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Tags 9/11 , collapse initiation , twin towers , wtc1 , wtc2

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Old 26th May 2015, 11:22 PM   #201
Oystein
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I must be looking at a different paper.
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Old 27th May 2015, 01:01 AM   #202
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Originally Posted by Oystein View Post
Huh? Appendix II? No. Bazant explains that IF (or SINCE) the top block rotates, why it doesn't pivot around its base.
He does not explain why the top block starts to move (descend and rotate) in the first place.
He asserts that it was perimeter led as a consequence of a movement equivalent to torque. Whether that is true or not it begs the question of what started the "movement equivalent to torque". And the explanation in the "Main Thread" outlines what actually happened in language intended to be accessible to a lay person. Bazant's "movement equivalent to torque" is at Step Q of that explanation.

Remember also that the referenced section of Bazant's paper was responding to "Why didn't the Top Block Topple?" There is a far simpler lay person's explanation avoiding the complexities of academic engineering expression. Once the Top Block started to descend bodily the pivot for toppling had failed - it was a "virtual pivot" formed by the columns which were holding up the Top Block. Once that support and pivot failed the "falling" speed simply out-raced any remnant "rotational momentum". You can see that simply in the following video clip - see how "falling" races away at the ~5 seconds mark:
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I AGREE


In fact look at Bazant's own drawing:

Then align it with the sequence posted in the "Main Thread":
Originally Posted by ozeco41 View Post
what do we see?
Step P - At 1 second -Settling - early motion - mostly vertical as columns failing in some sort of sequence; == Bazant's a and b
Step Q - By 4 seconds - significant tilt of the Top Block - Base of Top Block moves horizontally to the right - ensures column ends are out of line; == Bazant's c and d and where his torque is evident.
Step R - At ~5 seconds rapid downwards dropping with no obvious extra tilt; == Bazant's e
Step S - At 6 seconds - disappears into dust.


Originally Posted by Oystein View Post
I must be looking at a different paper.
Nah. You are reading the same paper as me. Forget that Bazant was a co-author and ask "Would I accept this in 2015 if it was anonymous/unsourced?" It was a good and influential first effort for 2001-2.

Last edited by ozeco41; 27th May 2015 at 01:17 AM.
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Old 27th May 2015, 05:39 AM   #203
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Originally Posted by ozeco41 View Post
I'm unclear what your problem is Sander.

......

There can be no question IMO about lots of mini jolts.

......

What do you mean by "translation" and how would it prevent those inevitable mini jolts?
My "problem" is not with the math of load redistribution and clearly if the top "hits" the section below there would have to be some manner of jolts or impacts... this is self evident. Clearly there was thousands if not tens or hundreds of thousands of "impacts" and jolts spread out through time to produce a sort of smoothing "effect" which concealed all the mini impacts. We know we did not have hundreds of columns loaded with the mass above dropping on to column ends below in the lower section. This would be impossible.

+++

The issue I do have is what IS "column failure"... Obviously when a column's axial capacity is reduced to below the load it must support it will fail and buckle. The mechanisms for axial capacity reduction as far as I know.... are:

a. reduce the section of the column
b. increased the slenderness ratio of the column
c. heat the column... as heated steel has lower "structural" capacity than room temperature steel
d. reduce the bearing area of the column

I suppose multiple factors could be in play.


Understand what happened to individual column capacity and therefore aggregate column capacity is the "story of the initiation" of the collapses. We do know that there were columns destroyed and perhaps some damaged by the plane impact. This reduced aggregate capacity but not low enough to initiate top drop.

Therefore we look to the effects of heat... and perhaps some additional mechanical "damage" caused indirectly by the heat during the post strike to release time frame.

So... what was happening? What was the heat doing to drive down individual and then aggregate column capacity?

Was the "drop" (as I suspect) core led... ie loss of core capacity. NIST seemed to suggest that the floor trusses bowed and misaligned the facade top and bottom... to promote buckling and that left the perimeter of the core holding up the floors and unable to it...

"My problem" has always been to understand the mechanisms/processes in play which initiated the top to drop and apparently displace (translate) laterally. I have found the NIST explanation unsatisfying.
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Old 27th May 2015, 06:32 AM   #204
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To those who think that there could never have been a possibility for jolts:

Since ozeco seems to be unable or unwilling to address the point that I'm making, and he didn't provide an answer to this question when he had the opportunity, I have to ask the others: what is the possible cause of misalignment at the point where the top has descended by the height of one floor?

Remember we're at a stage where the columns at one side have failed, and the top block is already in movement. Vertical motion is unequivocally detectable at the roof and if there is a jolt in the structure, it will be transmitted through the still resisting core to the roof.

I'm referring to the instant in time in which either of these happens, but specially the latter:





Some columns have failed, part of the roofline has moved downwards, and the bottom of one floor of the top block is at the same height as the top of another floor for the first time. I believe that's a point that ozeco calls "P" in his explanation.

What can possibly cause, at that point, a misalignment between top and bottom column ends? Alternatively, what can possibly cause that they are aligned but there is not jolt resulting from the impact, or that the jolt is not detectable in the roof?

It's clear to me that when the opposite side of the building starts to descend unequivocally, the tilt is already big enough as for the columns to be misaligned, as a result of the projection of the angled top block's bottom on the bottom block. That's the stage that ozeco calls "Q" and I agree that at that point there can't be any significant jolts. He answered why at that point there can't be any jolts, but I'm asking about an earlier point as indicated above, which, I believe, is the target of study in Szamboti's paper and femr2's refutation.
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Last edited by pgimeno; 27th May 2015 at 06:39 AM. Reason: correction (underlined)
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Old 27th May 2015, 06:34 AM   #205
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Originally Posted by GlennB View Post
Non sequitur (at best). Bazant's analyses were never intended to explain "actual collapse mechanisms". Virtually every regular here - over many years - has laboured this point to exhaustion. It isn't "forbidden territory", it's just that most understand the purpose of those models while you - here, anyway - set them up as a strawman to knock down for reasons unknown.

Meanwhile, check out how many times you say I/me/my/mine in your posts, eh?
He can speak for himself but the way I read Ozeco's point is that discussions get so much into the minutiae that people forget in the midst of the argument that at the end of the day Bazant's initial models were limit cases, he was clear about it, and yet a lot of discussions carry on as if it's being applied. Maybe not intentionally at that, but enough to where it does merit a reminder that such debates this late in the game don't need to be that complicated. I've wasted hours upon hours in the past dealing with the minutiae of whether his model was correct or not, and.... as far as I am concerned the first disclaimer you take is that whether it was wrong or not (another area that I think Ozeco's referring to), is irrelevant as long as the people criticizing it don't first realize everything in that work was based on hypotheticals with set conditions that most people know were never made to reflect the observed reality in the first place.

NOTE: I'm not suggesting that people are wrong to argue on the merits of the Bazant models.... but it does bear repeating that there's a certain scope cut off that can render the debates commonly dealt with on its relevance sort of moot. That's my opinion at least

Originally Posted by pgimeno View Post
It's clear to me that when the opposite side of the building starts to descend unequivocally, the tilt is already big enough as for the columns to be misaligned, as a result of the projection of the angled top block's bottom on the bottom block. That's the stage that ozeco calls "Q" and I agree that at that point there can't be any significant jolts. He answered why at that point there can't be any jolts, but I'm asking about an earlier point as indicated above, which, I believe, is the target of study in Szamboti's paper and femr2's refutation.
The simple answer to this - if i understand your question - is that TZ argues for a more severe jolt than could have ever happened. Not that there couldn't have been any jolts at all or anywhere in between. I am not sure of femr2's analysis but Szamboti unequivocally predicates his assumptions on the most literal interpretation of Bazant's model, and that is his ultimate failure with regards to any discussion about impacts or jolts at the point of collapse initiation. You may also take interest in reviewing WTC 2's collapse initiation and it reveals perhaps much more on this issue. The columns clearly flexed as the building began to tilt, and most of these failures were variations of buckling from the changing load dynamics.

Please feel free to clarify if you think I've misread.
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Old 27th May 2015, 07:05 AM   #206
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Originally Posted by JSanderO View Post
The mechanisms for axial capacity reduction as far as I know.... are:

a. reduce the section of the column
b. increased the slenderness ratio of the column
c. heat the column... as heated steel has lower "structural" capacity than room temperature steel
d. reduce the bearing area of the column
Not sure about terminology, but isn't there also deformation of the column by lateral forces, as in the observed bowing of the perimeter columns?

Dave
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Me: So what you're saying is that, if the load carrying ability of the lower structure is reduced to the point where it can no longer support the load above it, it will collapse without a jolt, right?

Tony Szamboti: That is right
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Old 27th May 2015, 08:19 AM   #207
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Originally Posted by Grizzly Bear View Post
The simple answer to this - if i understand your question - is that TZ argues for a more severe jolt than could have ever happened.
Given his sampling and smoothing methods, I agree and I stated so:
Originally Posted by pgimeno View Post
I believe that Tony's problem was that he used too imprecise measurements at a too low sampling frequency, introducing too much noise that he had to smooth, all these factors resulting in flattening the jolts out of existence. I don't remember the details, but I seem to recall that the jolts were expected to be shorter in duration than his sampling frequency.
But my explanation was denied with a claim that a macroscopic jolt would never have the chance to happen. So what I'm asking is why a macroscopic jolt would not be perceptible.

Originally Posted by Grizzly Bear View Post
I am not sure of femr2's analysis
I mean this one:

http://femr2.ucoz.com/photo/photo_1/6-0-583



It shows jolts at approximately 2 feet, 6 feet and 17 feet of descent. The latter might correspond with the top-to-bottom impact that I'm mentioning, as the height of a floor is ~12 feet and there is some angular effect and flexure to consider.
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Old 27th May 2015, 08:22 AM   #208
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Originally Posted by Dave Rogers View Post
Not sure about terminology, but isn't there also deformation of the column by lateral forces, as in the observed bowing of the perimeter columns?

Dave
I suppose that a column which is pushed or pulled "out of column" will lose strength. But yes definitely lateral distortion - expansion followed by contraction could be a mechanism which would distort column or push them out of axial alignment.

I am not sure that is the explanation for the IB of part of the facade. Those columns were somewhat asymmetrically loaded ... a bit by the floor load. However most of the axial load on the facade came from the columns above. In fact only every other column had a truss seat to carry local floor loads.

A typical floor load applied to a facade column is computed as half the distance to the core (30' or 17.5') and 6'-8" wide... dead and live load.

I don't know the lateral force that a sagging double truss would generate. It seems to me that the bolts of the seat would shear before the column would bow.

No?
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Old 27th May 2015, 08:35 AM   #209
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Originally Posted by JSanderO View Post
I don't know the lateral force that a sagging double truss would generate. It seems to me that the bolts of the seat would shear before the column would bow.

No?
The sagging trusses wouldn't need to supply all the force to cause the inward bowing. If they were simply no longer doing their job of restraining the columns horizontally, but instead were pulling the columns just slightly inward, the axial load of the building above would cause buckling.
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Old 27th May 2015, 08:37 AM   #210
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Originally Posted by pgimeno View Post
But my explanation was denied with a claim that a macroscopic jolt would never have the chance to happen. So what I'm asking is why a macroscopic jolt would not be perceptible.
More precisely, it was denied with the claim that column-to-column impacts never had a chance to happen. So I'm asking what would cause the misalignment that would prevent them from happening when reaching this point:



Or alternatively, how the situation in my diagram differs from the actual collapse so substantially that there was never a column-to-column impact.


ETA: Note that I see at least two possible answers, but it's not all that obvious to me that any of these was necessarily the case, as to disregard the possibility of axial impact as impossible.
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Old 27th May 2015, 10:03 AM   #211
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Originally Posted by WilliamSeger View Post
The sagging trusses wouldn't need to supply all the force to cause the inward bowing. If they were simply no longer doing their job of restraining the columns horizontally, but instead were pulling the columns just slightly inward, the axial load of the building above would cause buckling.
I don't believe that... maybe... The facade clearly could move laterally because there were dampers... How much lateral motion are you claiming would lead to buckling under normal axial loading? 1"... 2" one column connection? how many?
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Old 27th May 2015, 10:26 AM   #212
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Originally Posted by pgimeno View Post
More precisely, it was denied with the claim that column-to-column impacts never had a chance to happen. So I'm asking what would cause the misalignment that would prevent them from happening when reaching this point:

http://www.formauri.es/personal/pgim...t/anim0004.png

Or alternatively, how the situation in my diagram differs from the actual collapse so substantially that there was never a column-to-column impact.
I'll get into more detail tonight (once I have some IRL issues sorted) but as I mentioned earlier, WTC 2 IMO shows the issue more clearly as to why there wouldn't be a column-to-column impact:



For the record... "no chance" is probably the wrong word anyway IMO... the more accurate distinction at least in reference to the angle TS takes on is that the impact was "smoothed" or "distributed" by lateral forces and other dynamics causing the columns - if anything - to buckle or deflect similar to how you see above prior to them completely failing. There were likely such impacts, but the degree to which they affect matters is at a level of detail I would initially consider moot

Let me review the information you posted from femr2 and I'll take some additional time to give you a more complete response.

IMO the disagreement you and Ozeco are having on this matter seems to be a simple misunderstanding, but I'll worry about that after I've looked into everything
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Old 27th May 2015, 10:48 AM   #213
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Originally Posted by Dave Rogers View Post
Not sure about terminology, but isn't there also deformation of the column by lateral forces, as in the observed bowing of the perimeter columns?

Dave
Yes. And it is one of those issues where "both sides have got it wrong" - I was going to use it as an example in the "Main Thread Explanation" then changed my mind and chose not to.

Originally Posted by JSanderO View Post
I don't know the lateral force that a sagging double truss would generate. It seems to me that the bolts of the seat would shear before the column would bow.
FEA by enik and Newton's Bit say otherwise. There is a thread with extensive discussion - which BTW avoided the "both sides wrong" problem.

Originally Posted by WilliamSeger View Post
The sagging trusses wouldn't need to supply all the force to cause the inward bowing. If they were simply no longer doing their job of restraining the columns horizontally, but instead were pulling the columns just slightly inward, the axial load of the building above would cause buckling.
That is the correct explanation in a lay person nutshell. Thank you.

The wrong arguments took a single factor approach - that the sagging of trusses would not be enough to cause the observed 54" inwards bow in.

Didn't have to - only had to pull in till the critical p-delta point where the inwards bowing would continue to self propagate under the applied axial load. The distance to reach p-delta would be less with more axial load.

IIRC NewtonsBit explained it comprehensively.
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Old 27th May 2015, 11:00 AM   #214
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Originally Posted by JSanderO View Post
I don't believe that... maybe... The facade clearly could move laterally because there were dampers... How much lateral motion are you claiming would lead to buckling under normal axial loading? 1"... 2" one column connection? how many?
The tops of the trusses were bolted and welded on both ends, so the exterior columns were restrained laterally, relative to the core, in a "pinned" condition. The dampers were at the bottom of the trusses, to absorb moment forces caused by building sway. The effect of the sagging trusses, even ignoring the inward force produced, would be that the effective unbraced length of the columns would double at that floor, with the resulting loss of resistance to buckling. Add the inward force, and the buckling would be inward. Once that buckling began, at some point the buckling would be pushing the sagging even farther rather than the other way around, which is a point I think the denialists miss when they complain about not seeing enough buckling in the truss fire tests. I think an FEA would be required to put numbers to it.
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Old 27th May 2015, 11:22 AM   #215
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Originally Posted by WilliamSeger View Post
The tops of the trusses were bolted and welded on both ends, so the exterior columns were restrained laterally, relative to the core, in a "pinned" condition. The dampers were at the bottom of the trusses, to absorb moment forces caused by building sway. The effect of the sagging trusses, even ignoring the inward force produced, would be that the effective unbraced length of the columns would double at that floor, with the resulting loss of resistance to buckling. Add the inward force, and the buckling would be inward. Once that buckling began, at some point the buckling would be pushing the sagging even farther rather than the other way around, which is a point I think the denialists miss when they complain about not seeing enough buckling in the truss fire tests. I think an FEA would be required to put numbers to it.
I don't know the exact deflection that results in the column becoming unstable, but a 3-story unbraced length is unstable at 1.5in.

No FEA needed. See here: http://www.internationalskeptics.com...d.php?t=107267
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Old 27th May 2015, 11:25 AM   #216
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Originally Posted by Grizzly Bear View Post
IMO the disagreement you and Ozeco are having on this matter seems to be a simple misunderstanding,
It is. There are two parts to it (at least):
1) Looking for jolts? Why? The need is to understand how the cascade failure progressed. The focus on "Jolts" is a consequence of the Szamboti misuse of the Bazant assumption from B&Z 2002. The point I keep trying to make is that we are still seeing Bazant modelling blocking our thinking. The fact we are discussing "Jolts" proves that point. The need is to understand how the cascade progressed. We need to stop, back off. Wipe the slate clean of "Joltish ideas" and start again. Explaining it without reference to Jolts. Mea culpa on that BTW - I should try to heed my own advice rather than accommodate the "Bazant/Szamboti" tradition.

2) I am suggesting - as I routinely do for these types of issues - find a known point where you can be sure of the truth of the situation. The point I suggest is "Top Block Descending Bodily". Whether it is Step P or Q or R or matters not. At the point you are comfortable with the columns cannot be in line resisting the fall THEREFORE the ends of the columns if they are still present must be bypassing. That is the point where pgimeno is sticking as shown by this quote:
Originally Posted by pgimeno View Post
It's clear to me that when the opposite side of the building starts to descend unequivocally1, the tilt is already big enough as for the columns to be misaligned2, as a result of the projection of the angled top block's bottom on the bottom block. That's the stage that ozeco calls "Q" and I agree that at that point there can't be any significant jolts3. He answered why at that point there can't be any jolts, but I'm asking about an earlier point4 as indicated above, which, I believe, is the target of study in Szamboti's paper and femr2's refutation.5
1 I'm comfortable with "descend unequivocally" meaning the same as I intended with "falling bodily".
2 I agree the "columns...misaligned" - the point I am trying to make - titl is one of the factors and I won't get pedantic over other factors.
3 So pgimeno and I are in agreement that it reaches a stage where there is misalignment. That is the main point I was seeking to assert.
4 I suggest the issue is NOT whether there were or were not "Jolts" BUT what is puzzling pgimeno is how it got to that situation. He asks about an earlier point. This is where my reasoning doesn't lock up. This is my version - we know it got to a state of bypassing - why does it matter how it got to that state. Think that through everyone before you shoot me. Why are we interested in how it got there? There are multiple ways a column can buckle break or shear or... so what? The end point is bypassing. The clue as to why our thinking derails is in the next point.
5 Whoever was right they were both focussed on Jolts. Round the circle we go. We are chasing Jolts. Szambotian Jolts arising from the Bazant & Zhou artifice of "dropping the top block" as the means of starting the progression for the "Limit Case" analysis.

The "Limit Case" argument was for collapse progression - outside the scope of what we are currently discussing. The only Bazant aspect relevant to this part of the discussion of cascade failure initiation stage - the Bazant artifice of Dropping Top block which got the progression started for him.

Forget Jolts. We are already agreed the main point I wanted to make - the columns end up bypassing.
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Old 27th May 2015, 11:27 AM   #217
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Originally Posted by Newtons Bit View Post
I don't know the exact deflection that results in the column becoming unstable, but a 3-story unbraced length is unstable at 1.5in.

No FEA needed. See here: http://www.internationalskeptics.com...d.php?t=107267
Thanks - I'd forgotten the details but knew you had explained it.
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Old 27th May 2015, 11:58 AM   #218
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Originally Posted by Grizzly Bear View Post
Originally Posted by GlennB View Post
Non sequitur (at best). Bazant's analyses were never intended to explain "actual collapse mechanisms". Virtually every regular here - over many years - has laboured this point to exhaustion. It isn't "forbidden territory", it's just that most understand the purpose of those models while you - here, anyway - set them up as a strawman to knock down for reasons unknown.

Meanwhile, check out how many times you say I/me/my/mine in your posts, eh?
He can speak for himself but the way I read Ozeco's point is that discussions get so much into the minutiae that people forget in the midst of the argument that at the end of the day Bazant's initial models were limit cases,...
I sure can speak for myself

But if you look back you will see that GlennB was reacting to a light hearted comment I made to you. The situation relevant to this thread's discussion is:

1) We are discussing the WTC Twin towers cascade failure initiation stage and not the progression stage;

2) Bazant's 2002 paper with Zhou presents a valid in concept limiting case argument for progression stage. Not of current relevance here;

3) That B&Z 2002 used an artifice - an assumption of "Dropping Top Block" - as a simplified way to get his progression going. So that was Bazant's "initiation stage" and is relevant here;

4) That simplified assumption was valid IMO for Bazant's purpose BUT it was taken by T Szamboti as the literal mechanism of collapse initiation and T Sz went looking for a Jolt. That put "Jolt" into the vocabulary of discussion;

5) My main point - looking for Jolts has been and continues to be a big source of confusion to those seeking to understand the "initiation stage."

I disagree with several aspects of Glenn's comment but they are outside the scope of this thread so I won't pursue them.

Originally Posted by Grizzly Bear View Post
... he was clear about it, and yet a lot of discussions carry on as if it's being applied........ as far as I am concerned the first disclaimer you take is that whether it was wrong or not (another area that I think Ozeco's referring to), is irrelevant as long as the people criticizing it don't first realize everything in that work was based on hypotheticals with set conditions that most people know were never made to reflect the observed reality in the first place.
Which are aspects of my main themes stated in your words...Agreed.
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Old 27th May 2015, 12:10 PM   #219
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Originally Posted by Newtons Bit View Post
I don't know the exact deflection that results in the column becoming unstable, but a 3-story unbraced length is unstable at 1.5in.

No FEA needed. See here: http://www.internationalskeptics.com...d.php?t=107267
But it wasn't a 3 story unbraced length... it was a pull at one story location... no?
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Old 27th May 2015, 12:13 PM   #220
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Originally Posted by JSanderO View Post
But it wasn't a 3 story unbraced length... it was a pull at one story location... no?
Multiple storeys, from the appearance of the exterior. And I suspect that the difference between an unbraced column and a column subject to sideways forces pushing it out of alignment is not in the favour of the latter; in effect, it's experiencing the opposite effect to lateral bracing.

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Old 27th May 2015, 12:13 PM   #221
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Originally Posted by ozeco41 View Post
Think that through everyone before you shoot me. Why are we interested in how it got there? There are multiple ways a column can buckle break or shear or... so what? The end point is bypassing. The clue as to why our thinking derails is in the next point.
Forget Jolts. We are already agreed the main point I wanted to make - the columns end up bypassing.
This is of interest because it is where the explanation of the initiation of the movement/collapse would be. Your starting at the time the are miss aligned and falling is AFTER the initiation.

I want to know how it all got moving...
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Old 27th May 2015, 12:55 PM   #222
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Originally Posted by JSanderO View Post

I want to know how it all got moving...
My guess would be when the multi-storey, unbraced columns reached their capacity. The damage and fire was not confined to one floor.
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Old 27th May 2015, 01:15 PM   #223
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Originally Posted by JSanderO View Post
But it wasn't a 3 story unbraced length... it was a pull at one story location... no?
That would be a two story unbraced length then. I don't care to do the math, but I'd guess that it becomes unstable at about a ~2" horizontal deflection.
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Old 27th May 2015, 01:38 PM   #224
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Originally Posted by Grizzly Bear View Post
I'll get into more detail tonight (once I have some IRL issues sorted) but as I mentioned earlier, WTC 2 IMO shows the issue more clearly as to why there wouldn't be a column-to-column impact:

http://i.imgur.com/GWpX5v9.png
That's pretty convincing. Yes, that was the main mechanism I had in mind: the top block rotating with all columns failing sideways. The only thing left to know is whether that situation happened at the time of the first floor impact or later as the top gained rotational momentum.

The other mechanism I had in mind was the combined effect of a less powerful version of that effect (i.e. only a bit of displacement of the top due to a slight rotation backwards) with the angle of the fall. It's plausible that both together could accumulate to a full column width, resulting in the upper column falling outside the footprint of the lower column.

In the case of WTC1 the upper block (and thus the rotation axis) is much shorter, so if there was any misalignment it was probably due to that combined effect.

Can you point me to a good video that shows the side clearly? The image you posted, is it a still or a frame of a video?

I look forward to any more information you can provide.
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Old 27th May 2015, 03:18 PM   #225
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Originally Posted by ozeco41 View Post
The focus on "Jolts" is a consequence of the Szamboti misuse of the Bazant assumption from B&Z 2002. The point I keep trying to make is that we are still seeing Bazant modelling blocking our thinking. The fact we are discussing "Jolts" proves that point.
False. I haven't used Bazant's 1D blocks assumption when I asked my question about the fall of the first floor. I took into account the 3D reality and structure of the towers. Szamboti also took it into account, as I remember he calculated whether or not the angle was enough for the columns to miss, and concluded that it wasn't. He may not have taken into account the point that Grizzly is making, but that's not the argument you have brought up.

So, while it's correct that the focus on jolts stems on Szamboti, it's not true that it's the result of a misuse of Bazant's assumptions in his 2002 paper.


Originally Posted by ozeco41 View Post
4 I suggest the issue is NOT whether there were or were not "Jolts" BUT what is puzzling pgimeno is how it got to that situation.
No. What is "puzzling" me is why you say this:

Originally Posted by ozeco41 View Post
Errors and Misapplications of Bazant's "Limit Case"
and this:
Originally Posted by ozeco41 View Post
2) It presumes a "gap" to drop through... which means that the columns had failed and were no longer in the picture. That cannot be a valid explanation for the real cascade failure.
(when Bazant doesn't propose that as an explanation for a cascade failure)
and this:
Originally Posted by ozeco41 View Post
3) It assumes columns in line being crushed. They weren't in line or crushed.
(you can say they weren't at your stage "Q", but not at your stage "P")
and this:
Originally Posted by ozeco41 View Post
2) A paper co-authored by T Szamboti (The Missing Jolt: A Simple Refutation of the NIST-Bazant Collapse Hypothesis. G MacQueen & T Szamboti 2009) It accepts that there was a drop which should produce a macro scale impact - "The Missing Jolt". Both premises wrong. POSC
and this:
Originally Posted by ozeco41 View Post
3) Arguments about whether or not "Tilting" of the top blck would prevent or allow axial impact of the dropping column ends. (It is actualy the super set of which "Missing Jolt" is one example.) Makes the same two errors - Tilt was caused by column failure allowing one side of the Top Block to be lower. So the space occupied by the column is already shorter. The column cannot being that space unfailing. (Expect some "yes buts" on that assertion ) Plus the "anachronism" issue that failure of the column caused the drop which caused the tilt. POSC
and especially this:
Originally Posted by ozeco41 View Post
4) Confusion between the "macro jolt" of "Missing Jolt" and "micro jolts" which would occur in abundance as the level of individual members of the structure. There was no "macro jolt" because the scenario for one never exists. There wer lots of micro jolts" BUT "micro jolts" are not the jolts envisaged by "Missing Jolt". POSC
and this:
Originally Posted by ozeco41 View Post
You are confusing THE "Missing (macro) Jolt" which never happened with the multitude of mini jolts which did.

And then why you top it all with this:
Originally Posted by ozeco41 View Post
Let me suggest this test....If someone is referring to jolts in any explanation of Twin Towers collapse initiation I would expect that they are either using the Bazant modelling as basis for their argument - OR - less likely - using it to illustrate why Bazant was wrong - inapplicable - invalid - for WTC modelling.
AND this:
Originally Posted by ozeco41 View Post
IF you can perceive arrogance which is is unfounded - IF I am wrong in fact or argument - then prove it.
That's what's "puzzling" me.


Originally Posted by ozeco41 View Post
Forget Jolts. We are already agreed the main point I wanted to make - the columns end up bypassing.
I can forget jolts. But I will have a harder time forgetting the way you have criticized people in this forum through innuendo, false generalizations and false arguments. Bits that probably went under Georgio's and some more people's radars.
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Old 27th May 2015, 04:35 PM   #226
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I looked at femr2's graph. It appears consistent with what I've seen posted about the jolts. Femrs' graphics show deceleration - AKA, the jolts - that folks like TS said were missing. These jolts were significant but not to the magnitude that it would be distinctively perceptible amongst the rest of the "noise" of the collapses. You have to keep in mind that Tony is arguing one thing - an extreme - whereas femr's work was looking at purely objective measurements (well, with some decided starting points for the base line.... but anyway....)

The "no column to column impact issue" is probably oversimplified as a description o note about the deceleration of the "upper mass". Again, Tony's working off an extreme case that didn't happen - the key word phrase being "extreme case". Remove the criteria for the most "ideal" limiting case, and you generally have something in between which is what the measurements by femr2 = in context with the documented footage show that the jolts existed, but they were not as extreme as what TS estimates because the impacts collectively were not simply axial end to end impacts (we don't exclude smaller scale cases where this likely happened).


Originally Posted by pgimeno View Post
That's pretty convincing. Yes, that was the main mechanism I had in mind: the top block rotating with all columns failing sideways. The only thing left to know is whether that situation happened at the time of the first floor impact or later as the top gained rotational momentum.
I'm honestly not sure it matters whether it was by the time the "upper sections" started moving down as a whole, or if it was at the individual structural member level. The most basic mechanisms were essentially the same, and you had different magnitudes of these impacts taking place at all times during the collapse. The movement of the upper sections were just the largest "events" foir lack of better wording.

WTC 1 and 2 had some differences between each other, but because the latter's situation was more precarious and involved a much more sizeable chunk of the building it was just easier to observe.

Originally Posted by pgimeno View Post
The other mechanism I had in mind was the combined effect of a less powerful version of that effect (i.e. only a bit of displacement of the top due to a slight rotation backwards) with the angle of the fall. It's plausible that both together could accumulate to a full column width, resulting in the upper column falling outside the footprint of the lower column.
The rotation of the buildings that lead to the "tilt" was at it's roots because as a system the load redistribution got eccentric enough to induce it. It was noticeably less the case in wtc 1 because the collapse started more dead-center in the building, but consider that the tilt of the upper sections in any one direction was not the only concern, but also the buckling of the columns towards the inside. These get into meta details that IMO are not much worth discussing since the end result is immaterial..... that and because I suck at explaining things in detail verbally (I'll try though if need be but expect pictures more than words)


Originally Posted by pgimeno View Post
Can you point me to a good video that shows the side clearly? The image you posted, is it a still or a frame of a video?

I look forward to any more information you can provide.
Still frame that I photoshopped over to show the flexing. You can see it here if you want: https://www.youtube.com/watch?v=9SSS0DDqfm0. It says a lot more than my graphic since you see the flexing progress.
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Old 27th May 2015, 09:38 PM   #227
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Originally Posted by JSanderO View Post
This is of interest because it is where the explanation of the initiation of the movement/collapse would be. Your starting at the time the are miss aligned and falling is AFTER the initiation...
Correct.

Please follow the argument - it is transparent:

In the full explanation "Main Thread" I laid down explanation of the nature of a cascade failure PLUS enough explanation of the factors contributing to the cascade collapse mechanism;

I then needed to show how all those factors added up - "cascaded" - to failure:

So I needed an end point that was undeniably true which is why I selected that point as the END of the process. We know it got there. We know it started. We know some of the mechanisms and we know there were enough contributing mechanisms for the cascade to run from starting to completion.

We do not know - and IMO never will know the exact details for every column plus the sequencing and timings But we don't need it.

I took a known fact end point - cascade has completed - Top Block falling and THEREFORE the bleedingly obvious points that all columns have failed and the columns are bypassing. I thought that much would be easy. Didn't allow enough for the range of member approaches to reasoning the physics. Mea culpa maybe.

To me it is obvious - since it got started and reached that end point there must have been enough bits failing to lead from the start to the finish.

Thank you however for recognising that it is the finish and that it is a true statement. Getting agreement to that simple point has been like pulling teeth.


Originally Posted by JSanderO View Post
I want to know how it all got moving...
help me to help you. Which part of the explanation is it that you do not understand OR do not accept?
(A) How ONE column heated beyond the limit would fail; OR
(B) How it was a cascading failure where first to fail would be inevitably followed by second to fail THEN third -- fourth and on down the line. In one ruddy big rush.

Originally Posted by DGM View Post
My guess would be when the multi-storey, unbraced columns reached their capacity. The damage and fire was not confined to one floor.
I don't even speculate the type of first failure EXCEPT that it would be a heat driven increasing temperature trigger into axial overload. Couldn’t be one of the aircraft cut columns for obvious reasons - the delay. It was one confused mess BUT in all that mess increasing heat would be the key factor which tipped one column into overload. And it doesn't matter which column. EXCEPT when that first one went the second would follow then 3 >> 4 >> 5 >> whatever.
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Old 27th May 2015, 11:49 PM   #228
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Originally Posted by pgimeno View Post
More precisely, it was denied with the claim that column-to-column impacts never had a chance to happen. So I'm asking what would cause the misalignment that would prevent them from happening when reaching this point:



Or alternatively, how the situation in my diagram differs from the actual collapse so substantially that there was never a column-to-column impact.


ETA: Note that I see at least two possible answers, but it's not all that obvious to me that any of these was necessarily the case, as to disregard the possibility of axial impact as impossible.
In the image, you cut out the columns on the failed floor. Where are they? In order for the top block to go that far, something must alreade have happened to the columns to allow the drop.

In your other image, you had drawn columns buckled but still connected with two hinges - the "elbows" or "knees". And I think it way you who previously (some days ago) argued that when the knee closes, the top and bottom parts meet head-on with a chance to eventuate a considerably local jolt.

Now, could columns fail in different way - break clean at 1 hinge? Buckle at the splices? In that case, "descent" will imply that "top part bypasses bottom part".
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Old 28th May 2015, 04:30 AM   #229
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Originally Posted by Grizzly Bear View Post
Remove the criteria for the most "ideal" limiting case, and you generally have something in between which is what the measurements by femr2 = in context with the documented footage show that the jolts existed, but they were not as extreme as what TS estimates because the impacts collectively were not simply axial end to end impacts (we don't exclude smaller scale cases where this likely happened).
All I'm saying is that it's not all that obvious and clear that they didn't and couldn't happen.

It's obvious (I've looked it up as a refresher now) that Szamboti's 1-sample-every-5-frames (~6 Hz) is a low sampling frequency that may miss smaller-range features, that the eyeballed pixel position estimations introduce additional noise that is severely diminished by femr2's feature tracking, and that Tony's noise removal methods smooth out any remaining possible jolts in the data if present (as Dave Rogers has noted multiple times). Therefore his method for looking for jolts is flawed, and that alone disqualifies his paper.

Yes, in his paper Szamboti is basing his estimation on Bazant's model, and yes, the BLGB 2008 paper goes too far with the extrapolation of the model to the real world e.g. when mentioning the seismic record. But Szamboti has since somewhat moderated his claims to the point of looking for just one row of columns impacting, rather than all at the same time.


Originally Posted by Grizzly Bear View Post
I'm honestly not sure it matters whether it was by the time the "upper sections" started moving down as a whole, or if it was at the individual structural member level. The most basic mechanisms were essentially the same, and you had different magnitudes of these impacts taking place at all times during the collapse. The movement of the upper sections were just the largest "events" foir lack of better wording.
You're right that it doesn't matter. My problem is with the misrepresentation of the real situation to make claims about non-existent misconceptions or about irrational affiliations to a particular hypothesis.


Originally Posted by Grizzly Bear View Post
These get into meta details that IMO are not much worth discussing since the end result is immaterial..... that and because I suck at explaining things in detail verbally (I'll try though if need be but expect pictures more than words)
No need for you to bother. I think that the point is clear at this stage.


Originally Posted by Grizzly Bear View Post
Still frame that I photoshopped over to show the flexing. You can see it here if you want: https://www.youtube.com/watch?v=9SSS0DDqfm0. It says a lot more than my graphic since you see the flexing progress.
Thank you. I seem to see the start of a backwards movement before a one complete floor drop, so in that case it seems like a possible contributing factor for misalignment. Since that factor was never brought up by the proponents of the obviousness of the misalignment, I think I can call this a "case closed".
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Old 28th May 2015, 04:50 AM   #230
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Originally Posted by Oystein View Post
In the image, you cut out the columns on the failed floor. Where are they? In order for the top block to go that far, something must alreade have happened to the columns to allow the drop.

In your other image, you had drawn columns buckled but still connected with two hinges - the "elbows" or "knees". And I think it way you who previously (some days ago) argued that when the knee closes, the top and bottom parts meet head-on with a chance to eventuate a considerably local jolt.
That diagram served to illustrate why the alleged misalignment/bypassing didn't happen (or had a significant chance of not happening). It didn't really matter at what exact point the top part would meet the bottom part. It would still be in a very rapid sequence that could easily amount to a big macroscopic jolt.

In my initial draft I used both illustrations:




But I decided to remove the first one for clarity and simplicity, since the latter was the unavoidable situation that would eventually happen without any apparent or alleged mechanism for loss of alignment.


Originally Posted by Oystein View Post
Now, could columns fail in different way - break clean at 1 hinge? Buckle at the splices? In that case, "descent" will imply that "top part bypasses bottom part".
I still don't see how the latter can happen based solely on your premise. My point was all about non-obviousness. I asked to check if I was missing something very obvious, and I didn't.
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Old 28th May 2015, 08:38 AM   #231
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Originally Posted by pgimeno View Post
All I'm saying is that it's not all that obvious and clear that they didn't and couldn't happen.
.
I believe the misunderstanding there is that thats not really the claim. Given past discussions when exchanges get down to the meta details it probably came across that way many times, but i do not think that misapprehension was intentional. I was trying to explain that earlier though admittedly i dont think i did a good job at stating this in my follow ups.


TS made a claim about an extreme case/absolute and discussions pointed out it couldnt happen the way he envisioned it would. I believe this often got conveyed to sound like NONE such circumstances took place, in other words, sounding like an opposing, absolute

This stuff happens, but glad i was able to help clear some other matters up
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Old 28th May 2015, 09:07 AM   #232
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Just an FYI, since column-column impacts are being talked about again: columns that aren't perfectly in alignment can have bearing failures. The contact surface between the two columns are quite small (these are wide flanges or hollow tubes) when they are misaligned and there will be local failures in those regions. The full capacity of the column will not be developed.
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Old 28th May 2015, 09:19 AM   #233
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Originally Posted by Newtons Bit View Post
Just an FYI, since column-column impacts are being talked about again: columns that aren't perfectly in alignment can have bearing failures. The contact surface between the two columns are quite small (these are wide flanges or hollow tubes) when they are misaligned and there will be local failures in those regions. The full capacity of the column will not be developed.
Quite. Also (in my non-expert visualisations) if the column ends are cluttered by the remains of column/connection breakage then those remains will tend to be crushed by any 'pristine' column ends that they meet, once again causing local failure plus a tendency to deflect anything that was 'pristine'.
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Old 28th May 2015, 09:43 AM   #234
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Originally Posted by ozeco41 View Post

help me to help you. Which part of the explanation is it that you do not understand OR do not accept?
(A) How ONE column heated beyond the limit would fail; OR
(B) How it was a cascading failure where first to fail would be inevitably followed by second to fail THEN third -- fourth and on down the line. In one ruddy big rush.
My interest is not what happens once capacity drops below service loads... but actually not literally what is going on.. what are the heat driven mechanisms driving the loss of capacity? Is it:

Columns weakened below capacity from heat? How would that work? Does it buckle? compress? have web or flange crippling? If it has only lost a bit of capacity below service loads... is the "lost bit" of capacity redistributed? It's not a black or white thing is it? There one instant then a 100% failed column the next????

Are the column ends pushed out of alignment destroy bearing and causing web and flange crippling?

Is the middle of the column pushed out of column causing it to buckle? Do the floors restrain the buckling? (where the are floors)

What role is the bracing playing in column performance re heating?

++++

My hunch is that the key is lateral distortion and axial misalignment... more so than loss of axial capacity by the column section (heat weakening). I think this is so because the column ends had no restraint.

What say you?
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Old 28th May 2015, 12:18 PM   #235
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Originally Posted by Newtons Bit View Post
Just an FYI, since column-column impacts are being talked about again: columns that aren't perfectly in alignment can have bearing failures. The contact surface between the two columns are quite small (these are wide flanges or hollow tubes) when they are misaligned and there will be local failures in those regions. The full capacity of the column will not be developed.
That's a good point. However, I'm assuming that most impacts [ETA: if they happened] were "elbow-to-elbow", where the surface was bigger.
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Old 28th May 2015, 12:42 PM   #236
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Originally Posted by pgimeno View Post
That's a good point. However, I'm assuming that most impacts [ETA: if they happened] were "elbow-to-elbow", where the surface was bigger.
And I suspect there were precious few "elbows" in the initial collapse zone, and would hazard a guess that connections would tend to fail, or columns experience gross rupture, before elbows could form.

The debris was examined and photographed extensively, and I'm not seeing any evidence of the elbows that would certainly have attracted a lot of attention.
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Old 28th May 2015, 01:46 PM   #237
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Originally Posted by GlennB View Post
And I suspect there were precious few "elbows" in the initial collapse zone, and would hazard a guess that connections would tend to fail, or columns experience gross rupture, before elbows could form.

The debris was examined and photographed extensively, and I'm not seeing any evidence of the elbows that would certainly have attracted a lot of attention.
Essentially in that regard the "elbows" were the connection points rather than within the more monolithic mass of the main column
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Old 28th May 2015, 01:50 PM   #238
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Originally Posted by GlennB View Post
And I suspect there were precious few "elbows" in the initial collapse zone, and would hazard a guess that connections would tend to fail, or columns experience gross rupture, before elbows could form.
I'm not so sure. There were too few core columns recovered from the collapse zone. However, in NCSTAR 1-3B there are some pictures that may represent that kind of failures in columns of other areas. I'm lazy to capture and upload the figures, but figure 3-12 (d), top right, shows a column (C-60) with two clear "elbows". Figure 3.12 (h) is interesting. It seems to show a failure of the three-elbow kind, though one of the elbows didn't form because there was a connection and it apparently broke, but the angle of the web on the right suggests that end was an elbow too. Figure 3.13 (b) shows another two-elbow failure, though it didn't go too far.

Figure A-14 top (sample C-103) shows a two-elbow bend that I have a hard time interpreting


Originally Posted by GlennB View Post
The debris was examined and photographed extensively, and I'm not seeing any evidence of the elbows that would certainly have attracted a lot of attention.
Why would they? The ones above didn't attract any significant attention.
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Old 31st May 2015, 08:32 PM   #239
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Originally Posted by Fonebone View Post
Reconnoiter









Bic ?
HAT TRUSS OUTRIGGER and TRUSS TO INTERIOR CORE BRACING
GRAPHIC-


I have more images to add but I have reached the limit of 75 images.
Can my image limit be expanded ?
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Old 1st June 2015, 03:16 AM   #240
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The cartoon in Fonebone's image of the hat truss is inaccurate... or how does it work with the photos of the as built roof. Which column would the buckling cartoon represent... take a guess... what floor level... pick one of 47?
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