Failure mode in WTC towers

[R.Mackey]

Mackey:

Even if there were some combustibles in the core, the section factors of the core columns tell us the exposure times in a specified building fire to reach the critical temperature of A-36 steel. I am saying these times are too long for the WTC "office fires" to have heat weakened the WTC corner core columns significantly. Have you looked at the section factors for the core columns on say floor 80 and estimated these times?

If you have calculated the section factors, as I have, (its no big deal to do it, just a lot of number crunching!)), you would know what I am talking about.........

I have, and I'm agreeing with you. But those four core columns not being weakened does not mean the structure remains standing.

NIST also never claims the corner columns reach those temperatures, say in the more severe Case B of WTC 1. Here they show temperatures well below 350^oC, as seen in Chapter 9, NCSTAR1-5G. The collapse mechanism doesn't require these columns to be heated severely. There is still a contribution to buckling, however, since many of the cross-beams (much smaller in cross-section) were expected to heat significantly, reducing the corner columns' lateral restraint.

So, I'm not sure where you're going with this. NIST and I both agree with you.

 

[Newtons Bit]

I have, and I'm agreeing with you. But those four core columns not being weakened does not mean the structure remains standing.

NIST also never claims the corner columns reach those temperatures, say in the more severe Case B of WTC 1. Here they show temperatures well below 350^oC, as seen in Chapter 9, NCSTAR1-5G. The collapse mechanism doesn't require these columns to be heated severely. There is still a contribution to buckling, however, since many of the cross-beams (much smaller in cross-section) were expected to heat significantly, reducing the corner columns' lateral restraint.

So, I'm not sure where you're going with this. NIST and I both agree with you.

The corner columns (of the exterior frames) weren't really that important anyways, but that's a concept that requires an understanding that no one else here but maybe rwguinn would understand. I'm not about to explain shear lag in moment frames

 

[pomeroo]

The corner columns (of the exterior frames) weren't really that important anyways, but that's a concept that requires an understanding that no one else here but maybe rwguinn would understand. I'm not about to explain shear lag in moment frames

What can a non-engineer read to gain basic familiarity with the concepts you, Guinn, and Mackey discuss?

 

[Newtons Bit]

You are obviously misinterpreting what Timoshenko and Gere said and what I am saying. They are not talking about the situation you show with a column only under compressive loading. They are saying that there would be no eccentric loads in a situation where the columns have fixed end conditions due to the supports, to which they are fixed, providing an equal and opposite force and taking out the moment. They say this because the column is fixed against rotation. They are talking about floor loading type situations and they mean the horizontal supports such as beams, girders, or whatever you want to call them, would provide an opposing force to that developed by catenary action due to the floor deflection in your moment frame and eliminate the moment. Any unbiased and experienced mechanical or civil engineer, who has done structural design which wasn't canned in a manual, would see what I was saying as correct. You obviously have a hard time thinking through concepts and sound like you learned and do your job by rote. However, you do not have a problem being aggressive and have a huge amount of nerve, along with some of your little buddies here, talking about my abilities. It is you and rwguinn who decided to allow themselves to be less than civil and initiate name calling and castigation of another's abilities. You need to bear that in mind when reading my reply here.

I've highlighted the part of Mr. Szamboti's post here that shows exactly where his understanding fails. I'll explain why:

In engineering, we model reactions, or supports of structural elements in 2 categories for all axes of translation and rotation: free and supported. Free means that the support provides no support in that axes for that movement (translation or rotation); supported means that the member has zero movement in respect to that axes.

A pinned reaction would be supported in the two (or sometimes 3 for 3d applications) principle axes of translation, but free in rotation. 99.9% of wood to wood connections are designed this way. The truss to column supports in the WTC are pinned. (This is idealized, most connections have at least a minor amount of fixity in rotations, however it is typically ignored to make the calculations possible.)

A fixed reaction is where not only are the translational modes supported, but so are the rotations.

What Mr. Szamboti doesn't understand is the difference between a fixed reaction and a moment frame. It is true that under all loadings that don't destroy the members the column and the beam are at right angles. What he doesn't get is that the beam-column assembly itself rotates. The beams and columns stay at right angles to each other, but only at the connection itself. He imagines an idealized "fixed" connection where the beam and column connection can't move at all.

In my efforts to show him what the actual effective length factor of a column in a moment frame was, I supplied the AISC nomograph table that shows a sidesway uninhibited frame.


(click to enlarge)

Notice the how the beam-column assembly has rotated at point A and B. This is due to lateral forces acting on the entire structure OR it could be from eccentric loadings producing bending moments in the structure (the deflected shape would be slightly different however). The point here is that the upper connection A, is offset horizontally from connection B. This has significance in structural engineering.

What Mr. Szamboti has just said is that the columns can't rotate. If the columns can't rotate then the top of the tower can't sway in the wind, which we all know it did. This is why his claims are so preposterous to me. After the highlighted statement his comments get even more wild and idiotic, I can't make sense of them.

Confidential aside to Mr. Szamboti: You're intentional failure to try to hide how wrong you are, perhaps to keep the confidence of your unfortunate truther peons in you high, whatever, is what is invoking my ire. We've been patient and forthcoming with you for a long time, but you keep insisting on making up crap as concerns engineering and not listening to people who have diligently tried explaining how you are wrong. You are acting like a spoiled child. Do not be surprised that you are being treated like one.

 

[X]

What can a non-engineer read to gain basic familiarity with the concepts you, Guinn, and Mackey discuss?

Good question.
I'm studying engineering and I'm having trouble following them.

Now, R. Mackey is the only one of the three you listed whose credentials I'm aware of, and if they're anything to go by for Guin and Newtons Bit, those fellows are far and away beyond anything I'm likely to achieve.

I don't know how much you do know, Pomeroo, but there is a website called www.engineersedge.com that has lots of information. Unfortunately, it has a limit to the amount of free browsing you can do before it asks you to pay to join.

Personally, I'd recommend Googling any terms you're unfamiliar with as a start point. Google is free, and unless the term is really specific, you should get a worthwhile result. Hopefully.

 

[Newtons Bit]

What can a non-engineer read to gain basic familiarity with the concepts you, Guinn, and Mackey discuss?

I'm not sure. College taught the basics, but things didn't really "click" until I started practicing engineering. I wonder if it would be worthwhile to put together a "structural engineering for dummies" book to explain the various terms and concepts, with lots of pictures of course.

Then again, I've already promised a detailed reply to Greg on another thread (wihch I've yet to supply) as well as a couple other projects related to 911 and engineering already in the works. Maybe after those....

 

[Newtons Bit]

Good question.
I'm studying engineering and I'm having trouble following them.

Now, R. Mackey is the only one of the three you listed whose credentials I'm aware of, and if they're anything to go buy for Guin and Newtons Bit, those fellows are far and away beyond anything I'm likely to achieve.

I don't know how much you do know, Pomeroo, but there is a website called www.engineersedge.com that has lots of information. Unfortunately, it has a limit to the amount of free browsing you can do before it asks you to pay to join.

Personally, I'd recommend Googling any terms you're unfamiliar with as a start point. Google is free, and unless the term is really specific, you should get a worthwhile result. Hopefully.

Not just the normal search, but use the image search as well. You can get a lot of useful things that way.

 

[pomeroo]

I'm not sure. College taught the basics, but things didn't really "click" until I started practicing engineering. I wonder if it would be worthwhile to put together a "structural engineering for dummies" book to explain the various terms and concepts, with lots of pictures of course.

Then again, I've already promised a detailed reply to Greg on another thread (wihch I've yet to supply) as well as a couple other projects related to 911 and engineering already in the works. Maybe after those....

I'm not ashamed to confess that a "Dummies" or "Idiots" introduction to engineering would be most welcome. (I once told a clerk at Border's that I find the "Dummies" books too challenging and the "Idiots" books too simple--was there something written specifically for "Morons"?)

 

[Tony Szamboti]

I'm curious about something. As a non-engineer, I have difficulty following what you're saying here. I'm tempted to suggest that you're writing gibberish, but I can't be sure. I do notice that Newton's Bit, who clearly is vastly more knowledgeable than you, is much easier to follow. I'm guessing, then, that the murkiness of your prose reflects your own confusion about the concepts you're attempting to debate. Here's my question: Inevitably, Newton's Bit, or Mackey, or RWGuinn will take you to school on your latest effort. You will, of course, respond with more drivel. How does it end? If you were right, they would concede your point because--and this is important--they are interested in the truth. Obviously, you are not right; you are talking through your hat. As a conspiracy liar, you simply cannot display any intellectual integrity. Acknowledging that your position is untenable is not an option for a charlatan. You must retreat. There is no other choice. But, when you've finally fled this forum to proclaim your "victory" on the loon sites, don't YOU know that you were exposed? You feel that have so much invested in the nonsensical views you promote that you can't abandon them. What precisely have you invested?

I have nothing invested other than being interested in the truth as you say the others are. As a professional I would admit I was wrong if that were the case. It is not the case here.

This type of back and forth occurs in scientific debate and the reason to keep it civil is to allow for an admission of an error without castigation. The problem with some of the people you mentioned is they don't practice this behavior in their debates. They are very quick to name call and castigate and I might add so are you. I am also coming to the opinion that it is they who have a problem admitting they were wrong and di not understand. That would go hand in hand with their lack of civility.

 

[pomeroo]

I have nothing invested other than being interested in the truth as you say the others are. As a professional I would admit I was wrong if that were the case. It is not the case here.

This type of back and forth occurs in scientific debate and the reason to keep it civil is to allow for an admission of an error without castigation. The problem with some of the people you mentioned is they don't practice this behavior in their debates. They are very quick to name call and castigate and I might add so are you. I am also coming to the opinion that it is they who have a problem admitting they were wrong and di not understand. That would go hand in hand with their lack of civility.

The real engineers explain your errors in painstaking detail. Obviously, you are incapable of following them, as you are far from being on their level. But, you persist in acting as though a real debate is taking place. They are instructing you and you refuse to try to learn.

Pick out a statement by either Newton's Bit, RWGuinn, or Mackey and state why it is wrong. Thrash out the issue until one side or the other abandons its position. Prediction: you will drop out of the running, whining about something unrelated to technical matters. You will neither learn nor persuade.

 

[Tony Szamboti]

I've highlighted the part of Mr. Szamboti's post here that shows exactly where his understanding fails. I'll explain why:

In engineering, we model reactions, or supports of structural elements in 2 categories for all axes of translation and rotation: free and supported. Free means that the support provides no support in that axes for that movement (translation or rotation); supported means that the member has zero movement in respect to that axes.

A pinned reaction would be supported in the two (or sometimes 3 for 3d applications) principle axes of translation, but free in rotation. 99.9% of wood to wood connections are designed this way. The truss to column supports in the WTC are pinned. (This is idealized, most connections have at least a minor amount of fixity in rotations, however it is typically ignored to make the calculations possible.)

A fixed reaction is where not only are the translational modes supported, but so are the rotations.

What Mr. Szamboti doesn't understand is the difference between a fixed reaction and a moment frame. It is true that under all loadings that don't destroy the members the column and the beam are at right angles. What he doesn't get is that the beam-column assembly itself rotates. The beams and columns stay at right angles to each other, but only at the connection itself. He imagines an idealized "fixed" connection where the beam and column connection can't move at all.

In my efforts to show him what the actual effective length factor of a column in a moment frame was, I supplied the AISC nomograph table that shows a sidesway uninhibited frame.

[qimg]http://www.internationalskeptics.com/forums/imagehosting/thum_16329477c57124fc1f.jpg[/qimg]
(click to enlarge)

Notice the how the beam-column assembly has rotated at point A and B. This is due to lateral forces acting on the entire structure OR it could be from eccentric loadings producing bending moments in the structure (the deflected shape would be slightly different however). The point here is that the upper connection A, is offset horizontally from connection B. This has significance in structural engineering.

What Mr. Szamboti has just said is that the columns can't rotate. If the columns can't rotate then the top of the tower can't sway in the wind, which we all know it did. This is why his claims are so preposterous to me. After the highlighted statement his comments get even more wild and idiotic, I can't make sense of them.

Confidential aside to Mr. Szamboti: You're intentional failure to try to hide how wrong you are, perhaps to keep the confidence of your unfortunate truther peons in you high, whatever, is what is invoking my ire. We've been patient and forthcoming with you for a long time, but you keep insisting on making up crap as concerns engineering and not listening to people who have diligently tried explaining how you are wrong. You are acting like a spoiled child. Do not be surprised that you are being treated like one.

It is absolutely incredible that you use the towers swaying in the wind to claim the core columns could rotate due to floor loads when they were fixed end conditions restrained at both ends. Are you forgetting that the tower itself is a cantilevered beam on end which has a fixed end and a free end? It is a completely different problem from that of the columns inside the towers. The columns would need to be able to rotate 2.5 degrees to behave the way you say they would. That isn't happening with the fixed end conditions of the central core columns.

I can't believe I am answering you after the nastiness you exhibit and now this proof of a lack of understanding on your part. You see this is why we try to keep things civil so nobody gets egg on their face. You couldn't keep it civil from the gitgo. You have been known to be nasty by many for quite some time. Your letter to Gordon Ross last spring was a case in point.

What is also interesting in your use of the AISC nomograph is that you never show the accompanying one where the effective length factor can be less than one where there is sidesway inhibition. It is you who seem to want to limit the debate to what you want to show. I have shown people here how to calculate effective length factors and it shows you are erring favoring collapse initiation and progression.

 

[Tony Szamboti]

The real engineers explain your errors in painstaking detail. Obviously, you are incapable of following them, as you are far from being on their level. But, you persist in acting as though a real debate is taking place. They are instructing you and you refuse to try to learn.

Pick out a statement by either Newton's Bit, RWGuinn, or Mackey and state why it is wrong. Thrash out the issue until one side or the other abandons its position. Prediction: you will drop out of the running, whining about something unrelated to technical matters. You will neither learn nor persuade.

You don't know your behind from first base about engineering and are obviously not in any position to judge who is right here. The fact that you are willing to go out on a limb and say something like this exposes the fact that your bias has no basis.

 

[beachnut]

You don't know your behind from first base about engineering and are obviously not in any position to judge who is right here. The fact that you are willing to go out on a limb and say something like this exposes the fact that your bias has no basis.

At least you have company

 

[R.Mackey]

I'm not ashamed to confess that a "Dummies" or "Idiots" introduction to engineering would be most welcome. (I once told a clerk at Border's that I find the "Dummies" books too challenging and the "Idiots" books too simple--was there something written specifically for "Morons"?)

Let me echo Newton's Bit in saying that, for me, a lot of these concepts take time to sink in -- even if you're studying these things full-time, which I understand few of us are.

I don't know how to get a quick appreciation of the topics. The best I can recommend is to spend a full year in Calculus, a full year in Physics (community colleges are your friend), and then frequently refer to The Feynman Lectures and Schaum's Outline series.

That's no substitute for a full nine-year programme of study, but it's as good a fake as I can think of. That, and make friends with engineers and professors, ask for help frequently, and keep an open mind.

This stuff can be difficult. I'm counting on others to catch me where I screw up, too.

 

[rwguinn]

It is absolutely incredible that you use the towers swaying in the wind to claim the columns could rotate due to floor loads when they were fixed end conditions restrained at both ends. Are you forgetting that the tower itself is a cantilevered beam on end which has a fixed end and a free end? It is a completely different problem from that of the columns inside the towers. I can't believe I am answering you after the nastiness you exhibit and now this admission of a lack of understanding. You see this is why we try to keep things civil so nobody gets egg on their face. You couldn't keep it civil from the gitgo. You have been known to be nasty by many for quite some time. Your letter to Gordon Ross last spring was a case in point.

What is also interesting in your use of the AISC nomograph is that you never show the accompanying one where the effective length factor can be less than one where there is sidesway inhibition. It is you who seem to want to limit the debate to what you want to show. I have shown people here how to calculate effective length factors and it shows you are erring favoring collapse initiation and progression.

The two bolded statemeents are mutually exclusive.
The only sideways inhibition in a cantalever is the moment restraint at the "fixed" end.
Please--draw the free body diagram of NB's system and study it before you further embarass yourself.
You persist in confusing the detail with the system. you are treating the between-floor columns as being fixed at both ends. They are not. The only shear restraint that exists between them is the effect of the walls, which act as shear panels. Those walls were breeched by a large, fast-moving aircraft, and were thus comprimised. Without those shear panels, the upper floor is not restrained to move with the lower floor. The system of columns and walls imake up a segment of the overall structure. Stack 113 of them, one atop the other, and together they make up the cantalever structure known as WTC1 or WTC2.

 

[Gravy]

NVM: I misread something.

 

[pomeroo]

You don't know your behind from first base about engineering and are obviously not in any position to judge who is right here. The fact that you are willing to go out on a limb and say something like this exposes the fact that your bias has no basis.

But I acknowledge that I know little about engineering. You persist in arguing with people who know much more than you do. How do I arrive at that judgment? It's simple: they respond to specific points you make and show where you're going wrong. You are conspicuously incompetent to hold up your end of the discussion.

 

[rwguinn]

....

Actually, Gravy, that's a non sequiter.
That situation is true, but has nothing to do with the discussion under way.
Realcddeal is thinking local and applying it globally... (if it works for a 2X2 array, it works for an NXN--analysts will understand that one...)

ETA--I see you corrected. Thank you, sir.

 

[Newtons Bit]

Let me echo Newton's Bit in saying that, for me, a lot of these concepts take time to sink in -- even if you're studying these things full-time, which I understand few of us are.

I don't know how to get a quick appreciation of the topics. The best I can recommend is to spend a full year in Calculus, a full year in Physics (community colleges are your friend), and then frequently refer to The Feynman Lectures and Schaum's Outline series.

That's no substitute for a full nine-year programme of study, but it's as good a fake as I can think of. That, and make friends with engineers and professors, ask for help frequently, and keep an open mind.

This stuff can be difficult. I'm counting on others to catch me where I screw up, too.

The differential and integral calculus are mandatory. You can ignore the 3-dimensional calculus that universities offer. A course in Ordinary Differential Equations (ODE's) would also be required to get a grip of the upper level of undergrad engineering.

 

[Max Photon]

Icy corner core columns

Max:

Some core columns had cross-sectional areas of about 40 in^2 or less, with section factors ~ 80 m^-1, and would be quite susceptible to heat weakening.

However, this would NOT be true of the more massive "corner" core columns, say at the 80th floor of WTC 2, with section factors ~ 30^m-1. These were massive load carrying box columns, contributing more than 2 tonnes of steel per floor, and needing about 35 minutes exposure to combustion gases at 900 deg C to reach Tc (~ 650 deg C). This condition was not realized in the WTC fires even for totally unprotected core columns.

Remember, even NIST said, once the jet fuel burned off (after about 15 minutes), there were no combustibles in the WTC 1 & 2 cores!

Weight a moment...

What are the implications?

That corner core columns did not fail from heat-weakening?

That corner core columns did fail from heat-weakening, but that there was an unaccounted-for heat source?