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WTC design flawed (?)

Other 9/11 topics of a technical nature.

WTC design flawed (?)

Postby DGM » Thu Nov 17, 2016 10:31 pm

OneWhiteEye wrote:
DGM wrote:For what it's worth, I've seen no real interest in actual discussion here at all. :(

Discussion about what?


Exactly. :)

I gave one example. There has been countless claims the WTC buildings were "flawed" but no one wants to discuss these "flaws" in the light of economic or construction reality. The "flawed design" meme lives on here although there is no evidence it was the case.
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Re: Is this forum becoming JREF lite?

Postby SanderO » Fri Nov 18, 2016 2:13 am

I'll discuss it.... but not tonight... I am tired and going to bed.
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Re: Is this forum becoming JREF lite?

Postby DGM » Fri Nov 18, 2016 10:11 pm

SanderO wrote:I'll discuss it.... but not tonight... I am tired and going to bed.


I think it would be a very interesting topic for a thread. It would certainly be too complex of a topic to cover in a post or two.
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Re: Is this forum becoming JREF lite?

Postby SanderO » Sat Nov 19, 2016 2:36 am

Flawed

This may not be the best word. I would assert that the towers and to a lesser extent 7wtc were rather unorthodox designs from a structural POV. They look sort of convetional as far as "glass box" skyscapers go. 7wtc does have a typical no structural curtain wall skin... the thing we see coming down... the twins had very unorthodox and I believe never before done...a structural load 120" or so wide and 3 stories tall factory pre assembled panel system for the facade. It was all bolted together... no welds.

The floor system for all three was basically a long span column free donut surrounding a more conventional column grid. Another odd ball or unorthodox and never before seen was that 7 WTC was build using the air rights to an existing main power sub station. The massive transformers and equipment meant that the column grid of the tower above could not have all the columns axially bearing directly on the foundations. Instead several of the 40 story column loads were carried by massive site erected 3 story high truss floors 5-7 and most of the north facade above floor 7 was carried on the end of massive cantilever trusses... 9' deep.

One take away which is hard to dispute.... is that the FORM of collapse was very much a product of the structural *scheme* or design. We can discuss this.

One concept for structures is redundancy in the sense that loads can "easily" be redirected to other paths (columns). This of course requires that there be strong beams which can serve as the *pathway" for the loads.... and or that portions of slabs can function (not collapse) when they lose support on one side...and become cantilevered slabs.

Design is often a delicate balance.... lighter structure (dead loads) means smaller columns below. The presumed live loads would be the same on each floor so reducing the dead load will make the building lighter and less expensive to build.

react...
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Re: Is this forum becoming JREF lite?

Postby DGM » Sat Nov 19, 2016 10:33 pm

SanderO wrote:Flawed

This may not be the best word. I would assert that the towers and to a lesser extent 7wtc were rather unorthodox designs from a structural POV. They look sort of convetional as far as "glass box" skyscapers go. 7wtc does have a typical no structural curtain wall skin... the thing we see coming down... the twins had very unorthodox and I believe never before done...a structural load 120" or so wide and 3 stories tall factory pre assembled panel system for the facade. It was all bolted together... no welds.


Unorthodox is also a bad way to describe the way the twins were designed and really doesn't apply to WTC7. The structural wall of the twins was shown to be very good at redistributing loads after the high speed impacts they were subjected to.

SanderO wrote:The floor system for all three was basically a long span column free donut surrounding a more conventional column grid.


This is by no means unorthodox. In fact it's normal even today.

SanderO wrote:Another odd ball or unorthodox and never before seen was that 7 WTC was build using the air rights to an existing main power sub station. The massive transformers and equipment meant that the column grid of the tower above could not have all the columns axially bearing directly on the foundations. Instead several of the 40 story column loads were carried by massive site erected 3 story high truss floors 5-7 and most of the north facade above floor 7 was carried on the end of massive cantilever trusses... 9' deep.


Your describing an engineering solution to a field condition. Could you explain how this was "odd ball" or actually contributed to the demise of the building?

There have been several studies done, none to my knowledge have faulted the transfer truss system.

SanderO wrote:One take away which is hard to dispute.... is that the FORM of collapse was very much a product of the structural *scheme* or design. We can discuss this.


I wouldn't dispute this because it's true. It's also irrelevant when discussing the failure of a building that exceeded the expected (reasonable) design requirements.

SanderO wrote:One concept for structures is redundancy in the sense that loads can "easily" be redirected to other paths (columns). This of course requires that there be strong beams which can serve as the *pathway" for the loads.... and or that portions of slabs can function (not collapse) when they lose support on one side...and become cantilevered slabs.


Now we're getting into meat. How were the twins and WTC7 deficient in these requirements? Naturally this raises the question of what should be considered as a required redundancy.

SanderO wrote:Design is often a delicate balance.... lighter structure (dead loads) means smaller columns below. The presumed live loads would be the same on each floor so reducing the dead load will make the building lighter and less expensive to build.



I'm not sure where you are going here.

Yes, there is a balance between design and economics. If you're claiming economics are making (or made in the case of WTC) buildings unsafe then this is something you will need to substantiate.
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Re: Is this forum becoming JREF lite?

Postby SanderO » Sun Nov 20, 2016 12:14 am

DGM wrote:
SanderO wrote:
Unorthodox is also a bad way to describe the way the twins were designed and really doesn't apply to WTC7. The structural wall of the twins was shown to be very good at redistributing loads after the high speed impacts they were subjected to.

it obviously made the facade stronger than a typical curtain wall... but the floor system was markedly weaker and more vulnerable to collapse.

This is by no means unorthodox. In fact it's normal even today.

It wasn't then and if is now normalized it makes the designs vulnerable to a ROOSD type scenario

Your describing an engineering solution to a field condition. Could you explain how this was "odd ball" or actually contributed to the demise of the building?

There have been several studies done, none to my knowledge have faulted the transfer truss system.

No one should deny that the transfers were putting all the eggs in one basket... their failure, led to the total collapse of the building. And they were all interconnected not isolated.

I wouldn't dispute this because it's true. It's also irrelevant when discussing the failure of a building that exceeded the expected (reasonable) design requirements.

what are the expected reasonable design requirements? Sure these buildings were able to support the loads...but they came apart too easily ONCE they lost their sprinkler systems and were facing *normal fires*. What is .. too easily? THAT is the question. I maintain that treaditional grid designs without lots of transfer would do better.

SanderO wrote:One concept for structures is redundancy in the sense that loads can "easily" be redirected to other paths (columns). This of course requires that there be strong beams which can serve as the *pathway" for the loads.... and or that portions of slabs can function (not collapse) when they lose support on one side...and become cantilevered slabs.


Now we're getting into meat. How were the twins and WTC7 deficient in these requirements? Naturally this raises the question of what should be considered as a required redundancy.

correct.... lighter cheaper means less redundancy by definition... and less redundancy makes the structure more vulnerable to total collapse.

SanderO wrote:Design is often a delicate balance.... lighter structure (dead loads) means smaller columns below. The presumed live loads would be the same on each floor so reducing the dead load will make the building lighter and less expensive to build.



I'm not sure where you are going here.

Yes, there is a balance between design and economics. If you're claiming economics are making (or made in the case of WTC) buildings unsafe then this is something you will need to substantiate.


We saw what happened to these buildings... that's the evidence in my opinion.
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Re: Is this forum becoming JREF lite?

Postby DGM » Sun Nov 20, 2016 1:29 am

SanderO wrote: We saw what happened to these buildings... that's the evidence in my opinion.


I'll respond to your post in it's entirety but your choice of quoting => color requires more effort then I can muster at this time.

I do hope the response I did quote is not indicative of what you consider discussion.

I'll respond at length in the morning.
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Re: WTC design flawed (?)

Postby SanderO » Sun Nov 20, 2016 2:46 am

I apologize.... I never bothered to learn the post quote business... it's easier for me just to insert comments in color...

Engineers to not engineer how their designs will collapse... or design strategies to limit or arrest partial collapses.

If we are to accept the NIST thesis... a single girder failure at one column on one floor could lead to and entire 47 story building of 47 acres of floor space collapsing in less than 20 seconds. This to me is a bit concerning and I would consider this a conceptual flaw in the design.
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Re: WTC design flawed (?)

Postby OneWhiteEye » Sun Nov 20, 2016 3:02 am

SanderO wrote:If we are to accept the NIST thesis... a single girder failure at one column on one floor could lead to and entire 47 story building of 47 acres of floor space collapsing in less than 20 seconds. This to me is a bit concerning and I would consider this a conceptual flaw in the design.

Seconded.
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Re: WTC design flawed (?)

Postby SanderO » Sun Nov 20, 2016 11:44 am

And if we accept NIST's twin tower thesis... a few trusses which sagged from un-fought fires for less than a couple of hours could lead to complete collapse in less than 20 seconds. YES they were hit by a wide body and columns were destroyed and fuel entered the building. But they did remain standing straight until they collapsed like a house of cards. To me this is also a bit concerning and I would consider this a conceptual flaw in the design.

+++++

Ozzie and DGM and others would argue that the conditions were SO outlier that their total collapse would not mean the design was flawed because the engineers didn't design for those conditions. And this of course seems correct. But what sort of engineering did they do which dealt with containing serious damage or dealing with failed sprinkler systems in a fire? The systems were wet systems gravity fed and required pumps to life city water to sprinkler storage tanks. One can envision many scenarios where the sprinkler system could be rendered useless... Were the sprinkler system designs flawed if this is the case?

Thought experiment. Terrorist decide to take the one of the twins down. The sneak into the top mech floor and place a bomb (small) at the sprinkler tank. Then there partners start fires on several floors below the now non function water sprinkler tank. Fire, floods, no sprinklers, very high floor. Could the fire rage, un fought weaken whatever and kick off a ROOSD?
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Re: WTC design flawed (?)

Postby DGM » Sun Nov 20, 2016 5:37 pm

SanderO wrote:If we are to accept the NIST thesis... a single girder failure at one column on one floor could lead to and entire 47 story building of 47 acres of floor space collapsing in less than 20 seconds. This to me is a bit concerning and I would consider this a conceptual flaw in the design.


SanderO wrote:And if we accept NIST's twin tower thesis... a few trusses which sagged from un-fought fires for less than a couple of hours could lead to complete collapse in less than 20 seconds.


You do know that both of these arguments are a strawman? The NIST claims nothing of the kind.

I plan to respond more later as time allows.
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Re: WTC design flawed (?)

Postby DGM » Sun Nov 20, 2016 5:50 pm

SanderO wrote:Thought experiment. Terrorist decide to take the one of the twins down. The sneak into the top mech floor and place a bomb (small) at the sprinkler tank. Then there partners start fires on several floors below the now non function water sprinkler tank. Fire, floods, no sprinklers, very high floor. Could the fire rage, un fought weaken whatever and kick off a ROOSD?


I will respond to this now.

I don't think it would be likely to collapse.

For one thing the buildings structure would be "as built"(with safety margins still applicable), something that was not the case on 9/11. Another consideration would be the buildings fire compartmentalization would be intact, not allowing for a full chimney effect air driving fire temps higher then normal. The steels fire proofing would also be still in place.

For what it's worth, taking out the sprinkler tank would not render the sprinkler and more important, standpipe system useless.

Bottom line. The building would not be pre-weakened and much of it's fire protection systems would remain intact.
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Re: WTC design flawed (?)

Postby DGM » Sun Nov 20, 2016 7:33 pm

I got some time to respond to the earlier post:

SanderO wrote:
It obviously made the facade stronger than a typical curtain wall... but the floor system was markedly weaker and more vulnerable to collapse.


This could be said to be true about any truss floor system. We're back to defining what protections would be reasonable to ensure it's design safety.

Maybe you could define what you think is reasonable? Naturally, the events of 9/11 would be outside of this, correct? Please don't down play the severity of conditions on that day, I'm really getting tired of pointing out that strawman.

SanderO wrote:It wasn't then and if is now normalized it makes the designs vulnerable to a ROOSD type scenario


No it doesn't. ROOSD happened because of conditions where the floor system only played a small part.

SanderO wrote:No one should deny that the transfers were putting all the eggs in one basket... their failure, led to the total collapse of the building. And they were all interconnected not isolated.


Wait, where is there an engineering report that states this? Like I said, there has been several studies done and none (to my knowledge) have faulted the transfer truss system. If you know of a report I can read I'd like you to draw it to my attention.

SanderO wrote: What are the expected reasonable design requirements?


For the most part they are described in the building codes. Short answer would be, conditions that could occur naturally over the life of the building. (vague, yes)


SanderO wrote:Sure these buildings were able to support the loads...but they came apart too easily ONCE they lost their sprinkler systems and were facing *normal fires*. What is .. too easily? THAT is the question. I maintain that treaditional grid designs without lots of transfer would do better.


Why do you persist in advancing this false statement? I'd ask you to support it but that would be pointless because you can't. No study to date supports this.
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Re: WTC design flawed (?)

Postby DGM » Sun Nov 20, 2016 7:57 pm

The final one I haven't responded to:

SanderO wrote: But what sort of engineering did they do which dealt with containing serious damage or dealing with failed sprinkler systems in a fire? The systems were wet systems gravity fed and required pumps to life city water to sprinkler storage tanks. One can envision many scenarios where the sprinkler system could be rendered useless... Were the sprinkler system designs flawed if this is the case?



Do you not see that this is yet just another strawman? You present this argument as an either or. Was it not, in your opinion, a combination of both (plus other factors)?
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Re: WTC design flawed (?)

Postby SanderO » Sun Nov 20, 2016 9:39 pm

Engineering is an empirical application of physics - statics and materials science. Engineers design for dead and live loads and do not run models (I believe) for ANY unusual conditions such as unfought fires and failed sprinkler systems. They don't run simulations for their design with axial elements or main beams removed (failed). They see the world in a very static stable way.

No building will fail if the design loads are not exceeded by real world conditions with some factor of safety. But engineers are not looking at their buildings with columns or beams missing or removed by mischief or accident... with the same loads. Why not? Because they consider such things too far outside of normal expectations.

I would allege that sprinkler systems are far from fail safe and mission critical. Electrical systems likewise are not fail safe and wet sprinklers depending on electrical systems therefore are vulnerable.
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