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Any published papers criticizing NIST?

You know something? The funny thing is that, no matter what definition of "truss failure" you choose to use, it'll apply.
  • If you define "truss failure" like I was, and like Quintiere and NIST appeared to be, then the working definition was "failures involving the trusses in the structure". The trusses sagged, and created stresses that eventually separated them from the columns. That happened. It was a failure of the part of the "system" of structural components that involved the trusses.
  • If you define "truss failure" as the truss itself failing i.e. not becomeing disconnected, but actually breaking, well, that happened too. As NCSTAR 1-3C notes, much recovered truss material showed failure at the web-to-chord connections. NCSTAR 1-6C noted that much floor sag was due to the bucklling of truss web diagonals. Regardless, we know this occurred too, although the question of whether it was one of the initiating failures, or the result of the rubble piling onto the floors themselves is unclear.
  • If you define truss failure as stuff slamming into it and causing them to break somehow, well yes, that happened too. Remember, NIST didn't only study steel components from the collapse initiation zone; they came out and characterized steel in other areas too. They just didn't study all of it, nor spend much time on it.
    NCSTAR 1-3C p. xlvii said:
    The damage to truss seats on perimeter panels differed above and below the impact zone. The majority of perimeter panel floor truss connectors (perimeter seats) below the impact floors were either missing or bent downward. Above this level, the failure modes were more randomly distrubuted. This trend was observed for both towers)
    Click to expand...
About the only definition of "truss failure" that is ruled out by the recovered material is explosives demolition. But since we're talking about Quintiere's stance on the NIST report, that was never part of the topic to begin with.

At any rate, I drew out some distinctions above, but you all have to understand, that's starting to really get to the nitpick level. The point is that both NIST and Quintiere talk about truss sag as an integral component of the failure mechanisms. The only question is whether it's a primary - and indeed, an initiating - component as Quintiere suggests, or is simply another component in conjunction with core column shortening, as NIST states. Or was actually the result of core column shortening from heat, as NIST also states (I think they're actually stating different mechanisms between the North and South tower, but I need to read closer in order to clear that up. Someone else with better understanding can correct me on that). Regardless, separating truss sag from truss failure is just dumb. Truss sag is an integral component of truss failure; the former is simply one of the specific manifestations of the other.
 
ergo said:
That's OK. you've done enough in this regard. :rolleyes:

Looks like our "truss failure" semanticists have appropriately high-tailed it out of here.
Click to expand...

You've stopped making sense, if you ever did. The sagging trusses represents one type of failure, instrumental in causing the failure of the perimeter columns at those levels. The truss failures during the collapse once it was underway were failures of the seats, as can be seen in many of the videos where parts of the exterior walls appear to peal off the building.

Being intentionally obtuse doesn't help your argument any.
 
I saw this "Dilbert" comic this morning, Remind us of anyone?


debate.gif




:D
 
Keep the discussion civil please.
Replying to this modbox in thread will be off topic  Posted By: Gaspode
 
ElMondoHummus said:
The point is that both NIST and Quintiere talk about truss sag as an integral component of the failure mechanisms. The only question is whether it's a primary - and indeed, an initiating - component as Quintiere suggests, or is simply another component in conjunction with core column shortening, as NIST states.
Click to expand...

I think this summarizes your complete misunderstanding of the matter.

Quintiere does not talk about sag. The whole point of his critique was that he disagrees with the NIST truss sag-pulling-in-columns model.

From your own friggin' quote:

Quintiere said:
These are two different conclusions and the accountability for each is dramatically different
Click to expand...



ElMondoHummus said:
Or was actually the result of core column shortening from heat, as NIST also states ...Regardless, separating truss sag from truss failure is just dumb.
Click to expand...

Perhaps you should inform Quintiere.

Truss sag is an integral component of truss failure; the former is simply one of the specific manifestations of the other.
Click to expand...

No. It isn't. Trusses can fail without sagging, and they can sag without failing. Do you even know what you're saying?
 
ergo said:
No. It isn't. Trusses can fail without sagging, and they can sag without failing. Do you even know what you're saying?
Click to expand...

One of the first things we learned in Structural Analysis was that structural failure encompasses a range of things anywhere along the spectrum of possibilities. This can include anything from total collapse to the user feeling uncomfortable with how much a floor "bounces" when they walk on it. It is, in fact, sometimes necessary to use more steel than would be required simply to support a given load in order to prevent a floor structure from deflecting to such an extent that people are uncomfortable.

That said, no, floors cannot sag without failing, as no user would be comfortable with a sagged office floor. It constitutes a failure by any structural definition of the word.

Truther vocabulary notwithstanding, the more you dig yourself in, the more obvious it becomes how little you know.
 
ergo said:
...Trusses ... can sag without failing.
Click to expand...

You might as well say tendons can get strained without being injured, an apple can rot without being spoiled.

Failure <> utter, catastrophic destruction
 
ergo said:
I think this summarizes your complete misunderstanding of the matter.

Quintiere does not talk about sag.
Click to expand...


Again. If you actually read the report (that Dr. Q contributed to) you would know how stupid you look. Stop looking at quotes and read the freaking papers.

You're pathetic!

:o
 
sylvan8798 said:
That said, no, floors cannot sag without failing, as no user would be comfortable with a sagged office floor. It constitutes a failure by any structural definition of the word.
Click to expand...

Is that true? Real engineers, feel free to pipe in.

From a design perspective, you could argue that something that sags that is not supposed to is "failing" in its intended purpose. Obviously one doesn't want concave office floors.

In the context of the NIST collapse initiation model however, the two terms suggest completely different mechanics. A sagging truss is still carrying its load. A failed truss is not. NIST's sagging trusses apparently have the power to pull in consecutive steel box columns on the perimeter wall. A failed truss, one that has broken its connections, obviously cannot do this.

Saying that one is the other and it's all just One Big Blur of fires and failures is simply incorrect, and it completely misunderstands and misrepresents Quintiere's objections to NIST.
 
ergo said:
Is that true? Real engineers, feel free to pipe in.

From a design perspective, you could argue that something that sags that is not supposed to is "failing" in its intended purpose. Obviously one doesn't want concave office floors.
Click to expand...
I think one could also argue that once a structural component no longer meets its original minimum design specification, it has also failed. For example, if a floor joist is permanently sagged, then it no longer has the ability to support the design load. It has failed in both tension and compression, and if twisted, it has failed in torsion.

Materials can also fail from microscopic cracking, hydrogen embrittlement, and many other causes. Even wooden structural members rot or get insect damage to the point they no longer perform to minimum specifications. I would say these things are failures

In the context of the NIST collapse initiation model however, the two terms suggest completely different mechanics. A sagging truss is still carrying its load. A failed truss is not. NIST's sagging trusses apparently have the power to pull in consecutive steel box columns on the perimeter wall. A failed truss, one that has broken its connections, obviously cannot do this.
Click to expand...
This is just a matter of definition. Thinks can fail to meet the specifications for the material without having failed completely/destructively. This is part of the reason things are designed with a factor of safety.

Saying that one is the other and it's all just One Big Blur of fires and failures is simply incorrect, and it completely misunderstands and misrepresents Quintiere's objections to NIST.
Click to expand...
Again, saying one thing is the other is the difference I discussed above. Failure does not necessarily have to imply destructive failure.
 
ergo said:
Is that true? Real engineers, feel free to pipe in.

From a design perspective, you could argue that something that sags that is not supposed to is "failing" in its intended purpose. Obviously one doesn't want concave office floors.
Click to expand...

That smirk on your face looks pretty silly when you consider that I have a BS in structural engineering, an MA in math, a PhD in physics, a PE license, 7 years as a structural engineer, and numerous years teaching, facts which most posters here already know.

What you got? :cool:
 
sylvan8798 said:
That smirk on your face looks pretty silly when you consider that I have a BS in structural engineering, an MA in math, a PhD in physics, a PE license, 7 years as a structural engineer, and numerous years teaching, facts which most posters here already know.

What you got? :cool:
Click to expand...

Ignorance and incredulity
 
Mr. Skinny said:
Failure does not necessarily have to imply destructive failure.
Click to expand...

My guess is that in failure analyses, engineers need to be specific as to the causes and mechanisms. If engineers talk about truss sag, they are talking about trusses sagging. If they talk about truss failure, they are talking about broken or disconnected trusses, i.e., their inability to carry any load.
 
ergo said:
My guess is...
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And that's all you've presented. Stop embarrassing yourself. All you have demonstrated Ergo is that Dr. Q disagreed with NIST in some respect, and no one has disputed that point. The fact still remains that in his criticism he still supports collapse by fire and out of his suggested possible scenarios none include explosives, thermite, or ninjaneers.
 
ergo said:
Is that true? Real engineers, feel free to pipe in.

From a design perspective, you could argue that something that sags that is not supposed to is "failing" in its intended purpose. Obviously one doesn't want concave office floors.

In the context of the NIST collapse initiation model however, the two terms suggest completely different mechanics. A sagging truss is still carrying its load. A failed truss is not. NIST's sagging trusses apparently have the power to pull in consecutive steel box columns on the perimeter wall. A failed truss, one that has broken its connections, obviously cannot do this.

Saying that one is the other and it's all just One Big Blur of fires and failures is simply incorrect, and it completely misunderstands and misrepresents Quintiere's objections to NIST.
Click to expand...

False. A sagging truss is not carrying it's load, and further, is stressing the wall system to which it is attached. In an engineered system any out-of-tolerance movement is failure.
 
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