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Old 20th February 2018, 06:16 PM   #41
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Originally Posted by ahhell View Post
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.
In expect multi story column buckling to be at the column's weakest location... where one column butt to another.. with some rather insubstantial splice plates welded on.

The collapse was unlikely in the case of 7wtc due to heat heat from beams or girders displacing one column such that it loses so much axial alignment to make the columns above... These columns love down in that building has massive cross sectional area and ie would take a lot of movement to mis-align. Smaller rolled sections maybe. Not 79, 80 or 81 at floor 12/13

There may have been a multi floor collapse from heat failing beams/girders which led to dynamic impacts and multi floor collapse... leaving beams without bracing on perhaps one side them. If this happens the beams on the opposite side could then push the columns to the side of the floor collapse...causing mis alignment and collapse of the columns and the collapse might pull columns laterally as the collapse... gutting the interior.

Maybe
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Old 21st February 2018, 07:21 AM   #42
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Originally Posted by JSanderO View Post
In expect multi story column buckling to be at the column's weakest location... where one column butt to another.. with some rather insubstantial splice plates welded on.
In theory, the splices would be stronger than the rest of the beam, both for the additional plates and that full pen welds should be as strong or stronger than the base metal.

Quote:
The collapse was unlikely in the case of 7wtc due to heat heat from beams or girders displacing one column such that it loses so much axial alignment to make the columns above... These columns love down in that building has massive cross sectional area and ie would take a lot of movement to mis-align. Smaller rolled sections maybe. Not 79, 80 or 81 at floor 12/13
I can't really follow what your saying there. My understanding of the initiating mechanism of WTC7 was that it was the beam to column connection that failed first do to lateral displacement not the column failing first due to lateral displacement.

Quote:
There may have been a multi floor collapse from heat failing beams/girders which led to dynamic impacts and multi floor collapse... leaving beams without bracing on perhaps one side them. If this happens the beams on the opposite side could then push the columns to the side of the floor collapse...causing mis alignment and collapse of the columns and the collapse might pull columns laterally as the collapse... gutting the interior.

Maybe
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Old 21st February 2018, 10:59 AM   #43
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Originally Posted by ahhell View Post
In theory, the splices would be stronger than the rest of the beam, both for the additional plates and that full pen welds should be as strong or stronger than the base metal.

I can't really follow what your saying there. My understanding of the initiating mechanism of WTC7 was that it was the beam to column connection that failed first do to lateral displacement not the column failing first due to lateral displacement.
You obviously are not familiar with column 79... it did not have.... could not have full pen welds

Beams and girders cannot displace... ie expand and push columns laterally if the columns are too stiff and well braced. The heated beam will sag not displace the column... If you think that happened... I have a few nice bridges to sell you.
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Old 21st February 2018, 11:08 AM   #44
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Originally Posted by JSanderO View Post

Beams and girders cannot displace... ie expand and push columns laterally if the columns are too stiff and well braced. The heated beam will sag not displace the column... If you think that happened... I have a few nice bridges to sell you.
In order for the beam to sag, the connection must fail leaving the column un-braced. Correct?
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Old 21st February 2018, 06:46 PM   #45
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Originally Posted by DGM View Post
In order for the beam to sag, the connection must fail leaving the column un-braced. Correct?
So you have a beam spanning between two columns... it gets heated and begins to expand... but it can't because it is restrained on both ends... so it bows downward... and with loss of strength it might collapse under load...and develop inward lateral forces in the process.
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Old 21st February 2018, 06:53 PM   #46
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Originally Posted by JSanderO View Post
So you have a beam spanning between two columns... it gets heated and begins to expand... but it can't because it is restrained on both ends... so it bows downward... and with loss of strength it might collapse under load...and develop inward lateral forces in the process.
The beam will displace the column up to the strength of the connection.
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Old 21st February 2018, 07:22 PM   #47
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Originally Posted by DGM View Post
The beam will displace the column up to the strength of the connection.
The beam can't displace a column if it sags and collapses.

How are you correlating "strength of connection" with lateral displacement?

Color me confused.
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Old 21st February 2018, 09:02 PM   #48
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Originally Posted by JSanderO View Post
The beam can't displace a column if it sags and collapses.

How are you correlating "strength of connection" with lateral displacement?

Color me confused.
A beam can displace a column by sagging up to the strength of the connection. This is not really the point. If a beam sags, the connection must fail leaving the column un-braced. Correct?

You seam to be looking at each member in isolation. This is never the case in a chaotic real world situation.
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Old 22nd February 2018, 07:16 AM   #49
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Originally Posted by JSanderO View Post
The beam can't displace a column if it sags and collapses.

How are you correlating "strength of connection" with lateral displacement?

Color me confused.
Why not? As it sags it will apply tension to the connection, one or more of several things can happen as a result. The column deflects, or the connections yields until one of them fails or the beam fails.
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Old 22nd February 2018, 01:44 PM   #50
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Originally Posted by ahhell View Post
Why not? As it sags it will apply tension to the connection, one or more of several things can happen as a result. The column deflects, or the connections yields until one of them fails or the beam fails.
Often in fires, the beam expands pushing the column and shearing the connection. When things cool down the beam simply walks off the seat. I've witnessed this several times.
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Old 22nd February 2018, 02:33 PM   #51
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Originally Posted by DGM View Post
Often in fires, the beam expands pushing the column and shearing the connection. When things cool down the beam simply walks off the seat. I've witnessed this several times.
This is the likely mechanism for WTC7's failure, but apparently its impossible because of my personal incredulity and this anomaly. My understanding is that they were shear tabs without a seat so they didn't wait to cool down before they fell, I could be wrong about that bit though.

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Old 22nd February 2018, 02:36 PM   #52
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Originally Posted by JSanderO View Post
The beam can't displace a column if it sags and collapses.

How are you correlating "strength of connection" with lateral displacement?

Color me confused.
The beam will deform and until the connection fails it will impart a lateral load on the column which may cause the column to deform. As a beam sags, it would be in some state between a rigid beam and a catenary, there will be some lateral tension as a result.

But see above for the proposed mechanism for the WTC7 failure as I understand the final report on the matter. The beams expanded, shear the bolts on simple shear tab connections then the fell to the floor below.
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Old 22nd February 2018, 04:34 PM   #53
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Originally Posted by ahhell View Post
This is the likely mechanism for WTC7's failure, but apparently its impossible because of my personal incredulity and this anomaly. My understanding is that they were shear tabs without a seat so they didn't wait to cool down before they fell, I could be wrong about that bit though.
"Truthers" love to claim the beam could not walk off the seat during cooling citing the distance the beam could shorten due to compression or sag. They ignore the fact the column was also displaced during expansion when the connection likely failed.
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Old 22nd February 2018, 05:45 PM   #54
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Originally Posted by ahhell View Post
The beam will deform and until the connection fails it will impart a lateral load on the column which may cause the column to deform. As a beam sags, it would be in some state between a rigid beam and a catenary, there will be some lateral tension as a result.

But see above for the proposed mechanism for the WTC7 failure as I understand the final report on the matter. The beams expanded, shear the bolts on simple shear tab connections then the fell to the floor below.
I kinda doubt that the girder framed into col 79 would budge the column much...
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Old 22nd February 2018, 05:50 PM   #55
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Originally Posted by JSanderO View Post
I kinda doubt that the girder framed into col 79 would budge the column much...
Make up your *********** mind, will ya?
Regardless of how it failed-shearing the ties and falling off(do the thermal calculations--the force exerted by a heated steel member is very large), or sagging--the lateral connection and support for the column is gone!
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Old 23rd February 2018, 03:19 AM   #56
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Originally Posted by rwguinn View Post
Make up your *********** mind, will ya?
Regardless of how it failed-shearing the ties and falling off(do the thermal calculations--the force exerted by a heated steel member is very large), or sagging--the lateral connection and support for the column is gone!
If the connection is destroyed from HEAT a floor section may drop losing axial support. Don't know how large a section of floor would be released if the connection failed at one end. For the floor section to be released multiple connection locations to the composite would have to fail. Would this lead a progressive spreading radiating floor collapse or remain an isolated locale event?
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Old 25th February 2018, 10:08 AM   #57
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Originally Posted by JSanderO View Post
If the connection is destroyed from HEAT a floor section may drop losing axial support. Don't know how large a section of floor would be released if the connection failed at one end. For the floor section to be released multiple connection locations to the composite would have to fail. Would this lead a progressive spreading radiating floor collapse or remain an isolated locale event?
Let me put it in more basic terms: if the lateral tie to a column breaks, or if the lateral tie to a column turns into boiled spaghetti, it is no longer a lateral tie and the column length is now increased, making the column less capable of maintaining an axial load.
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Old 25th February 2018, 03:43 PM   #58
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Originally Posted by rwguinn View Post
Let me put it in more basic terms: if the lateral tie to a column breaks, or if the lateral tie to a column turns into boiled spaghetti, it is no longer a lateral tie and the column length is now increased, making the column less capable of maintaining an axial load.
no one is disputing this... The issue in my mind is if the very stout col 79 at flrs 12/13 would weaken sufficiently to cause any change in the structure?

Presumably the design of the columns includes a factor of safety... which I believe is typical between 1.5 and 2.

Since you're an engineer perhaps you can provide some insight as to what would have to the column's strength from loss of one brace.
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Old 26th February 2018, 04:50 AM   #59
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There's a thread on MetaBunk:

https://www.metabunk.org/how-much-ir...0/#post-219630

which includes photos of the Deutschbank buiilding with a gash in its north facade at least 8 stories high.

https://www.metabunk.org/attachments...-13-jpg.31968/

Building did not "progressively" collapse... columns above the 8 story missing column did not appear to buckle or sag.

Interesting.
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Old 26th February 2018, 05:32 AM   #60
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No building collapsed due to a gash in the fašade. What's your point?
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Old 26th February 2018, 05:35 AM   #61
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My point is that taking out a single column of 8 stories low down in a building does not lead to buckling of the column above or progressive collapse.

Do you agree with this statement?
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Old 26th February 2018, 08:58 AM   #62
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Originally Posted by JSanderO View Post
My point is that taking out a single column of 8 stories low down in a building does not necessarily lead to buckling of the column above or progressive collapse.

Do you agree with this statement?
With the word I've added (in underline), I agree.
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Old 26th February 2018, 09:35 AM   #63
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Originally Posted by JSanderO View Post
My point is that taking out a single column of 8 stories low down in a building does not lead to buckling of the column above or progressive collapse.

Do you agree with this statement?
Even though I know next to nothing about structural engineering, I can see the flaw in this statement; clearly, whether or not taking out a single column of 8 storeys low down in a building leads to buckling of the column above or progressive collapse depends on the design of the building.

Dave
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Old 26th February 2018, 03:17 PM   #64
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Originally Posted by Dave Rogers View Post
Even though I know next to nothing about structural engineering, I can see the flaw in this statement; clearly, whether or not taking out a single column of 8 storeys low down in a building leads to buckling of the column above or progressive collapse depends on the design of the building.

Dave
well yea Dave... but the Deutchbank build looks to be a typical grid of columns steel frame... surrounding a service core.

WTC7 is not quite that:

trapezoid plan form
40 stories built over a power station w/ multiple massive transfer structures
47 stories overall... no basements
multiple diesel generators... with fuel stored on premesis.

There was a thread on this site about total building collapse from a single column failure.... DB was one that didn't collapse.... no progression of failures. Better design????
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Old 26th February 2018, 07:19 PM   #65
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Originally Posted by JSanderO View Post
well yea Dave... but the Deutchbank build looks to be a typical grid of columns steel frame... surrounding a service core.

WTC7 is not quite that:

trapezoid plan form
40 stories built over a power station w/ multiple massive transfer structures
47 stories overall... no basements
multiple diesel generators... with fuel stored on premesis.

There was a thread on this site about total building collapse from a single column failure.... DB was one that didn't collapse.... no progression of failures. Better design????
WTC7 also lost at least a column (probably more) from the perimeter without collapsing. In that sense, it performed like DB. We don't know what would have happened to DB if it lost one core column (if it has a core).

The devil is in the details. Which exact column failed is sometimes important. Previous damage is sometimes important too.
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Old 27th February 2018, 02:15 AM   #66
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Originally Posted by JSanderO View Post
well yea Dave... but the Deutchbank build looks to be a typical grid of columns steel frame... surrounding a service core.

WTC7 is not quite that:
Yeah, that's pretty much my point; the designs of the buildings are radically different, so their response to a specific form of damage would be radically different. The Deutschbank looks a lot more resilient, but presumably would have smaller areas of open space internally.

Originally Posted by JSanderO View Post
Better design????
It depends on the design criteria. It seems a better design for tolerance to structural damage. One lesson of the WTC collapses may be that steel tube-in-tube structures don't decline gracefully.

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Old 27th February 2018, 05:00 AM   #67
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Originally Posted by Dave Rogers View Post
Yeah, that's pretty much my point; the designs of the buildings are radically different, so their response to a specific form of damage would be radically different. The Deutschbank looks a lot more resilient, but presumably would have smaller areas of open space internally.



It depends on the design criteria. It seems a better design for tolerance to structural damage. One lesson of the WTC collapses may be that steel tube-in-tube structures don't decline gracefully.

Dave
or buildings with a lot of massive load transfers inside them at lower levels drop straight down.... lickity split...

NB that the regions above the transfer (floor 8 up_ was standard framing aside from the plan shape. The supposed "buckling" occurred above the transfers in a "vanilla" regions to a very stout column.

++++

The unorthodox nature of the structural design of 7wtc was not discussed much by NIST I believe.... AE never considered 7WTC anything but a garden variety steel high rise... The twin towers and 7 WTC were unusual structural designs to say the least although the outward appearance was pretty vanilla.

It has been my belief once I looked at the collapse form/progression that the structural design was a huge factor in these collapses and largely ignored... at least down played as to make it seem as it was not a main factor.
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Old 5th March 2018, 10:01 AM   #68
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Originally Posted by JSanderO View Post
There's a thread on MetaBunk:

https://www.metabunk.org/how-much-ir...0/#post-219630

which includes photos of the Deutschbank buiilding with a gash in its north facade at least 8 stories high.

https://www.metabunk.org/attachments...-13-jpg.31968/

Building did not "progressively" collapse... columns above the 8 story missing column did not appear to buckle or sag.

Interesting.
Well, didn't the Deuthschbank have alot more columns per floor (steel-reinforced concrete even?), firewalls and much less open office-space by comparison? WTC7 had pretty much the exact opposite, and with extended members only tested for a mere portion if its connected length (for example; trusses at 54-57 feet, though just tested at 17 feet).
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Old 5th March 2018, 01:32 PM   #69
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Originally Posted by Jono View Post
Well, didn't the Deuthschbank have alot more columns per floor (steel-reinforced concrete even?), firewalls and much less open office-space by comparison? WTC7 had pretty much the exact opposite, and with extended members only tested for a mere portion if its connected length (for example; trusses at 54-57 feet, though just tested at 17 feet).

Well the DB certainly answered the question posed in another thread if a sin gle column failure leads to total building collapse.

In the case of DB there seems to not even be local floor slabs dropping... not columns above buckling.

take away might be... 7wtc was of a similar design... OOS with no columns between the core and the facade... except for the 3 bastards 79, 80 and 81... not in for and in the middle of the OOS.

OOS is ROOSD friendly....7wtc... had OOS and likely was a ROOSD.
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Old 5th March 2018, 06:31 PM   #70
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Originally Posted by JSanderO View Post
Well the DB certainly answered the question posed in another thread if a sin gle column failure leads to total building collapse.

In the case of DB there seems to not even be local floor slabs dropping... not columns above buckling.

take away might be... 7wtc was of a similar design... OOS with no columns between the core and the facade...
And 7wtc performed similarly when hit by debris from 1wtc: it remained standing after losing at least one column at its base (SW corner). I've already told you that. It's a lot about which column(s) and under which conditions, not about whether making one random column fail suffices to bring a building down.
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Old 5th March 2018, 06:43 PM   #71
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Originally Posted by pgimeno View Post
And 7wtc performed similarly when hit by debris from 1wtc: it remained standing after losing at least one column at its base (SW corner). I've already told you that. It's a lot about which column(s) and under which conditions, not about whether making one random column fail suffices to bring a building down.
The total collapse occurred because the transfers were involved... Likely cause of both DB and 7wtc not collapsing from one column failures is because both column loses were in a strong rigid exterior moment frames.

The failure of the 7wtc transfers would take out the east, north and west OOS flooring plus the core. The collapsing core likely pulled the south OOS floor down and finally the moment frame and curtain wall went down... with no support below floor 8.
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Old 5th March 2018, 07:15 PM   #72
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Originally Posted by JSanderO View Post
The total collapse occurred because the transfers were involved... Likely cause of both DB and 7wtc not collapsing from one column failures is because both column loses were in a strong rigid exterior moment frames.

The failure of the 7wtc transfers would take out the east, north and west OOS flooring plus the core. The collapsing core likely pulled the south OOS floor down and finally the moment frame and curtain wall went down... with no support below floor 8.
I'd like to understand your concern over the design.

If WTC7 had been involved in a fire on any normal day, do you think it would have failed? Do you think the damage inflicted on that morning should have been seen as "predictable" and then designed to withstand?

Personally, I think the building failed because of the circumstance of the day and not the design.
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Old 6th March 2018, 12:45 AM   #73
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Originally Posted by DGM View Post
Personally, I think the building failed because of the circumstance of the day and not the design.
There can be no serious doubt that you are right.

BUT it is an area where many people are confused - and some persons manipulate the confusion - whether deliberately or not is a different issue.

The designs of all the towers were valid practice for their era. Valid or "accepted practice" is a moving target and the towers were at the frontiers of design competence at the time.

The key factors often overlooked or confused esp by "truther" claims:
1) Steel framed buildings are vulnerable to fire and all high rise steel frames are designed with due regard to that vulnerability and the need for active fire fighting.
2) Both Twin Towers and WTC 7 were subjected to conditions outside the valid design envelope - the "Twins" in the extent of inflicted trauma, WTC7 essentially in being left to its fate with no active fire fighting undertaken.
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Old 6th March 2018, 04:21 AM   #74
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Originally Posted by DGM View Post
I'd like to understand your concern over the design.

If WTC7 had been involved in a fire on any normal day, do you think it would have failed? Do you think the damage inflicted on that morning should have been seen as "predictable" and then designed to withstand?

Personally, I think the building failed because of the circumstance of the day and not the design.
My hunch is that 7wyc would have done perfectly fine with a fire under "normal" conditions... ie adequate fire fighting and fire suppression. If a fire us out down and prevented from spreading and the exits paths are not blocked... the building would have been like many other high rises which survived extensive fire.

I am also of the mind that the use of transfers PROMOTED a local collapse to a global one. Transfer trusses did what they were designed for but in reverse... ie a local "collapse issue" was moved laterally by the transfer trusses.

The transfer trusses played a key roll in the global collapse in my opinion. It may be possible that one transfer truss on the East side LED the entire collapse... or that it was the first victim of a local NE quadrant ROOSD and tranfer truss failures were the mechanism for westward propagation of the global collapse. I don't think there is data to determine which came first.... local ROOSD or a East side collapse of a transfer truss.

The twin towers tops sections collapses are not unlike... in my opinion what happened to 7wtc... both were undermined by mass collapsing... in the twins this mass became the ROOSD driver... in 7WTC the a local ROOSD mass destroyed the transfers (or the destroyed transfers caused the ROOSD).

Twins' tops were undermined from severe mechanical damage from the plane strikes and extensive fire. But the tops collapse had different drivers because of the location of the plane destroyed columns and the fact the 1wtc's hat truss supported a concentrated antenna load which failed and top drop ensued.
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Old 6th March 2018, 04:13 PM   #75
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Originally Posted by JSanderO View Post
My hunch is that 7wyc would have done perfectly fine with a fire under "normal" conditions... ie adequate fire fighting and fire suppression. If a fire us out down and prevented from spreading and the exits paths are not blocked... the building would have been like many other high rises which survived extensive fire.
I agree, there is no reason to fault the building design under normal conditions or expectations.

Originally Posted by JSanderO View Post
I am also of the mind that the use of transfers PROMOTED a local collapse to a global one. Transfer trusses did what they were designed for but in reverse... ie a local "collapse issue" was moved laterally by the transfer trusses.
But, this was also after the reasonable design conditions for the building were exceeded, correct?

Originally Posted by JSanderO View Post
The transfer trusses played a key roll in the global collapse in my opinion. It may be possible that one transfer truss on the East side LED the entire collapse... or that it was the first victim of a local NE quadrant ROOSD and tranfer truss failures were the mechanism for westward propagation of the global collapse. I don't think there is data to determine which came first.... local ROOSD or a East side collapse of a transfer truss.
I know you want to blame the unique design of the transfer trusses for the global collapse. You are also correct in saying that there is no data to support this belief. We've talked before about this and there has never been evidence of condition favorable for their failure.

Originally Posted by JSanderO View Post
The twin towers tops sections collapses are not unlike... in my opinion what happened to 7wtc... both were undermined by mass collapsing... in the twins this mass became the ROOSD driver... in 7WTC the a local ROOSD mass destroyed the transfers (or the destroyed transfers caused the ROOSD).
This is true, the bold would need more evidence to become a leading theory.

Originally Posted by JSanderO View Post
Twins' tops were undermined from severe mechanical damage from the plane strikes and extensive fire. But the tops collapse had different drivers because of the location of the plane destroyed columns and the fact the 1wtc's hat truss supported a concentrated antenna load which failed and top drop ensued.
The drivers were the same. The things you mention only create subtle difference in the appearance of the collapse.
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Old 6th March 2018, 05:03 PM   #76
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Originally Posted by DGM View Post
I agree, there is no reason to fault the building design under normal conditions or expectations.



But, this was also after the reasonable design conditions for the building were exceeded, correct?



I know you want to blame the unique design of the transfer trusses for the global collapse. You are also correct in saying that there is no data to support this belief. We've talked before about this and there has never been evidence of condition favorable for their failure.



This is true, the bold would need more evidence to become a leading theory.



The drivers were the same. The things you mention only create subtle difference in the appearance of the collapse.
My point about the structural design in the WTC collapses is not that they were in adequate.. they surely were. It's that the structural design including but not limited to details DETERMINED the determined the FORM and SEQUENCE of the collapse. The designed had no ability to ISOLATE local failures therefore they would progress to catastsophic global ones. For example the tops of the twins were severely damaged and suffered terrible fires.... but the lower portions were virtually intact and the DESIGN led to a total collapse. And so I believe the transfers and an OOS system with long span beams lead to the total collapse of the 7wtc.

I have no "proof" but my analysis reveals this conclusion.

And so these buildings were far from "typical" office towers.... garden variety seen allover the country. They were unique designs and unfortunately it appears that those designs played a role in the total collapse.
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Old 6th March 2018, 06:23 PM   #77
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Originally Posted by JSanderO View Post

And so these buildings were far from "typical" office towers.... garden variety seen allover the country. They were unique designs and unfortunately it appears that those designs played a role in the total collapse.
This goes without saying. It also does not mean that a more conventional design (by this I think you mean older grid framing, like ESB) would not have suffered the same fate given the same circumstance.

The Plasco building collapse is a good example. Conventional design with little to no fire protection. Same thing could apply to any tall building. Building design has changed in the last decade in response to the 9/11 events. It has not gone back to redundant grid.
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Old 6th March 2018, 06:35 PM   #78
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Shorter spans don't automagically make buildings invulnerable to a cascade collapse.

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Old 7th March 2018, 03:41 AM   #79
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@pigemno.... no they don't... but that tend to isolated the local collapse better.

@DGM You won't be seeing long span light weight floor joists not massive load transfers and towers build over power sub stations with lots of fuel stored inside.
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Old 7th March 2018, 11:36 AM   #80
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Originally Posted by JSanderO View Post

@DGM You won't be seeing long span light weight floor joists not massive load transfers and towers build over power sub stations with lots of fuel stored inside.
Actually, none of these things are regulated any different in response to 9/11.

The amount of fuel stores was restricted long before. There's really no evidence to show it was a factor on 9/11.

Long span trusses are still used and load transfer solutions for design considerations are done all the time.

Mostly now, designs are driven by how to get everyone out and protect the fire safety systems should the **** hit the fan. The use of concrete in the core is in direct response to 9/11.
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