The NIST report, start to finish

Originally posted by esdad71
reply to post by psikeyhackr

 

Still standing means they are still standing. Not the entire buildings but the core and outer columns, you know, the ones you keep saying where crushed along with all of your concrete.

This thread seems to be about being able to give stars to friends rather than keeping up a good conversation.

Yes, that STILL STANDING is literally correct, but they were wobbling and did not stay up for another 20 seconds.

YOU WIN! whoop-de-do

psik

Originally posted by exponent
I specifically asked for this utter idiocy to be kept out of this thread.

Aww come on, you were the one to start it again, with your arguments of "you're wrong because you left out a word," when you were saying nothing about the columns being pulled out of place at all, and even denying that it had anything to do with the mechanism, and that the columns were only deflected, three or four pages ago.

Azp you have provided an excellent debate in this thread, and while I do think you are wrong I can't easily prove it in a few sentences. We have a 4 day weekend over here so hopefully I will find the time, if not I will respond to you early next week.

At least we are making progress.

The only question that should remain for you at this point is 'which would happen first?': a column section being completely ripped out at the bolts and spandrel plates by a truss, or the truss itself failing?

Originally posted by NIcon
If this is the position of the NIST Investigation, why is this "critical amount of inward bowing" never examined in the report? Where is the measurement of this "critical amount" to differentiate it from a non-critical amount? Where is the examination of this "snapping" of columns? He makes pretty darn clear this is what happened before the top "started moving downward."

If this is not the position of the NIST Investigation, then why is, at the time, the active leader of the NIST Investigation presenting this as a certainty? Did he come to the wrong conclusion of the very same report he lead? Should we yell and scream that Shyam is out spreading "disinformation" like I see so many on here accusing the "conspiracy" sites of doing?

Those are all good questions too actually, besides what would fail first structurally.

As far as "where is the measurement of this "critical amount" [of column failure/buckling/being "snapped out/etc.] to differentiate it from a non-critical amount," I think we both realize they never provided any such analysis, and simply assumed this "must have been" what happened since they never considered any other possibility in the first place.

reply to post by bsbray11

I think that's what my overall opinion of this. It was all sound and fury over predetermined conclusions and assumptions, signifying nothing. We get very detailed models of airplane engines and no models of collapse initiation.

I like how this guy put it after living through the NIST experience:

According to Glenn Corbett, a technical adviser to NIST and fire science professor at John Jay College, NIST is not aggressive enough to carry out major forensic investigations. He says, “Instead of a gumshoe inquiry that left no stone unturned, I believe the investigations were treated more like research projects in which they waited for information to flow to them.”
www.historycommons.org...

And I haven't seen anything in this thread that's even made me stop and reconsider, yet. But that airplane model was very cool, though.

Originally posted by esdad71
reply to post by ANOK

 

I have explained, posted pictures and videos that show how the core columns were severed.

No you haven't. There is no videos that show the core columns were severed. Complete nonsense.

How many time have the physics been explained to you that contradicts your claims?

There are accounts from survivors.You cannot argue that there were no columns were severed. Not all, I believe less than 10% severed and 25% damaged. The south tower had most of the damage to one corner of the inner core. The north was more to the center.

What witnesses? When you make claims like that you need to cite your source, you expect me to take your word for it? Yes I can say NO columns were severed for two reasons, 1. No evidence, 2. Not physically possible. An aluminum plane can not sever 4" thick box columns. That would mean the plane would have to go through the first 4" wall of the first box column, then the next 4" thick wall of the box column, not to mention the two 4" thick side walls of the box column. All that after it's KE was reduced from flying through the outer mesh columns. Do you forget about that?

You know there were 47 columns in the core right? IF 10% were severed the weight, as you mentioned, would be taken up by the other columns with no problem. Factor of safety would allow this.

But again esdad there is NO evidence that columns were severed, you are basing your argument once again on assumptions, not reality.

When this happens, the bulk of the load would transfer to the outer columns. It has to transfer somewhere. This is where the sagging trusses of multiple floors comes into play also. There are plenty of pictures of this.If it is trying to compensate for the inner columns damage as well as being bowed by the sagging floors it is no longer stable.

There are no pictures, stop lying. You are contradicting yourself. Why would the bulk of the load transfer to the outer columns? That is just another false assumption.

IF core columns were severed then why did the towers not collapse immediately after impact? Why were floors trusses not severed by the planes, and the initiating truss failure happen immediately? The planes impact covered more than one floor, and yet the lightweight trusses, the weak point according to the OS, didn't fail from the impact, but waited for the magic super fire that caused them to take on a force all of their own that was more powerful than the massive columns holding them? The columns snapped from this massive force caused by sagging trusses, and then gained KE as it collapsed through the path of most resistance? Is that really what you are claiming?

Again your contradictions abound. But you would have to understand building design and physics in that context to understand why.

reply to post by -PLB-

That is why I talked about 2 distinct situations, one where the compressive diagonals are intact (and the truss can be seen as one body),

This situation would generate no significant pull-in force on the columns so is irrelevant.

"Department of Civil and Structural Engineering, University of Sheffield" does the trick for me. If you give me reason to doubt their qualification, I may further investigate. Better yet, show they are not qualified.

The omission of qualifications and that I have seen many undergraduate reports of much higher quality is what made me wonder as to how qualified these authors really are. Although I don't value qualifications as much as most people, to me correct work is correct work and vice versa, just thought you might want to know, since you place a higher emphasis on qualifications when determining if a model is trustworthy.

There is definitely catenary action in their simulation. But during the time there is catenary action, all truss members are still intact, so the truss should be able to hold as it is designed to do. That means your calculations do not apply to the model, and you have not to proved it to be wrong.

The truss was not designed to hold anything with tension in the top chord.

I strongly disagree that the ~85kN pull-in force claimed by the model was as a result of catenary action while all truss members were intact (although the poorly and confusing way it is written doesn't help). Perhaps you could quote some relative sections to clear this up? If you are able to show that this is indeed the case I would like to do some calculations to determine what is going on with the internal forces. Taking their word for it is not good enough for me.

It is of my opinion and understanding that a properly designed and typical truss is physically unable to carry a load via a catenary mechanism while all of its elements are intact.

I would also like to add that the report we have been discussing also casts doubt over whether the bolts would be able to transfer the pull-in force to the column.

reply to post by exponent

Azp you have provided an excellent debate in this thread, and while I do think you are wrong I can't easily prove it in a few sentences. We have a 4 day weekend over here so hopefully I will find the time, if not I will respond to you early next week.

Cheers mate, looking forward to it.

Originally posted by Azp420
This situation would generate no significant pull-in force on the columns so is irrelevant.

You mean the situation where the truss is still intact? If yes, can you show what you base this on?

The truss was not designed to hold anything with tension in the top chord.

I strongly disagree that the ~85kN pull-in force claimed by the model was as a result of catenary action while all truss members were intact (although the poorly and confusing way it is written doesn't help). Perhaps you could quote some relative sections to clear this up? If you are able to show that this is indeed the case I would like to do some calculations to determine what is going on with the internal forces. Taking their word for it is not good enough for me.

It is of my opinion and understanding that a properly designed and typical truss is physically unable to carry a load via a catenary mechanism while all of its elements are intact.

I would also like to add that the report we have been discussing also casts doubt over whether the bolts would be able to transfer the pull-in force to the column.

In the text it sais:

The unprotected models under 4.8kN/m2 and 3.9kN/m2 loadings are shown in Fig 6 to have their first local instability at 16.1 and 18.0 minutes of the standard fire.

If you look at the figure you will notice the lines stop at these times. Additionally, there is a label in the figure pointing to these points that says "2nd compression diagonal buckles".

Originally posted by -PLB-
You mean the situation where the truss is still intact? If yes, can you show what you base this on?

This has been explained to you by more than one poster.

The steel is fixed between two solid points, the outer mesh and core columns, IF the steel expands from heat that expansion has to go somewhere. The natural tendency would be for the expanding steel to push outwards. When the columns do not allow this the steel has no choice but to sag down instead. Now if it sags because it can not push out, it is also not going to be able to pull in. Pushing out and pulling takes the same amount of force. IF the trusses could have put a force on the columns it would have been a push force not a pull force.

Cantenary action has nothing to do with it, sagging trusses do not act like chains.

If you were to put a weight on a chain, or wire, hanging between two points, and it can't hold the weight, the chain will break, IF it doesn't break then yes it could pull in the columns it's attached to. If you put a weight on a beam sagging because it is malleable from heat the beam will either break at the weak points, or it will just sag more. The catenary action of a malleable sagging beam can not pull in the columns they were attached to. You are just twisting and confusing physics principles in order to create an argument.

reply to post by -PLB-

You mean the situation where the truss is still intact? If yes, can you show what you base this on?

Yes, the truss cannot exert a pull-in force on the column and carry the load in a regular way, which is with compression in the top chord. If the top chord somehow gets into tension due to catenary action with the other members intact (in my opinion this would be extremely unlikely) then the other members will essentially just be hanging there as dead weight.

In the text it sais:

The unprotected models under 4.8kN/m2 and 3.9kN/m2 loadings are shown in Fig 6 to have their first local instability at 16.1 and 18.0 minutes of the standard fire.

If you look at the figure you will notice the lines stop at these times. Additionally, there is a label in the figure pointing to these points that says "2nd compression diagonal buckles".

The confusion is caused from their poor wording and poor layout (would not surprise me if inexperienced undergrads wrote this). They don't define tension failure as a "local instability", only compressive buckling.

It can be seen from Fig 7 that the horizontal reaction changes in direction from outward to inward at 11.7 minutes of the standard fire. This occurs as yielding spreads from mid-span outwards in the members of the bottom chord.

The bottom chord begins to yield at 11.7 minutes. 11.7 minutes comes before 16.1 and 18.0 minutes. You cannot ignore this. 11.7 minutes is the point where the top chord supposedly starts taking most of the imposed load in tension.

Therefore my calculations still stand, the report and model are rubbish.

Originally posted by Azp420

You mean the situation where the truss is still intact? If yes, can you show what you base this on?

Yes, the truss cannot exert a pull-in force on the column and carry the load in a regular way, which is with compression in the top chord. If the top chord somehow gets into tension due to catenary action with the other members intact (in my opinion this would be extremely unlikely) then the other members will essentially just be hanging there as dead weight.

It seems to me that as long as all members are intact the truss still behaves like a regular beam. Catenary action happens progressively, until a member fails.

The bottom chord begins to yield at 11.7 minutes. 11.7 minutes comes before 16.1 and 18.0 minutes. You cannot ignore this. 11.7 minutes is the point where the top chord supposedly starts taking most of the imposed load in tension.

Therefore my calculations still stand, the report and model are rubbish.

The text is not clear when exactly the top chord takes the majority of the load. I don't see a reason to assume that already happened during the simulation. But again, email the writers and get it cleared up, if you think this is a relevant issue.

reply to post by -PLB-

It seems to me that as long as all members are intact the truss still behaves like a regular beam. Catenary action happens progressively, until a member fails.

Trusses never behave like regular beams. Also, just because something "seems" to your uneducated opinion, doesn't make it so.

The text is not clear when exactly the top chord takes the majority of the load.

It can be seen from Fig 7 that the horizontal reaction changes in direction from outward to inward at 11.7 minutes of the standard fire. This occurs as yielding spreads from mid-span outwards in the members of the bottom chord. Once this condition occurs, the moment resistance of the composite truss, generated by the lever arm between top and bottom chords, begins to cease to carry the majority of the load. The load-carrying mechanism changes progressively to catenary action, shown in Fig. 8(c), in which both the slab and top chord carry most of the imposed load in tension rather than in balanced compression and tension with the bottom chord.

Seems pretty clear to me.

I don't see a reason to assume that already happened during the simulation.

It had already happened during the simulation, whether your beliefs allow you to see it or not. It was, after all, a catenary action simulation.

But again, email the writers and get it cleared up, if you think this is a relevant issue.

I see no need to email the authors. I'm satisfied that my interpretation of the report is accurate and see nothing to gain by obtaining clarification on a bunk model. This doesn't affect my beliefs regarding 9/11.

You, on the other hand, listed this report as one your fundamental evidences to justify your belief in the official version of events. If you don't want to gain clarification for yourself so be it, faith can fill the void which you once considered credible evidence (though I have no doubt your faith will assure you it is still credible, based on the University of Sheffield mention).

Originally posted by Azp420
Trusses never behave like regular beams. Also, just because something "seems" to your uneducated opinion, doesn't make it so.

It also "seems" like that according to Wikipedia. I have no reason to believe Wikipedia is wrong and you are right. You will have to make clear why regarding the (intact) truss to behave similar as a beam is wrong, just asserting it does not cut it.

Seems pretty clear to me.

It had already happened during the simulation, whether your beliefs allow you to see it or not. It was, after all, a catenary action simulation.

Yes, "shown in Fig. 8(c)". That is where that condition is depicted. It nowhere says that this condition was simulated. In fact, it is pretty clear to me it was not, as they say simulation ended at first buckling of a compressive member, depicted in 8(b), which happens before situation 8(c).

I see no need to email the authors. I'm satisfied that my interpretation of the report is accurate and see nothing to gain by obtaining clarification on a bunk model. This doesn't affect my beliefs regarding 9/11.

You, on the other hand, listed this report as one your fundamental evidences to justify your belief in the official version of events. If you don't want to gain clarification for yourself so be it, faith can fill the void which you once considered credible evidence (though I have no doubt your faith will assure you it is still credible, based on the University of Sheffield mention).

I do not have the issues with the paper that you do, I interpret it differently than you do, and I think you are wrong. You claim things that are simply not stated in the paper. The burden of proof that your claims are correct is on you. It is just not realistic to expect that I present your case to the authors, not only because the burden of proof is on you, but also because you will likely present your own case much better. If you just don't care, then thats ok, we will just leave it at that.

reply to post by -PLB-

It also "seems" like that according to Wikipedia. I have no reason to believe Wikipedia is wrong and you are right. You will have to make clear why regarding the (intact) truss to behave similar as a beam is wrong, just asserting it does not cut it.

Certainly. Beam members typically carry loads in bending. Truss members carry loads either in tension or compression.

Yes, "shown in Fig. 8(c)". That is where that condition is depicted. It nowhere says that this condition was simulated.

It says that this condition began to occur after 11.7 minutes. Read it carefully and with a mind that is unfiltered by beliefs.

In fact, it is pretty clear to me it was not, as they say simulation ended at first buckling of a compressive member, depicted in 8(b), which happens before situation 8(c).

Neither the diagrams or written report are laid out in chronological order (poor, I know, but I'm not choosing to base my beliefs on this garbage). As I pointed out earlier, the report claims compressive buckling occurs after there has already been widespread tension yielding.

Also, why would they give an in depth description of the top chord taking most of the load in tension, if this was not a result of their model? Why would they dedicate amount of words to pure speculation, and not make it clear that it was merely speculation and not a result of the model? Your interpretation doesn't add up.

You claim things that are simply not stated in the paper.

Such as?

The burden of proof that your claims are correct is on you.

I've provided mathematical proof for all my claims. I've assumed a moderate level of understanding and glossed over some of the basic stuff but have always been happy to clarify or go into more depth.

It is just not realistic to expect that I present your case to the authors

Present your case then and get them to clarify that you have interpreted correctly, that the top chord never took the majority of the load when achieving the maximum pull in force. That's just a suggestion. I like to ensure my beliefs are based on solid evidence.

If you just don't care, then thats ok, we will just leave it at that.

It's been fun debating with you. I'm sorry that I can come off a bit harsh at times.

Originally posted by Azp420
It says that this condition began to occur after 11.7 minutes. Read it carefully and with a mind that is unfiltered by beliefs.

Neither the diagrams or written report are laid out in chronological order (poor, I know, but I'm not choosing to base my beliefs on this garbage). As I pointed out earlier, the report claims compressive buckling occurs after there has already been widespread tension yielding.

Also, why would they give an in depth description of the top chord taking most of the load in tension, if this was not a result of their model? Why would they dedicate amount of words to pure speculation, and not make it clear that it was merely speculation and not a result of the model? Your interpretation doesn't add up.

The paper states that the simulation ends when the first compressive diagonal fails. Agreed?
This is before situation 8(c) is reached. Agreed? I don't see why this doesn't add up.

Another part says:

Through a progressive load redistribution process, illustrated in Fig. 8(b), the compressive diagonals then successively buckle at the same temperature. Eventually, this series of local instabilities causes the remaining part of the composite truss to collapse through tension of the slab and top chord.

If you agreed to the points above, we know the simulation stops when the first compressive diagonal fails. So it stops where 8(b) starts. In the above snippet it says that with each diagonal failing, more load is redistributed to the top chord, until the top chord fails. And that is basically what you are saying, when the load on the top truss is too large, it will fail. If it already carries the majority of the load, I don't see how the above snippet makes any sense.

Let me ask you this: Do you believe there is a period where a pull force is exerted at all? If not, why? If so, how large do you predict this pull force would be?

Such as?
I've provided mathematical proof for all my claims. I've assumed a moderate level of understanding and glossed over some of the basic stuff but have always been happy to clarify or go into more depth.

I am talking about your claim that the top chord carries (nearly) all the load in their simulations. I think that never happened, and my reasoning is explained above.

Present your case then and get them to clarify that you have interpreted correctly, that the top chord never took the majority of the load when achieving the maximum pull in force. That's just a suggestion. I like to ensure my beliefs are based on solid evidence.

I may drop them a mail, but I really think the mail should include your case. If you can give a short summery of your case I can include it unedited.

It's been fun debating with you. I'm sorry that I can come off a bit harsh at times.

Likewise. I'm fine with harsh, as long as you make relevant points, even though we disagree.

reply to post by -PLB-

The paper states that the simulation ends when the first compressive diagonal fails. Agreed?

Agreed with clarification. Assuming that the time from the first compressive diagonal failure to the successive compressive failures and total collapse is more or less instantaneous. It sounds like (and I would expect) the simulation ends at total collapse of the truss, which sounds like is at about the same time the first compressive diagonal fails.

This is before situation 8(c) is reached. Agreed? I don't see why this doesn't add up.

Disagree.

As I pointed out in my last post, page 5 is not written in chronological order (for some strange reason and is the cause of all this confusion). The diagrams are labeled in the order they are referred to, not in chronological order either. 8(c) actually comes before 8(b).

I have no idea why it was written like that, it's madness.

Let me ask you this: Do you believe there is a period where a pull force is exerted at all? If not, why? If so, how large do you predict this pull force would be?

Under the maximum deflections which I have seen estimated I don't believe a significant pull-in force due to catenary action is possible. 85kN is around the upper limit of pull-in force the bolts can take, so at this deflection the top chord is required to carry bending also, which it would be unable to do.

You claim things that are simply not stated in the paper.

Such as?

I am talking about your claim that the top chord carries (nearly) all the load in their simulations. I think that never happened, and my reasoning is explained above.

It was stated in the paper. I posted the relevant section several times and then bolded the exact wording.

I may drop them a mail, but I really think the mail should include your case. If you can give a short summery of your case I can include it unedited.

Let me know if you still disagree with me and maintain that the diagrams are in chronological order and I'll whip something up.

Originally posted by Azp420
Disagree.

As I pointed out in my last post, page 5 is not written in chronological order (for some strange reason and is the cause of all this confusion). The diagrams are labeled in the order they are referred to, not in chronological order either. 8(c) actually comes before 8(b).

I have no idea why it was written like that, it's madness.

Then here we disagree. I can't really see how situation 8c can occur before any diagonal has failed. As long as the diagonals are intact you will have at least some compression in the upper chord and tension in the lower chord as result of bending of the truss. The mechanism is similar to a regular I-beam. 8c depicts the situation where there is full catenary action. Per definition that means there are no bending forces at all.

Under the maximum deflections which I have seen estimated I don't believe a significant pull-in force due to catenary action is possible. 85kN is around the upper limit of pull-in force the bolts can take, so at this deflection the top chord is required to carry bending also, which it would be unable to do.

Ok. But I give the people who actually modeled it and published their results a lot more credit than assertions from an anonymous person on a forum.

It was stated in the paper. I posted the relevant section several times and then bolded the exact wording.

The exact wording was "as shown in Fig. 8(c)" and not "as simulated" or something similar.

Let me know if you still disagree with me and maintain that the diagrams are in chronological order and I'll whip something up.

Ok

OK I have a few minutes to myself here and I think this is the last point I got up to. I will have more time over the next few days.

I have read the discussion between you and PLB, and frankly I think that it's a little pointless considering that neither of you seem to have attempted to contact the authors and ask these questions. I certainly don't think that it's been reliably demonstrated that this model is invalid, and that's what I obviously want to focus on.

The 11.6 degrees I calculated from the claimed deflection, which was the same as the deflection you quoted me. I posted a link to the equations I used in a previous post.

The only equations I found in previous posts was a list of common calculations for beam deflection, but these require quantities that we have not seen supplied or agreed upon. Could you post these calculations in detail?

Not sure where you got that. I showed that under "full" or majority catenary action, the claimed actions are not possible, leaving the majority of load to still be carried in bending. I later showed them to also be not possible for a minority catenary action, with the bending moments easily failing the chord.

In a full catenary the forces applied to the top chord would be purely in tension, and so if the top chord was unable to carry this it would presumably fail as the catenary developed. However I have not seen the calculations you have done to support this either. Perhaps I didn't read through the thread thoroughly enough but could you again provide the specific calculations?

The truss applying no weight was the hypothetical argument you brought up when you were claiming my equation was wrong at a zero degree deflection. I showed you that it was actually correct, and that the equation I used would correctly produce an applied load of zero to an undeflected catenary, as it is only possible to have an undelfected catenary if there is no load applied to it.

Your calculation was purely a vector one, there was no consideration for catenary behaviour, and yet you used it as justification for criticising the paper.

Frankly, I am finding it difficult to understand exactly what your position is and what you believe supports it. If you would be so kind, please lay out your calculations showing problems with this paper so we can actually discuss it.

With regard to your discussion of bolt failures or similar, I will supply the appropriate references from the NIST report discussing the behaviour of truss seats. I really don't want to get into an argument where we try and out authority each other, if this model is wrong then I have no particular loyalty to it, I just don't quite get how you calculated identical angles for non identical deflections for example.

Originally posted by bsbray11
Aww come on, you were the one to start it again, with your arguments of "you're wrong because you left out a word,"

Uh, not sure that was me.

The only question that should remain for you at this point is 'which would happen first?': a column section being completely ripped out at the bolts and spandrel plates by a truss, or the truss itself failing?

There's no way that the image you're showing is accurate. I don't think NIST used more than about 6kips force anywhere in the conclusion, and this would not be anywhere near a significant enough force.

What likely happened is that the weight of the building above contributed to the inward deflection. We know that the columns were not moment framed to defeat this, and only the staggering effect would have served to resist this action. With WTC2 we can confirm this a little more I believe as the close up shots of the north-eastern corner at failure show the columns buckling and springing out over a very small area. This is the initiation of a progressive collapse, the most loaded columns give way and the load is redistributed in greater and greater quantities to identical columns which must also fail.

Originally posted by ANOK
Yes I can say NO columns were severed for two reasons, 1. No evidence, 2. Not physically possible. An aluminum plane can not sever 4" thick box columns. That would mean the plane would have to go through the first 4" wall of the first box column, then the next 4" thick wall of the box column, not to mention the two 4" thick side walls of the box column. All that after it's KE was reduced from flying through the outer mesh columns. Do you forget about that?

Ok so how exactly does your first point help your second point here? You claim there's no evidence of it, but then go on to say you know it didn't happen because of your own personal intuition.

That's not evidence.

In fact there is evidence for it, in that at least 4 different simulations by different groups have now shown it to occur in plane impacts on the towers, even in the most conservative estimates.

How exactly do you think that your personal incredulity should be believed more than the tests by hundreds of qualified engineers?

Originally posted by exponent
Uh, not sure that was me.

It was PLB, who you were talking about agreeing with. If you agree with him then I can only guess you'd be trying to make the same argument.

The only question that should remain for you at this point is 'which would happen first?': a column section being completely ripped out at the bolts and spandrel plates by a truss, or the truss itself failing?

There's no way that the image you're showing is accurate. I don't think NIST used more than about 6kips force anywhere in the conclusion, and this would not be anywhere near a significant enough force.

But... the photo was developed with the help of NIST.... and the leader investigator of the NIST report, Shyam Sunder, even describes the very same image as you are staring at it in the PBS documentary that NIST itself was involved with.

What likely happened

Well that's according to you. "What likely happened" to me is a different story, but we're not even going to go there, because opinions about 9/11 are "a dime a dozen" as they say.