Does the exclusion of stiffness from Nordenson's falling girder calculations demonstrate anything?

[Polly Math]

So, wouldn't rule 702(c) apply to Nordenson's testimony?
https://www.rulesofevidence.org/article-vii/rule-702/


"Rule 702 – Testimony by Expert Witnesses -

A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:
(c) the testimony is the product of reliable principles and methods"

 

[Jeffrey Orling]

Making mistakes does not remove the qualification as being an expert. Experts have different opinions. If the facts of a case were self evident the court would not use experts.

Trust but verify

 

[Polly Math]

Making mistakes does not remove the qualification as being an expert.

Actually Jeffrey, it kind of does in terms of the specific evidence subjected to the error in question. That's why, like Nordenson, you take out error and omission insurance in order to give evidence on that basis. Although the absence of loss or harm to any third party does not relieve the burden of accuracy on expert witness. I am not saying that Nordenson has broken any laws here, what I am saying is that it appears that an objection to Nordenson's analysis at the discovery stage of this case, under 702(c) might well have been accepted, compelling him to review and amend his analysis.
The fact that the rule WOULD HAVE applied is important. Presuming the stiffness objection valid, if I cited that analysis, or repeated the presumed error in a court today in an unconnected case, would that be valid? Of course not, and that is why it should be amended.

Experts have different opinions. If the facts of a case were self evident the court would not use experts.

That experts have differing opinions is irrelevant. Whether the value for K should be infinite and what effect that has is definitive and measurable, is however, not a matter of opinion as per Nordenson's analysis.

Trust but verify

Yes. Trust. That is the whole issue surrounding this. I trust Mr. Nordenson entirely as a man of integrity, academically and otherwise, and no doubt he will do the right thing here if indeed he has erred in applying an infinite value to stiffness and in doing so has presented a route to progressive failure erroneously.

You, yourself have argued that the shear studs on the girder would have no material effect on NISTs or ARUPs analysis. Presuming that you actually believe that, you cannot deny an onus on Nordenson to amend what looks very much like an error in his analysis when in the very same case Bailey saw fit to return an amended statement to the court having discovered evidence that he had made a erroneous claim. It's what experts who are at the top of their field do when they make mistakes.

 

[benthamitemetric]

Actually Jeffrey, it kind of does in terms of the specific evidence subjected to the error in question. That's why, like Nordenson, you take out error and omission insurance in order to give evidence on that basis. Although the absence of loss or harm to any third party does not relieve the burden of accuracy on expert witness. I am not saying that Nordenson has broken any laws here, what I am saying is that it appears that an objection to Nordenson's analysis at the discovery stage of this case, under 702(c) might well have been accepted, compelling him to review and amend his analysis.
The fact that the rule WOULD HAVE applied is important. Presuming the stiffness objection valid, if I cited that analysis, or repeated the presumed error in a court today in an unconnected case, would that be valid? Of course not, and that is why it should be amended.


That experts have differing opinions is irrelevant. Whether the value for K should be infinite and what effect that has is definitive and measurable, is however, not a matter of opinion as per Nordenson's analysis.


Yes. Trust. That is the whole issue surrounding this. I trust Mr. Nordenson entirely as a man of integrity, academically and otherwise, and no doubt he will do the right thing here if indeed he has erred in applying an infinite value to stiffness and in doing so has presented a route to progressive failure erroneously.

You, yourself have argued that the shear studs on the girder would have no material effect on NISTs or ARUPs analysis. Presuming that you actually believe that, you cannot deny an onus on Nordenson to amend what looks very much like an error in his analysis when in the very same case Bailey saw fit to return an amended statement to the court having discovered evidence that he had made a erroneous claim. It's what experts who are at the top of their field do when they make mistakes.

E&O Insurance is not used for expert testimony in litigations (at least not in the US). To the extent that Nordenson's analyses were incorrect, it would have been the burden of the defense expert witness to critique and discredit them. If the error here led to erroneous conclusions, Nordenson would have doubtlessly amended his expert report to correct it once that was pointed out.

In this case, however, the claims never made it far enough to be challenged in that way. The case is now dismissed and the report is moot. There is nothing to amend.

 

[Jeffrey Orling]

The intent of the lawsuit, which was dismissed and never tried...nor was there any discovery... was the claim that the design had flaws which led to the collapse... it that the fires and the mechanical damage from falling debris were not sufficient to lead to global collapse. The plaintiff experts sought to find aspects of the design in addition to the failure of the sprinkler system which were contributory to the collapse. They were not offering a proof and we can see that all these after the fact analyses relied on many assumptions in their forensic "conclusions".

It's been noted multiple times that alter the assumptions and the conclusion changes. And that is the problem in a nut shell. Truth guys pile on NIST over isolated details and ignore the fact that the NIST model was also a set of assumption and grossly simplified to show HOW a girder might come free of a column, leading that column's unbraced length to increase, reducing its capacity and so on.

The industry has code requirements for usually 2 hr rating of steel protection This is presumably ample time to evacuate the structure. Codes are life safety driven not about the sustainability of the physical property. This building burned for 7 hours with no fire fighting well beyond the 2 hr code rating and remained intact for an additional 5-6 hrs.

The suit was about property damage as the collapse was a total loss. High rise buildings are vulnerable to total collapse because the natural of stacking one floor above the other... and engineers have strategies to contain the spread of fire as well as suppress it once it starts. If those systems don't work... all bets are off.

This case's dismissal does nothing to bolster the assertion that the only explanation for the collapse was an 8 story CD of all the columns... the core claim of the truth movement.

 

[Tony Szamboti]

E&O Insurance is not used for expert testimony in litigations (at least not in the US). To the extent that Nordenson's analyses were incorrect, it would have been the burden of the defense expert witness to critique and discredit them. If the error here led to erroneous conclusions, Nordenson would have doubtlessly amended his expert report to correct it once that was pointed out.

In this case, however, the claims never made it far enough to be challenged in that way. The case is now dismissed and the report is moot. There is nothing to amend.

The NIST WTC 7 report claims that a G44-79 girder walk-off failure at the 13th floor caused a collapse propagation of eight floors which then left column 79 in a slender state causing it to buckle. Knowing what you have seen here what do you think should be done with regards to the NIST claim?

 

[Jeffrey Orling]

Which claim? That fire caused the collapse? That there was nothing to suggest CD? That col 79 and perhaps 80 failed low down in the building?

YES I accept these

Or that the temps were so and so... and things move to the fraction of an inch as they claimed?

No... I haven't a clue, can't show they were right or were wrong and it's a detail that in the scheme of things matters not.

 

[Tony Szamboti]

Which claim? That fire caused the collapse? That there was nothing to suggest CD? That col 79 and perhaps 80 failed low down in the building?

YES I accept these

Or that the temps were so and so... and things move to the fraction of an inch as they claimed?

No... I haven't a clue, can't show they were right or were wrong and it's a detail that in the scheme of things matters not.

With the determination that a falling girder in the northeast corner could not have caused a cascading floor collapse, it appears that the official NIST WTC 7 report has no basis for its collapse hypothesis. This is also a report that recommended a number of structural changes to the building code. Most would think that is a problem that needs to be addressed.

Why anyone would think it doesn't matter is hard to understand. However, it is even harder to understand your position, where in the same breathe you admit you don't have a clue but insist it doesn't matter.

Here is a Scientific American article from August 31, 2011 that quotes both Shyam Sunder and Guy Nordenson. In it Sunder says nobody has shown cause for NIST to reevaluate its findings.

http://www.scientificamerican.com/article/twin-towers-forensic-investigation-revise-building-codes/

I think Dr. Sunder is going to have to reevaluate his position now.

 

[Jeffrey Orling]

With the determination that a falling girder in the northeast corner could not have caused a cascading floor collapse, it appears that the official NIST WTC 7 report has no basis for its collapse hypothesis. This is also a report that recommended a number of structural changes to the building code. Most would think that is a problem that needs to be addressed.

Why anyone would think it doesn't matter is hard to understand. However, it is even harder to understand your position, where in the same breathe you admit you don't have a clue but insist it doesn't matter.

Here is a Scientific American article from August 31, 2011 that quotes both Shyam Sunder and Guy Nordenson. In it Sunder says nobody has shown cause for NIST to reevaluate its findings.

http://www.scientificamerican.com/article/twin-towers-forensic-investigation-revise-building-codes/

I think Dr. Sunder is going to have to reevaluate his position now.

As you may recall... my suspicion is the collapse began with some failure in the transfer region.. BELOW 79.... TT1, or TT2. Once one of those fails... 79 and 80 collapse and this would produce the visuals we see. But this was not explored because there was NO DATA about fires there. Not there was no fire... No data does not mean there was no fire.

All the so called "fire" data is barely data because it is derived from photos of the outside of the building and a bunch of calculations based on assumptions, CALCULATIONS are not data... and they are not proof nor can they disprove anything about these collapses.

We witnessed / read the gross abuse/simplification to "explain" the collapses by Bazant... championed as the limiting case. Who gives an eff?

The tower came down when something in the NE region... quite low down failed... the structure and floors above it collapsed (EPH)... the next visual are the roof structures collapsing east to west and then the moment frame drops about 100 feet with little resistance which suggests it lost its support at the 8th floor.

I am sorry to say these maths show nothing much.

Here is the money quote from the SA article:

"The problem many have with the World Trade Center investigation is that it wasn't as open and not adequately peer reviewed, due in part to the veil of security concerns, so lots of people can disagree with the conclusions," Nordenson says. For instance, Nordenson himself is part of litigation suggesting the collapse of WTC 7 was not inevitable, but was due to design flaws in both the fire protection and some aspects of the structure."

It makes perfect sense.

 

[Tony Szamboti]

As you may recall... my suspicion is the collapse began with some failure in the transfer region.. BELOW 79.... TT1, or TT2. Once one of those fails... 79 and 80 collapse and this would produce the visuals we see. But this was not explored because there was NO DATA about fires there. Not there was no fire... No data does not mean there was no fire.

All the so called "fire" data is barely data because it is derived from photos of the outside of the building and a bunch of calculations based on assumptions, CALCULATIONS are not data... and they are not proof nor can they disprove anything about these collapses.

We witnessed / read the gross abuse/simplification to "explain" the collapses by Bazant... championed as the limiting case. Who gives an eff?

The tower came down when something in the NE region... quite low down failed... the structure and floors above it collapsed (EPH)... the next visual are the roof structures collapsing east to west and then the moment frame drops about 100 feet with little resistance which suggests it lost its support at the 8th floor.

I am sorry to say these maths show nothing much.

Here is the money quote from the SA article:

"The problem many have with the World Trade Center investigation is that it wasn't as open and not adequately peer reviewed, due in part to the veil of security concerns, so lots of people can disagree with the conclusions," Nordenson says. For instance, Nordenson himself is part of litigation suggesting the collapse of WTC 7 was not inevitable, but was due to design flaws in both the fire protection and some aspects of the structure."

It makes perfect sense.

While it was open and transparent it has been shown that Nordenson's analysis is in error and that the girder failure would not cause a cascade of collapsing floors.

This means the present hypothesis is not viable and simply saying "fire did it" is not an acceptable explanation.

NIST does need to reevaluate things and conduct a new investigation.

 

[Jeffrey Orling]

Tony.... I can't say I have a problem with a new study to match the mechanisms to the visuals. I don't what actually can be "investigated" as opposed to producing models with realistic assumptions/inputs which produce a close approximation to the real world observed behavior.

I think you don't even accept the failure of column 79 low down in the building... despite evidence of this.

 

[Tony Szamboti]

Tony.... I can't say I have a problem with a new study to match the mechanisms to the visuals. I don't what actually can be "investigated" as opposed to producing models with realistic assumptions/inputs which produce a close approximation to the real world observed behavior.

I think you don't even accept the failure of column 79 low down in the building... despite evidence of this.

Matching the mechanism to the visuals has not been done to this point and it needs to be done. I am sure if it is we will have an answer to what the most probable cause truly was.

What you do in a situation like that is to remove different parts until you match the observations and then look for what could legitimately have caused those initial parts to fail.

It could not have been a girder failure of the type NIST claimed in their first report on the collapse.

 

[DGM]

Matching the mechanism to the visuals has not been done to this point and it needs to be done. I am sure if it is we will have an answer to what the most probable cause truly was.

What you do in a situation like that is to remove different parts until you match the observations and then look for what could legitimately have caused those initial parts to fail.

It could not have been a girder failure of the type NIST claimed in their first report on the collapse.

So write up a report with equal detail for the theory you support, that way every detail can be examined. That shouldn't be too hard.

 

[Tony Szamboti]

So write up a report with equal detail for the theory you support, that way every detail can be examined. That shouldn't be too hard.

The reality of the girder walk-off or pull-off being a no go is going to be written up and the NIST will be notified about it.

 

[DGM]

The reality explaining why the girder walk-off or pull-off is a no go is going to be written up and the NIST will be notified about it.

Are you writing a report on the theory you support?

 

[Tony Szamboti]

Are you writing a report with the theory you support?

Aren't you moving a little too far downfield? This thread is about the pertinence of the girder walk-off or pull-off not being able to cause a cascading collapse of floors in the northeast corner and precipitating the collapse.

If that is what you really want to talk about maybe you need to start a new thread asking if people are going to write up their individual overall theories. Otherwise, please stick to the subject here.

 

[DGM]

Aren't you moving a little too far downfield? This thread is about the pertinence of the girder walk-off or pull-off not being able to cause a cascading collapse of floors in the northeast corner and precipitating the collapse.

It is indeed. You now claim it's impossible where you have not supported this. Nordenson uses several conservative assumptions that could easily cover the energy gap.

 

[Tony Szamboti]

It is indeed. You now claim it's impossible where you have not supported this. Nordenson uses several conservative assumptions that could easily cover the energy gap.

You really need to explain how you still feel Nordenson's analysis could cause the lower floor girder to fail. Otherwise, you are just making unsupported assertions.

I provided an analysis which showed the load could not be amplified to anywhere near the shear capacity of the girder seat at column 79. Are you having a hard time understanding it?

 

[DGM]

You really need to explain how you still feel Nordenson's analysis could cause the lower floor girder to fail. Otherwise, you are just making unsupported assertions.

I provided an analysis which showed the load could not be amplified to anywhere near the shear capacity of the girder seat at column 79. Are you having a hard time understanding it?

Did Nordenson use conservative assumption in his analysis such as low live loads and and no damage assessment to floors under 13? You can't claim something impossible without exploring all the details.

Do you agree?

 

[Tony Szamboti]

Did Nordenson use conservative assumption in his analysis such as low live loads and and no damage assessment to floors under 13? You can't claim something impossible without exploring all the details.

Do you agree?

You aren't being explicit and sound like you are simply reaching for something in hopes of maintaining Nordenson's analysis results. Do some work yourself and provide some legitimate details to support your contentions if they exist. I already did and if you don't you will have to be ignored.

 

[DGM]

You aren't being explicit and sound like you are simply reaching for something in hopes of maintaining Nordenson's analysis results. Do some work yourself and provide some legitimate details to support your contentions if they exist. I already did and if you don't you will have to be ignored.

I don't need to be explicit. Section B3.0 explains the energy dissipation assumptions that were conservative to determine an upper bound.

Do you think his energy dissipation approach was not conservative?

 

[Tony Szamboti]

I don't need to be explicit. Section B3.0 explains the energy dissipation assumptions that were conservative to determine an upper bound.

Do you think his energy dissipation approach was not conservative?

I do not think Nordenson's energy approach was conservative. I think it was moderate at best and possibly a little exaggerated. He had 46,000 lbs. impacting from a 7 foot vertical drop. The steel frame weighed about 20,000 lbs., and a case can be made that the concrete would not have been a part of it. The welded wire reinforcement would have kept it from dropping all the way to the floor on top of the frame since it was still connected to the south and west beams which had not collapsed. There is also a moment arm consideration where the Cg is about half the distance so the force on the girder end would have been half of it.

The energy also is really not quite the issue as it is how fast the energy is transferred that determines the force in an impulse. The problem for Nordenson is the stiffness of the falling girder was far too low to allow an impulse that would amplify 46,000 lbs. into 632,000 lbs. of force.

I am not going to continue arguing your niggling generic comments. If you don't provide some specific details supporting your argument you and I have nothing to discuss.

 

[DGM]

I do not think Nordenson's energy approach was conservative. I think it was moderate at best and possibly a little exaggerated. He had 46,000 lbs. impacting from a 7 foot vertical drop. The steel frame weighed about 20,000 lbs. A case can be made that the concrete would not have been a part of it, as the welded wire reinforcement would have kept it from dropping all the way to the floor on top of the frame since it was still connected to the south and west beams which had not collapsed. There is also a moment arm consideration where the Cg is about half the distance so the force on the girder end would have been half of it.

The energy also is really not quite the issue as it is how fast the energy is transferred that determines the force in an impulse.

I am not going to continue arguing your niggling generic comments. If you don't provide some specific details supporting your argument you and I have nothing to discuss.

He used the SAP2000 model where the connection at column 79 was removed and used the gravity reaction to come up with that value. The slab failure energy was part of his loss calculations.

I don't care if you want to continue, seems the vast majority of engineers in the world don't also.

 

[Tony Szamboti]

He used the SAP2000 model where the connection at column 79 was removed and used the gravity reaction to come up with that value. The slab failure energy was part of his loss calculations.

I don't care if you want to continue, seems the vast majority of engineers in the world don't also.

It is clear that you don't have anything specific to contribute, and seem to be just trying to raise flags with no sound basis provided, so there is no use discussing anything with you.

 

[Polly Math]

The 2nd of Nordensons PDFs, Page 251 says,

" The analysis approach undertaken is transparent and straightforward and does not rely on a complex computer analysis that may obscure assumptions inherent to the process"

Nordenson used hand calculations to justify collapse propagation. If he had checked his findings on the "complex computer analysis" equipment at his disposal the issue of stiffness would have been flagged up in the FEA. I can understand where hand calculations would be preferable (you'd typically get a higher stiffness in a FEA compared to hand) but the decision not to check that his result was at least in the ballpark by running a relatively straightforward analysis is one that I can imagine Nordenson having trouble justifying.

 

[Jeffrey Orling]

Nordenson and Tony have different goals. Tony seeks to show that a progressive collapse was not possible without CD devices (unspecified). Nordenson is attempting to show that the structure had design flaws and the plaintiffs probably seeking to subrogate and stick at least part of the cost of replacement etc. on others... such as the surety for the designers/engineers/contractors and so on.

http://apps.americanbar.org/ababoards/blog/blogpost.cfm?catid=14909&threadid=29641

and

"7WTC stood on the northern edge of the World Trade Center site and as the North Tower collapsed on September 11, 2001, it damaged 7WTC. After burning for seven hours, 7WTC collapsed, destroying the electrical substation owned by Con Ed directly beneath the building. Con Ed, along with its insurers, filed suit against defendants, who designed, built, operated, and maintained 7WTC, alleging in relevant part that defendants' negligence caused the building to collapse. The court concluded that Con Ed failed to present evidence sufficient to raise a genuine issue of fact as to whether defendants' negligence was the cause-in-fact of Con Ed's injury. The court had little trouble concluding that the confluence of events that day demonstrated that 7WTC would have collapsed regardless of any negligence ascribed by plaintiffs' experts to the design and construction of 7WTC more than a decade earlier. It was simply incompatible with common sense and experience to hold that defendants were required to design and construct a building that would survive the events of September 11, 2001. Accordingly, the court affirmed the dismissal of the claims against defendants on this alternative ground. "

more about the extensive fires:

http://caselaw.findlaw.com/us-2nd-circuit/1651388.html

It seems absurd to consider one beam, one connection when so much of the building was being assaulted for hours by fire. The court found the extensive fires were a sufficient cause of collapse not construction flaws.. whether they existed or not.

 

[Oystein]

The equation you are using for stiffness (40.5EI/L^3) is very near that of a simply supported beam (where the stiffness is 48EI/L^3) and that would hardly seem likely with one end of girder 44-79 hanging out in space.

But that's the result I got - I presented my argument in full, the assumptions, the graphics, the formulas used and the algebra done. If there isn't anything wrong with any of these, then the result is correct.

I finished and ran my finite element analysis and it shows the stiffness of the assembly of the five beams attached at the east wall, three support beams attached at the north wall, with the girder just sitting unrestrained on its seat, has a natural frequency of 0.52 Hz.

This appears to me as a good, correct way to model the steel frame of the floor, and I understand crudely that FEA can give you a natural frequency and that natural frequency is leads to stiffness via the formula you provide here:

Fn = 1/2pi * SQRT(K/m)

Stiffness (K) can then be found with the equation

K = (Fn * 2pi)^2 * mThe weight of the beams and girder is just over 20,000 lbs., so mass = 20,000/32.174 = 622 slugs so

K = (0.52 * 6.28)^2 * 622 = 6,633 lbs./inch

You lost me here somewhat:
1. I have to think about slugs - damn the USA and her imperial units!
2. "just over 20,000 lbs" is over 21,000 lbs, isn't it? Girder is 547 inches * 133 lbs/12 in = 6063 lbs. Each (?) of the 5 long beams is 644 inches * 55 lbs/12 in = 14758 lbs total. I am at 20,821 lbs, add to that the three support beams connecting to the north wall (ok, that's a nitpick)
3. At some point, we'll have to wedge in the mass of of the floor slabs...
4. K = 6,633 lbs./inch is precisely the same result you got in post #97, albeit with a different frequency and different mass (using Nordenson's mass of 46,000 lbs that includes floor slab). Weird coincidence?

Using Nordenson's potential energy of 3,473,000 in-lbs. and the same standard equation he uses to find deflection

P.E. = 1/2K *D^2

D = SQRT(2*P.E./K) = 32.4 inches

Now using the standard equation Nordenson uses to find force

F = K * D = 6,633 lbs./inch * 32.4 inches = 214,909 lbs.

This is nearly three times less than the 632,000 lb. shear capacity of the seat and proves that the falling girder would not have sheared the seat and the northeast corner of floor 12 would not have collapsed if a girder at floor 13 came off its seat at column 79.

The calculation is correct for K = 6,633 lbs/in.

Before concluding too much, I want at least three of us to be on the same page.

My main problem at this point is that I cannot check your FEA - I don't have all your files, and if I had them, I wouldn't have the software to use them; and if I had the software, I'd lack the expertise using it. Sooo who is here to help and offer a criticism of Tony's approach?

Also, I question (this is an open question to all) if it is ok to ignore the floor slab in the FEA. Sure, I ignored the slab, and the beams, in my own model of "rotating girder - 2/3L load point". This is a difficult thing to model, for the slab has already broken and partially disconnected.


I think what we can agree on at this point is that Nordenson's Appendix B would need rework and refinement if it were to be used again, for his rather clear result of "will fail" would shift into "may not fail" territory and possibly beyond. This could be a worthwhile question to be put to Dr. Hulsey and his PhD students.

What I cannot agree on is your (Tony's) conclusion that your partial FEA "proves that the falling girder would not have sheared the seat". You make a good case showing that it may not, but there are too many unknowns at this point to be sure.

 

[Oystein]

I do not think Nordenson's energy approach was conservative. I think it was moderate at best and possibly a little exaggerated.

My impression is that his initial PE and the 6 bits of plastic deformation he derived in B3 were neither particularly conservative nor apparently exaggerated.
The two main points of conservatism come in one and more steps later:
1. Assuming that the connection on floor 12 still has full capacity after fires and the general deformation of the structure certainly is conservative. NIST finds it undamaged in their Case B fire scenario after 4 hours (Figure 11–34 of NCSTAR 1-9), but does "undamaged" imply "full capacity"? I'd rather say no, but we don't know if and how much it would have been diminished.
2. For the following falling floors (12 onto 11, 11 onto 10), he disregarded that mass would accumulate. That surely is very conservative, but irrelevant if the floor 12 connection doesn't fail.

Neither point affects the equivalent force we are discussing here.

He had 46,000 lbs. impacting from a 7 foot vertical drop. The steel frame weighed about 20,000 lbs., and a case can be made that the concrete would not have been a part of it. The welded wire reinforcement would have kept it from dropping all the way to the floor on top of the frame since it was still connected to the south and west beams which had not collapsed.

If "a case can be made", then make it!

Nordenson accounts for the tearing, breaking and deforming of the floor slab in various places. Not sure how he determined, or how sure he is, that the floor slab would break, but it appears plausible, given the extreme spans.
Nordenson takes care of the floor slab connection to the south and west beams in "B3.2 Composite Slab Tensile Fracture" and "B3.3 Composite Slab Shear Fracture", which are rich in detail on metal deck and reinforcement. The results in Table B6.1 show that these fractures on the south and west side consume relatively little energy (only roughly 1% of PE).

There is also a moment arm consideration where the Cg is about half the distance so the force on the girder end would have been half of it.

The energy also is really not quite the issue as it is how fast the energy is transferred that determines the force in an impulse. The problem for Nordenson is the stiffness of the falling girder was far too low to allow an impulse that would amplify 46,000 lbs. into 632,000 lbs. of force.

But these issues are precisely what we are taking care of by determining the correct stiffness for the situation here!

 

[Seymour]

As you may recall... my suspicion is the collapse began with some failure in the transfer region.. BELOW 79.... TT1, or TT2. Once one of those fails... 79 and 80 collapse and this would produce the visuals we see. But this was not explored because there was NO DATA about fires there. Not there was no fire... No data does not mean there was no fire.

All the so called "fire" data is barely data because it is derived from photos of the outside of the building and a bunch of calculations based on assumptions, CALCULATIONS are not data... and they are not proof nor can they disprove anything about these collapses.

We witnessed / read the gross abuse/simplification to "explain" the collapses by Bazant... championed as the limiting case. Who gives an eff?

The tower came down when something in the NE region... quite low down failed... the structure and floors above it collapsed (EPH)... the next visual are the roof structures collapsing east to west and then the moment frame drops about 100 feet with little resistance which suggests it lost its support at the 8th floor.

I am sorry to say these maths show nothing much.

Here is the money quote from the SA article:

"The problem many have with the World Trade Center investigation is that it wasn't as open and not adequately peer reviewed, due in part to the veil of security concerns, so lots of people can disagree with the conclusions," Nordenson says. For instance, Nordenson himself is part of litigation suggesting the collapse of WTC 7 was not inevitable, but was due to design flaws in both the fire protection and some aspects of the structure."

It makes perfect sense.

From NIST 1-9, page 432 and 433/797 - "These figures show that Column 79 was located in the same space as the four generators in the northeast quadrant. Column 80, Truss 1, and Truss 2 were located in the
Ventilation and AC Equipment space, which was enclosed with masonry walls. Column 81 was located
within the transfer corridor. Thus, of these critical structural components, only Column 79 could have
been exposed to heating from a diesel fuel fire on Floor 5."........

So exactly what do you "speculate" caused the failure of the transfer trusses?

 

[Jeffrey Orling]

From NIST 1-9, page 432 and 433/797 - "These figures show that Column 79 was located in the same space as the four generators in the northeast quadrant. Column 80, Truss 1, and Truss 2 were located in the
Ventilation and AC Equipment space, which was enclosed with masonry walls. Column 81 was located
within the transfer corridor. Thus, of these critical structural components, only Column 79 could have
been exposed to heating from a diesel fuel fire on Floor 5."........

I am not in possession of the drawings which show the risers, the piping, the tanks and the generators... I can't speculate more than that there was stored diesel in this region AND the building's engineer Cantor mentioned he believed diesel fires were what caused the trusses to fail. Take it up with him... I am sure he has more detail!

So exactly what do you "speculate" caused the failure of the transfer trusses?

 

[Tony Szamboti]

But that's the result I got - I presented my argument in full, the assumptions, the graphics, the formulas used and the algebra done. If there isn't anything wrong with any of these, then the result is correct.


This appears to me as a good, correct way to model the steel frame of the floor, and I understand crudely that FEA can give you a natural frequency and that natural frequency is leads to stiffness via the formula you provide here:


You lost me here somewhat:
1. I have to think about slugs - damn the USA and her imperial units!
2. "just over 20,000 lbs" is over 21,000 lbs, isn't it? Girder is 547 inches * 133 lbs/12 in = 6063 lbs. Each (?) of the 5 long beams is 644 inches * 55 lbs/12 in = 14758 lbs total. I am at 20,821 lbs, add to that the three support beams connecting to the north wall (ok, that's a nitpick)
3. At some point, we'll have to wedge in the mass of of the floor slabs...
4. K = 6,633 lbs./inch is precisely the same result you got in post #97, albeit with a different frequency and different mass (using Nordenson's mass of 46,000 lbs that includes floor slab). Weird coincidence?


The calculation is correct for K = 6,633 lbs/in.

Before concluding too much, I want at least three of us to be on the same page.

My main problem at this point is that I cannot check your FEA - I don't have all your files, and if I had them, I wouldn't have the software to use them; and if I had the software, I'd lack the expertise using it. Sooo who is here to help and offer a criticism of Tony's approach?

Also, I question (this is an open question to all) if it is ok to ignore the floor slab in the FEA. Sure, I ignored the slab, and the beams, in my own model of "rotating girder - 2/3L load point". This is a difficult thing to model, for the slab has already broken and partially disconnected.


I think what we can agree on at this point is that Nordenson's Appendix B would need rework and refinement if it were to be used again, for his rather clear result of "will fail" would shift into "may not fail" territory and possibly beyond. This could be a worthwhile question to be put to Dr. Hulsey and his PhD students.

What I cannot agree on is your (Tony's) conclusion that your partial FEA "proves that the falling girder would not have sheared the seat". You make a good case showing that it may not, but there are too many unknowns at this point to be sure.

Actually, the girder cannot be 547 inches long as that is the center to center distance between columns 44 and 79. It seems Nordenson had a slight error there also. The drawing for girder A2001 was not released by NIST to the general public, so I don't have it, but am pretty sure the ARUP guys did. See the attached which is a drawing for girder 4349 which is between columns 44 and 79 at the 43rd floor. The center to center distance between columns is shown at the top of the drawing. The length of the girder at the 43rd floor is actually 44' 8-7/8" which is 536.875 inches and this is with a W14 x 193 for column 79 and a W14 x 145 for column 44 so it would have to be longer than the one at the 13th floor where the columns were W14 x 730 with side plates for column 79 and W14 x 665 for column 44.

I was doing the 20,000 pounds from memory while writing the post. I think I checked the mass in the FEA, which would have been very accurate. By hand I get

33 x 130 girder A2001 = 45 feet x 130 lbs./foot = 5,850 lbs.
24 x 55 beams K3004, C3004, B3004, A3004 = 53 feet x 55 lbs./foot = 2,915 lbs. each
21 x 44 beam G3005 = 52 x 44 lbs./foot = 2,288 lbs.
12 x 19 lateral support beams K3007, G3007, S3007 = 4 feet x 19 lbs./foot = 76 lbs. each

So I get 5,850 + (4 x 2,915) + 2,288 + (3 x 76 lbs.) = 20,026 lbs.

The reason I get 6,633 lbs./inch with the little higher frequency here is that I used the steel mass as it is what is relavent and what the natural frequency is dependent on. In the earlier calculation I had used the Nordenson load of 46,000 lbs. and that was not correct. If the slab were included it would make the natural frequency and stiffness even lower as without shear studs it adds nothing but mass. You can't use the slab mass with the 0.52 Hz frequency in the frequency equation as the frequency will go down in the FEA due to the greater mass and no addition of stiffness.

You can make the steel weight 21,000 if you like, as I do some rounding and averaging here. However, beam G3005 is a 21 x 44, not a 24 x 55, and your estimate loses 11 lbs. per foot for it, and the beam is actually a couple of feet shorter than the K3004 beam, so that would be about 600 lbs.. Adjustment of your estimate for that beam alone takes it down to about 20,200 lbs.. Just to show you that this is not significant, for 21,000 lbs. the stiffness is 6,960.5 lbs./inch., deflection is 31.6 inches, and generated load is 219,881 lbs.. This is only a few percent difference and does not change things at all and the weight was much closer to 20,000 lbs. anyway as you had the G3005 error.

I deleted the earlier post as I had messed up the quote of your post and it did not indent. This post is the same but with fixed indenting of your post.

I am editing this post to add a more accurate weight calculated in the attached spreadsheet. The drawings are also provided for anyone who would like to check the figures. I used drawing 4349 in lieu of A2001, but with a 537 inch length. The weight of the steel frame turns out to be 19,795 lbs., which is just a little under 20,000 lbs. and would have made my analysis conservative as the stiffness would have been slightly higher using 20,000 lbs..

 

[Tony Szamboti]

Nordenson and Tony have different goals. Tony seeks to show that a progressive collapse was not possible without CD devices (unspecified). Nordenson is attempting to show that the structure had design flaws and the plaintiffs probably seeking to subrogate and stick at least part of the cost of replacement etc. on others... such as the surety for the designers/engineers/contractors and so on.

http://apps.americanbar.org/ababoards/blog/blogpost.cfm?catid=14909&threadid=29641

and

"7WTC stood on the northern edge of the World Trade Center site and as the North Tower collapsed on September 11, 2001, it damaged 7WTC. After burning for seven hours, 7WTC collapsed, destroying the electrical substation owned by Con Ed directly beneath the building. Con Ed, along with its insurers, filed suit against defendants, who designed, built, operated, and maintained 7WTC, alleging in relevant part that defendants' negligence caused the building to collapse. The court concluded that Con Ed failed to present evidence sufficient to raise a genuine issue of fact as to whether defendants' negligence was the cause-in-fact of Con Ed's injury. The court had little trouble concluding that the confluence of events that day demonstrated that 7WTC would have collapsed regardless of any negligence ascribed by plaintiffs' experts to the design and construction of 7WTC more than a decade earlier. It was simply incompatible with common sense and experience to hold that defendants were required to design and construct a building that would survive the events of September 11, 2001. Accordingly, the court affirmed the dismissal of the claims against defendants on this alternative ground. "

more about the extensive fires:

http://caselaw.findlaw.com/us-2nd-circuit/1651388.html

It seems absurd to consider one beam, one connection when so much of the building was being assaulted for hours by fire. The court found the extensive fires were a sufficient cause of collapse not construction flaws.. whether they existed or not.

I am seeking to show what actually happened and the natural progressive collapse explanations have been seriously lacking and I have no confidence that any form of the "it was the transfer trusses" theory will explain the observations. This theory also has serious evidentiary problems.

NIST omitted and ignored a significant number of things that would have precluded their hypothesis and now we see ARUP/Nordenson made a serious error with not accounting for the stiffness of the falling girder that would stop any progression.

What is absurd is to simply say "it doesn't matter fire did it" and have no problem with NIST omitting and ignoring pertinent things and not having an actual explanation that is viable. There was also a dissenting opinion in the court and the judge who wrote it did so as he felt there was a need to determine how the building actually did come down. See http://www1.ae911truth.org/en/news-...-collapse-dissenting-judge-asks-what-did.html

 

[Seymour]

Transfer trusses

It appears that would be impossible, since there wasn't any way that diesel would be in the area of the trusses, since they were segregated behind a masonry wall. Read that quote again. It's a cop out to say that you aren't in possession of plans, since they are indeed available. Educate yourself some and speculate again.

 

[Seymour]

See http://www1.ae911truth.org/en/news-...-collapse-dissenting-judge-asks-what-did.html

Interesting quote in that link. The plaintiffs seem to agree that fire alone brought down the building.

" the building was designed and erected in such a way that it was subject to failure if a fire broke out that could not be quelled."


So, how does this help the CD case, when they acknowledge that fire did it?

 

[Seymour]

deflection is 31.6 inches, and generated load is 219,881 lbs.. ..

So the falling girder deflects 31.6"?

Presumably in the middle?

Seems like a lot....

 

[Tony Szamboti]

So the falling girder deflects 31.6"?

Presumably in the middle?

Seems like a lot....

The girder bends in the middle, and deflects at its impact end.

Do the math and you will see. If it was just a cantilever it would have deflected about twice as much with a 219,881 lb. force at its end.

Simply saying "seems like a lot" is a meaningless statement.

 

[Tony Szamboti]

Interesting quote in that link. The plaintiffs seem to agree that fire alone brought down the building.

" the building was designed and erected in such a way that it was subject to failure if a fire broke out that could not be quelled."


So, how does this help the CD case, when they acknowledge that fire did it?

Just saying "fire alone brought down the building" does not mean anything especially once the report of those saying it is shown to be fatally flawed in trying to show a falling girder could cause a cascading floor collapse.

 

[Jeffrey Orling]

Mr Butz... I am not in possession of the construction drawings, the shop drawings, construction logs and so forth. Almost everyone weighing in on what happened has made errors including NIST. As I haven't seen the documents I am relying on some very basic information and the statement by Cantor. That's all I will say. Thank you.

 

[Tony Szamboti]

Mr Butz... I am not in possession of the construction drawings, the shop drawings, construction logs and so forth. Almost everyone weighing in on what happened has made errors including NIST. As I haven't see the documents I am relying on some very basic information and the statement by Cantor. That's all I will say. Thank you.

Those postulating a natural cause have made fatal errors, so we presently don't have an official answer as to why the building came down.

 

[Jeffrey Orling]

Those postulating a natural cause have made fatal errors, so we presently don't have an official answer as to why the building came down.

I think in the case of 7wtc it seems to be a progressive failure low down which progressed east to west.. That's why it came down. What started that cascade is in question.