of the first impact of the upper section of WTC 1.

Now I'm really confused....... Why the change of tune?

[einsteen]

What do you consider near freefall? Within 10%? 20%?
That doesn't matter, a CD always starts accelerating with a<g and the ratio depends on the mass/structure etc. If you compare the drop (as function of time) of an implosion with that of one of the three wtc towers you will see it all goes slower than g . Some time ago it seemed that even the Landmark and wtc1's drop were indistinguishable although the collapses were totally different.

[Dave Rogers]

Gregory,

I agree with Frank - the statement that "This amounts to 1.8 GJ per floor on average, which can easily account for all energy requirements including breaking the structure, comminution of concrete, ejection of debris, air expulsion, adiabatic heating, and other less significant factors" is too significant a result to quote without either derivation or reference. I think you need to justify the inequality. I'm a little surprised you didn't, because as far as I recall you've already done all these calculations. At the moment you've left JON-ES with a good reason to reject a paper that disagrees with its usual slant, whereas with the numbers for energy loss per floor in place I think you've got a solidly reasoned conclusion.

Dave

[MRC_Hans]

I don't think the collapse speed has anything to do with CD/non CD. In both cases, once the supporting structure is broken down, either by explosives or by whatever damage suffered, the collapse will commence at near free-fall. This is simply a property of a progressive, self-sustained collapse.

There are really, apart from an entirely hypothetical knife-edge scenario, only two scenarios:

1) Progressive collapse, where the descend of the upper part of the structure releases more energy than needed for maintaining the collapse.

2) Unprogressive collapse, where the released energy is insuffucient, and the collapse is halted.

Hans

[bofors]

Consequently, while it is reasonable to say that WTC1 fell at near freefall speed,
this is in no way indicative of assisted collapse. - Gregory Urich

Given that controlled demolitions usually proceed at near freefall speed and gravity-driven collapses do not, this statement is obviously false.

Furthermore, I would argue that the only time gravity-driven collapses approach free-fall speed is with a "pancaking" mechanism. Since the WTC twin towers did not "pancake", controlled demolition is indicated by the speed of their destruction alone.

[uk_dave]

Since the WTC twin towers did not "pancake", controlled demolition is indicated by the speed of their destruction alone.

Except that they did, just not at the collapse initiation.

Please do try to keep up.

[MRC_Hans]

Given that controlled demolitions usually proceed at near freefall speed and gravity-driven collapses do not, this statement is obviously false.
Circular argumentation. The WTC collapses did proceed at near freefall speed, and since you have not proven they were not gravity-driven, your statement falls.

Controlled demolitions are also gravity-driven, once the demolition charges have been detonated.

Hans

[Apollo20]

I think the important thing to note is that GU has only considered the energy requirements for a COMPLETE collapse of WTC 1. This is fine, but not the most important issue which is how much KE was available AT THE START of the collapse - say in the first 3 seconds. To determine this you need to consider the energy dissipation as a fraction of the KE available from a free fall drop of an upper block through a distance of 3.7 meters. If the post-impact KE is sufficient to keep the upper block moving, a self-sustaining progressive collapse is possible. After about 3 seconds into the destruction of WTC 1, a CD would be essentially indistinguishable from a gravity driven collapse!

[CHF]

Given that controlled demolitions usually proceed at near freefall speed and gravity-driven collapses do not...

What exactly are you comparing the WTC collapses to as a point of reference?

Furthermore, I would argue that the only time gravity-driven collapses approach free-fall speed is with a "pancaking" mechanism. Since the WTC twin towers did not "pancake", controlled demolition is indicated by the speed of their destruction alone.

Pancaking was ruled out as being what started the collapse.

[Newtons Bit]

Given that controlled demolitions usually proceed at near freefall speed and gravity-driven collapses do not, this statement is obviously false.

Prove it.

[Dave Rogers]

Consequently, while it is reasonable to say that WTC1 fell at near freefall speed,
this is in no way indicative of assisted collapse. - Gregory Urich

Given that controlled demolitions usually proceed at near freefall speed and gravity-driven collapses do not, this statement is obviously false.

You haven't defined "near-freefall", nor have you given any examples of gravity-driven collapses that proceed at speeds significantly different to freefall (where "significantly different" means not conforming to your definition of "near-freefall"). You're therefore committing yet another unevaluated inequality fallacy. And before you ask, I'm not going to get tired of saying that until you and the rest of the truth movement stop producing them.

Furthermore, I would argue that the only time gravity-driven collapses approach free-fall speed is with a "pancaking" mechanism.

So what you're saying is that gravity-driven pancake collapses proceed at near-freefall speeds whereas gravity-driven collapses don't proceed at near-freefall speeds, from which we can infer that you believe pancake collapses are not a subset of collapses. This is an utterly idiotic position.

Why do you persist in making such a fool of yourself in public?

Dave

[Disbelief]

That doesn't matter, a CD always starts accelerating with a<g and the ratio depends on the mass/structure etc. If you compare the drop (as function of time) of an implosion with that of one of the three wtc towers you will see it all goes slower than g . Some time ago it seemed that even the Landmark and wtc1's drop were indistinguishable although the collapses were totally different.

I understand completely, I was just trying to get a definition of near freefall, which I see thrown around alot. I think that a big problem with many CTists, is that they don't understand that within 4 seconds of freefall (which sounds close) is more than 40% slower than freefall.

[Apollo20]

Here are some MEASURED data for WTC 1, (taken from the Sauret video):

Time (s); Drop(m); Accel(m/s^2)

t d acc
------------------
0; 0; 0
0.5; 1.0; 8.0
1.0; 4.2; 8.4
1.5; 8.3; 7.4
2.0; 14.0; 7.0
2.5; 20.0; 6.4
3.0; 27.6; 6.1

Now is this near "free fall" or not?

[Dave Rogers]

Now is this near "free fall" or not?

Depends on your definition of "near". It's all within an order of magnitude, so if you're a cosmologist or a SIMS analyst that's not "near", it's "precisely equal to". None of it is within 10%, so if you're an engineer...

I just remembered who I'm talking to. Best not go there.

Dave

[Apollo20]

Dave Rogers:

Engineers!

Engineers are ok...... Gustave Eiffel was an engineer, and he was a genius!

The question is: could the WTC 1 collapse accelerations I quoted above be produced without the help of explosives/pyrotechnics?

The answer appears to be yes!

Certainly if you carry out a momentum transfer calculation for a progressive collapse of a WTC-type tower you can obtain numbers close to the accelerations I quoted.

[Disbelief]

Dave Rogers:

Engineers!

Engineers are ok...... Gustave Eiffel was an engineer, and he was a genius!

The question is: could the WTC 1 collapse accelerations I quoted above be produced without the help of explosives/pyrotechnics?

The answer appears to be yes!

Certainly if you carry out a momentum transfer calculation for a progressive collapse of a WTC-type tower you can obtain numbers close to the accelerations I quoted.


I still think the disconnect with the truth movement is that they do not comprehend what near free fall is. Like I said, they will say that it only took 4seconds longer than freefall (only 4seconds:jaw-dropp), instead of saying it was 40% slower. Understand why this might be an issue?

[GregoryUrich]

Gregory Urich:

I do not find your new JONES paper very convincing of anything!

You state WITHOUT PROOF (or any attempt at calculations) that 1.8 GJ per floor "can easily account for all energy requirements including breaking the structure, comminution of concrete, ejection of debris, air expulsion, adiabatic heating, and other less significant factors."?

I thought someone might call me on that. I'm finishing up the companion paper which has the energy estimates. Given my last OT regarding collapse continuation most of the energy factors are known. Air expulsion is the only one I'm no sure about yet. But, adding up everything we know for the 98th floor:

elastic energy 85 MJ
inelastic buckling 171 MJ
comminution of concrete 302 MJ
adiabatic compression 200 MJ
----------------------------
we get 758 MJ. Not even half of the budget for one floor. Plenty of energy left to expel air and wreck everthing else. I'll try to quantify everthing else but no way we are going to find 1000 GJ.

Well, it is precisely these energy requirements that have been called into question by many "truthers" - including you! Did you not recently claim you had a problem with concrete comminution at 8.5 m/s -the velocity of the first impact of the upper section of WTC 1.

Now I'm really confused....... Why the change of tune?

I was pointing out the problem with Ross's analysis in that he over-estimated pulverization on the first impacted floor. Are you suggesting there would be significant comminution (read pulverizing) at 8.5 m/s such that 302 MJ are consumed?

I don't think I have ever claimed there was a general energy deficit. If I did, I demonstrate my right and willingness to change my mind.

[GregoryUrich]

I think the important thing to note is that GU has only considered the energy requirements for a COMPLETE collapse of WTC 1. This is fine, but not the most important issue which is how much KE was available AT THE START of the collapse - say in the first 3 seconds. To determine this you need to consider the energy dissipation as a fraction of the KE available from a free fall drop of an upper block through a distance of 3.7 meters. If the post-impact KE is sufficient to keep the upper block moving, a self-sustaining progressive collapse is possible. After about 3 seconds into the destruction of WTC 1, a CD would be essentially indistinguishable from a gravity driven collapse!

With all the numbnuts running around claiming that near-freefall proves controlled demoltion, I thought this would be a useful contribution. I am in full agreement that collapse initiation is the key to proving one way or the other. Which way are you leaning these days?

[GregoryUrich]

You say near-freefall behaviour is no evidence of CD. Do you mean with this that only freefall is evidence of CD? If we look at wtc7 it was also no freefall, it was fast, more near g than wtc1,2 but no freefall. There is also no CD that goes with freefall. CDs are always near freefall, never freefall. I think that the point you are making is that the potential energy is sufficient, but we knew that already.

I should have said near-freefall in WTC1 is not evidence of CD in WTC1. It is not a conclusive test for or evidence of either gravity driven collapse or controlled demolition. The claim that near-freefall collapse indicates CD is a superficially convincing, but fallacious claim.

[aggle-rithm]

With all the numbnuts running around claiming that near-freefall proves controlled demoltion, I thought this would be a useful contribution. I am in full agreement that collapse initiation is the key to proving one way or the other. Which way are you leaning these days?

It's been seven long years. Someday, however, I am sure the truth movement will put their heads together and come up with a plausible controlled demolition hypothesis. Maybe in another seven years.

Then all they have to do is show that "controlled demolition" = "inside job". That could take maybe another fourteen years.

Will any of the evildoers still be alive to be brought to justice?

[beachnut]

But seriously folks, my hatred of Bush would not lead me to fabricate his involvement in conspiracies. On the other hand, a seemingly trustworthy person (with no ulterior motives) is saying they have spoken with whistleblowers who indicate that the government at least had foreknowledge. To me that's a no-brainer. Time to investigate.
With all the numbnuts running around claiming that near-freefall proves controlled demoltion, I thought this would be a useful contribution. I am in full agreement that collapse initiation is the key to proving one way or the other. Which way are you leaning these days?
So you are going to agree that gravity is the driving force of CD and non CD events. That is common knowledge if you only researched this when you first signed the petition blaming Americans for the murder of 3000 on 9/11. This have been know before 9/11. Not new, nothing but you setting up the scientific proof for blaming Americans on the initiation of the WTC failure. Whereas the impact and resultant fires were the cause of the initiation of failure.

But it seems now you will try to back in CD as the initiation of the WTC events. And since you are a Jones truth engineer, I suspect you will finally get around to thermite. And if you only had some piles of iron made during the fall of the WTC you would have a done deal, and realcddeal could be so happy his political rant in his scientific papers had some realcd evidence in the form of piles of iron. Or gee, what if you had some thermit cutting devices used to bring down the WTC, there had to be many of them to make it happen, where did they go? They would be present like the tower was found on the WTC, and they would be unique, and they would be used to find the bad guys. But the bad guys on 9/11 were 19 terrorists, and now the only bad guys left are the false information experts you support know as 9/11 "truth". Irony.

Congratulation you have discovered gravity is the driving force (main energy source) in CD and also in the WTC destruction. Wow, you attempt to educate the drone of 9/11 truth membership is noteworthy.

[Apollo20]

GregoryUrich:

I am focussing on the first floor failure in WTC 1 because if this is a go, everything else follows - especially the collapse of WTC 2! But if it's a no-go, well, .... we have a problem! Now if I use your mass estimates I believe the upper block of WTC 1 would be about 33,000 tonnes (well down from Bazant's estimate of 58,000 tonnes!) and this mass supplies about 1198 MJ of KE to the structure below assuming the block falls 3.7 meters AT FREE FALL. Now you estimate that a minimum of 758 MJ of energy was consumed by the impact - the final total possibly being 50 MJ higher, say 800 MJ, if all energy sinks are included. This is uncomfortably close to the available energy of 1198 MJ, especially when you consider that the upper section actually tilted (rather than dropped), so that the the effective velocity of the upper block may have been less than the free fall value of 8.5 m/s.

So I would like to see your energy calculations. I still believe the destruction of WTC 1 was a gravity-driven collapse; I would just like to see realistic energy balance calculations to back this up!

[Mangoose]

I don't know how truthers who claim free-fall who say "just look at the video" don't notice things like this:

http://img222.imageshack.us/img222/1648/freefallzd4.jpg

[GStan]

You haven't defined "near-freefall", nor have you given any examples of gravity-driven collapses that proceed at speeds significantly different to freefall (where "significantly different" means not conforming to your definition of "near-freefall"). You're therefore committing yet another unevaluated inequality fallacy. And before you ask, I'm not going to get tired of saying that until you and the rest of the truth movement stop producing them.


Seems so easy to spot now that there is a name for it. ;)

[rwguinn]

Seems so easy to spot now that there is a name for it. ;)
I dunno
AuiF is so...awkward...
and hard to pronounce...

[einsteen]

The question is: could the WTC 1 collapse accelerations I quoted above be produced without the help of explosives/pyrotechnics?

The answer appears to be yes!

Certainly if you carry out a momentum transfer calculation for a progressive collapse of a WTC-type tower you can obtain numbers close to the accelerations I quoted.

But there is something to add, if you estimate the energy to collapse a floor and estimate E1 on the behavior in the first few seconds then its value is based on demolished stories. Now assume that a demolished story requires E1 to collapse and an intact one Ei>E1 then your whole collapse model is in fact a demolition model.

[aggle-rithm]

I don't know how truthers who claim free-fall who say "just look at the video" don't notice things like this:

http://img222.imageshack.us/img222/1648/freefallzd4.jpg

Well, obviously, there are rockets attached to some of the debris to make it fall faster.

(No...really...that's what some of them have said.)

[GregoryUrich]

GregoryUrich:

I am focussing on the first floor failure in WTC 1 because if this is a go, everything else follows - especially the collapse of WTC 2! But if it's a no-go, well, .... we have a problem! Now if I use your mass estimates I believe the upper block of WTC 1 would be about 33,000 tonnes (well down from Bazant's estimate of 58,000 tonnes!) and this mass supplies about 1198 MJ of KE to the structure below assuming the block falls 3.7 meters AT FREE FALL. Now you estimate that a minimum of 758 MJ of energy was consumed by the impact - the final total possibly being 50 MJ higher, say 800 MJ, if all energy sinks are included. This is uncomfortably close to the available energy of 1198 MJ, especially when you consider that the upper section actually tilted (rather than dropped), so that the the effective velocity of the upper block may have been less than the free fall value of 8.5 m/s.

So I would like to see your energy calculations. I still believe the destruction of WTC 1 was a gravity-driven collapse; I would just like to see realistic energy balance calculations to back this up!

Actually, I think 758 is the absolute maximum because I am using 304 MJ for comminution of concrete to the extent that wouldn't occur until much further down. Again, I get the value from Ross who I believe used your value. Do you think that's reasonable? I'm also using 85 MJ of elastic energy that is mostly stored and returned in inelastic buckling. Then there are all the assumptions in favor of survival...remember this post (http://forums.randi.org/showthread.php?postid=3486921#post3486921)?

I think a more realistic value would be closer 400 MJ, but of course I'll need to motivate it. Uhg!

I think we have to be careful and not mix the collapse continuation problem with the general energy problem. I think the general energy problem can be done on a floor by floor basis as long as continuation is proven, but continuation involves both the upper and lower parts as energy sinks and temporary storage (elastic PE).

[Apollo20]

Gregory:

I agree that GR used one of my earlier estimates for concrete comminution ... I would say 300 MJ maybe a little high, but I also think your inelastic buckling number may be too low.

Anyway, I certainly would like to see your detailed calculation because once all the numbers are determined (as best as is realistically possible) it is possible to calculate the rate of collapse of WTC 1 & 2 and compare the results with observations (at least for the first 3 or 4 seconds of motion).

[jaydeehess]

Gahhhh

"Near" free fall again!

I am "nearly six feet tall, 92% of six feet tall in fact.
If an average height for a cauccsoid north american male is 5'8" then I am just over 97% of that.

well now that makes me feel a lot better, all this time I thought I was significantly shorter than average. Turns out that using 'truther' math I can be considered of average height.

I am also 10% heavier than my optimum weight (according to a chart in my doctor's office). Turns out that using truther math I am close enough to call it even.
Well now I feel better!

"Near" doesn't count for anything except in horse shoes and hand grenades.

[boloboffin]

I don't know how truthers who claim free-fall who say "just look at the video" don't notice things like this:

http://img222.imageshack.us/img222/1648/freefallzd4.jpg

Wonderful illustration.

[GregoryUrich]

Gregory:

I agree that GR used one of my earlier estimates for concrete comminution ... I would say 300 MJ maybe a little high, but I also think your inelastic buckling number may be too low.

Anyway, I certainly would like to see your detailed calculation because once all the numbers are determined (as best as is realistically possible) it is possible to calculate the rate of collapse of WTC 1 & 2 and compare the results with observations (at least for the first 3 or 4 seconds of motion).

Ross assumed buckling on both floors in the inital impact. I've used Newton's Bit's number for the inelastic buckling which I believe is pretty close. Remember, in this context it's only for one floor. NB does have an error in his derivation but he uses a larger cross-sectional area for the steel than is given in the NIST SAP2000 data so it balances out. I'm going to calculate it again just to be sure. Eventually I'll get around to formatting all those ugly formulas.

[rwguinn]

Ross assumed buckling on both floors in the inital impact. I've used Newton's Bit's number for the inelastic buckling which I believe is pretty close. Remember, in this context it's only for one floor. NB does have an error in his derivation but he uses a larger cross-sectional area for the steel than is given in the NIST SAP2000 data so it balances out. I'm going to calculate it again just to be sure. Eventually I'll get around to formatting all those ugly formulas.

You keep saying Newtons Bit has an error in his derivation, yet you continually refuse to show where...
Lets see some numbers and calculations, please.

[Newtons Bit]

You keep saying Newtons Bit has an error in his derivation, yet you continually refuse to show where...
Lets see some numbers and calculations, please.

He's correct, I do. And he's the one who found it too.

[rwguinn]

He's correct, I do. And he's the one who found it too.
Where?
I fully admit I am not a buckling expert. I still want to see it!

[R.Mackey]

My latest submission (http://www.cool-places.0catch.com/docs/FalaciousCdArguments2_14.pdf) to the Journal of 9/11 Studies.

...more truth from a "truther".

Along with your derivation on the inevitability of gravity-driven collapse, I find this well done. I'll be interested to see what the JONES does with it, since it openly contradicts several of their earlier whitepapers.

Regarding the energy difference, it would be reasonable to use the acceleration seen at initiation to estimate the actual resistance offered by the structure, and compare that to the upper bound you propose here. Naturally the real structure is tough to model, with effects like the tilt producing penetration rather than equal loading of all columns, and weakening of the structure immediately below initiation from fire and preexisting damage, so I wouldn't be surprised to find a factor of two or so difference between them.

The only thing I'm worried about is that some less rational Truth Movement supporter will take this comparison, and then say "see! It was weaker than it should have been! Explosives must have been used!" and thereby totally misunderstand the value of a bounding envelope. Not to mention never explaining why the NWO would bother planting bombs if the structure was going to fall anyway -- just, evidently, not fast enough.

Or perhaps I underestimate them. :o

[einsteen]

I'm such a less rational Truth Movement supporter Ryan.

Assume you have a long wooden table and a wooden block which you give some speed it will stop at a certain time because of the frictional force which is opposite to the direction of movement. Now someone oiled the table and the block doesn't stop and falls from the table. What you now are saying is: This is a very unique table, let's see if this is possible by looking at the deceleration of the wooden block in the beginning. This is of course physically a complete different situation but it shows the invalidity of the method. Alternatively if the collapse was assisted what would be the difference in speed ?

[e^n]

Alternatively if the collapse was assisted what would be the difference in speed ?

Please be more specific.

[einsteen]

Please be more specific.
Glad that you agree with the other part of the post e^n, you're improving!
What do you want me to post, how specific needs one to be ? If you demolish the core from the top to 1/3 how would the falling mass behave ?

[Dave Rogers]

Assume you have a long wooden table and a wooden block which you give some speed it will stop at a certain time because of the frictional force which is opposite to the direction of movement. Now someone oiled the table and the block doesn't stop and falls from the table. What you now are saying is: This is a very unique table, let's see if this is possible by looking at the deceleration of the wooden block in the beginning. This is of course physically a complete different situation but it shows the invalidity of the method.

If I understand your analogy correctly, even in this totally unrelated case your conclusion doesn't follow from your reasoning. What Ryan Mackey is suggesting is this, in your analogy:

We can measure the actual rate of deceleration of the wooden block. From this, we can determine the coefficient of friction of this specific wooden block against this specific table. We can make some estimate of what the coefficient of friction of wood on wood should be, although the precise value depends on the surface of the specific block of wood. If we then compare the two results, we can see whether the coefficient of friction we've measured looks reasonable.

Unfortunately, your analogy breaks down very badly here. Firstly, Mackey is suggesting comparing a measurement with an estimate to see whether the two are consistent. I don't know of any way to estimate a coefficient of friction from first principles, so in your analogy there's no equivalent of Gregory Urich's calculation of the resistance of the structure. Secondly, pushing a block of wood along a wooden table typically tends not to cost several billion dollars, so you'd find it trivially easy to perform the analogue to crashing an identical airliner into an identical building to see what happens, multiple times if necessary. That's a luxury we don't have in reality.

Finally, of course, there's the question of whether a block of wood slides a greater or a lesser difference along an oiled table compared to an un-oiled one. I suspect the oil would make a varnished table stickier and slow the block down.

Bottom line: analogies are good for illustrating a point, but useless for proving one.

Dave

[einsteen]

Dave, perhaps oil is not the best example, but let's assume there is
some stuff that decreases the friction.

Which two results are you comparing ? Of course they compare very well
because they are both based on a table with that stuff on it.
If you conclude the deceleration is insufficient in the beginning (measure #1) and the wood falls from the table (measure #2) then it is consistent with each other, of course... sigh...because....same table, same stuff.

This is no example in which you use the energy to compact the stories derived from first principles, but an example in which you look at the drop to estimate your energy. Well that drop occurs, we saw it didn't we, let's draw conclusions from it. Of course that is consistent with the rest of the collapse. This is a kind of methodical error.

[Dave Rogers]

This is no example in which you use the energy to compact the stories derived from first principles, but an example in which you look at the drop to estimate your energy. Well that drop occurs, we saw it didn't we, let's draw conclusions from it. Of course that is consistent with the rest of the collapse. This is a kind of methodical error.

What Ryan Mackey is suggesting is that Gregory Urich calculate the energy to collapse a storey from first principles, based on the known failure properties of steel, then compare it with the energy absorption required to give the observed deceleration. Did you not understand that?

Dave

[einsteen]

I looked at his preprint and I though that he based it on the estimated collapse times etc. I was referring to “it would be reasonable to use the acceleration seen at initiation to estimate the actual resistance offered by the structure,” but if Gregory is doing it from first principles then it is great! That will be difficult because you need to take the complexity of the structure into account. Dave do you know what also strange is, if you measure the drop and on the hand you conclude it is 0.5 GJ but on the other hand you say that the drop is due to funneling of floors and breaking the connections only then those connections are frigging strong, but that's an other story.

[Dave Rogers]

Dave do you know what also strange is, if you measure the drop and on the hand you conclude it is 0.5 GJ but on the other hand you say that the drop is due to funneling of floors and breaking the connections only then those connections are frigging strong, but that's an other story.

You're trying a little too hard to find fault here. We know that the column-on-column model is vastly oversimplified. A model that considered floor connections and funnelling only would be even more vastly oversimplified, because it would leave the columns all still standing, and it's clear that they wouldn't be stable without the lateral bracing of the floor trusses. So any model that's based on floor connections separating would then have to consider the unbraced column failures separately, because they would also retard the fall of the upper block.

Dave

[GregoryUrich]

Where?
I fully admit I am not a buckling expert. I still want to see it!

Actually I think it was Tony Szamboti or Gordon Ross that found the error. NB assumes an rotation 30 degrees for each of three buckle points in his formula for calculating Ubend, but uses Pi/12 = 15 degrees. This gives half the energy. I think he should be using Pi/3 for the total rotation because once the middle buckle reaches 30 degrees then the other buckles will only be a 15 degrees. He ends up with Pi/4 for the total rotation which decreases the energy by 1/3. However his cross-sectional area is about 50% larger than the actual value from the SAP data so it balances out for an effective length factor slightly less than 1. The upper bound would be for an effective length factor of 0.7 for fixed ends which is probably what I will use. In the context of continued collapse I don't think it will be significant.

One thing I think some people are missing is that the columns probably failed one or a few at a time due to the tilting so a huge impulse as in the Bazant model was not necessary. Accounting for the tilting will be a pain in the butt but I'll try and find a decent way of dealing with it.

[R.Mackey]

I'm such a less rational Truth Movement supporter Ryan.

You are, indeed, a less-rational Truth Movement member. Dave Rogers has you covered, but let me try again anyway.

What GregoryUrich has calculated is the expected power the lower structure exerts during the initial phases of collapse. However, in order to do so, he is forced to use several simplifying assumptions, ones that we know bias his estimate upwards. What he's computed is a theoretical upper limit. This is sufficient to answer the question of whether or not a total collapse is expected, and it is, confirming prior results by Bazant, Seffen, Greening, and so on.

Dr. Greening observed that the actual collapse initiation happened quickly. From this, one can estimate the actual power exerted by the structure.

The first is theory. The second is experiment.

We don't expect them to match, because again, we know the real-life situation did not proceed according to Gregory's model. We know, for instance, that impact and heat damage would have reduced the lower structure's strength versus the "ideal" figure he computed. We also know that tilting creates an oblique impact, destroying floors and thus the columns' bracing, which also reduces their ability to oppose collapse. We further know that tilting induces fracture of connections, as discussed above.

What we can do, however, is check to see just how close the simplified model is to reality, in a quantitative sense, by comparing the two results.

Your objection, that this discrepancy implies "invalidity of the method," is a steaming load of crap. Gregory's model is far from perfect, but it is a valid upper estimate, and thus it is sufficient to answer the question for which it was designed. The qualitative result of his model is correct. It is the quantitative error we are attempting to estimate.

You have commited what I have suggested (http://forums.randi.org/showthread.php?postid=3483830#post3483830) we name the "qualitative-quantitative" logical fallacy. Please try to understand the difference between the two questions asked, and understand that inaccuracy in the latter does not cast doubt upon the former.

No explosives are needed. This result confirms it. QED.

[einsteen]

I'm not sure if your reply has to do with what I was saying. If you derive the collapse energy from first principles then it's fine to compare it with the collapse behavior at the beginning. I was not talking about a discrepancy implying "invalidity of the method". I only said that the total collapse time is expected (within error margins) if you estimate the collapse energy empirically based on the first movement, you compare B1 with B2, even if they differ there is no reason to reject your model because the collapse energy is not constant for each story. I only said that if A1 and A2 are the gravity driven results they are unknown unless someone derives a C1 from first principles. Greening did it and came with 0.63GJ based on Wierzbicki's radial plane impact and Bazant before used 0.5GJ without derivation.

[Newtons Bit]

Actually I think it was Tony Szamboti or Gordon Ross that found the error. NB assumes an rotation 30 degrees for each of three buckle points in his formula for calculating Ubend, but uses Pi/12 = 15 degrees. This gives half the energy. I think he should be using Pi/3 for the total rotation because once the middle buckle reaches 30 degrees then the other buckles will only be a 15 degrees. He ends up with Pi/4 for the total rotation which decreases the energy by 1/3. However his cross-sectional area is about 50% larger than the actual value from the SAP data so it balances out for an effective length factor slightly less than 1. The upper bound would be for an effective length factor of 0.7 for fixed ends which is probably what I will use. In the context of continued collapse I don't think it will be significant.

One thing I think some people are missing is that the columns probably failed one or a few at a time due to the tilting so a huge impulse as in the Bazant model was not necessary. Accounting for the tilting will be a pain in the butt but I'll try and find a decent way of dealing with it.


Greg... the effective length factor for a column in a moment frame is a minimum of 1. It can be no lower. There is a vast difference between fixed ends (i.e. supports) that the columns in the towers did not have, and fixed connections, which means that they can SWAY.

[rwguinn]

Actually I think it was Tony Szamboti or Gordon Ross that found the error. NB assumes an rotation 30 degrees for each of three buckle points in his formula for calculating Ubend, but uses Pi/12 = 15 degrees. This gives half the energy. I think he should be using Pi/3 for the total rotation because once the middle buckle reaches 30 degrees then the other buckles will only be a 15 degrees. He ends up with Pi/4 for the total rotation which decreases the energy by 1/3. However his cross-sectional area is about 50% larger than the actual value from the SAP data so it balances out for an effective length factor slightly less than 1. The upper bound would be for an effective length factor of 0.7 for fixed ends which is probably what I will use. In the context of continued collapse I don't think it will be significant.

One thing I think some people are missing is that the columns probably failed one or a few at a time due to the tilting so a huge impulse as in the Bazant model was not necessary. Accounting for the tilting will be a pain in the butt but I'll try and find a decent way of dealing with it.

Well, Doh! I missed it too. Thanks
I was thinking you were looking at his effective length calcs, which people I know and trust seem to agree with as being 1, rather than <1
The simulation is indeed biased in favor of non-collapse for just the reason you state, although not necessarily due entirely to tilting--load paths change very quickly under non-design loads, and parts initially fail one at a time (where dT>0, but still small). After that, how small a time division is "simultaneous"?:D
Its a domino effect...

[GregoryUrich]

I have updated my article (http://www.cool-places.0catch.com/911/FalaciousCdArguments2_14.pdf) and submitted it to the Journal of 9/11 Studies.

[jaydeehess]

Here are some MEASURED data for WTC 1, (taken from the Sauret video):

Time (s); Drop(m); Accel(m/s^2)

t d acc %g
------------------
0; 0; 0 0
0.5; 1.0; 8.0 87
1.0; 4.2; 8.4 91
1.5; 8.3; 7.4 80
2.0; 14.0; 7.0 76
2.5; 20.0; 6.4 70
3.0; 27.6; 6.1 66

Now is this near "free fall" or not?

Added a column

a rough average of 75% the accelleration due to gravity