CTBUH Comments on Nist Recommendations for Performance Based Design of Tall Buildings

[ctbuh]

This thread is managed by the CTBUH Fire & Safety Working Group (http://www.ctbuh.org/AboutCTBUH/WorkingGroups/FireSafetyGroup/tabid/98/Default.aspx) Co-Chairs: Simon Lay and Daniel O'Connor

[ctbuh]

Last week the National Institute of Science and Technology (NIST) issued its draft report on the fire and collapse of World Trade Center 7. This document is very interesting reading for all tall building designers and it can be found at www.nist.gov (http://www.nist.gov)

Tower 7 collapsed as a result of the fire that was ignited during the 9/11 terrorist attack. The report concludes that the collapse was solely a result of the fires that started on ten levels following the initial attack. The failure occurred approximately eight and half hours after the first attack. The collapse of the WTC1 and 2 severed the water mains and the firefighting effort was abandoned after the collapses of the twin towers.

NIST notes that the failure was caused by the effects of thermal expansion. While fire engineers are well aware that the effects of thermal expansion and thermal contraction (during the cooling phase) are often substantially more significant than the effects of heat reducing the strength of materials. This understanding needs to extend to architects and engineers that are involved in the high rise industry and an introduction to the subject is described in the paper David Scott presented at the NIST Chicago workshop. The paper “Fire Induced Progressive Collapse “ by Scott, Lane and Gibbons can be found online and on the CTBUH website.

[ctbuh]

The NIST report recommends that in future buildings should be designed so that they do not collapse, even in an extreme fire, even if the sprinkler system fails or is overwhelmed by the fire. The approach recommended by NIST is essentially a performance based approach which explicitly checks the performance of structure in fire. Although this approach has already been used on many tall buildings it is much less common on normal towers, and it marks a substantial change of design philosophy, from the prescriptive code method of applying a thickness of fire protection to all elements.

[DScott1]

The Council is collecting comments and ovservations from the NIST report with a view to presenting the opinion of our members to NIST.

The report is very interesting but it does not describe the detail failure mechanism nor does it explain to designers what were the main charecteristics of the building that led to the collapse. What the industry needs is to learn what types of details and configurations create poor performance, and why.

The fire induced failure of WTC 5/6 show that short slotted holes in primary beams do not work. What did the failure of WTC 7 show ? and what can be done to make a similar building perform better.?
1. if the primary beam had shear studs would it have failed..
2. If the girders had fin plates or end plates would the building have survived
3. Did the floors fail on the heating or cooling cycle… and theoretically what was worse?
4. How effective was the slab to tie the floors over the column… what were the catenary forces and how effective was the reinforcement
5. Normal fire codes assumes a fire only occurs on one floor and much of the fire protection design is to stop flame spread between floors. WTC 7 started with fires on 10 floors and the report is vague if this had an impact on the failure.
6. Would the tower have failed if the fire was only at one level. The report is not clear on this issue

We need to understand what happened at WTC 7 and how the collapse could be prevented. In general the industry needs to share much more information on performance and how we achieve it and where things do not work. This is where the WTC report is lacking and needs to be expanded.

D Scott

[HenryM]

I cant understand why people say that Tower 7 performed well just because it lasted 8 hours without sprinklers and fire fighting. If you look at the report you can see the following

Chapt 9-9
If you look at the fire spread diagrams you can see that the fire was on level 7 for only an hour. I thought towers were supposed to last at least 2 hours before there was any failure.

You can also see that their was a full flashover fire at level 12 that lasted until it burnt out. So why did level 7 fail and not level 12?

Chapt 10
If you look at both simulations A and B, the floors are subject to critical heat for less than an hour.

So does this imply that the tower would have fallen down under a normal fire if the sprinklers didn't work?

[HenryM]

So NIST want us to design all our building by modeling fire performance. The implication is that this is not difficult and can be part of the normal process.

So why dont NIST take the WTC 7 floor plan, model it in fire and change the design to make it work in a fire, and show the public what it takes and how easy it would be.

That way designers can see the type of changes that would need to be incorporated in the design

[HenryM]

How would NIST estimate the max design fire for a building Sure it is a function of the contents, but the Nist report says the WTC 7 fire started on 10 floors simultaneously. What are Nist recommending for fire modelling

Normal codes assume that there is a fire on only one floor at a time. Are Nist recommending that all floors are on fire. Based on the WTC 7 fire I would assume a maximum of 2 floors, but some other fires had many floors on fire. What guidance would Nist give.

If we keep on adding up extreme approaches we could get some extreme buildings
- assume sprinklers do not work
- assume fire fighting does not occur
- assume 2, 5, 10 levels on fire simultaeneously

[HenryM]

Can someone tell me how much it would cost to do the type of analysis that Nist are suggesting... on say a 40 story 800,000 sq ft building.

Is there enough people who can do this type of analysis and who are they.?

[live2c]

My take on the Nist report was that they are saying that the building fell down when Col 79 collapsed. And Col 79 collapsed when the floors failed... So the real cause was the floor failure... any ideas how many floors failed?

The Nist report says that the floor failed because of the joint detailing... but also after shear stud failure.. and it doesnt really say what happened.

If the floor fails in a ductile way, surely the catenary forces the floor puts on the column are massive. And its that pulling that causes the collapse.

Why doesn't the Nist report document the key events that started the initial failure. Sounds like the building fell down because of a shear connection failure in a primary beam.. or was it because it was a few shear studs too few... not good

[live2c]

How would NIST estimate the max design fire for a building Sure it is a function of the contents, but the Nist report says the WTC 7 fire started on 10 floors simultaneously. What are Nist recommending for fire modelling

Normal codes assume that there is a fire on only one floor at a time. Are Nist recommending that all floors are on fire. Based on the WTC 7 fire I would assume a maximum of 2 floors, but some other fires had many floors on fire. What guidance would Nist give.

If we keep on adding up extreme approaches we could get some extreme buildings
- assume sprinklers do not work
- assume fire fighting does not occur
- assume 2, 5, 10 levels on fire simultaeneously
...........

If you look at the report the fire took several hours to work its way around a floor and it looks to me as if only two floors immediately adjacent to each other were on fire at any one time. If you based your design on WTC 7 fire then it would be reasonable to only design for two adjacent floors on fire at any one time.
What do the fire experts say and what do NIST say? ...when they design skyscrapers for fires, do they consider more than one floor on fire? How many? I remember seeing pictures of a tower on fire and it looked like all the floors were on fire at the same time.

[HenryM]

On page 330 NIST say that "the challenge was to determine if a fire-induced floor system failure could occur in WTC7 under an ordinary building contents fire" But I can not find where they address this challenge in their report.

If NIST are advocating that engineers analyze building performance as part of the normal design process, then surely they can answer the challenge they set themselves. Did their analysis show that the building would fail under a normal contents fire?

[HenryM]

The NIST analysis pg 353, shows that shear studs and the bolts holding the primary to Col 79 failed before the temperature of the steel reached 200degC.

These temperatures are very low compared to a fire protection test that assumes that steel loses strength at 550degC.

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It looks like the finite analysis model they did was very small Fig 8-22, and it seems to me that this is too small to pick up all the local effects around col 79.

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I am surprised to see failure of shear studs, since I would expect the beam to simply bend out the way and for the end connections to buckle like they did at Cardington.

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I cannot see why the top bolts of the girder would fail at connection to Col 79, because if it did then that would mean the slab had moved relative to col 79.

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Did NIST look at any cooling cycle effects? Because if cooling had started after the bolts connecting to Col 79 had failed would the connection be stable?

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But I am most surprised about the failure initiation event which NIST seem to say was the local buckling of a secondary beam away from the floor slab that led to a global buckling of the floor.

Nist also do not describe how the local floor failure led to the global failure.?

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I would interested in any opinions on these issues from a fire expert?

[ctbuh]

Hello. Am I to understand that you find the NIST report believable, and that fire can be seen as a real cause for the symmetrical collapse of a steel framed skyskraper? Thank you. Joseph Ciolino NYC Joseph Ciolino

[DScott1]

I am not sure I understand your question. I believe that the NIST report is a responsible attempt to find the cause of the failure, however there are many questions that are not answered in any detail and several of these questions are already on the discussion forum. I think that with a responsible dialog and debate that the NIST report can be much better and clearer than it is in the current form.

However, that being said, I would like to be clear that I see no credibilty whatsoever in the 911 truth movement and I believe, like the vast majority of tall building professionals, that all the failures at the WTC ( WTC 1, 2, 5, 6 and 7) were a direct or indirect result of the planes that were flown into the two towers. I have carefully looked at the evidence that the 911 truth movement presents and I cannot see any evidence of a controlled demolition. Unfortunately the 911truth movement web site does not allow any opinions contrary to their own, or I would have presented my views.

David Scott - CTBUH Chairman

[Profjoe223]

David,
Thanks for the reply. Really, what I find has not been explained to even my own understanding are the following:

) How do we account for the evenness, totality, and swiftness of all thee collapses, in 2 entirely different types of structures?

2) How do we account for the pools of molten metal at all 3 sites of destruction, when office fires can't possibly get hot enough to cause that?

If anything, the NIST cartoon depicted (if it would have allowed itself to play out to the collapse itself) looked like a very asymmetrical collapse. This is very disturbing along with Dr. Sunder's statement that "Buildings were not constructed to withstand airline impacts." (sic!)

Very disturbing and usettling.

Thanks.

[DScott1]

David,
Thanks for the reply. Really, what I find has not been explained to even my own understanding are the following:

) How do we account for the evenness, totality, and swiftness of all thee collapses, in 2 entirely different types of structures?

2) How do we account for the pools of molten metal at all 3 sites of destruction, when office fires can't possibly get hot enough to cause that?

If anything, the NIST cartoon depicted (if it would have allowed itself to play out to the collapse itself) looked like a very asymmetrical collapse. This is very disturbing along with Dr. Sunder's statement that "Buildings were not constructed to withstand airline impacts." (sic!)

Very disturbing and usettling.

Thanks.
This forum is for a technical debate about the report and its recommendations. We do not want to talk about general opinions unless they are detailed and focused. These comments are too general and not technical and they do not help the debate. Future comments like these will be removed. Also the forum is also about WTC 7 only.

"1. How do we account for the evenness, totality, and swiftness of all thee collapses, in entirely different types of structures?"
The inside of WTC 7 collapsed first, followed by a buckling failure of the perimeter in the lower 15 floors. A non-linear collapse analysis would verify the speed of failure. From my perspective the building behaves as expected. Once the building collapse had started and momentum gained there is nothing of substance to arrest it.

"2) How do we account for the pools of molten metal at all 3 sites of destruction, when office fires can't possibly get hot enough to cause that?"
I dont know, but what hypothesis is being proposed?

The forum does not wish to engage in a debate about conspiracy theories and the 911truth movement. However if there is enough interest we will start a separate thread. Please do not post any views on 911truth in this forum, but write separately to info@ctbuh.org

David Scott CTBUH Chairman

[Profjoe223]

David,

I apologize if I have violated the rules of this forum. It was your invitation to post my question so I thought... well, it doesn't matter what I think.

However, I am not part of any movement, nor have I espoused any "conspiracy theories" either my own or of any "movement." If you read my post carefully there are none present.

I believed that I was questioning the report juxtoposed to particular and specific verifiable facts.

I had hoped that this, in and of itself, does not violate the spirit of this forum.

[simonflay]

I think there was up to 10 floors on fire at any one time, that may well have been critical to the overall collapse. After all, that's a major deviation from the standard fire tests.

[simonflay]

The shear stud failure does seem a bit odd. I tihnk that the temperature regime of the slabs may have impacted on the stud failure prediction. The top of the slabs were I think modelled as being hotter than the underside of the slabs, that might cause an upward bow, against the typical downward deflection of the steel deck, adding stress to the shear studs?

[simonflay]

I think we need to be careful when we talk about 'the studs failed' or 'the beam collapsed'. Remember, the modelling that NIST undertook was extremely complex and yes, produced results that appear to mimic to a good approximation the overall effects. However, we must remember that a model is a model and where partial modelling results are fed back into the model (shear stud failure being such an example), caution needs to be taken.

It is a brave effort by NIST to try to model 'reality' so closely, but I am sure that like any modelling exercise, it is ultimately a model, not the real thing?

[simonflay]

The NIST report does make some attempt to determine whether the fire would have, on it's own lead to a collapse. The conclusion drawn is that this is the case.

However, we must be careful not to necessarily presume that this means that a fire can drop a high-rise steel building.

Without the specific initiating event of a type which lead to multiple fires simultaneously on multiple floors, it is not clear that the fire alone would have lead to collapse.

[NickM]

Does the CTBUH agree that a performance based design should be used on all tall buildings?

[DScott1]

Does the CTBUH agree that a performance based design should be used on all tall buildings?

I believe that Performance Based Design should be used more frequently than it currently is. However I am not sure If I would recommend a performance based design approach on a regular 40 story tower. It depends to some extent on how fire engineers are able to demonstrate the value and benefit of PBD... either as improved performance, certainty of performance or improved value

D Scott - CTBUH Chairman

[DScott1]

So NIST want us to design all our building by modeling fire performance. The implication is that this is not difficult and can be part of the normal process.

So why dont NIST take the WTC 7 floor plan, model it in fire and change the design to make it work in a fire, and show the public what it takes and how easy it would be.

That way designers can see the type of changes that would need to be incorporated in the design
I think this is an excellent idea

D Scott CTBUH Chairman

[live2c]

I think there was up to 10 floors on fire at any one time, that may well have been critical to the overall collapse. After all, that's a major deviation from the standard fire tests.

But if you look at the NISt report there were only two or three floors on fire where the failure was initiated. This was in an area of the building that was undamaged, and the fire had only been in the failure area for an hour or two, which is a relatively short length of time, and well within the time frame that I would expect the floors to have survived. So the implication is that the building would have failed in a fire only. So if there is something wrong with how we design tall buildings I would like to know it.

I would like Nist to come out and say if they think the fire only would have caused the building to fail. And if the failure would have been predicted by the Performance Based design approach that they are recommending... and if so what could be done to stop that failure.

[live2c]

The NIST report does make some attempt to determine whether the fire would have, on it's own lead to a collapse. The conclusion drawn is that this is the case.

However, we must be careful not to necessarily presume that this means that a fire can drop a high-rise steel building.

Without the specific initiating event of a type which lead to multiple fires simultaneously on multiple floors, it is not clear that the fire alone would have lead to collapse.

I think your statement is inconsistent. NIST are saying that the fire caused the failure and you are saying that fire cannot drop a high-rise steel building.

If you look at the size of the fire in the area that started the failure it does not look very big to me and it did not last very long. A few storys on fire and a few hours.. most of the fire appears to have burnt out. Are you saying that you do not think that this size of fire could have occurred in a normal condition when the sprinklers failed?

[ctbuh]

The CTBUH have issued a draft response providing feedback on the NIST report. To view this draft, click here (http://www.ctbuh.org/Portals/0/People/WorkingGroups/Fire&Safety/CTBUH_NISTwtc7_%20DraftReport.pdf).

[live2c]

Check out what other bloggers are saying about the CTBUH report......

The Council on Tall Buildings and Urban Habitat (CTBUH) has published comments on the NIST WTC 7 Report. The CTBUH questions critical points of the NIST WTC 7 collapse theory and also highlights problems with the writing NIST report itself.

The CTBUH criticisms focus on two technical issues The conjectured failure of shear studs and bolts on the supposedly critical Column 79:

Several conclusions drawn in the NIST report on the contribution of structural
components in failure initiation are unexpected and have raised concerns
within the Council. These conclusions involve the role of both shear studs and
local global buckling of the floor beams in failure initiation. The Council
believes that the local connection performance was a significant part of the
global failure and would like to have seen a more explicit analysis of the
connection failure. (See also comment on Chapters 11-13.)

The NIST analysis (p. 353), shows that shear studs and the bolts holding the
primary Column 79 failed before the temperature of the steel reached 200˚C.
This implies a fundamental weakness that would be picked up by a
conventional PBD analysis. These temperatures are very low compared to a
fire protection test that assumes that steel loses strength at 550˚C.

The failure of shear studs is surprising, and has been modeled in a very
simplistic way, which may overestimate the failure of this element. Prior
studies and real fire cases have not previously identified shear stud failure as
a significant possibility Page 5

...

It is difficult to understand why the top bolts of the girder would fail at
connection to Column 79 Page 5

...

The report does not describe the detail failure mechanism of the girder
connection to Column 79. Since this was critical to the failure we would
expect to see diagrams of it, in its deflected, deformed shape immediately
prior to collapse. Page 7

And NIST's assertion that column buckling proceeded floor collapse:

We strongly believe that the initiating event was the
failure of the floor and the girder connections to the main column and that this
should be documented in Section 14.3.4. Page 7

...

The Council does not agree with the NIST statement that the failure was a
result of the buckling of Column 79. We believe that the failure was a result of
the collapse of the floor structure that led to loss of lateral restraint and then
buckling of internal columns. Page 10

However, the CTBUH also casts serious doubt on NIST's entire thermal expansion fairy tale by suggesting that cooling was in fact taking place around the magical Column 79 at the time of failure:

It appears that the fire on Level 12 had passed its peak in the area of Column
79. Is it possible that failure occurred as part of the cooling cycle? Page 6

And questions NIST's hypothesis about floor beams buckling both theoretically and with experimental data:

It is surprising to see in-plane buckling of the beam as being a key generation
of the initial failure, since it would be expected that the floors would bend out
of the way on their major axis, combined with a local buckling of the bottom
flange, like those found in the Cardington Fire Tests. Page 6

Finally, the CTBUH states that it finds the NIST report confusing and contradictory:

The report is rather confusing because the floor analysis is considered in
Sections 8, 11 and 12. It would be better if there was a complete
reconciliation of the analysis models. Page 6

...

In these sections NIST states that the initial failure was caused by the failure
of the floor system, in particular the connections to Column 79, that led to the
column becoming excessively slender and buckling. These statements
contradict the summary section 14.3.4 that identifies the initiating event as the
buckling of Column 79. Page 7

But don't expect the CTBUH to come out and endorse 9/11 Truth either:

The Council would like to make it clear that it sees no credibility whatsoever in
the 911 ‘truth movement’ and we believe, with the vast majority of tall building
professionals, that all the failures at the WTC (WTC 1, 2, 5, 6 and 7) were a
direct or indirect result of the planes that were flown into the two towers. We
have carefully looked at the evidence that the 911 ‘truth movement’ presents
and we cannot see any credible scientific evidence of a controlled demolition
on WTC 7 or any of the other WTC buildings. The Council considers that the
‘truth movement’ is a distraction and should not obfuscate the performance
issues which should be at the center of the debate about how best to continue
to improve and develop fire and life safety in tall buildings. Page 4

So, on the one hand the CTBUH provides at least three good reasons to dismiss the NIST report as a blatant fraud: (a) phenomenal shear-stud and bolt failure at Column 79, (b) cooling around Column 79 at the supposed time of thermal expansive failure and (c) mystical floor beam buckling. But on the other hand, the CTBUH ignores the blatant evidence of controlled demolition in WTC 7 for no technical reason what-so-ever.

(I do not include the CTBUH's insistence that floor failure proceeds column failure as a reason to disregard NIST because the idea that either could cause any kind of a collapse that could be confused with a controlled demolition is plainly absurd).

It should be note the CTBUH chairman and lead author of its NIST WTC 7 Comments, David Scott, has some interesting conflicts of interest (as apparently do his co-authors):

He was in New York on 9-11, 2001 and witnessed the attack on the World Trade Center and was part of the SEAoNY engineering team that worked at Ground Zero to assist with the search, recovery and clean-up.

Following 9-11 he was extensively involved in the industry review of design standards and procedures for tall buildings in extreme events. He has authored papers on Fire Induced Progressive Collapse, and was a reviewer of the US Governments (GSA) design requirements to mitigate progressive collapse, that were issues in 2002. He also worked extensively with Daniel Libeskind on the WTC masterplan and his design for Freedom Tower.

[DScott1]

This is meant to be a technical forum and I will ask the moderator to remove the email above and this response, as it adds no technical merit However I have responded to the comments and have deep .

"However, the CTBUH also casts serious doubt on NIST's entire thermal expansion fairy tale by suggesting that cooling was in fact taking place around the magical Column 79 at the time of failure:..."

No, the Council does not cast doubt on what you call NIST’s thermal expansion fairy tale. We believe that the failure was caused by thermal expansion but perhaps the critical point of time was as the expanded beam returns back to its original position. This is part of the thermal expansion theory

"Finally, the CTBUH states that it finds the NIST report confusing and contradictory:"

Yes there are aspects of the report that we think could be better but not in the way that is implied. NIST issued the report for comment and the plan was to make it better

So, on the one hand the CTBUH provides at least three good reasons to dismiss the NIST report as a blatant fraud: (a) phenomenal shear-stud and bolt failure at Column 79, (b) cooling around Column 79 at the supposed time of thermal expansive failure and (c) mystical floor beam buckling. But on the other hand, the CTBUH ignores the blatant evidence of controlled demolition in WTC 7 for no technical reason what-so-ever.

This is certainly not what we say. The NIST report is written by engineers and is about technical issues that can and should be discussed on a technical basis. The videos on the 911truth and ae911truth web sites are not technical and it is difficult to say any more than is contained in the NIST report. There is no blatant evidence in support of controlled demolition.

"It should be note the CTBUH chairman and lead author of its NIST WTC 7 Comments, David Scott, has some interesting conflicts of interest (as apparently do his co-authors)":

Interestingly I recieved a very similar accusation by email today which I will post below.

D Scott - CTBUH Chairman

[DScott1]

The following is a copy of an email sent out earlier today
..........
Thank you for your comments and questions. My response to your comments are given below, in blue and highlighted bold.

Please note that the Council reserves the right to publish this correspondence. Please confirm if you have any objection to this.

Regards
David
_____________________________________________
David Scott
Chairman - Council on Tall Buildings and Urban Habitat

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From: xxxx [mailto:xxxxxxx@gmail.com]
Sent: Monday, October 13, 2008 8:22 PM
To: David Scott
Subject: WTC 7 Comments/Conflict of Interest?

Dear Mr. Scott,

I have glanced through the CTBUH Comments on the NIST WTC 7 report. You are the first author on this document. I have several questions about it.

(1) Will you acknowledge that you have overt conflicts of interest in commenting on 9/11 and WTC 7?

"He was in New York on 9-11, 2001 and witnessed the attack on the World Trade Center and was part of the SEAoNY engineering team that worked at Ground Zero to assist with the search, recovery and clean-up.

Following 9-11 he was extensively involved in the industry review of design standards and procedures for tall buildings in extreme events. He has authored papers on Fire Induced Progressive Collapse, and was a reviewer of the US Governments (GSA) design requirements to mitigate progressive collapse, that were issues in 2002. He also worked extensively with Daniel Libeskind on the WTC masterplan and his design for Freedom Tower."

http://www.ctbuh.org/People/DavidScott/tabid/143/Default.aspx

I am chairman of the Council on Tall Buildings and Urban Habitat. I am a practicing tall building engineer. I have written papers on fire induced progressive collapse. I witnessed the collapse of the towers. I participated in the rescue and then the clean up and all the time I was questioning how and why. I was involved in a review of the new GSA standards for progressive collapse. And I worked with Libeskind on his design for Freedom Tower.

I cannot see why you could assume that this makes me have a conflict of interest. What interests? I just want the truth.

The ae911truth movement is not interested in truth. It presents one side of the argument and ignores all the facts that indicate that they may be wrong.

(2) Where is the data to back up your claim about the "vast majority of tall building professionals"?

"The Council would like to make it clear that it sees no credibility whatsoever in the 911 ‘truth movement’ and we believe, with the vast majority of tall building professionals, that all the failures at the WTC (WTC 1, 2, 5, 6 and 7) were a direct or indirect result of the planes that were flown into the two towers."

As Chairman of the CTBUH I am well connected to most of the leading practitioners of tall building design. The Council represents organizations with well more than 100,000 employees. I do not know anyone or organization in the Council that supports the controlled demolition theory. The ASCE has an engineering membership of 120,000 and they participated in the production of the NIST report. NIST itself employs about 2,900 scientists, engineers, technicians, and support and administrative personnel and hosts about 2,600 associates.

Against this you have the ae911truth movement which has support from approximately 80 licensed structural or civil engineers, who have signed its petition. Now in proportion to the industry the level of support that the 911truth movement is tiny. However I can understand why 80 people did, because the response from government was slow and the one side videos the 911truth movement show are very compelling, if you do not review them critically.

Some people will never believe we landed on the moon and some people will never believe that the planes that crashed into the towers, eventually brought them down. From my perspective both of these statements are equally preposterous. However the 911truth movement only provides one side of the argument and any organization that does so is not interested in truth. There are numerous answers to the questions they raise and the overwhelming evidence is that CD played no part in the collapse.

(3) How are all of the numerous videos which document the "collapse" of WTC 7 as a perfect controlled demolition not credible scientific evidence?

"We have carefully looked at the evidence that the 911 ‘truth movement’ presents and we cannot see any credible scientific evidence of a controlled demolition on WTC 7 or any of the other WTC buildings."

Well, if you only look at the 911truth videos then you have to remember that you are only looking at one side of the argument. Much of the evidence is circumstantial and is presented in a highly biased and emotive way. I have taken several of my family members through the ae911truth presentation and videos when they first came out and there was nothing that I saw, that could not be explained as a reasonable part of a collapse. Much of this information can be extracted from the NIST reports or from various contradictory web-sites..

My main concern is that the debate is that the CD theory is a distraction. 9/11 raises many issues about building performance, terror attacks and how structural steel behaves in extreme fire conditions. These issues need to be properly discussed and debated and every time the conversation starts, then CD takes us wildly of course.

Sincerely yours,
~xxxxxxxxx

..................................................................
Post by D Scott - CTBUH Chairman

[Chris Sarns]

I think there was up to 10 floors on fire at any one time, that may well have been critical to the overall collapse. After all, that's a major deviation from the standard fire tests.There were fires on floors 8, 11, 12 and 13 in the east end of the building where the collapse began. The fire on floor 12 had burned out by about 4:45 p.m.

NIST L pg 22-26 [26-30 on pg counter]
http://wtc.nist.gov/progress_report_june04/appendixl.pdf

[Chris Sarns]

CTBUH pg 5
The failure of shear studs is surprising, and has been modeled in a very simplistic way, which may overestimate the failure of this element. Prior studies and real fire cases have not previously identified shear stud failure as a significant possibility

In addition, it appears NIST incorrectly stated that there were no studs in the girder.

NIST L pg 6 [10 on pg counter]
Most of the beams and girders were made composite with the slabs through the use of shear studs. Typically, the shear studs were 0.75 in. in diameter by 5 in. long, spaced 1 ft to 2 ft on center. Studs were not indicated on the design drawings for many of the core girders.

NCSTAR 1-9 vol.1 pg 15 [59]
Most of the beams were made composite with the slabs through the use of shear studs. Typically, the shear studs were 0.75 in. in diameter by 5 in. long, spaced 2 ft on center. Studs were not indicated on the design drawings for the girders.

1-9 vol.1 Pg 342 [386]
Figure 8–16 is a partial floor framing plan of the northeast corner of WTC 7[1], which contains interior Column 79, a 13.7 m (45 ft) long girder (W33x130) framing between Column 79 and Column 44 without shear studs[2]

1 Taken from Erection Drawings, Sheet E12/13, 12th & 13th Floor Framing Plan.
2 The number of shear studs on a floor beam is indicated on erection drawings between brackets “〈…〉” as shown in Figure 8–16.
Based on erection drawing of Floors 12/13 (Frankel Steel 1985)

Figure 8-16 on pg 343 shows the exterior girders are 9' 10'' o.c. They also have 〈28〉 shear studs(?)
The drawing on pg 343 is based on erection drawing of Floors 12/13 (Frankel Steel 1985)
It is not the actual drawing and it does not show the legend.

It appears that NIST has misinterpreted the meaning of the number in the “〈…〉”

[Chris Sarns]

NIST L pg 6 [10 on pg counter]
Most of the beams and girders were made composite with the slabs through the use of shear studs. Typically, the shear studs were 0.75 in. in diameter by 5 in. long, spaced 1 ft to 2 ft on center. Studs were not indicated on the design drawings for many of the core girders.

NCSTAR 1-9 vol.1 pg 15 [59]
Most of the beams were made composite with the slabs through the use of shear studs. Typically, the shear studs were 0.75 in. in diameter by 5 in. long, spaced 2 ft on center. Studs were not indicated on the design drawings for the girders.

NCSTAR 1A pg 49 [87]
At Column 79, heating and expansion of the floor beams in the northeast corner caused the loss of connection between the column and the key girder. Additional factors that contributed to the failure of the critical north-south girder were (1) the absence of shear studs that would have provided lateral restraint and (2) the one-sided framing of the east floor beams that allowed the beams to push laterally on the girders, due to thermal expansion of the beams.


I'm a carpenter. If I install a floor where the girders are level with the floor joists, I would definitely secure the floor to the girder.

I ask any structural engineers who read this:
Is this the case in steel frame buildings with concrete slab floors?

[Jan]

This discussion forum is now closed. The CTBUH comments on the NIST report on WTC 7 were issued to NIST in October 2008. Any further comments on the NIST Report should be sent directly to NIST.

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