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Old 15th February 2018, 02:31 PM   #1
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Physical Evidence of buckled columns?

We hear mention of buckled columns in the 3 collapsed of the WTC buildings. I suppose there were some for sure.

However... how many physical examples of buckling are there from the 3 buildings?

Can anyone cite photos of them? the floor on which they were and of course the building they came from.
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Old 15th February 2018, 02:59 PM   #2
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I've certainly seen a few such photos, but the real question is: why, at the time when the samples were freely available, would anybody have been very interested in cataloguing them?

Column failure mechanisms on 9/11 only really became an issue when 9/11 CT came along.
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Old 15th February 2018, 03:08 PM   #3
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Major_Tom has an extensive catalog of images at his site. There is no shortage there.

http://www.sharpprintinginc.com/911/...AGER_section=1

This is a very good source for ground zero images. Kudos should be given for his effort to preserves these in one place...
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Old 15th February 2018, 03:11 PM   #4
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Originally Posted by GlennB View Post
I've certainly seen a few such photos, but the real question is: why, at the time when the samples were freely available, would anybody have been very interested in cataloguing them?

Column failure mechanisms on 9/11 only really became an issue when 9/11 CT came along.
The forensic engineering investigators would certainly have made note, I'm not sure when they were brought in though. Its pretty typical after disaster to have structural engineers gather at the site and try and figure out what caused structures to fail in hopes of learning something. Clearing the debris would likely have taken precedent as the cause was pretty evident at the time.

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Old 15th February 2018, 03:19 PM   #5
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Originally Posted by JSanderO View Post
We hear mention of buckled columns in the 3 collapsed of the WTC buildings. I suppose there were some for sure.

However... how many physical examples of buckling are there from the 3 buildings?

Can anyone cite photos of them? the floor on which they were and of course the building they came from.
Why would buckling be unusual or suspicious anyway?

I'm not a scientist or engineer, but I have a good understanding of basic Newtonian physics. Of course, at some point, the structure will twist and buckle.
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Old 15th February 2018, 04:50 PM   #6
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So here's my thinking.

Buckling pretty much is about load exceeding capacity for a column. We know that all the column sections were chosen with a safety factor... so they could carry all the calculated loads... dead and superimposed loads expected.

We also know that a column's strength is related not only its cross section but it's unbraced length. Short columns of x section support more load than the same column section with a longer unbraced length. At some point a column's slenderness ratio will be so large... (longest plan axis / length) that it can self buckle... This is called Euler buckling.

This sort of buckling likely was a mechanism in the collapse of the core of the twins after the floors along with bracing was stripped away in the floor slab collapse. The remaining very tall column had no bracing.... some were jostled by the collapse and toppled over others... the very longest may have "self buckled"... breaking into segments at the column to column end connections.... which were not very robust.

The facade peeled away likely pushed outward by over pressure from air in a piston effect... or by growing mass of the floor material as it descended.

Then we have 7 WTC. The most accepted explanation posits that column 79 buckled as a result of a girder (brace) coming off at floor 12... This was a very massive column with a large cross section. I seriously doubt it would buckle in one 2 story column length. But maybe. How much capacity is lost when one brace is removed?

More likely to buckle... this would have to be a multi story matter... braces over many floors of the stack of 2 story length columns would presumably have to be removed to weaken the column, increase the unbraced length past is capacity leading to its buckling and busting apart at the column to column end connections. Possible I suppose. How may story heights of bracing had to be or were removed for 79 to buckle?

Then there's the matter of other columns bucking because of load redistribution. Here the design load is exceeded because new loads appear via braces... loads that weren't there before. Presumably this means that the loads carried by 2 adjacent columns on beams and girders.. is then ENTIRELY carried by one... the other having buckled.

But wouldn't the buckling column also take some or the floor load with it? Didn't it buckle because the brace failed and the brace was what supported the floor load and shared equally by 2 adjacent columns. What this seems like is an UNLOADING of the remaining column not increasing its loads. But perhaps it too now loses its bracing and buckles and so on and so on. This seems like the mechanism for lateral collapse propagation.... NOT load redistribution. And the collapse should show basically intact broken apart into their original length segments.... like a collapse of stacked jenga blocks.... no bent mangled columns except from collision impact.

any comments?
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Old 15th February 2018, 06:17 PM   #7
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Originally Posted by JSanderO View Post
We hear mention of buckled columns in the 3 collapsed of the WTC buildings. I suppose there were some for sure.

However... how many physical examples of buckling are there from the 3 buildings?

Can anyone cite photos of them? the floor on which they were and of course the building they came from.
You can see columns buckling in the videos of WTC2 collapsing. Most perimeter columns on two sides buckle visibly.

After the collapse, it's more difficult to determine whether a twisted column was the result of buckling or of crushing.

And in the case of WTC7, there's the additional problem that the columns weren't marked, therefore we don't know where they were located, so they weren't saved.
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Old 15th February 2018, 06:41 PM   #8
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Originally Posted by pgimeno View Post
You can see columns buckling in the videos of WTC2 collapsing. Most perimeter columns on two sides buckle visibly.

After the collapse, it's more difficult to determine whether a twisted column was the result of buckling or of crushing.

And in the case of WTC7, there's the additional problem that the columns weren't marked, therefore we don't know where they were located, so they weren't saved.
Columns breaking apart at their connections are not necessarily from buckling. The facade broke into sections... small and some very very large... they bolts were torn out or sheared off... splice plates bent like wet noodles.

Buckling is the result of axial loading exceeding capacity...

Capacity is reduced when / if the unsupported length increases. Agreed. How many braces have to be removed to buckle a column like 79...

Anyone?

Note.... my (likely incorrect) calculation for self buckling related to slender columns... maximum ht before self buckling is 21 stories or 274 ft... And the profile likely tapered as it ascended higher making the max hit possible less
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File Type: jpg col 79.jpg (50.5 KB, 5 views)
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Old 15th February 2018, 08:10 PM   #9
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Originally Posted by JSanderO View Post
Columns breaking apart at their connections are not necessarily from buckling. The facade broke into sections... small and some very very large... they bolts were torn out or sheared off... splice plates bent like wet noodles.

Buckling is the result of axial loading exceeding capacity...

Capacity is reduced when / if the unsupported length increases. Agreed. How many braces have to be removed to buckle a column like 79...

Anyone?

Note.... my (likely incorrect) calculation for self buckling related to slender columns... maximum ht before self buckling is 21 stories or 274 ft... And the profile likely tapered as it ascended higher making the max hit possible less
NO! Stop right there
Buckling is a large increase in deformation with a small increase in applied load
It doesn't even require permanent deformation
https://www.coursera.org/learn/mater...olumn-buckling
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Old 16th February 2018, 03:29 AM   #10
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Originally Posted by JSanderO View Post
Columns breaking apart at their connections are not necessarily from buckling. The facade broke into sections... small and some very very large... they bolts were torn out or sheared off... splice plates bent like wet noodles.
At the very start of the collapse, you can see the inward bowing turning into buckling. I suspect several columns were already buckled by then.
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Old 16th February 2018, 03:52 AM   #11
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Originally Posted by pgimeno View Post
At the very start of the collapse, you can see the inward bowing turning into buckling. I suspect several columns were already buckled by then.
The leaning indicated loss of capacity, and buckling of the last columns as the hinge.
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Old 16th February 2018, 03:58 AM   #12
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Originally Posted by rwguinn View Post
NO! Stop right there
Buckling is a large increase in deformation with a small increase in applied load
It doesn't even require permanent deformation
https://www.coursera.org/learn/mater...olumn-buckling
His course explanation refers to slender columns and Euler buckling...

I don't see this explanation as applicable for so please explain this for column 79.

I don't see any increase in load and I don't see a large increase in deformation...

Thank you!

++++

It appears to me.. that the mechanism causing column collapse was lateral displacement rather than buckling.
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Old 16th February 2018, 06:23 AM   #13
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Originally Posted by JSanderO View Post
So here's my thinking

Then there's the matter of other columns bucking because of load redistribution. Here the design load is exceeded because new loads appear via braces... loads that weren't there before. Presumably this means that the loads carried by 2 adjacent columns on beams and girders.. is then ENTIRELY carried by one... the other having buckled.

But wouldn't the buckling column also take some or the floor load with it? Didn't it buckle because the brace failed and the brace was what supported the floor load and shared equally by 2 adjacent columns. What this seems like is an UNLOADING of the remaining column not increasing its loads. But perhaps it too now loses its bracing and buckles and so on and so on. This seems like the mechanism for lateral collapse propagation.... NOT load redistribution. And the collapse should show basically intact broken apart into their original length segments.... like a collapse of stacked jenga blocks.... no bent mangled columns except from collision impact.

any comments?
This is almost certainly incorrect. Load will distribute to the more rigid(not yet buckled columns.) As a simple example:

Imagine a beam with column A at the left end, Column B in the middle, and column C at the end. Column B fails. the Beam will likely deflect but until the beam fails, the load that was carried by column B is now carried by columns A and C. So, which fails first, the beams or the Columns, depends on the factor of safety for each element.

Also, the buckling column wouldn't take more floor load with it. It fails and can't carry any load. The loads above the point of buckling are now carried by the floor above the point of failure, probably increasing the dead load to the floor above.
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Old 16th February 2018, 06:36 AM   #14
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Originally Posted by JSanderO View Post

It appears to me.. that the mechanism causing column collapse was lateral displacement rather than buckling.
The too things aren't mutually exclusive.

In structural engineering, the P-Δ or P-delta effect refers to the abrupt changes in ground shear, overturning moment, and/or the axial force distribution at the base of a sufficiently tall structure or structural component when it is subject to a critical lateral displacement. A distinction can be made between P-delta effects on a multi-tiered building, written as P-Δ, and the effects on members deflecting within a tier, written as P-δ.[1]:lii

https://en.wikipedia.org/wiki/P-delta_effect
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Old 16th February 2018, 06:36 AM   #15
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Originally Posted by ahhell View Post
This is almost certainly incorrect. Load will distribute to the more rigid(not yet buckled columns.) As a simple example:

Imagine a beam with column A at the left end, Column B in the middle, and column C at the end. Column B fails. the Beam will likely deflect but until the beam fails, the load that was carried by column B is now carried by columns A and C. So, which fails first, the beams or the Columns, depends on the factor of safety for each element.

Also, the buckling column wouldn't take more floor load with it. It fails and can't carry any load. The loads above the point of buckling are now carried by the floor above the point of failure, probably increasing the dead load to the floor above.
Your description of the framing is not what what used in 7wtc or even the twin towers.

Beams were connected with one of 3 types of connections to the SIDES of 2 and 3 story columns but not at the column ends.

Your explanation may apply to some frames... but not the the WTC buildings.
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Old 16th February 2018, 06:41 AM   #16
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Originally Posted by ahhell View Post
The too things aren't mutually exclusive.

In structural engineering, the P-Δ or P-delta effect refers to the abrupt changes in ground shear, overturning moment, and/or the axial force distribution at the base of a sufficiently tall structure or structural component when it is subject to a critical lateral displacement. A distinction can be made between P-delta effects on a multi-tiered building, written as P-Δ, and the effects on members deflecting within a tier, written as P-δ.[1]:lii

https://en.wikipedia.org/wiki/P-delta_effect
explain that in laymen speak please
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Old 16th February 2018, 06:48 AM   #17
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Originally Posted by JSanderO View Post
Your description of the framing is not what what used in 7wtc or even the twin towers.

Beams were connected with one of 3 types of connections to the SIDES of 2 and 3 story columns but not at the column ends.

Your explanation may apply to some frames... but not the the WTC buildings.
You are incorrect. The side connection doesn't affect my explanation. Even if you magically remove the column at one end of a beam. The other supporting beam is now carrying the entire load from the beam that it used to carry only half of. Unless the a portion of the beam was also removed.
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Old 16th February 2018, 06:53 AM   #18
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Originally Posted by JSanderO View Post
explain that in laymen speak please
As the column displaces laterally the effects of the load change making the column susceptible to certain kinds of buckling failure.

Keep in mind, there are a few different ways a W Flange section(I/H shape) can buckle.
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Old 16th February 2018, 06:55 AM   #19
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then there's the shear studs which resisted lateral expansion of the beam which supported them:

"It was formerly known that steel subjected to extreme heat experienced a significant reduction in strength due to material degradation. However, tests of steel beams with composite concrete decking found that the response of the structure is dominated by thermal expansion, and that the effects of material degradation and gravity loading are secondary (Gillie, M., Usamani, A. S., and Rotter, J. M. 2001). Thermal expansion is typically resisted in composite construction by shear studs embedded into the concrete decking and by the connections to supporting members. This resistance results in axial stresses which cause steel members to yield or buckle."

and this:

"These weakened floors could not sustain the impact from the above floors, which led to the progressive collapse of the floor framing around Columns 79 to 81. As the floor beams and girders failed, the unbraced length of Columns 79 to 81 increased and eventually reached critical conditions for buckling. After these columns buckled, the above floors fell downward creating a vertical progression of floor collapses."

about unbraced length.... unspecified nor described in detail
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Old 16th February 2018, 06:57 AM   #20
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Originally Posted by ahhell View Post
You are incorrect. The side connection doesn't affect my explanation. Even if you magically remove the column at one end of a beam. The other supporting beam is now carrying the entire load from the beam that it used to carry only half of. Unless the a portion of the beam was also removed.
INCORRCT...

If you remove one beam in a of a simply supported beam between two columns.... the beam collapse because the connection is not designed to support the beam as a cantilever.
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Old 16th February 2018, 07:04 AM   #21
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Originally Posted by ahhell View Post
As the column displaces laterally the effects of the load change making the column susceptible to certain kinds of buckling failure.

Keep in mind, there are a few different ways a W Flange section(I/H shape) can buckle.
Kindly describe the buckling of column 79 shown above from displacement.

Would the heat expanded beams buckle would they push the columns out of alignment when they were restrained on the opposite side?

The attached shows column 704 up at the top of the twin towers which COULD displace a small amount... as little as 1/2" and lead to web and flange crippling/buckling.

THIS DID not happen to column 79. We are told the girder slide off the beam seat. so it didn't displace it laterally
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File Type: pdf col 704 flr 88 push.pdf (5.9 KB, 0 views)
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Old 16th February 2018, 07:07 AM   #22
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Originally Posted by ahhell View Post
As the column displaces laterally the effects of the load change making the column susceptible to certain kinds of buckling failure.

Keep in mind, there are a few different ways a W Flange section(I/H shape) can buckle.
AKA "crippling ". A side load or deflection on a column under compression will cause failure sooner than a pure compression load. It matters not where the side load is applied. Top, bottom, or in between.
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Old 16th February 2018, 07:15 AM   #23
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If the columns failed from buckling... loss of lateral support... it was due to one thing... floor collapses and the collapse of the transfers below the columns on the west side - 79.80 and 81.. the north office floor area failed and collapsed when the transfer girder over the north line of core columns failed...

The floor collapses progressed from the north east quadrant westward.... until there were no floors left to brace the columns... the core had hardly any floor area to brace the core... The lateral instability of columns was more likely induced by the overspill of the collapsing floor debris...at the bottom. THERE HAD TO HAVE BEEN A MECHANISM for the destruction to progress westward... THAT was E-W load transfers failing... directing the failures from east to west.
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Old 16th February 2018, 07:24 AM   #24
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here is a crippled WF column... much much smaller than 79

https://ixquick-proxy.com/do/spg/sho...a5eceb25dc5882

it appears to be the result of heat weakening not additional of load or displacement.
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Old 16th February 2018, 07:28 AM   #25
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Originally Posted by JSanderO View Post
here is a crippled WF column... much much smaller than 79

https://ixquick-proxy.com/do/spg/sho...a5eceb25dc5882

it appears to be the result of heat weakening not additional of load or displacement.
Heating has the same effect as increasing the load.
Do try to learn some basic engineering before you start trying to play expert. Those of us who do it for a living get very tired of pretenders.
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Old 16th February 2018, 09:33 AM   #26
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Originally Posted by rwguinn View Post
Heating has the same effect as increasing the load.
Do try to learn some basic engineering before you start trying to play expert. Those of us who do it for a living get very tired of pretenders.
Excuse me?

I am not playing expert... and I think that remark was a bit aggressive.

I do know basic engineering... I have been practicing architecture for 46 years.

Do you want to tell the board your professional qualifications?

++++

The OP was about PHYSICAL evidence of column buckling. If you have it.... show it.
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Old 16th February 2018, 10:11 AM   #27
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Originally Posted by JSanderO View Post
Excuse me?

I am not playing expert... and I think that remark was a bit aggressive.

I do know basic engineering... I have been practicing architecture for 46 years.

Do you want to tell the board your professional qualifications?

++++

The OP was about PHYSICAL evidence of column buckling. If you have it.... show it.
Registered PE.; BSME.
As it has been pointed out, buckling can occur below yield. No physical evidence possible without pictures taken during the process.
If you want to move the goalposts, carry on.
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Old 16th February 2018, 10:34 AM   #28
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During the process?

How about from AFTER the collapse during the clean up phase?

I believe NIST saved a lot of steel for study... some staged to Fresh Kill and then moved to a NIST facility.

Should there be images of "buckled columns" amongst the saved material? Why would they save steel which would not help in understanding the collapse?
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Old 16th February 2018, 10:37 AM   #29
ahhell
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Since we're whipping them out.

PE, MS Structural Engineering.

Originally Posted by JSanderO View Post
INCORRCT...

If you remove one beam in a of a simply supported beam between two columns.... the beam collapse because the connection is not designed to support the beam as a cantilever.
This assume that the connection fails completely when its more likely to have failed as a hinge and it ignores any load caring capacity of the flooring system. A much more probably failure would be one of many columns fails but the associated beams are partially supported by the associate flooring and secondary structural members, thus transferring load to the remaining columns.

You actually provided a photo that demonstrates exactly what I'm talking about. The floor above the buckled area is still mostly intact and imparting load to the column.
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Old 16th February 2018, 11:00 AM   #30
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Originally Posted by ahhell View Post
Since we're whipping them out.

PE, MS Structural Engineering.


This assume that the connection fails completely when its more likely to have failed as a hinge and it ignores any load caring capacity of the flooring system. A much more probably failure would be one of many columns fails but the associated beams are partially supported by the associate flooring and secondary structural members, thus transferring load to the remaining columns.

You actually provided a photo that demonstrates exactly what I'm talking about. The floor above the buckled area is still mostly intact and imparting load to the column.
The discussion was disconnecting a simply supported beam from one or two columns.

I would expect the connection to the remaining column to be ripped off...

But sure maybe it twists and hangs there... depends... and if it did load would be added to the standing column.
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Old 16th February 2018, 11:07 AM   #31
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NCSTAR 1-3B has plenty of photographs of twisted columns. Take a look and come back to tell us whether you think none of them looks like it could have failed by buckling.
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Old 16th February 2018, 11:30 AM   #32
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Originally Posted by pgimeno View Post
NCSTAR 1-3B has plenty of photographs of twisted columns. Take a look and come back to tell us whether you think none of them looks like it could have failed by buckling.
I don't have it...

Can you post a link to it?

When I do a google search of WTC recovered steel I only see steel from the twin towers.
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Old 16th February 2018, 11:35 AM   #33
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They're all here:

https://www.nist.gov/engineering-lab...-investigation

NCSTAR 1-3B:

http://ws680.nist.gov/publication/ge...?pub_id=101430
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Old 16th February 2018, 11:56 AM   #34
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Originally Posted by DGM View Post
Thank you!

+++++

Photos in this report are all of WTC 1 and 2
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Old 16th February 2018, 12:02 PM   #35
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Originally Posted by JSanderO View Post
When I do a google search of WTC recovered steel I only see steel from the twin towers.
As I said,
Originally Posted by pgimeno View Post
And in the case of WTC7, there's the additional problem that the columns weren't marked, therefore we don't know where they were located, so they weren't saved.

Edit: Anyway, your OP said:
Originally Posted by JSanderO View Post
We hear mention of buckled columns in the 3 collapsed of the WTC buildings. I suppose there were some for sure.

However... how many physical examples of buckling are there from the 3 buildings?

Can anyone cite photos of them? the floor on which they were and of course the building they came from.
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Old 17th February 2018, 04:51 AM   #36
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I peruses the photos of recovered steel. Lots of facade columns from the twins.

And there were a number of mangled twisted and bent up steel wide flange beams..

How much of the distortion of those beams was due to heat weakening under load?

How much was due to mechanical collisions?

How much was due to buckling?

Of course this is hard to know.

It seems logical to me that buckling in multi story columns would manifest at them breaking cleanly at their end connections into basically undistorted sections. We do see this in the debris pile. around the twin towers.

This sort of coming apart of the frame seems to be related to the fact that the connections though designed to carry the static loads they saw... were too weak for the dynamic loads seen when floor slabs collapse.

The floor slabs of course were continuous and reinforced with mesh and rebar in many areas. But if the beam or joist connections failed it's conceivable that the slab they supported would break into fragments and drop.... becoming a dynamic load.

If heat from fire were the proximate cause of the destruction it likely acted on the weakest link... the connections of steel to steel and this would lead to the floor collapses.. the unbraced and therefore unstable columns which in turn also collapsed.

Conceptually joint failures from heat seems the logical explanation as the initiating mechanism for the collapses of a stable system.
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Old 17th February 2018, 05:41 AM   #37
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Originally Posted by JSanderO View Post
I peruses the photos of recovered steel. Lots of facade columns from the twins.

And there were a number of mangled twisted and bent up steel wide flange beams..

How much of the distortion of those beams was due to heat weakening under load?

How much was due to mechanical collisions?

How much was due to buckling?

Of course this is hard to know.
My point exactly. Post-collapse photographic evidence of columns warped or bent or twisted is mostly useless. Even if columns from WTC7 were saved, the same would apply. That's why I pointed you to the precise instant of the collapse of WTC2, since that one is recorded in video as it happened, and provides one way to be sure that what we see is buckling.
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Old 17th February 2018, 06:50 AM   #38
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Originally Posted by pgimeno View Post
My point exactly. Post-collapse photographic evidence of columns warped or bent or twisted is mostly useless. Even if columns from WTC7 were saved, the same would apply. That's why I pointed you to the precise instant of the collapse of WTC2, since that one is recorded in video as it happened, and provides one way to be sure that what we see is buckling.
yes... as the axial support on one side was lost the remaining columns DID see over loading and a hinge formed at first to columns projecting from the lower section to the falling upper one... Then bent severely and then I suppose some snapped.
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Old 20th February 2018, 02:24 AM   #39
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Originally Posted by DGM View Post
Major_Tom has an extensive catalog of images at his site. There is no shortage there.

http://www.sharpprintinginc.com/911/...AGER_section=1

This is a very good source for ground zero images. Kudos should be given for his effort to preserves these in one place...
I agree, he really puts forth a positively exhaustive assembly. Good source!
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Old 20th February 2018, 07:13 AM   #40
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Originally Posted by JSanderO View Post

It seems logical to me that buckling in multi story columns would manifest at them breaking cleanly at their end connections into basically undistorted sections. We do see this in the debris pile. around the twin towers.
I'm not sure why you would expect to see a clean break, can you explain that?

Side note, at least with the WTC the issue with the connections wasn't the dynamic loads, it was the lateral loads. The suspected failure mechanism was that the beams expanded due to heating resulting in lateral loads to the connections that they weren't designed for. The some of the connects failed in a brittle manner. The floors dropped and loaded up the floor beneath beyond its carrying capacity ect.
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