Failure mode in WTC towers

[GregoryUrich]

I believe Gregory started this thread because collapse initiation comments were taking his original thread in an ambiguous direction?

Myriad, I mentioned that buckling was obviously not the main collapse mechanism in the core or the perimeter.

This is because we aren't seeing many buckled columns in the rubble.


Collapse initiation may, and probably does, involve a different mechanism.

If allowed, I'd like to put forth and discuss certain curious phenomena witnessed during collapse initiation and just after these initial moments.

A collapse continuation mechanism involving "assisted weld failure" as opposed to weld failure may also be another parallel topic for this thread.

Isn't it possible to have three hinge buckling failure in the core with a six floor buckle? I'm not sure how realistic that is, but then I'm pretty new to collapse analysis.

 

[GregoryUrich]

Well no. Not as far as I can tell. What do you think? If you feel it does have relevance perhaps you'd be so good as to explain what that relevance is?

Well, Major Tom has a PNAC (Pre-planned Nefarious Assisted Collapse) theory based on the failure mode and the appearance of structural steel in photos. Perhaps that theory can be validated or invalidated.

 

[Reality Believer]

Well, Major Tom has a PNAC (Pre-planned Nefarious Assisted Collapse) theory based on the failure mode and the appearance of structural steel in photos. Perhaps that theory can be validated or invalidated.

The evidence of CD is based on the failure mode? Not in my world. Evidence of CD is based on direct evidence of materials, men and methods.

 

[R.Mackey]

The evidence of CD is based on the failure mode? Not in my world. Evidence of CD is based on direct evidence of materials, men and methods.

Assuming you're talking about the entire population of structural members, this is actually a good point. Even if the Towers were demo'd, i.e. by a reasonably intelligent, professional, efficient demo, we'd except only a few connections to have been destroyed by explosives -- and the remainder would look just like any ordinary collapse. That's because a professional demolition basically is a gravity-driven collapse.

The typical Truth Movement crap, however -- explosives at every 30 feet, ala Dr. Griffin or Jim Hoffman -- would create such a plethora of anomalous failure modes, not to mention demolition-specific debris and residue, that you'd practically trip over it.

 

[Reality Believer]

Assuming you're talking about the entire population of structural members, this is actually a good point. Even if the Towers were demo'd, i.e. by a reasonably intelligent, professional, efficient demo, we'd except only a few connections to have been destroyed by explosives -- and the remainder would look just like any ordinary collapse. That's because a professional demolition basically is a gravity-driven collapse.

The typical Truth Movement crap, however -- explosives at every 30 feet, ala Dr. Griffin or Jim Hoffman -- would create such a plethora of anomalous failure modes, not to mention demolition-specific debris and residue, that you'd practically trip over it.

Exactly, that is why I try and drive the perspective back out toward the big picture. If the big picture hypothesis makes sense, then attempt fill it in with investigation and evidence. If CD is the hypothesis, then fill it in with ALL aspects of CD. This is the scientific method, that we often forget here when debating minutia. Structural response is nothing without men, methods and materials.

 

[eeyore1954]

As Mackay has stated

Even if the Towers were demo'd, i.e. by a reasonably intelligent, professional, efficient demo, we'd except only a few connections to have been destroyed by explosives -- and the remainder would look just like any ordinary collapse. That's because a professional demolition basically is a gravity-driven collapse.

All of the structure from the floors above the collapse would have looked the same regardless of the cause of the collapse and everything from the floors below where the collapse initiated would have looked the same regardless of the cause of the collapse.

unless you subscribe to a theory that many floors were rigged to bring the building down.

also how does Major Tom think he has seen pictures of the majority of the wreckage. One of the towers had the rubble from about a 40 story building above the collapse point. Is he sure he has seen photographs from all levels of the debris.

 

[Newtons Bit]

When I think of member failure, I think of member ruptures, fractures or bending 30 degress or more, which should be fairly easy to see. I'm not really sure if this is standard terminology. Surely there is some accepted, more rigorous definition.

I am not ruling out buckling in the form of elastic bending or even some inelastic bending followed by weld or bolt connection failure. I think we can safely say though that there is a very small proportion of member failure in the columns as opposed to connection failure. This can be contrasted with a higher proportion of member failure in horizontal members as opposed to connection failure. I think this is an important piece of the puzzle in understanding how this building failed.

I still don't see how this is evidence of PNAC (Pre-planned Nefariously Assisted Collapse--coined by jhunter, refined by your's truly).

No, this is patently false. Even an A36 hot-rolled wide-flange will not undergo 30 degrees of rotation. When cold It will maybe do 12 degrees (at the upmost) before fracturing. A cold built up box-plate column made up of high strength materials will rotate far far less.

However this is all dependent upon the entirety of the structural column to resist the bending moments introduced at the cusp of buckling. I've already posted the below in an attempt to explain what is going on, hoping that yourself and/or Major Tom would think about what is actually going on to no avail.



Let's look at the column on the left. It has an area of A(in^2) and a plastic bending modulus of Z (in^3). It is made up a material that has a yield strength of Fy (ksi). Thus its axial capacity, Pn is defined as Fy*A. It has a bending capacity of Mn, defined as Fy*Z. The axial demand, or force on the column is defined as Pu. The bending demand, Mu, on the column is P*e. Under normal conditions, the bending moment along the height of the column varies linearly from the maximum of P*e to roughly zero at the base. If the diaphragm connection is severed, the bending moment through the entire column is a constant P*e (assuming that the reaction at the base can resist a moment).

The demand-to-capacity-ratio (DCR) of the column is defined as Pu/Pn + Mu/Mn (roughly, I do not wish to get into stress interaction here). If at any time Pu/Pn + Mu/Mn is greater than one, the column is said to have failed. You may also say that is has failed through compressive buckling.

The important thing is to know what mechanically happens when a column buckles. The column still resists a decreasingly amount of axial stress, but the bending moment at the plastic hinges is at the absolute maximum. In other words, Mu = Mn, varying from +Mn to -Mn between the hinges.

We already know that the splices are substantially weaker than the column itself and that a hinge is close to the column splice. The splices have a far less bending capacity (Mn) than the column does. The splice fails when the column is still fairly lightly stressed.

This should be obvious.

 

[Newtons Bit]

Assuming you're talking about the entire population of structural members, this is actually a good point. Even if the Towers were demo'd, i.e. by a reasonably intelligent, professional, efficient demo, we'd except only a few connections to have been destroyed by explosives -- and the remainder would look just like any ordinary collapse. That's because a professional demolition basically is a gravity-driven collapse.

The typical Truth Movement crap, however -- explosives at every 30 feet, ala Dr. Griffin or Jim Hoffman -- would create such a plethora of anomalous failure modes, not to mention demolition-specific debris and residue, that you'd practically trip over it.

I've been loathe to offer this to the various Truthers so as to give them more ammunition. But they really don't realize that it would not have taken much to cause a progressive collapse. A charge on three or four columns on two different floors would probably have done the trick.

 

[Newtons Bit]

Isn't it possible to have three hinge buckling failure in the core with a six floor buckle? I'm not sure how realistic that is, but then I'm pretty new to collapse analysis.

Buckling would occur at all points of the column roughly simultaneously. If the diaphragm is intact, you could expect three buckles on each of the three stories in a length of column. The bottom story, just before the splice, would have the largest stress acting on it however.

 

[R.Mackey]

I've been loathe to offer this to the various Truthers so as to give them more ammunition. But they really don't realize that it would not have taken much to cause a progressive collapse. A charge on three or four columns on two different floors would probably have done the trick.

I don't think we have much to worry about. I described a CD situation in my whitepaper, even one that could have survived the aircraft impact, with a relatively small amount of explosives (relatively small being a few hundred kilos). They haven't picked it up.

Part of the reason they haven't, I believe, is that they'd have to admit all of their other fantasies are wrong -- "exploding" debris, witness statements taken out of context, "dustification," columns broken into truck-sized lengths, "too fast," etc. ad infinitum. They'd have to grapple with the fact that all of those things are totally consistent with NIST, and inconsistent with all the books they've written and T-shirts they've sold.

And even if they get over that, they still have no explanation for the inward bowing initiating collapse. Or the clean seismographs. Or the lack of booms on the video. Or any explanation why.

When you get right down to it, the whole CD idea (I have yet to see a "hypothesis," apart from Max's far-out stories) is just plain stupid.

P.S.: Nice diagram. High marks for your educational content. There's a typo, though -- "Pn is defined as Fy*Pn" should be Fy*A. Sorry if that was a trap laid out for Truthers.

 

[Major_Tom]

To some avail, NB. Thanks for providing a model.

At present I am a bit short of research tools, as my web server experienced a major hard-drive crash. They are uploading my web site in parts and it will take a day or two more for me to have access to my usual links.

As part of this thread I would like to also include a list of curious phenomena which will cover the events leading up to collapse initiation.


Curioso #1: There were 2 strange things witnessed to happen to the North Tower as the second aircraft was striking the South Tower. They are both included in the short video clip linked below.

I would appreciate your learned opinions.

What certainly looks like a small explosion or ignition to the unlearned can be seen just along the northwest corner, floor 97, North Tower, just as the second plane hits.


http://www.youtube.com/watch?v=ciFGdAczRBM


There is other activity along the east face at the same time but I'd like to focus on the NW corner for now.

Please help me understand what that fireball really is. Thanks.


(Note to NB: Your model is here to stay and will be addressed. There are many oddities to discuss and I am not ignoring you. Thanks again.)

 

[Norseman]

Curioso #1: There were 2 strange things witnessed to happen to the North Tower as the second aircraft was striking the South Tower. They are both included in the short video clip linked below.

I would appreciate your learned opinions.

What certainly looks like a small explosion or ignition to the unlearned can be seen just along the northwest corner, floor 97, North Tower, just as the second plane hits.

http://www.youtube.com/watch?v=ciFGdAczRBM

There is other activity along the east face at the same time but I'd like to focus on the NW corner for now.

Please help me understand what that fireball really is. Thanks.

Major Tom, what you see in that video is a direct consequence of the second plane crash and the huge fireball the jet fuel created in WTC 2. The impact created a pressure pulse that pushed smoke and flames out of the windows of WTC 1. The main source of that pulse would be the very rapid local pressure increase created when the jet fuel ignited and deflagrated in an enormous fireball. But the fact that the aircraft caused the whole structure of WTC 2 to swing north on impact should also be expected have some effect, that was a large surface pushing air north.

Next when the fireball started to rise up outside WTC 2 it created a local low pressure that sucked smoke out of WTC 1 and of course air from the surrounding area.

And again, if you had devoted some time to look at the NIST report you would not have asked this question. This is described in NIST NCSTAR 1-5A paragraph 8.2 Response of WTC 1 to the Impact of United Airlines Flight 175 on WTC 2.

You do not even have to look at the NIST report to understand the cause and effect of what's going on in that video.

Again Major Tom you are coming here pretending to be unsure, while you on your website clearly gives a different impression, when I looked at it some time back. But you have to be pretty paranoid to think that what you see in the video was created by something else than the crash of Flight 175.

 

[Major_Tom]

And again, if you had devoted some time to look at the NIST report you would not have asked this question. This is described in NIST NCSTAR 1-5A paragraph 8.2 Response of WTC 1 to the Impact of United Airlines Flight 175 on WTC 2.

I did, but it does not serve as a holy text for me. I read it, and then I look with my own eyes. The link below is a short clip that shows the airplane impact and the small fireball along the NW corner, floor 97 of the North Tower.

http://www.youtube.com/watch?v=v2oUD1XWmB8

The useful information is only within the first 20 seconds of the clip.


Just push "stop" when you see the small fireball on the NW corner of the North Tower. At this instant please look at the stage of developement of the fireball created by the airplane.

The impact created a pressure pulse that pushed smoke and flames out of the windows of WTC 1.

Norseman, thanks for the response. But this is what I would refer to a standard justification, not an explanation.

Refer to your Bible, insult the person asking questions and give some totally inadequate response.


Next I'll try to extract the frame in which the small fireball on the NW corner of the North Tower, floor 97, is clearly visible. We will compare that with the stage of developement of the large fireball created by the airplane impact.

 

[DGM]

I did, but it does not serve as a holy text for me. I read it, and then I look with my own eyes. The link below is a short clip that shows the airplane impact and the small fireball along the NW corner, floor 97 of the North Tower.

http://www.youtube.com/watch?v=v2oUD1XWmB8

The useful information is only within the first 20 seconds of the clip.


Just push "stop" when you see the small fireball on the NW corner of the North Tower. At this instant please look at the stage of developement of the fireball created by the airplane.




Norseman, thanks for the response. But this is what I would refer to a standard justification, not an explanation.

Refer to your Bible, insult the person asking questions and give some totally inadequate response.


Next I'll try to extract the frame in which the small fireball on the NW corner of the North Tower, floor 97, is clearly visible. We will compare that with the stage of developement of the large fireball created by the airplane impact.

So we are clear you should give your reason for it and your justification for this reason. Just saying you don't believe what's explained in the report adds zero to a logical conversation.

 

[Major_Tom]

Below is an extracted frame from the second video clip. This is the moment when those puffs and a small fireball appears in the NW corner, floor 97, North Tower. The arrow indicates floor 97.

So you and NIST think the small fireball is caused by an overpressure wave caused by the second airplane impact?

It is on the opposite side of the building.

Notice in the video that no "pressure wave" can be detected by the way the smoke is moving in the gaping hole that the aircraft made in the North Tower at this time (nor anywhere else on the north face of the North Tower).

So we are clear you should give your reason for it and your justification for this reason. Just saying you don't believe what's explained in the report adds zero to a logical conversation.

According to the videos, your belief in the Word of NIST shows a great faith, but not much reason, in your arguments.

 

[GregoryUrich]

Buckling would occur at all points of the column roughly simultaneously. If the diaphragm is intact, you could expect three buckles on each of the three stories in a length of column. The bottom story, just before the splice, would have the largest stress acting on it however.

Do you mean 7 buckles in a three story length of column and two at the connections? I don't think we have a single photo showing this.

 

[pomeroo]

Below is an extracted frame from the second video clip. This is the moment when those puffs and a small fireball appears in the NW corner, floor 97, North Tower. The arrow indicates floor 97.

http://www.sharpprintinginc.com/911_curiosos/frame_265_g1.jpg


So you and NIST think the small fireball is caused by an overpressure wave caused by the second airplane impact?

It is on the opposite side of the building.

Notice in the video that no "pressure wave" can be detected by the way the smoke is moving in the gaping hole that the aircraft made in the North Tower at this time (nor anywhere else on the north face of the North Tower).




According to the videos, your belief in the Word of NIST shows a great faith, but not much reason, in your arguments.

So, you think a random fireball is likely the result of randomly-placed explosives and this explanation satisfies you as being logical, rather than faith-based. It is has been shown that your imaginary conspiracy lacked any sort of coherent motive and could not have overcome the logistical problems associated with wiring the Towers for demolition. You are, however, untroubled by those considerations. You think that accepting a report produced by a thousand researchers is not reasonable, but advocating a preposterous fantasy is.

 

[gumboot]

Well, Major Tom has a PNAC (Pre-planned Nefarious Assisted Collapse) theory based on the failure mode and the appearance of structural steel in photos. Perhaps that theory can be validated or invalidated.

I can see how Major Tom's theory would be a very appropriate topic for discussion in this subforum, and I can see how the topic of this particular thread can link to that, in which case fair enough, discuss away. However I must just muse that I have seen very little effort to connect the two thus far (although I see now that Major Tom has joined the thread so that will no doubt change).

It seems to me discussing the type of failure is pointless unless one of the two types of failure cannot occur in the sort of structural collapse that NIST proposes, and can only occur in some sort of PNAC (as you phrase it).

Regardless of what actually did happen, when a large steel building collapses I personally cannot see any reason why steel members could not fail by either buckling or weld failures (or perhaps even both?). Do you feel that either buckling or weld failure of steel structural members would be impossible in a gravity driven structural collapse?

Unless you feel one or the other would be impossible, it seems to me that determining what actually happened on 9/11 is moot.

 

[Newtons Bit]

Do you mean 7 buckles in a three story length of column and two at the connections? I don't think we have a single photo showing this.

Yes you do: every single picture that shows a relatively straight column broken at the splice.

 

[DGM]

Below is an extracted frame from the second video clip. This is the moment when those puffs and a small fireball appears in the NW corner, floor 97, North Tower. The arrow indicates floor 97.

[qimg]http://www.sharpprintinginc.com/911_curiosos/frame_265_g1.jpg[/qimg]


So you and NIST think the small fireball is caused by an overpressure wave caused by the second airplane impact?

It is on the opposite side of the building.

Notice in the video that no "pressure wave" can be detected by the way the smoke is moving in the gaping hole that the aircraft made in the North Tower at this time (nor anywhere else on the north face of the North Tower).




According to the videos, your belief in the Word of NIST shows a great faith, but not much reason, in your arguments.

The issue here is the fact you give no argument. You simply say that it can't be but offer nothing in return. It would be like me saying,"everything that Major Tom says is baseless and should be ignored". No explanation just a statement. It's time you poop or get off the pot.
What exactly is you basis for argument? So far all I see is you don't understand what you see.