Challenge: Demonstrate Sagging floor Trusses Pulling in Perimeter Columns

[Newtons Bit]

You have no idea what that quote means. (hence the smile)

I know, right? "truthers" have "ah hah!" moments based on complete ignorance of the topic.

 

[DGM]

You're welcome to explain it for me, DGM.

Why would I? Bask in your "victory".

 

[ergo]

Why would I? Bask in your "victory".

Okay then.

 

[Newtons Bit]

Why would I? Bask in your "victory".

I've even linked ergo to the thread that shows the failure mode that enik and I are talking about here. It's almost identical to the mode that Usmani proposes. That much would be obvious even if he only looked at the pictures.

 

[ergo]

I don't believe NIST's scenario talks about failing core columns. Does it?

And you're aware that Usmani et al don't talk about a pull-in force?

 

[DGM]

I don't believe NIST's scenario talks about failing core columns. Does it?

And you're aware that Usmani et al don't talk about a pull-in force?

You might want to stop "explaining".

 

[ozeco41]

I don't believe NIST's scenario talks about failing core columns. Does it?

And you're aware that Usmani et al don't talk about a pull-in force?

The explanation is still valid despite those two issues.

You might want to stop "explaining".

I've posted the simple "Column Inwards Bowing For Dummies" version several times.

#######Simple Version#######
1) We know that the columns across an extended bit of tower wall actually did bow in - so that much is known fact.

2) Heated sagging floor trusses would initiate inwards bowing but would not produce 54" without another factor.

3) Once a column bends out of line the vertical axial load will start to impose another bending force. That is the other factor.

4) That bending force - look for p delta in the mathy stuff - will tend to continue the bending if the combination of other factors allows. (My explanations were always qualitative and relied on "someone do the maths" at this point)

5) NB's earlier explanation shows that heat weakening is needed so that the "other factors allow" and p delta can "run-away".

#######End Simple Version#######

Extra comments:

Whether we need to add any "support" from Usmani's paper or core column failure is a separate issue of complication.

The more important complication is that the recent discussions in this thread have focused on a simplified one column one truss model. That does not meet the OP challenge which was clearly a "full WTC actual collapse" setting involving failure of multiple columns and trusses.

The one column/one truss model is orders of magnitude simpler to analyse than the full setting of the actual cascade failure. And the isolated single column will fail easier that the same single column would fail if it was joined to its neighbours in the whole of wall real collapse. (How big the difference would be is difficult - maybe impossible to say. One big factor would be temperature variance along the building.)

So reality of WTC on 9/11 is more complicated than the simplified model. Nothing new in that - we have threads discussing applicability of simplified models. This is just another example. Doesn't change the reality that cascade failure caused Twin Towers collapse initiation - and that perimeter failure was a part of the "cascade" - it just makes the numbers harder to work out.

 

[ergo]

The explanation is still valid despite those two issues.

Valid to whom? It's not NIST's model.

The more important complication is that the recent discussions in this thread have focused on a simplified one column one truss model. That does not meet the OP challenge which was clearly a "full WTC actual collapse" setting involving failure of multiple columns and trusses.

The one column/one truss model is orders of magnitude simpler to analyse than the full setting of the actual cascade failure. And the isolated single column will fail easier that the same single column would fail if it was joined to its neighbours in the whole of wall real collapse. (How big the difference would be is difficult - maybe impossible to say. One big factor would be temperature variance along the building.)

Yes, and I understand that NIST used random and hypothesized truss disconnections, not core column failure, to get the sag they needed on the remaining pull-in trusses. So of what relevance is Newton's explanation?

 

[Newtons Bit]

Valid to whom? It's not NIST's model.




Yes, and I understand that NIST used random and hypothesized truss disconnections, not core column failure, to get the sag they needed on the remaining pull-in trusses. So of what relevance is Newton's explanation?

Could you state, in your own words, what you think my explanation is?

 

[ergo]

Could you state, in your own words, what you think my explanation is?

In this post, which you linked to, the primary pull-in force you are describing is from the downward displacement of a severed core column.

 

[ozeco41]

Valid to whom? It's not NIST's model.

A) Valid for anyone interested in what actually happened with inwards bowing.
B) The objective is "Explain the inwards bowing which actually happened" not "Was NIST right?"

...Yes, and I understand that NIST used random and hypothesized truss disconnections, not core column failure, to get the sag they needed on the remaining pull-in trusses.

I'm explaining what happend - not defending NIST.

So of what relevance is Newton's explanation?

Newton's (and enik's) explanation is a valid explanation of the main part of the mechanism viz a one truss one column simplified model. It doesn't lose validity if we take out the specific initiator of core column movement the key points are that:
1) Inwards pull from a sagging truss could start bending of the peripheral column - no matter what caused the truss to pull inwards; AND
2) The force of 6Kips would be enough to start the inwards bowing without shearing the attachment bolts.
THEN
3) Once started and with heated columns (Newton's numbers show that reduced E is needed) the inward bowing will continue to propagate under applied axial load. i.e. the truss doesn't have to pull in the full 54".

ADD to that my proviso that it will take more pull in force in the real scenario. Not a lot more seeing as many columns bowed inwards at near enough the same time. No point me going further into details until we get the basics agreed - and someone wants to look at more details.

 

[Newtons Bit]

In this post, which you linked to, the primary pull-in force you are describing is from the downward displacement of a severed core column.

Where did I say that the core column displacement was the primary cause?? Are you making stuff up again?

 

[ergo]

Where did I say that the core column displacement was the primary cause?? Are you making stuff up again?

Newton's Bit, could you state, in your own words, what you think your explanation is?

 

[Newtons Bit]

Newton's Bit, could you state, in your own words, what you think your explanation is?

Sure, ergo.

The exterior columns failed through a combination of heat, loss of lateral support and a small pull-in force. The pull-in force could have been from core displacement or tension developed from the floor trusses in catenary action or some combination of the two. The primary mode of failure is p-delta, a fairly typical and well understood topic in structural engineering.

I've provided hand-calcs performing a second-order analysis that shows a single column under this small pull-in force is unstable. I've also provided a first-order linear FEA analysis in RISA showing that the deflection of the aforementioned column is very large and that the column has failed. Using engineering principles, its easy to conclude that the latter analysis would result in a continuing deflection.

Now, compare that with your explanation of my analysis:

In this post, which you linked to, the primary pull-in force you are describing is from the downward displacement of a severed core column.

You can't even get the source of the pull-in force right, much less figure out the details of what the pull-in force is actually doing. But go ahead and try to teach me how to do structural engineering.

 

[ergo]

Sure, ergo.

The exterior columns failed through a combination of heat, loss of lateral support and a small pull-in force. The pull-in force could have been from core displacement or tension developed from the floor trusses in catenary action or some combination of the two.

Really? You show all that in your single post? Wow.

You realize, I hope, that this is all just hypothetical and that NIST does not identify core column displacement as the cause of the truss sag. So as an academic exercise I'm not sure why this is even in the 9/11 subforum. But hey, have fun.

Now, compare that with your explanation of my analysis:

You can't even get the source of the pull-in force right, much less figure out the details of what the pull-in force is actually doing. But go ahead and try to teach me how to do structural engineering.

You told me to look at the "pictures". Your "pictures" describe a pull-in force occurring from downward displacement of a severed column. Moreover, as I've pointed out before, that post seems to want to give the impression that you're explaining the NIST WTC failure model, which you're not. I just want the casual reader to understand this. Do you agree?

 

[NoahFence]

I just want the casual reader to understand this.

That would be me I guess.

No matter what the result of this discussion is between you, ozeco and Newtons Bit is, I am 100% confident, even as a casual reader, that I know what didn't happen to WTC 7.

No explosives, no nano termites.

1) Damage from the attack started
2) Fire and that fire was never fought. First time that's ever happened. And because of it,
3) Damage and fire took down WTC7. Took like 7 hours. It was a long, long process.

 

[Newtons Bit]

Really? You show all that in your single post? Wow.

Yea, it's long and full of math. You may want to actually look at it.

You realize, I hope, that this is all just hypothetical and that NIST does not identify core column displacement as the cause of the truss sag. So as an academic exercise I'm not sure why this is even in the 9/11 subforum. But hey, have fun.

NIST's explanation is quite irrelevant to this thread. Stop trying to lurch off-topic.

You told me to look at the "pictures". Your "pictures" describe a pull-in force occurring from downward displacement of a severed column.

My pictures show both core column displacement and catenary action from the floor trusses. See?

I never made any claims as to the specific magnitude of forces developed from core column displacement or from catenary action.

Moreover, as I've pointed out before, that post seems to want to give the impression that you're explaining the NIST WTC failure model, which you're not. I just want the casual reader to understand this. Do you agree?

I never claimed to be explaining the NIST model. All I did was show the math behind why the exterior columns would bow as much as they did.

Anyways, you've exhausted my quota of "explain easy things to stubborn ignorant people" for the month. Back on ignore you go.

 

[Newtons Bit]

That would be me I guess.

No matter what the result of this discussion is between you, ozeco and Newtons Bit is, I am 100% confident, even as a casual reader, that I know what didn't happen to WTC 7.

No explosives, no nano termites.

1) Damage from the attack started
2) Fire and that fire was never fought. First time that's ever happened. And because of it,
3) Damage and fire took down WTC7. Took like 7 hours. It was a long, long process.

For the record, this is about WTC1&2. Though a few people do keep trying to shift it to WTC7 or to the NIST reports (which is not the topic of this thread either).

 

[NoahFence]

For the record, this is about WTC1&2. Though a few people do keep trying to shift it to WTC7 or to the NIST reports (which is not the topic of this thread either).

my bad...

Sometimes its hard to tell because the arguments are nearly the same.

 

[ozeco41]

I just want the casual reader to understand this.

That would be me I guess.

No matter what the result of this discussion is between you, ozeco and Newtons Bit is, I am 100% confident, even as a casual reader, that I know what didn't happen to WTC 7.

No explosives, no nano termites.

Correct on "No CD" but it is not the topic. The thread is about a challenge to prove some engineering aspects of WTC1/WTC2 collapse. Ergo keeps trying to derail the thread.

The situation is that enik, Newtons Bit and ozeco41 are in full agreement on the engineering principles and 95% agreement in the details. and the 5% difference is of no consequence other than to the engineers looking at the details.

My following comments are mainly for you Noah.

...NIST's explanation is quite irrelevant to this thread. Stop trying to lurch off-topic...

Correct and both Newton and ozeco have "called" ergo for the attempted derails and off topic nonsense.

...I never claimed to be explaining the NIST model. All I did was show the math behind why the exterior columns would bow as much as they did....

Correct. Newton has several times shown the maths and I have repeatedly outlined the principles involved.

...Anyways, you've exhausted my quota of "explain easy things to stubborn ignorant people" for the month. Back on ignore you go.

Agreed as this comment relates to ergo...however for NoahFence's benefit my recent post may help - I called it the "Column Inwards Bowing For Dummies" version and it is in post #267.

Stated simply inwards bowing of these columns needed two factors - some inwards pull to get bending started THEN the second factor cuts in. The column will tend to keep bending under its existing load. And Newton has shown that the bending would runaway if the steel was heated. All of that is basic engineering and nothing to do with NIST or any other of ergo's bits of evasion. And Newton, enik and ozeco are correct on that engineering.

For the record, this is about WTC1&2. Though a few people do keep trying to shift it to WTC7 or to the NIST reports (which is not the topic of this thread either).

Correct. It is the specific inwards bowing mechanism observed for WTC1 - mostly analysed by means of a simplified model.

my bad...

Sometimes its hard to tell because the arguments are nearly the same.

Understood and agreed. However just sort the arguments into ones which deal with the topic - and those ones have been well answered already - and those which are derail or evasion attempts which don't need to be answered in this thread.