WTC: Rate of Fall (rate of crush)

The above is as lucid and impartial an appraisal as I have seen you do thus far.
I have a long history of criticizing Bazant, it's just that circumstance usually puts me in the position of defending him.

I am now curious to hear your take on the NIST WTC 7 report's omissions of critical structural features in its collapse initiation analysis.
Uhh... can I just leave it as "I'm no fan of NIST, either"? I do like their online engineering toolbox.
 
It's a fair enough request, but I'll summarize: (most of) the issues surrounding WTC7 are well outside my ability to analyze. So all I have are a few opinions about this and that, and opinions like that are basically worthless. About the only criticism I have that would probably hold water is that I feel their physics simulation displayed excessive ductility, which is why it wrinkled up like a beer can. This, you'll note, is the same criticism I have of your partner's three hinge FEA, though to different result.

I am now curious to hear your take on the balance of criticisms I've leveled against the Some Misunderstandings paper. But, before that, I'd like to yield the floor to qed, who's had outstanding questions to you for some time which you've opted to ignore.
 
It's a fair enough request, but I'll summarize: (most of) the issues surrounding WTC7 are well outside my ability to analyze. So all I have are a few opinions about this and that, and opinions like that are basically worthless. About the only criticism I have that would probably hold water is that I feel their physics simulation displayed excessive ductility, which is why it wrinkled up like a beer can. This, you'll note, is the same criticism I have of your partner's three hinge FEA, though to different result.

I am now curious to hear your take on the balance of criticisms I've leveled against the Some Misunderstandings paper. But, before that, I'd like to yield the floor to qed, who's had outstanding questions to you for some time which you've opted to ignore.
I haven't taken the time to answer qed's questions because they can be answered by reading the paper.
 
I haven't answered qed's questions because they can be answered by reading the paper. If he doesn't understand the paper, as he claims in some of his questions, then he doesn't have much business asking the kind of questions he is asking.

Maybe you can attempt to answer them as you said you understood the paper very well.

If he doesn't understand the paper, perhaps it's because you don't communicate your point very well?

Don't you have a goal of making your argument accessible and understandable? Surely the clearer it it, the more traction you will get? Don't you want people to understand? Why do you engage on internet forums with lay people like me if you are only interested in convincing "qualified" people?
 
I discovered this article today - it gives a nice overview of why "truther physics" is a myth.
Dave Thomas' theory on why there is no observed deceleration in the North Tower completely disregards and does not account for column energy dissipation, as right from the start he has the fall accelerating at free fall between floor impacts, which is impossible in a natural collapse with column resistance.

Thomas also quotes Zdenek Bazant, whose papers on the WTC tower collapses have been shown to be fraudulent due to his extreme embellishment of the kinetic energy available, by his use of free fall through the first story and nearly double the actual mass of the upper section, and knowing underestimate of velocity loss due to conservation of momentum and column energy absorption.

Both Thomas and Bazant have been confronted on the above and could not defend what they had said.

So much for your "nice overview". A more legitimate description for it would be "false propaganda". The only thing you seem right about here is that you posted it in the right thread.
 
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If he doesn't understand the paper, perhaps it's because you don't communicate your point very well?

Don't you have a goal of making your argument accessible and understandable? Surely the clearer it it, the more traction you will get? Don't you want people to understand? Why do you engage on internet forums with lay people like me if you are only interested in convincing "qualified" people?
Mick, why do I have the feeling you are being disingenuous here? You seemed plenty capable of understanding the technical details when you actually had an argument to make, like that on the thermal expansion of the beams and actual CTE average over a temperature range on the NIST omissions thread.
 
Mick, why do I have the feeling you are being disingenuous here? You seemed plenty capable of understanding the technical details when you actually had an argument to make, like that on the thermal expansion of the beams and actual CTE average over a temperature range on the NIST omissions thread.
Took me a while though.

The point is that it's best to try to explain without assumptions of knowledge.
 
Took me a while though.

The point is that it's best to try to explain without assumptions of knowledge.
In reality, there is an onus on the reader. Textbooks are written with a presumption of a certain level of knowledge. That is why college courses have prerequisites.

For instance, one should not have to teach someone what the concepts of moment, distance to neutral axis, and moment of inertia are when discussing bending stress on a beam. If the reader does not understand the equation

bending stress = (moment x distance to neutral axis) / moment of inertia

then they really are not up to the level required to participate in that discussion and need to do some work on their own rather than ask those discussing the issue to teach them each and every lower level concept.
 
@Tony Szamboti
I do understand the equation, but I need to know how long you take the initial buckling column to be (in your paper).
The column has buckled due to the pull of the floor and can no longer support it's load.
  • How long is this column?
 
@Tony Szamboti
I do understand the equation, but I need to know how long you take the initial buckling column to be (in your paper).
The column has buckled due to the pull of the floor and can no longer support it's load.
  • How long is this column?
The initial column failure occurred in core of the 98th floor in the North Tower, and the pull-in of the perimeter at the spandrels through the floors would have caused it to be a two story fall.

Bazant talks about a one story fall in his paper from January 2011. The ratio of kinetic energy for a one story fall to the minimum energy absorbed by the columns below of 1.686 MN-m is 0.368. This ratio would be 0.736 for a two story fall. So it does not matter whether the fall was one or two stories, as there still was not enough kinetic energy involved to continue the collapse.

At a bare minimum in a natural collapse of two stories there should have been an enormous deceleration, but there is no deceleration observed at all.
 
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In reality, there is an onus on the reader. Textbooks are written with a presumption of a certain level of knowledge. That is why college courses have prerequisites.

And yet you seem quite happy to discuss things with Ben Swann, who clearly has no relevant knowledge of physics whatsoever.

That aside, I think it would be a reasonable goal for anyone involved in such discussion to provide a pathway to understanding of the points. The onus should not be a certain level of knowledge, but a certain level of intelligence - the ability to look things up. This is not some elite, scientists only, club. And your physics is really not that complicated.
 
@Tony Szamboti
Code:
↓
) 7.4m
  1. Which of your references determine the load displacement response of an initially bowed column subject to an axial load? I ask as I do not have access to all the references.
  2. Am I correct that you prove that if such a bowed column begins collapsing under the weight of the upper section, the response ensures that the column stabilizes (and resumes transfering force to the lower columns) before the mass drops the full 7.4m?
 
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@Tony Szamboti

In your paper you assert that the columns are stout. This appears to be the key distinction with Bazant. I cannot find your justification for this assertion.

  • Please can you justify why a 7.4m SHS of 356mm side length is stout.
 
The initial column failure occurred in core of the 98th floor in the North Tower, and the pull-in of the perimeter at the spandrels through the floors would have caused it to be a two story fall.

Bazant talks about a one story fall in his paper from January 2011. The ratio of kinetic energy for a one story fall to the minimum energy absorbed by the columns below of 1.686 MN-m is 0.368. This ratio would be 0.736 for a two story fall. So it does not matter whether the fall was one or two stories, as there still was not enough kinetic energy involved to continue the collapse.

At a bare minimum in a natural collapse of two stories there should have been an enormous deceleration, but there is no deceleration observed at all.


The North Tower had fire on several floors. The 98th floor was above other floors that had been on fire and thus damaged. Why would one expect a column failure on 98 to be arrested within two stories, when the structure beneath was being weakened prior to that time?
 
The North Tower had fire on several floors. The 98th floor was above other floors that had been on fire and thus damaged. Why would one expect a column failure on 98 to be arrested within two stories, when the structure beneath was being weakened prior to that time?
So how much did the fire weaken the structure?
 
@Tony Szamboti

In your paper you assert that the columns are stout. This appears to be the key distinction with Bazant. I cannot find your justification for this assertion.

  • Please can you justify why a 7.4m SHS of 356mm side length is stout.
First, the stout term applied to the unsupported length of one story tall columns of the towers and then by inference to the impacted columns of a single story below, which is what the energy calculations were done for. The single story perimeter columns actually had an unsupported length between spandrels of 92 inches (2.3m) although the calculations were done for full story height 3.7m unsupported length columns. It was not the columns involved in the initiation as you imply.

Additionally, the perimeter columns involved in a two story initiation did not have a 7.4m unsupported length. The unsupported length there would be the distance between the spandrels over two stories and is 92+52+92 = 236 inches (6.0m). Although it is a moot point, it might be interesting to you to know that a 6m long 14 inch square box column with a .270" wall thickness and fixed at both ends has a slenderness ratio of about 27. That is far from what is considered slender for a structural steel column, and where elastic buckling would occur, which would be a value over 100.

The 3.7m long 14 inch square box column with a .270" wall thickness fixed at both ends would have a slenderness ratio of about 17 and that would be considered stout. The stout column comment also included the core columns which were even more stocky.
 
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So how much did the fire weaken the structure?


It seems to me, that is what you should be telling me. You base a 1 to 2 story arrested collapse on criteria of an undamaged building below the failed component. There was an out of control fire ravaging the floors below the failed component.

If i jump up and down on a piece of brand new 3/4 inch ply wood, it will hold my weight. If the wood is weathered and rotted, i will fall through. Floors below 98 were being "weathered and rotted" by the fire.
 
It seems to me, that is what you should be telling me. You base a 1 to 2 story arrested collapse on criteria of an undamaged building below the failed component. There was an out of control fire ravaging the floors below the failed component.

If i jump up and down on a piece of brand new 3/4 inch ply wood, it will hold my weight. If the wood is weathered and rotted, i will fall through. Floors below 98 were being "weathered and rotted" by the fire.

We actually don't say there was no damage to the floors below. We derated the strength of the floor below to 75% of its intact capacity and the energy absorption was still far above the available kinetic energy to continue the collapse. You can see this on the first paragraph of page 6 of the paper.

It sounds like you feel you are knowledgeable about the strength of steel in fire conditions. So I would hope you know that there are permanent changes in the microstructure when steel is heated to the point where it has lost strength. Can you tell us what evidence NIST had for steel from the twin towers that showed the steel had lost strength?

Don't you think it strange that there is no deceleration observed, given the large energy absorption capacity, even if the damage had been more extensive?
 
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We actually don't say there was no damage to the floors below. We derated the strength of the floor below to 75% of its intact capacity and the energy absorption was still far above the available kinetic energy to continue the collapse. You can see this on the first paragraph of page 6 of the paper.

It sounds like you feel you are knowledgeable about the strength of steel in fire conditions. So I would hope you know that there are permanent changes in the microstructure when steel is heated to the point where it has lost strength. Can you tell us what evidence NIST had for steel from the twin towers that showed the steel had lost strength?

Don't you think it strange that there is no deceleration observed, given the large energy absorption capacity, even if the damage had been more extensive?


No, i don't think that it is strange there was no deceleration observed. I think it is strange that anyone is trying to claim that the Towers collapsed due to anything other than damage as a result of the out of control fires.

The fire was obviously hot enough to affect the strength of the structural steel. Floor to ceiling flames and beyond, poured out the windows. I don't need any explanation from NIST in order to be able to see that for myself. The purpose of insulating the steel, was to protect it from heat due to fire.

The epicenter of collapse in both Towers occurred within the fire zone, not somewhere else in the building.

"We derated the strength of the floor below to 75% of its intact capacity and the energy absorption was still far above the available kinetic energy to continue the collapse."

I think you need to go back and figure out what is wrong with your calculations. There obviously was plenty of kinetic energy to continue the collapse. The top section of the building fell down into the remaining floors like a knife through butter. It wasn't because of Chandler's imagined cutter charges.
 
No, i don't think that it is strange there was no deceleration observed. I think it is strange that anyone is trying to claim that the Towers collapsed due to anything other than damage as a result of the out of control fires.

The fire was obviously hot enough to affect the strength of the structural steel. Floor to ceiling flames and beyond, poured out the windows. I don't need any explanation from NIST in order to be able to see that for myself. The purpose of insulating the steel, was to protect it from heat due to fire.

The epicenter of collapse in both Towers occurred within the fire zone, not somewhere else in the building.

"We derated the strength of the floor below to 75% of its intact capacity and the energy absorption was still far above the available kinetic energy to continue the collapse."

I think you need to go back and figure out what is wrong with your calculations. There obviously was plenty of kinetic energy to continue the collapse. The top section of the building fell down into the remaining floors like a knife through butter. It wasn't because of Chandler's imagined cutter charges.
All I can say to this, based on your comments, is that there is no science behind your thinking and that you are just believing what you want to believe.

Actually, the collapses in both towers initiated on floors which were just above the major aircraft impact damage. Even NIST admits that to be true. See http://www.journalof911studies.com/volume/2008/FentonWTCInitiationFloors.pdf
 
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Yes, there is massive weight acting straight down and there is equally massive force holding it up. But if the centre of gravity of the top gets shifted enough to one side then its possible for it fall unimpeded over the side. I'm assuming some perimeter columns would fail first so the sideways motion is introduced as it pivots on the core structure.

What you describe here is correct, the centre of gravity shifts. However, for sidesway to occur in the manner that you are referring to, a lot of rotation needs to happen in the perimeter of the building. For rotation to happen you need tough joints. The perimeter columns were bolted very lightly ( 4 bolts?) - they could not accommodate the tensions generated from the huge rotations that you expect, so they would have failed, leading to a downward fall rather than lateral movement.
 
All I can say to this, based on your comments, is that there is no science behind your thinking and that you are just believing what you want to believe.

Actually, the collapses in both towers initiated on floors which were just above the major aircraft impact damage. Even NIST admits that to be true. See http://www.journalof911studies.com/volume/2008/FentonWTCInitiationFloors.pdf


Yes, the collapses occurred within the fire zone, as i said.

You are believing what you want to believe. Both Towers were under major assault from out of control fires, which resulted in the collapse of each Tower. That is science based. Controlled demolition has no science to back it up.
 
Yes, the collapses occurred within the fire zone, as i said.

You are believing what you want to believe. Both Towers were under major assault from out of control fires, which resulted in the collapse of each Tower. That is science based. Controlled demolition has no science to back it up.
It is apparent that you have nothing to contribute to the discussion here other than your opinion. If you are fair minded you would refrain from trying to make unsupported claims.
 
The bottom line here is that a natural one or two story fall of the 12 story upper section of the North tower would have arrested due to the column energy absorption being greater than the kinetic energy available.

Bazant deceptively embellishes kinetic energy and underestimates column energy absorption in a surreal fashion, to even make his hypothesis plausible. It isn't just a small engineering disagreement.

Sorry Tony but the bottom line is the building had clearly distorted and continued to distort as the collapse initiated. The idea of the upper columns somehow perfectly landing on the lower columns is a nice theoretical idea but it completely ignores reality and the recorded video evidence when you look closely at the various photo studies done.

The column capacity is irrelevant here. I would suggest you look closely at the floor truss connections which had little redundancy.

I also suggest you listen to this interview by Thornton (who eats towers for breakfast).

Pretty much sums it up, but I would only agree with him to the point that the towers were "crap" in accommodating the scenario that they encountered.

The design was lightweight, elegant, conceived in more innocent times.
 
Sorry Tony but the bottom line is the building had clearly distorted and continued to distort as the collapse initiated. The idea of the upper columns somehow perfectly landing on the lower columns is a nice theoretical idea but it completely ignores reality and the recorded video evidence when you look closely at the various photo studies done.

The column capacity is irrelevant here. I would suggest you look closely at the floor truss connections which had little redundancy.

I also suggest you listen to this interview by Thornton (who eats towers for breakfast).

Pretty much sums it up, but I would only agree with him to the point that the towers were "crap" in accommodating the scenario that they encountered.

The design was lightweight, elegant, conceived in more innocent times.


The main floor trusses were 32 inches deep and there were two of them together (double trusses) every 80 inches with 24 inch deep bridging trusses every 13 feet. The trusses were also made composite with the floor slab and had two layers of welded wire fabric which was equivalent to a 9/16" diameter rebar in each direction in each square foot of floor slab. The floors outside of the core were a substantial structure. My calculations show they would only sag 2 inches at 700 degrees C. It is also true that the floors could take a static load of about 12 times their own weight. The NIST FAQ admits this but tries to claim the entire upper section weight was applied suddenly to the floor which would double the stress. That is nonsense. A 12 story 73 million lb. mass does not move laterally while falling without a significant lateral load on it. There was no lateral load on the upper section during the early stages of the collapse and it would have fallen in place, with real column impacts occurring in a natural collapse. We would have at least seen an enormous deceleration.

I see nothing but unsupported conjecture from people like Charlie Thornton. The NIST model couldn't pull the perimeter columns inward due to truss sagging, so they applied an artificial lateral load to the columns. So according to people like Charlie Thornton and the NIST authors the buildings came down due to fictitious lateral loads. That is the real crap we are dealing with here.

Do some calculations of your own and stop listening to conjecture like what Charlie Thornton is spouting here about crappy design. It simply is not true and calculations prove it isn't.
 
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Nothing but unsupported conjecture from both you and Charlie Thornton. The NIST model couldn't pull the perimeter columns inward due to truss sagging, so they applied an artificial lateral load to the columns. So according to people like you, Charlie Thornton, and NIST the buildings came down due to fictitious lateral loads. That is the real crap we are dealing with here.

The main floor trusses were 32 inches deep and there was two of them together (double trusses) every 80 inches with four bridging trusses and were also made composite with the floor slab. The floors outside of the core were a substantial structure. My calculations show they would only sag 2 inches at 700 degrees C and the shear connections at their ends would have had little stress.

Tony,

It's supported in hundreds of photos and videos which I'm sure you've seen. I can post some if you want, just tell me what isn't clear.

Do we really care what NIST says? Even the original FEMA report has enough photos to make up your own mind on the subject. You seem to be an engineer. Look at the photos. There was visible Euler buckling occurring at the perimeter columns (which gradually worsened over time, as shown in the photo timeline). There was a gaping hole under the upper floors. You can see from video footage of the north tower that a clear rotation of the upper section occurred which follows even basic rigid body principles.

The centre of gravity was eccentric from the available un-cut columns and their arrangement in plan. There is a good video earlier in this thread which shows an overlay of the columns as the upper section of tower rotates. You can clearly see that the columns above crash into the floors (not columns) below.

The trusses were exactly as Thornton described - open web bar joists. The connections to the core and perimeter grillage were flimsy. You need to analyse the weakest link, (ie the connection).

I fully agree that the columns had huge dynamic capacity. But without lateral restraint from the floors (crushed from falling floors above), the columns had no chance.

Can you please post your calcs for the truss?
 
Tony,

It's supported in hundreds of photos and videos which I'm sure you've seen. I can post some if you want, just tell me what isn't clear.

Do we really care what NIST says? Even the original FEMA report has enough photos to make up your own mind on the subject. You seem to be an engineer. Look at the photos. There was visible Euler buckling occurring at the perimeter columns (which gradually worsened over time, as shown in the photo timeline). There was a gaping hole under the upper floors. You can see from video footage of the north tower that a clear rotation of the upper section occurred which follows even basic rigid body principles.

The centre of gravity was eccentric from the available un-cut columns and their arrangement in plan. There is a good video earlier in this thread which shows an overlay of the columns as the upper section of tower rotates. You can clearly see that the columns above crash into the floors (not columns) below.

The trusses were exactly as Thornton described - open web bar joists. The connections to the core and perimeter grillage were flimsy. You need to analyse the weakest link, (ie the connection).

I fully agree that the columns had huge dynamic capacity. But without lateral restraint from the floors (crushed from falling floors above), the columns had no chance.

Can you please post your calcs for the truss?
Attached is a spreadsheet that Ron Brookman and I did for the main and bridging trusses in the Twin Towers. The double main truss composite floor system moment of inertia of 4,750 in^4 shows it was equivalent to having W30 x 108 beams every 80 inches in the span from the perimeter to the core. That is substantial.

I have analyzed the connections of the trusses and while they were strong enough to pull the perimeter columns inwards they should not have even come into play because there would not have been a lateral load applied, due to essentially no sagging taking place. Even if the sagging was there the connections could have taken it. The problem for NIST is the truss sagging can't apply enough force to bow the perimeter columns inward. That happened when the core was removed to start the collapse.

There is no visual evidence that the columns missed each other at the beginning of the North Tower fall. That is nonsense.

The columns in the Twin Towers could have gone at least four stories without lateral support before buckling. They were stout. My argument that there should have been at least a severe deceleration, if not an actual arrest, concerns the first several stories of the collapse.
 

Attachments

  • Actual Main and Bridging truss deflection at elevated temperatures.xlsx
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A 12 story 73 million lb. mass does not move laterally while falling without a significant lateral load on it. There was no lateral load on the upper section during the early stages of the collapse
Except, of course, the co-ordinated lateral force of dozens of columns buckling in almost perfect simultaneity. That force.

It simply is not true and calculations prove it isn't.
And to check that out we can type "911 wtc towers fire sagging" into Google Image and SEE what crap you come up with. I cannot see 2 inches of sag here, can you?

More like ten feet of sag.

Reality sucks, eh?
 
Except, of course, the co-ordinated lateral force of dozens of columns buckling in almost perfect simultaneity. That force.


And to check that out we can type "911 wtc towers fire sagging" into Google Image and SEE what crap you come up with. I cannot see 2 inches of sag here, can you?

More like ten feet of sag.

Reality sucks, eh?
Can you quantify the lateral force on the upper section, that you seem to be imagining, which would move its columns out of alignment with those of the lower section?
 
See this link http://img683.imageshack.us/img683/2553/view2.gif for a kinematic animation of column alignment while falling in the North Tower. This is a view looking from the west side.

There are two more links of similar views but looking from the southwest and a close up of the core here http://img23.imageshack.us/img23/5203/view1.gif and here http://img251.imageshack.us/img251/9278/view3.gif

The animations need to load fully by moving through all of the images once, and it will then play and loop in real time. The download of the images may take up to 30 seconds, depending on the download speed of one’s computer, but is worth the time to gain the visualization based on the actual measurements.
 
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Can you quantify the lateral force on the upper section, that you seem to be imagining, which would move its columns out of alignment with those of the lower section?
Yes.

But do explain how two inches (of your imagining) differs so remarkably from ten feet in reality, first, and stop playing your stupid games of omission.
 
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Yes.

But do explain how two inches (of your imagining) differs so remarkably from ten feet in reality, first, and stop playing your stupid games of omission.
There are no stupid games of omission going on. It sounds like you are having a problem distinguishing the floor damage due to the initial fuel/air detonation from what NIST wants to claim caused the initiation of the collapse due to fire heating up the trusses and causing them to sag and pull the perimeter columns inwards. The latter was also on the complete opposite side of the building from the aircraft impact in the case of the North Tower and is nothing more than a fantasy.
 
There are no stupid games of omission going on. It sounds like you are having a problem distinguishing the floor damage due to the initial fuel/air detonation from what NIST wants to claim caused the initiation of the collapse due to fire heating up the trusses and causing them to sag and pull the perimeter columns inwards. The latter was also on the complete opposite side of the building from the aircraft impact in the case of the North Tower and is nothing more than a fantasy.

Do you have this argument in diagram form?
 
1988 Charlie Thornton Interview

So Charlie Thornton (of the NIST oversight committee) finally tells the "TRUTH" . . . the WTC Towers were cheap, flawed, and didn't meet minimal strength design for a high rise construction . . . the perfect storm for a chance demolition . . . well . . . I have to say it makes more sense than anything I have heard of since this whole debate began . . . write the hole thing off as people using the cheapest route to a project that should allow the victims to sue the Port Authority for incompetence and negligence . . .
 
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