1999 replies to this topic

[skyeagle409]

WTC7

Almost unnoticed by most on Sept. 11 was the collapse of WTC 7, which occurred about 5:20 pm that afternoon. Although not struck by a jet, the building suffered damage from debris—in addition to a few other factors.“Ultimately, the failures were due to a complex interaction between structural damage (loss of structural components upon impact), non-structural damage (destruction of all fire and life safety systems upon impact) and fire effects,” says Carter. “Thus, it cannot be said that the WTC is the only fire-protected steel building to completely fail structurally from fire. It was heavily damaged and had no fire protection in its damaged state.”

My link

[flyingswan]

Q24, on 10 March 2012 - 12:50 PM, said:

It really is something when an engineer needs a layman to explain basics of the towers’ construction.

Need you to explain?  You don't half flatter yourself.  I was merely trying to find out what bit of the NIST report you were misinterpreting this time.

Quote

Now, the NIST report won’t help me but it would certainly help you.

I was well aware of the vertical load redistribution, it's a factor I mentioned in my early attempts to explain the fundamentals of structural engineering to you years ago.  What I asked for was some indication in the NIST report that the pattern of observed bowing could be explained by invoking the hat truss, and I'm still waiting.

Quote

Knowing this, it must be asked why NIST did not use the obvious answer - increased loads to the perimeter, transferred from the core - to explain the bowing?  Why did NIST instead choose to promote a more challenging answer - a degree of floor truss pull-in forces not supported by their own model and analysis?

If you read NCSTAR1-6, section 4.3, you will see that they indeed increased the vertical loads in their isolated wall model to see how it would fail, but to get the observed shape of the wall, they also had to add the pull-in forces which you so dislike.  If the floors were not exerting horizontal forces, at all levels, not just where the bowing occurred, the vertical load capability would be much less.

Quote

NIST simply could not reproduce the necessary core damage through their impact and fire hypothesis to increase the perimeter column load sufficiently to induce the observed bowing.  No, the NIST theory was forced to work in reverse – attempting to come up with a way that the perimeter failure could occur first and spread to the core.  It was hopeless, in their desperation manually inputting pull-in forces ‘cartoon-like’ where their own physics model predicted none.

You have got it completely about face.  They established that the observed bowing was incompatible, ie far too large, with just an added vertical load, so had to add the pull-in forces.

The difference between your hypothesis and NIST's is that NIST's fits the observed bowing and yours doesn't.  Apart from that, the extended time-scale of the bowing is incompatible with your hypothesis.  If the bowing is purely due to increased vertical loads, it will increase rapidly once the critical load is reached because the bowing makes the wall weaker.  If the bowing is due to pull-in forces, the weaker wall can stand for the observed length of time with a vertical load that is less than the critical one.

Quote

What you actually appear to be speculating, is that had NIST adjusted only the aircraft kinetic energy, rather than a full seven variables for each tower, it would have had the same effect (or close to).  Well good luck in proving that.  Personally I think it silly to declare considerable adjustment to variables such as mass and strength of the building to be “pretty insignificant”.

Yes, I think an error range of around 20% in energy input is going to far outweigh any other parameter.  They didn't actually vary building mass or strength between cases, just contents mass and failure strain, very different.

Quote

Also, only adjustment to the angle of aircraft attack affected “which bits” of the building fell in the impact path.  NIST’s best estimate of the angle meant that energy was expended in impacting the floor structure.  The severe case adjusted the angle to avoid the floor structure and impart more energy to the core.  This has potential to be highly significant.

You have been arguing up to now that the floors are weak, now suddenly you want them to be very strong.

Quote

You misunderstand that the factors determine how much kinetic energy is generated.

You misunderstand that the energy available is determined solely by the moving mass and the distance dropped.  Some is absorbed by damaging the building structure, the rest goes into kinetic energy.  Bazant assumes conservatively the maximum damage to the building, hence minimum kinetic energy.  Any of your quibbles means more kinetic energy, not less.

I've repeatedly asked you to back up your claim - that Bazant makes assumptions that ignore Newton's Third Law - by showing exactly where he does that.  As you have failed to come up with anything, are you going to admit you were wrong?

Quote

The core issues of Manning’s complaint are in regard to comprehensive physical investigation of the steelwork, government incompetence and fear that studies would rely on politically driven, computer generated, hypothetical simulations.  Focusing on his reference to FEMA (the investigative body at the time), shows only your capacity to miss the point.

This isn't the first time that you've claimed that criticism of the investigation, even criticism of the right investigation, means support for your position.  It doesn't.  Manning no more supports controlled demolition than does your earlier hero Quintiere.

Edited by flyingswan, 11 March 2012 - 12:32 PM.

[Q24]

flyingswan, on 11 March 2012 - 12:23 PM, said:

If you read NCSTAR1-6, section 4.3, you will see that they indeed increased the vertical loads in their isolated wall model to see how it would fail, but to get the observed shape of the wall, they also had to add the pull-in forces which you so dislike.  If the floors were not exerting horizontal forces, at all levels, not just where the bowing occurred, the vertical load capability would be much less.

You have got it completely about face.  They established that the observed bowing was incompatible, ie far too large, with just an added vertical load, so had to add the pull-in forces.

Quote it (specifically the red text).

Because right now I’m calling that out as unfounded rubbish, i.e. interjections from you rather than anything NIST confirmed.

NIST only applied vertical forces in their isolated wall model to the point where instability occurred.  NIST did not continue the analyses to determine just how far the wall could bow given a greater load transfer from the core.  With the immense force potential available it is obvious that had NIST done so, it would produce the degree of bowing observed.

NIST did not do so because it would have required explanation as to how the core failed first.

flyingswan, on 11 March 2012 - 12:23 PM, said:

The difference between your hypothesis and NIST's is that NIST's fits the observed bowing and yours doesn't.

NIST’s fantasy pull-in forces, added where their model predicted none, fit the observed bowing.
NIST did not explore how continued load transfer from the core would produce the bowing.

flyingswan, on 11 March 2012 - 12:23 PM, said:

The difference between your hypothesis and NIST's is that NIST's fits the observed bowing and yours doesn't.  Apart from that, the extended time-scale of the bowing is incompatible with your hypothesis.  If the bowing is purely due to increased vertical loads, it will increase rapidly once the critical load is reached because the bowing makes the wall weaker.

The time scale of the bowing is entirely compatible with load transfer from the core.  With each core column that is cut, the bowing increases a degree further.  Each core column failure will indeed produce a rapid increase of the bowing.  There is no minute by minute analysis of the observed bowing so there is nothing to say it occurred gradually rather than in rapid movements.

flyingswan, on 11 March 2012 - 12:23 PM, said:

If the bowing is due to pull-in forces, the weaker wall can stand for the observed length of time with a vertical load that is less than the critical one.

You don’t really believe that the wall was still ‘standing’ prior to collapse do you?  In WTC1 there was an approximate 5ft deflection in the South wall 5 minutes prior collapse… and you think that was still supporting anything?

I don’t think so - the wall was shot; crushed by leaning of the upper block.  The demolition ravaged remnants of the core was all left holding the structure together.  The upper block was on the brink of collapse.  The wall was not standing; only being held in place.

flyingswan, on 11 March 2012 - 12:23 PM, said:

Yes, I think an error range of around 20% in energy input is going to far outweigh any other parameter.  They didn't actually vary building mass or strength between cases, just contents mass and failure strain, very different.

Noted shift from “insignificant” to “outweigh”.

Contents mass means any non-structural component, such as the concrete floors for example.  

So yes, NIST did vary mass of the building.

I know you have a hang-up about the word “strength” (a technical quibble for your lack of better argument) but that is NIST’s own terminology.

NCSTAR1-2: -

“These variation contributed to more severe damage to the tower structure, by making the tower structure weaker and the aircraft structure stronger.

…

These differences were due to the larger impact speed, the increased weight and toughness of the aircraft, and the reduced contents mass and material toughness of the towers for the more severe case.”

So yes, NIST did vary strength/toughness of the building in their model.

Quibble over the technical term all you like, makes no difference.

flyingswan, on 11 March 2012 - 12:23 PM, said:

the energy available is determined solely by the moving mass and the distance dropped.

Exactly.

This is why the collapse onset and tilt (distance dropped) and crush-up (moving mass) are so important.

flyingswan, on 11 March 2012 - 12:23 PM, said:

I've repeatedly asked you to back up your claim - that Bazant makes assumptions that ignore Newton's Third Law - by showing exactly where he does that.  As you have failed to come up with anything, are you going to admit you were wrong?

This has already been addressed – last sentence, post #492.

Then your response got silly and I left it.

flyingswan, on 11 March 2012 - 12:23 PM, said:

This isn't the first time that you've claimed that criticism of the investigation, even criticism of the right investigation, means support for your position.  It doesn't.  Manning no more supports controlled demolition than does your earlier hero Quintiere.

You are easily confused.

Manning and Quintiere support that the official investigation was a farce.

That’s it.

[flyingswan]

Q24, on 12 March 2012 - 11:54 AM, said:

Because right now I’m calling that out as unfounded rubbish, i.e. interjections from you rather than anything NIST confirmed.

NIST only applied vertical forces in their isolated wall model to the point where instability occurred.  NIST did not continue the analyses to determine just how far the wall could bow given a greater load transfer from the core.  With the immense force potential available it is obvious that had NIST done so, it would produce the degree of bowing observed.

Case 9, vertical load, instability and maximum column force at 5.2 in. deflection.  You don't appear to understand what that means:  instability is the point at which a very rapid buckling occurs.

Case 8, horizontal load, instability at 10.2 in. deflection, so you can get about double the deflection before rapid failure starts if you combine pull-in forces with a smaller vertical load.

My claim follows from the above and NIST's repeated statement that the pull-in forces were needed to match the observed bowing.

Quote

NIST’s fantasy pull-in forces, added where their model predicted none, fit the observed bowing.
NIST did not explore how continued load transfer from the core would produce the bowing.

You keep claiming that NIST's model (presumably you mean the floor model) predicted no pull-in forces.  I suggest you read the report again.  They started with a detailed model that predicted the pull-in forces, but to incorporate the floors in their global model without getting something too big to work with, they went to a simplified floor model that didn't capture the pull-in forces of the detailed model.  This was why they went for the alternative of manually adding the pull-in forces needed to account for the observed bowing.  The added forces were all less that the predicted maximum from the detailed model.

This use of such a hierarchy of models is a standard engineering approach, by the way.

Quote

The time scale of the bowing is entirely compatible with load transfer from the core.  With each core column that is cut, the bowing increases a degree further.  Each core column failure will indeed produce a rapid increase of the bowing.  There is no minute by minute analysis of the observed bowing so there is nothing to say it occurred gradually rather than in rapid movements.

Not if the observed bowing is greater than the value at instability for a vertical load.

Quote

You don’t really believe that the wall was still ‘standing’ prior to collapse do you?  In WTC1 there was an approximate 5ft deflection in the South wall 5 minutes prior collapse… and you think that was still supporting anything?

I don’t think so - the wall was shot; crushed by leaning of the upper block.  The demolition ravaged remnants of the core was all left holding the structure together.  The upper block was on the brink of collapse.  The wall was not standing; only being held in place.

No, I believe the loads transferred back to the core, you are the one claiming that the walls are supporting an ever-increasing load.

You've just shot down your own hypothesis.

Quote

Quibble over the technical term all you like, makes no difference.

It makes a big difference, because, for example, a 25% variation in contents mass is only a 5% variation in total building mass.

Quote

This is why the collapse onset and tilt (distance dropped) and crush-up (moving mass) are so important.

Why?  If the top block is at an angle where, for example, one side drops to hit the structure below before the other side moves, the centre of gravity only falls half the distance, but the initial impact is concentrated into just one edge of the structure and by the time the far edge impacts, the distance fallen and energy available has increased.  Crushing a structure from edge to edge is going to take the same energy as crushing it all at once.  Peeling the wall away, as shown actually happening in Boony's video, will take even less energy.

As to this obsession of yours with the possibility of a major crush-up, Bazant's calculations show that this doesn't occur and I've explained the reason in simple words to you often enough.

Quote

This has already been addressed – last sentence, post #492.

Bazant doesn't just assume no crush-up, he produces the calculations to show how the crush progresses in both blocks.  You are confusing assumptions and conclusions again.

Quote

Manning and Quintiere support that the official investigation was a farce.

That’s it.

Whatever their opinions of the investigation, Manning and Quintiere don't conclude that a controlled demolition is required, therefore their criticism of the investigation isn't support for your ideas.

That's it.

Edited by flyingswan, 12 March 2012 - 03:48 PM.

[Q24]

flyingswan, on 12 March 2012 - 03:35 PM, said:

Case 9, vertical load, instability and maximum column force at 5.2 in. deflection.  You don't appear to understand what that means:  instability is the point at which a very rapid buckling occurs.

Case 8, horizontal load, instability at 10.2 in. deflection, so you can get about double the deflection before rapid failure starts if you combine pull-in forces with a smaller vertical load.

My claim follows from the above and NIST's repeated statement that the pull-in forces were needed to match the observed bowing.

What a surprise you could not back your claims with quotes from NCSTAR1-6 Section 4.3

As I said in my last post, the above are maximum deflections leading to instability of the external columns.  They are not maximum limits that the wall can possibly be deflected.  After the external column(s) fail, deflection can and will continue with leaning of the upper block.  You must remember that in reality, rather than an isolated wall model, the exterior wall is still connected to the rest of the structure and will remain in place even when overloaded/buckled.

flyingswan, on 12 March 2012 - 03:35 PM, said:

You keep claiming that NIST's model (presumably you mean the floor model) predicted no pull-in forces.

*strawman alert #1*

The correct argument is that NIST’s analysis reproduced neither the degree of pull-in forces nor required locations to match the observed bowing.  The argument is not as you misrepresent, that “NIST’s model predicted no pull-in forces”.  Of course isolated trusses could fail and induce some level of pull-in… nothing of the severity NIST describe though… according to their own model.

This is how NIST input the pull-in forces to their model…

NCSTAR 1-6: -

… loaded with an inward force where inward bowing was observed…

Not predicted by the model but – where it was observed.

If we wanted to model the physics of Will E. Coyote suspended in the air before his drop, because we have all observed that, perhaps we could ask NIST to input some imaginary, non-physics predicted force for us?

flyingswan, on 12 March 2012 - 03:35 PM, said:

Not if the observed bowing is greater than the value at instability for a vertical load.

Yes, even where the column has failed – see first response above.

flyingswan, on 12 March 2012 - 03:35 PM, said:

No, I believe the loads transferred back to the core, you are the one claiming that the walls are supporting an ever-increasing load.

You've just shot down your own hypothesis.

*strawman alert #2*

It was inherent in my question that I don’t think the walls are supporting anything.

flyingswan, on 12 March 2012 - 03:35 PM, said:

It makes a big difference, because, for example, a 25% variation in contents mass is only a 5% variation in total building mass.

Thanks for that – it is still not “pretty insignificant”.

flyingswan, on 12 March 2012 - 03:35 PM, said:

Bazant doesn't just assume no crush-up, he produces the calculations to show how the crush progresses in both blocks.  You are confusing assumptions and conclusions again.

Oh he certainly produces the calculations.

I’m a little bored of the Bazant discussion and your continual failure to understand how his papers do not compare in any shape or form to observable reality.  Please refer to my post #507.  I’ll leave it at that… along with that cracking quote of yours:  “You want reality to have hard limits, but it doesn't.”

http://www.unexplain...dpost&p=4225335

If you think hypothetical non-limited calculations trump reality then so be it.

flyingswan, on 12 March 2012 - 03:35 PM, said:

Whatever their opinions of the investigation, Manning and Quintiere don't conclude that a controlled demolition is required, therefore their criticism of the investigation isn't support for your ideas.

That's it.

*strawman alert #3*

I explicitly stated what Manning and Quintiere support… and still you hit on the strawman.

There are multiple facets to my opinion.

At a high level, two of them are: -

• that the official ‘investigation’ was a farce
  
• that demolition brought down the WTC buildings

Manning and Quintiere support the first, not the second.

So do you want to avoid the point yet again and tell us once more that they don’t support the second?




Back to the bowing…

The above discussion has been confined to the hypothetical simulations of how the bowing could occur.

But what about the physical evidence?

The ‘competing’ theories: -

• load transfer from the core
  
• truss sagging pull-in forces

The first is confirmed present through physical observation of the event.

NCSTAR1-8: -

“10:20 a.m. NYPD aviation unit reports that the top of the tower [WTC1] might be leaning.”

Incidentally that is 8 minutes prior collapse - good match to the 7 minutes prior collapse that the WTC2 thermite flow is known to have initiated.

And further evidence the upper block was leaning: -




So we know that the upper block of the tower was leaning, thus corroborating the fist hypothesis.

Onto the second theory…

NIST claim there was an expansive area of numerous floor failures across the collapse zone.

Where is the evidence for this?

Not in photographs where only a few areas of floor failure are seen.
Not in NIST’s own tests which could not reproduce the degree of sagging or bowing.
Not in physical evidence that showed insufficient heating of the steelwork.

Once again the hard evidence, observation of the bowing, favours demolition over impact/fire.

[Simbi Laveau]

OK,im very late here,and if im off topic,im sorry ,as i cannot read all 36 pages.

Let me start by saying, i am a 911 first responder,so this is ....near and dear to my heart.
i dont give a crap about any of the alleged physics,chemistry ,or thermal whatever, and wether or not there was an explosion ,or it was bludging .
Tower 7 should have not been affected at all,given its distance,and it wasnt hit by anything .  

In the years since the WTC,a lot has come out,that has made me rethink,it all,and suspect that it was not a terrorist attack.
i think the original bombing ,was,and it gave someone else,an idea.

NO ONE,in any NYC blue collar agency ,to my knowledge,had prior knowledge.
FDNY protocols always err on the side of safty for the members...unless of course they are EMS *clears throat loudly*.
Members of agencies arriving at the scene later,FBI,FEMA etc,said things that made some people very suspicious of them having prior knowledge of the events that unfolded.

I heard none of it,but friends of mine did . No one thought anything of it at the time,as we were all just wigged out .

Amongst my particular service,none of us think WTC 7 came down by itself ,,ok .Thats a lot of blue collar workers .

I can only speculate about the towers,but the huge muslim gathering the night before was witnessed by a lot of people.

If no one knows that story ,a huge gathering of muslims congregated ifo tower 1,and they kneeled and prayed.
People knew. They werent involved .It was more like they were praying for it not to happen.People knew .

I dont think Ghoulianni knew ,and i do think something about all of it was covered up later. He was shell shocked in my opinion,but hes far from an angel .

13 of my friends died on 911,and more,close friends ,died later,from either disease or war ,2ndary to it .

My health has suffered since then ,and i dont care if its related to the fact i spent time there.I wont even go for the physical they keep pestering me about .

The FDNY keeps statistics of all of us who went .
Fire,PD,EMS,Red Cross.
Who has what disease now,whos died,whos MIA.

They have their charts and graphs,and know how many are sick or dead,but none of it happened because of the air etc down there...
We are all getting mesothelioma because we knew a guy 18 years ago that was a brick layer.
uh huh...
please.....
No one gives a crap about the people who put their lives on the line for things like this,which is very apparent when they crap on us after the job is done .

This is why i dont trust our govt ,at ALL.
So when i rant and rave,its partly because ive seen it all first hand .

But yah,i went to both WTCs.93,and 2001,and the first time ,not even the tables and chairs moved from their spots in the restaurant on the first floor of tower 1,and there was a giant blast hole in the floor of the room ....
The fact all the towers collapsed ,compared to the first time,says a lot to me .
Just my 2 cents .

Edited by missymoo999, 12 March 2012 - 07:58 PM.

[Babe Ruth]

Thanks for the input Missy, and thanks for your service to your fellow man.

Oh, they were terrorist attacks, but the terrorists are not who you think they are or might be.  Highly likely that the actual terrorists wear business suits with american flag lapel pins.

I thing Rudy DID know, and I think that is why he insisted and fought the entire city council for years to have the EOC put in WTC7.

Thanks again.

[Czero 101]

missymoo999, on 12 March 2012 - 07:55 PM, said:

Let me start by saying, i am a 911 first responder,so this is ....near and dear to my heart.

Thank you for putting your life on the line to save others.

Quote

Tower 7 should have not been affected at all,given its distance,and it wasnt hit by anything .

Apparently FDNY Battalion Chief John Norman disagrees with you:

Quote

From there, we looked out at 7 World Trade Center again. You could see smoke, but no visible fire, and some damage to the south face. You couldn’t really see from where we were on the west face of the building, but at the edge of the south face you could see that it was very heavily damaged.

[SOURCE]

FDNY Engine 94 Captain Chris Boyle also disagrees with you:

Quote

{Boyle:} A little north of Vesey I said, we’ll go down, let’s see what’s going on. A couple of the other officers and I were going to see what was going on. We were told to go to Greenwich and Vesey and see what’s going on. So we go there and on the north and east side of 7 it didn’t look like there was any damage at all, but then you looked on the south side of 7 there had to be a hole 20 stories tall in the building, with fire on several floors. Debris was falling down on the building and it didn’t look good.

...

Firehouse: When you looked at the south side, how close were you to the base of that side?

Boyle: I was standing right next to the building, probably right next to it.

Firehouse: When you had fire on the 20 floors, was it in one window or many?

Boyle: There was a huge gaping hole and it was scattered throughout there. It was a huge hole. I would say it was probably about a third of it, right in the middle of it. And so after Visconti came down and said nobody goes in 7, we said all right, we’ll head back to the command post. We lost touch with him. I never saw him again that day.

[SOURCE]

And then there's this NIST / NYPD photo:







Cz

[Q24]

missymoo999, on 12 March 2012 - 07:55 PM, said:

OK,im very late here,and if im off topic,im sorry ,as i cannot read all 36 pages.

Let me start by saying, i am a 911 first responder,so this is ....near and dear to my heart.
i dont give a crap about any of the alleged physics,chemistry ,or thermal whatever, and wether or not there was an explosion ,or it was bludging .

It’s always nice to hear a different perspective on here, it doesn’t have to be about science and whatnot.

missymoo999, on 12 March 2012 - 07:55 PM, said:

But yah,i went to both WTCs.93,and 2001

Were you there on the day of 9/11 missy?

Czero 101, on 12 March 2012 - 08:35 PM, said:

Apparently FDNY Battalion Chief John Norman disagrees with you:


FDNY Engine 94 Captain Chris Boyle also disagrees with you:


And then there's this NIST / NYPD photo:

This is irrelevant as NIST confirmed the WTC7 debris damage was superficial.  Of course when there is a hole in the building face it might look bad, though structurally it had no bearing whatsoever on the collapse initiation.  missy’s point that distance of WTC7 from the towers meant it was not significantly affected by any impact is correct.

[Czero 101]

Q24, on 12 March 2012 - 09:03 PM, said:

missy’s point that distance of WTC7 from the towers meant it was not significantly affected by any impact is correct.

No, Q. What she actually said was that "it wasn't hit by anything".

missymoo999, on 12 March 2012 - 07:55 PM, said:

it wasnt hit by anything .  

The quotes I provided from FDNY personnel as well as the NIST / NYPD image I provided show that it was.

You'll notice that I made no mention of the amount of damage, significant or not, just that there was eyewitness and photographic evidence of impact damage.





Cz

[Q24]

Czero 101, on 12 March 2012 - 09:59 PM, said:

No, Q. What she actually said was that "it wasn't hit by anything".

Quite right.

missymoo999, on 12 March 2012 - 07:55 PM, said:

Tower 7 should have not been affected at all,given its distance, and it wasnt hit by anything .  

You were referring to this, which I pointed out is irrelevant.
I was emphasising that, which I feel is the significant point.

[skyeagle409]

Q24, on 12 March 2012 - 09:03 PM, said:

This is irrelevant as NIST confirmed the WTC7 debris damage was superficial.  Of course when there is a hole in the building face it might look bad, though structurally it had no bearing whatsoever on the collapse initiation.  missy's point that distance of WTC7 from the towers meant it was not significantly affected by any impact is correct.

Then you disagree with missymoo999, because missymoo999, said:

Quote

missymoo999, on 12 March 2012 - 08:55 PM

...Tower 7 should have not been affected at all,given its distance,and it wasnt hit by anything .  

[flyingswan]

Q24, on 12 March 2012 - 06:22 PM, said:

What a surprise you could not back your claims with quotes from NCSTAR1-6 Section 4.3

What a surprise that once again you misunderstand something obvious to an engineer.

Quote

As I said in my last post, the above are maximum deflections leading to instability of the external columns.  They are not maximum limits that the wall can possibly be deflected.  After the external column(s) fail, deflection can and will continue with leaning of the upper block.  You must remember that in reality, rather than an isolated wall model, the exterior wall is still connected to the rest of the structure and will remain in place even when overloaded/buckled.

You are completely wrong there.  An instability limit is the both the maximum load point and the maximum static deflection case.  Increase the load beyond that point and collapse is pretty well instant. It's the tipping point between a reversible bowing and a non-reversible buckling failure.

Quote

This is how NIST input the pull-in forces to their model…

NCSTAR 1-6: -

… loaded with an inward force where inward bowing was observed…

Not predicted by the model but – where it was observed.

If the observed bowing is beyond anything that can be sustained with a vertical load, there must instead be a pull-in load present.  

Quote

It was inherent in my question that I don’t think the walls are supporting anything.

Now you are really confusing me as to what you are claiming.  I thought your scenario was that the columns were being demolished, loading up the walls, and the collapse began when the walls couldn't carry the extra load any more.  If the walls are only under vertical load and the load is reduced, the bowing reduces too unless there are pull-in forces to keep it bowed.

Quote

Oh he certainly produces the calculations.

I’m a little bored of the Bazant discussion and your continual failure to understand how his papers do not compare in any shape or form to observable reality.  Please refer to my post #507.

In other words you can't back up your claim, you can't understand the calculations, and it is all a bit of an embarrassment to you.

Quote

Back to the bowing…

The above discussion has been confined to the hypothetical simulations of how the bowing could occur.

But what about the physical evidence?

The ‘competing’ theories: -

• load transfer from the core
  
• truss sagging pull-in forces

The first is confirmed present through physical observation of the event.

No-one is doubting that there is an initial load transfer due to the impact damage.  However, there is no initial bowing visible.  The bowing develops during the subsequent fire and is too great to match the extra vertical load that you want without pull-in forces which the floors are easily capable of producing.

If you don't believe the computational methods, I'm surprised you ever enter a modern building, because those same methods are used for the design.

Quote

Where is the evidence for this?

Not in photographs where only a few areas of floor failure are seen.
Not in NIST’s own tests which could not reproduce the degree of sagging or bowing.
Not in physical evidence that showed insufficient heating of the steelwork.

Seeing the complete lack of any physical evidence whatever for your demolition system, you have a nerve claiming this.

You know perfectly well that NIST's tests were to resolve doubts about the adequacy of the building's fire insulation and were conducted with insulation in place.  In the actual event, the impacts could hardly be expected to leave the insulation undamaged.

[Q24]

flyingswan, on 13 March 2012 - 11:13 AM, said:

What a surprise that once again you misunderstand something obvious to an engineer.

I accept your admission that the claims I highlighted in red were your personal “obvious” interjections rather than actual facts demonstrated in NCSTAR1-6 section 4.3.  It was rather deceptive to present your own claims as those of NIST.

flyingswan, on 13 March 2012 - 11:13 AM, said:

You are completely wrong there.  An instability limit is the both the maximum load point and the maximum static deflection case.  Increase the load beyond that point and collapse is pretty well instant. It's the tipping point between a reversible bowing and a non-reversible buckling failure.

If the observed bowing is beyond anything that can be sustained with a vertical load, there must instead be a pull-in load present.  

Apparently you do not understand the difference between an isolated model and a full model.  Though I’m sure you must know.  More likely you are again choosing to be intentionally deceptive.  I don’t know why I’m bothering as this is not an honest discussion on your part, but tell me…

If, “collapse is pretty well instant” after exceeding the maximum load, then how did the bowing of the exterior wall exceed the maximum deflection… without collapsing?

As we know, the South wall of WTC1 bowed approximately 5ft, compared to NIST’s “instability at 10.2 in. deflection”, but had not yet collapsed.  Do you know how/why?  Because it was not an isolated wall model, but connected to the rest of the structure.

The wall was already shot before collapse; it was not supporting anything with the degree of bowing observed.  The loads must have been taken up by the core by that point in time, which in itself proves a damage event must then have occurred in centre of the towers to initiate the collapses – the wall had already failed in a load bearing capacity prior to collapse.

flyingswan, on 13 March 2012 - 11:13 AM, said:

Now you are really confusing me as to what you are claiming.  I thought your scenario was that the columns were being demolished, loading up the walls, and the collapse began when the walls couldn't carry the extra load any more.  If the walls are only under vertical load and the load is reduced, the bowing reduces too unless there are pull-in forces to keep it bowed.

I don’t invoke the walls as the collapse initiator, that is what NIST do because their impact and fire cannot damage the core sufficiently alone.  To hell with the walls.  So far as I’m concerned, a whole level of perimeter columns could be ripped out (assuming a reasonably intact core) and the building would hold up.

The core columns are being demolished, correct, and primarily on the side where the main body of elevator banks happened to be located, the same side as the bowing.  The whole core is put off-kilter.  This exerts vertical force on the wall, which bows inward past its maximum stable deflection, but is held in place through connection to the structure.  The core is then forced to take up the additional loading alone but is now under huge strain on the brink of collapse… soon to be finished off by the thermite charges initiated 7-8 minutes prior collapse (incidentally, same time the WTC1 bowing initiated).

The load is never reduced on the exterior wall so the bowing can never decrease – once the core suffers asymmetric damage and tilts, it cannot right itself.  It is simply a case of the wall being crushed and bowing inward under the tilting motion of the core.  Remember that the core structure is vastly stronger than any exterior wall.

flyingswan, on 13 March 2012 - 11:13 AM, said:

In other words you can't back up your claim, you can't understand the calculations, and it is all a bit of an embarrassment to you.

Knowing your disingenuity, I do understand how you would turn what I actually said into your “other words”.

flyingswan, on 13 March 2012 - 11:13 AM, said:

Seeing the complete lack of any physical evidence whatever for your demolition system, you have a nerve claiming this.

Oh dear, I ask where is the physical evidence for these extensive truss failures, your centerpiece observation for natural collapse, and this is your best answer; to deflect?  How dare I ask for a speck of physical evidence when we have quite fine, politically driven, computer generated, hypotheticals; a place where we know reality has no limits (it’s going to amuse me forever you admitted that).

flyingswan, on 13 March 2012 - 11:13 AM, said:

You know perfectly well that NIST's tests were to resolve doubts about the adequacy of the building's fire insulation and were conducted with insulation in place.  In the actual event, the impacts could hardly be expected to leave the insulation undamaged.

This is hilarious considering our past discussion.  You remember, when I showed an exterior wall panel from the fire zone in an area NIST depicted as 1,000^oC, yet physical analysis proved the panel did not exceed 600^oC.  Oh, the fire-proofing must have been intact on that one, you cried!

Yet that panel was just as close to the impact as the numerous levels of floor trusses where you need the fire-proofing to be ‘shaken off’, i.e. not in the impact path.  It seems you want to have your cake and eat it.

[flyingswan]

Q24, on 13 March 2012 - 01:25 PM, said:

I accept your admission that the claims I highlighted in red were your personal “obvious” interjections rather than actual facts demonstrated in NCSTAR1-6 section 4.3.  It was rather deceptive to present your own claims as those of NIST.

NIST did the investigation that you claimed they didn't, and my conclusion is obvious from the results of that.

Quote

If, “collapse is pretty well instant” after exceeding the maximum load, then how did the bowing of the exterior wall exceed the maximum deflection… without collapsing?

As we know, the South wall of WTC1 bowed approximately 5ft, compared to NIST’s “instability at 10.2 in. deflection”, but had not yet collapsed.  Do you know how/why?  Because it was not an isolated wall model, but connected to the rest of the structure.

I agree that the numbers are not directly comparable because the 55 in. observed point is at a floor level on a six-floor bow length, while the 10.2 in. deflection is for the mid point of an unsupported column. What makes the difference is the support of intermediate floors.  However, if the load was purely vertical as you claim, those floors would not be adding the horizontal forces that make the difference.  With the NIST picture of unloading vertical forces and pull-in forces present, there is not the same problem.

Quote

To hell with the walls.  So far as I’m concerned, a whole level of perimeter columns could be ripped out (assuming a reasonably intact core) and the building would hold up.

So there are no forces in the wall?

Quote

The load is never reduced on the exterior wall so the bowing can never decrease....

Now those big wall forces are back again?

Quote

Knowing your disingenuity, I do understand how you would turn what I actually said into your “other words”.

What else am I to assume from your desire to avoid discussing something that was a key argument of yours a few days ago?

Quote

Oh dear, I ask where is the physical evidence for these extensive truss failures, your centerpiece observation for natural collapse, and this is your best answer; to deflect?  How dare I ask for a speck of physical evidence when we have quite fine, politically driven, computer generated, hypotheticals; a place where we know reality has no limits (it’s going to amuse me forever you admitted that).

I have great confidence in computational methods because they work, they are used every day, all modern buildings are designed with them.

The methods are not predicting anything extraordinary.  Steel truss failures during a fire are not exactly uncommon.  The photographic evidence is absent because the trusses are inside the building.

The physical evidence is there in the bowing, and there is no other physical explanation for that apart from pull-in forces.

Q24, on 12 March 2012 - 06:22 PM, said:

Thanks for that – it is still not “pretty insignificant”.

Missed this topic in my last post.  I'll try another approach to explaining why you can't multiply probabilities to get your astronomical answer.  Perhaps you'll agree that there is an equivalent change in impact energy that will compensate for any change in the other six parameters, say 5% more impact energy to compensate 5% less energy required to damage structure with reduced failure strain or whatever.  With that, you can say that the severe case is equivalent to, say, increasing the impact energy by a bit more than the error range and keeping the other parameters unchanged.  This gets you back to the probability of matching or exceeding the error limit, and this does not get into the astronomically low probabilities you claim unless you exceed it by a very large amount.  For instance, even double the error range will still happen nearly 5% of the time.