OK, so how do thermite demolitions work again?

[tempesta29]

Let's assume that the structural resistance is about 10% of the overall retardation.

I love how these conclusive analyses are predicated on such baseless assumptions.

I have an idea: the wicked crash zones which caused the most heinous structural failures in human history should actually have been capable of producing measurably less resistance than pristine, untouched, over-engineered steel and concrete.

 

[A W Smith]

I love how these conclusive analyses are predicated on such baseless assumptions.

I have an idea: the wicked crash zones which caused the most heinous structural failures in human history should actually have been capable of producing measurably less resistance than pristine, untouched, over-engineered steel and concrete.

knock yourself out dude
http://www.tutor4physics.com/workenergy.htm

 

[adkinsjr]

I love how these conclusive analyses are predicated on such baseless assumptions.

It isn't baseless,

Referring to Frank Greening's work at http://www.911myths.com/WTCREPORT.pdf, an estimate of retardation times gives 2.4 seconds for momentum conservation and 0.2 seconds for WTC1, indicating that momentum conservation is in fact the dominant term.

So go ahead and redo the calculation using your own figure then. Make it as high as you want, using the information above.

I've done it...

 

[GlennB]

Oh does it? A 15% percent reduction in load bearing capacity of the crash zone caused a sudden collapse did it? This building was way over-engineered. Are you implying that a 15% increase in load would have caused this building to just collapse on itself?

If you had bothered reading properly you'd have noticed this was the estimated reduction in strength caused by aircraft impact alone. At which point the building was still standing, as we saw. Fire then further weakened it to the point of collapse.

 

[tsig]

Oh does it? A 15% percent reduction in load bearing capacity of the crash zone caused a sudden collapse did it? This building was way over-engineered. Are you implying that a 15% increase in load would have caused this building to just collapse on itself?

And then I could point out how unscientific your "reasonable" assessment is, but that seems unnecessary.

You're right. It's well known that engineers are denser than others and there were far too many of them in the towers so when a plane (hologram) flew by they all ran to one side to look causing the towers to fall.

 

[davefoc]

I just read through the report linked to above by F. R. Greening.

A few comments about the article:
I understood the arguments about how the fall times were determined by the momentum of the falling and stationary flows and how predicted fall times were determined based on this method that were in agreement with the fall times measured by visual analysis and analysis of the seismic data.

I did not understand as well the energy based arguments for why the strength of the structure played only a small role in reducing the collapse times. However even if the analysis was off by a fairly large amount it appears that the fall times would still not have been greatly affected by the structural strength of the building.

I was surprised that the author was not in agreement with what I thought was principal theory for the cause of the collapse, the heating and weakening of the floor joists that caused vertical columns to buckle. His theory was that the damage done by the airplanes was enough to weaken the support for a localized area of the building which thereby caused unbalanced loading on the remaining columns which was sufficient to start a chain reaction once the buckling of the asymmetrically loaded columns was above a certain amount. Without taking the time to work through his calculations, this idea struck me as very plausible. It is easy to imagine that an evenly distributed 30% reduction in the support structure for a floor would not weaken it enough to cause a collapse, but if that reduction in the support structure was concentrated in a particular area the load on the columns next to that area might be enormous as building tilt focused the load of the structure above the damaged floor to the remaining columns next to the area with destroyed columns.

A few questions for tempesta29 based on the above:
1. Have you read the report?
2. If you have read the report to what degree do you understand the calculations?
3. If you have read and understood the report, have you done your own calculations to determine whether Greenings assumptions that the strength of the structure played only a small role in retarding the acceleration of the collapsing structure are correct? If you have, what were the results of those calculations and what is the time that your calculations predict for the collapse?
4. You seem to have rejected the possibility that the building's collapse could have been caused by either the destruction of the support columns or the weakening of the steel due to the fires. Have you done calculations that predict how many columns in a particular area needed to be destroyed or damaged before asymmetrical loading caused by building tilt would have caused the building to collapse? Have you done calculations on the effect of the weakened steel on the columns compressive strength and the effect of floor joist weakening on the structure from the fires?

I assume, based on the answers provided so far in this thread, that you have not done your own calculations. There is nothing wrong with that, I didn't either. But there is a difference. I suspect that the guy who wrote the report is right and I suspect that the report has been widely circulated and that if there were significant errors in the calculations they would have been found and noted by various people who have read the report. You think the guy is wrong. That's fine there's nothing wrong with that. I think lots of people aren't right about a lot of stuff. But when somebody backs up his theories with calculations and data the only intellectually honest way to disagree with him is by finding errors in his analysis or his data and you don't seem to have done that and you don't seem to have any inclination to do that. And that is fine also, but do you understand that means that your disagreement has no credibility and no probative value that goes to the cause of the World Trade Center collapse?

 

[Seymour Butz]

It is easy to imagine that an evenly distributed 30% reduction in the support structure for a floor would not weaken it enough to cause a collapse, but if that reduction in the support structure was concentrated in a particular area the load on the columns next to that area might be enormous as building tilt focused the load of the structure above the damaged floor to the remaining columns next to the area with destroyed columns.

NIST details exactly this in their post plane impact analysis.

2 was hit off center, and their study indicates, and they even state, that 2 was much closer to collapse because of this and the greater velocity of that plane.

This also explains why 2 fell first - less fire damage was necessary to weaken it to the point of total collapse.

 

[TJM]

allegedly

 

[Dave Rogers]

Oh does it? A 15% percent reduction in load bearing capacity of the crash zone caused a sudden collapse did it? This building was way over-engineered. Are you implying that a 15% increase in load would have caused this building to just collapse on itself?

No. Read the NIST report if you want to understand the reasons for collapse initiation. Your argument was that the section damaged by the airliner should have presented less resistance than the undamaged section, in case you've forgotten. The collapse was initiated by progressive creep and bowing at the top of the impact-damaged section. If you want to argue that there whould have been an initial acceleration close to 1g as the top block falls through the height of the initial column failures, please feel free; then go back to Chandler's data and you'll find that there appears to be a very brief period of greater acceleration over the first one or two points. This is largely due to uncertainty in when to define the moment of initiation of the collapse, but the point is that there is no reason to suspect that this initial period of higher acceleration didn't happen. The next few storeys were damaged by the aircraft impact, but collapse through these less seriously damaged regions will give a negligible reduction in acceleration.

And then I could point out how unscientific your "reasonable" assessment is, but that seems unnecessary.

No, please go ahead and show me how your unsupported guesswork is more scientific than my order-of-magnitude estimate. I could do with a good laugh.

Dave

 

[jaydeehess]

The fact that any man of adequate intelligence can, with a straight face, tell another man that steel and concrete that is so badly damaged that it causes this kind of epic failure will provide negligibly less resistance than structure untouched by any weakening agents--the fact that someone can peddle this garbage and mean it is just sad.

Want a personal example of the power of dynamic forces?
take a 1/4" nut and place it on the top of your head. You could keep it there for years and never have a problem with it.

Now have a friend (?) drop it on your head from 8 feet up.
It will hurt. It may even draw blood. How is it possible that a mere 1/4" nut could cause such damage"

Now, do not try this next one but think about it.

Determine the max load you can hold on your head using your arms only to keep it balanced. This would be around 100 pounds. Divide by 10. You could walk about with a 10 pound weight on your head with no problem for a long time. Now this friend(?) is to drop this load from 8 feet up. You will be lucky not to have your neck snap.

 

[jaydeehess]

Your analysis was nothing more than a mass of assumptions, one of which found based on some anti-9/11 truth website.

You have been presented with a senario derived by NIST and other structural engineers whose education and training allows them to make such determinations. These are not anti-9/11 'truth' websites.

Rather than consider the senario given you attempt to call them into question based upon your uneducated, untrained, personal incredulity. More than that you appear to bask in the fact that you have not the training or education, indeed you are lacking in basic math skills, and try to tell us that THIS is the way to investigate technical matters.

Amazing, truly amazing, it would be even more so were you alone in this illogical manner of thinking.

 

[tempesta29]

Want a personal example of the power of dynamic forces?
take a 1/4" nut and place it on the top of your head. You could keep it there for years and never have a problem with it.

Now have a friend (?) drop it on your head from 8 feet up.
It will hurt. It may even draw blood. How is it possible that a mere 1/4" nut could cause such damage"

Now, do not try this next one but think about it.

Determine the max load you can hold on your head using your arms only to keep it balanced. This would be around 100 pounds. Divide by 10. You could walk about with a 10 pound weight on your head with no problem for a long time. Now this friend(?) is to drop this load from 8 feet up. You will be lucky not to have your neck snap.

This doesn't address my point at all. My point is that a mass will only accelerate at a constant rate through a path of resistance if that resistance itself is constant. We know with absolute certainty that the resistance would not have been constant had the upper sections actually been responsible for destroying the lower sections. I hear ad nauseam how badly damaged these crash zones were. 1800+ degrees F right? Yet they provide no less resistance than the undamaged structure below? Impossible.

 

[Julio]

This doesn't address my point at all. My point is that a mass will only accelerate at a constant rate through a path of resistance if that resistance itself is constant. We know with absolute certainty that the resistance would not have been constant had the upper sections actually been responsible for destroying the lower sections. I hear ad nauseam how badly damaged these crash zones were. 1800+ degrees F right? Yet they provide no less resistance than the undamaged structure below? Impossible.

And how much resistance you say the structure should have provided? Care to show a magnitude (and the related math)?

 

[jaydeehess]

This doesn't address my point at all. My point is that a mass will only accelerate at a constant rate through a path of resistance if that resistance itself is constant. We know with absolute certainty that the resistance would not have been constant had the upper sections actually been responsible for destroying the lower sections. I hear ad nauseam how badly damaged these crash zones were. 1800+ degrees F right? Yet they provide no less resistance than the undamaged structure below? Impossible.

Yes I have, in the past, addressed EXACTLY this point.
The fact is that the falling mass was not appreciably impacting the COLUMNS of the towers..
I asked you before what mechanism could be envisioned by which the bulk of the forces of that falling mass would be transfered to the columns.

You have been silent on this issue. I predict you will remain so.

Why is this point important? Because the ability of any individual floor pan to support a load is essentially the same from the second floor to the 110th. It was the floor pans that were destroyed ahead of the column systems. without the floor pans and trusses the columns were long unbraced structures and failed due to long column stresses AND extreme buffeting by falling debris.

As such the collapse zone acelerrates at the same rate all the way down as it would be expected to.

 

[tfk]

tempesta,

I love how these conclusive analyses are predicated on such baseless assumptions.

The original citation provided links to Greening's analysis. Sorry you couldn't find it.

I have an idea: the wicked crash zones which caused the most heinous structural failures in human history …

There was nothing "heinous" about the collapse. It was steel doing what steel does under those circumstances.

The heinous part was hijacking & flying a jet into the building.

… should actually have been capable of producing measurably less resistance than pristine, untouched, over-engineered steel and concrete.

Please explain to me at what point the descending upper block crashed into a structure that was "pristine, untouched, over-engineered steel and concrete".

Let's examine the upper block hitting the 50th floor as an example.

When the upper block hit the 53rd floor, it ripped out the columns joined to the tops of 1/3rd of the columns for the 50th floor. (1/3 of the 3-story core & peripheral columns reached from the 53rd to the 50th floor.) Ripped the columns & their lateral supports out rather bluntly & violently.

When the upper block hit the 52st floor, it destroyed 1/3rd of the supports for the 50th floor. (1/3 of the 3-story core & peripheral columns reached from the 52nd to the 49th floor.) Ripped the columns & their lateral supports out rather bluntly & violently.

When the upper block arrived at the 51st floor, another 1/3rd of the supports for the 50th floor were ripped away. (1/3 reached from the 51st to the 48th floors.) Ripped the columns & their lateral supports out rather bluntly & violently.

So when the upper block arrived at the 50th floor, fully 2/3rds of the column supports (both core & peripheral) and attached trusses had already been ripped out of that floor. The columns attached to the remaining 1/3rd of the supports from above also had been violently ripped away.

So, please explain to me: at what point the descending upper block crashed into a structure that was "pristine, untouched, over-engineered steel and concrete".

tk

 

[twinstead]

So, please explain to me: at what point the descending upper block crashed into a structure that was "pristine, untouched, over-engineered steel and concrete".

I don't normally bump, but I'd like an answer to this too from tempesta.

 

[tfk]

This doesn't address my point at all. My point is that a mass will only accelerate at a constant rate through a path of resistance if that resistance itself is constant. We know with absolute certainty that the resistance would not have been constant had the upper sections actually been responsible for destroying the lower sections. I hear ad nauseam how badly damaged these crash zones were. 1800+ degrees F right? Yet they provide no less resistance than the undamaged structure below? Impossible.

No, it's not impossible. It's certain.

Big picture first.

1. The "resistance" offered by each floor is due primarily to …
a) column strength of each floor?
or
b) inertia of each floor?

2. The inertial resistance of each floor depends upon that portion of the mass of each floor that gets incorporated into the descending block. This mass …
a) gets larger for the lower floors?
or
b) stays approximately the same for all floors?
___

The latticework support assembly consisted of:

the core columns
the core lateral beams
the peripheral columns
the diagonal bracing on the mechanical floors
the concrete floors
the spandrel plates
the spandrel to spandrel welds
the trusses
the inner & outer truss seats
the truss to seat bolts
the outer truss seat to spandrel welds
the inner truss seat to core beam welds
the column to column bolts
bolts & welds for the diagonal bracing on the mechanical flors
___

In the list above, which components of this support assembly - exactly - were bigger & stronger in the lower floors as compared to the upper floors?

Which components of the support assembly - exactly - stayed about the same size & strength?

Which components of the support assembly - exactly - had to be destroyed during the disassembly of each floor in order for the collapse to continue? Which components were destroyed? Which components were left relatively intact after the collapse?

Of the massive components (#1 thru #6 in the list), which components were incorporated into the descending block? Which ones were not?
___

Are you getting a raging clue yet?

tk

 

[chipmunk stew]

But Richard Gage says it's like dropping a small cardboard box on top of a big one!

 

[twinstead]

Well, if Gage says it, I'll buy it!

 

[Dave Rogers]

Well, if Gage says it, I'll buy it!

Only if you can afford it.

Dave