Moderated Steel structures cannot globally collapse due to gravity alone

[bill smith]

This is a basic structural issue. Let me explain.

Concrete is very strong is compression but poor in tension. In a floor slab, the top face is in compression (there is a downwards vector arrising from both dead and live loadings) and the lower face in tension. We therefore have to make the concrete so massivly thick that it spans itself - a nearly impossible task - or we introduce reinforcement.

In the case of the towers this comprisesd a lightweight permanent profiled steeled formwork, then layers of reinforcement, then the concrete (which was comparatively thin) was cast.

The size and spacing of the reinforcement varies depending upon a wide range of issues including loading, intermediate support, impact of the formwork, and so on. It's not like doing a simple domestic foundation where we might use just a plain 12 or 15mm mesh.

As Al says, this reinforcement isn't infinitely strong. It's designed to work as part of an overall structural system. And it's only designed for credible loads (which generally will not include the floor above landing on it).

Useful information. Thanks. I note that 15mm mesh is still over half-inch.It's not exactly going to disappear.....and if that was the lightest reinforcing ?

 

[bill smith]

If the core columns had knelt there would have been visible rotation at the top of WTC1. If there was no such rotation then the upper block C columns did not tear themselves off the lower part A core colmns either. So if they didn't tear, and they didn't kneel- what happened to them ? They didn't just disappear surely ? Was it hot enough for the steel to have become so plastic that it just gave up the ghost and squashed down flat ?

 

[Heiwa]

1. When you say "they" convinced you it was 100% lies, who are you referring to?

2. What kind of courses or studying have you done?

3. Also, I'm sure you've noticed, but there are a few people in this thread who seem to be very well educated on those subjects. ("Architect" is apparently an architect, go figure!) I've noticed that you like to bring up a lot of hypothetical examples and get feedback. Have you found the information from them interesting?

1. Common sense and clear thinking. Not me, Smith and Wesson!

2. http://heiwaco.tripod.com/cv.htm

3. Not really - but sometimes I get useful info. That's one reason I participate at JREF. Main reason is to educate the masses.

 

[Heiwa]

Then perhaps you could explain exactly what is happening in the following video, in which an upper part of a structure is dropped on the lower part of the same structure, destroying both.

http://www.wideo.fr/video/iLyROoaftc9z.html

Part A looks pretty well destroyed here, doesn't it? Watch carefully, as the upper part initially crushes down the lower, in exactly the way everybody in the truth movement says it shouldn't, then crushes up as it hits the ground. According to your repeated assertions, this is impossible. Is this video entirely faked, or are you wrong? Or are you, perhaps, going to invent some third possibility, in which you admit that the upper part of a structure can destroy the lower part when dropped on it, but (for some reason that you also haven't made up yet) this doesn't apply to the WTC towers?

Dave

No, video is the controlled demolition of an HLM (reinforced concrete building - little steel - Low Rent Social Housing) at Vitry/France last year. It clearly proves my point.

First they destroy (controlled demolition) floors 4-6 (part B) with explosives - BANG - (note the debris formed, etc) so that the top part C (say 6 floors 7-12) can drop down on lower part A (floors 0-3) due to gravity. At contact part A produces failures on part C and part C produces failures on part A. As top part C is bigger than part A, the whole building is destroyed. We French are pretty clever you know.

A sub-optimal solution would have been to destroy part A (floors 0-3) with controlled demolition and allow parts B and C to drop but then you need more dynamite down below to initiate the destruction and you never know where parts B and C end up. Actually parts B and C may not break up completely.

 

[phunk]

I don't understand why truthers think the crush should be symetrical to begin with. The impact force may be equal and opposite, but gravity is not. If you add up all of the forces at play, gravity is adding to the downward force on the lower block, but it's in the opposite direction of the upward force on the upper block. It's not a symetrical situation.

 

[Shalamar]

Then perhaps you could explain exactly what is happening in the following video, in which an upper part of a structure is dropped on the lower part of the same structure, destroying both.

http://www.wideo.fr/video/iLyROoaftc9z.html

Part A looks pretty well destroyed here, doesn't it? Watch carefully, as the upper part initially crushes down the lower, in exactly the way everybody in the truth movement says it shouldn't, then crushes up as it hits the ground. According to your repeated assertions, this is impossible. Is this video entirely faked, or are you wrong? Or are you, perhaps, going to invent some third possibility, in which you admit that the upper part of a structure can destroy the lower part when dropped on it, but (for some reason that you also haven't made up yet) this doesn't apply to the WTC towers?

Dave

The building would have survived if it was made of cardboard pizza boxes!

Joking aside, was that at controlled demo? My french is.. erm, rusty (Or non-existant), and Heiwa will likely just continue his claims that anything can't destroy anything, and therefor, that was a CT.

 

[Heiwa]

Joking aside, was that at controlled demo? My french is.. erm, rusty (Or non-existant),

Actually, they stripped the Vitry HLM building of items to recycle; windows, piping, cables, outfit, lifts, etc, so there was just a concrete cage left. Then walls at floors 3-6 was knocked off by CD and the result was a nice pile of concrete to sweep up (and probably to be re-used too - land fills, etc).

 

[Dave Rogers]

How many lies are you going to tell this time, Heiwa?

First they destroy (controlled demolition) floors 4-6 (part B) with explosives - BANG - (note the debris formed, etc) so that the top part C (say 6 floors 7-12) can drop down on lower part A (floors 0-3) due to gravity.

Why post things that can be seen to be false simply by watching the video? Firstly, there weren't any explosives used. Secondly, anyone who actually counts the storeys can see that the bottom part has six floors, so does the top part, and it's floors 7-9 that are removed. So you're lying about the process.

At contact part A produces failures on part C and part C produces failures on part A. As top part C is bigger than part A, the whole building is destroyed.

Part C is six floors, and part A six floors, and we can expect that the lower floors are more strongly constructed than the upper, in order to bear the greater dead loads. So you're lying about the top block being larger than the bottom block.

We French are pretty clever you know.

And you're not even French.

Edited by Gaspode: 

Edited for civility

Dave

 

[L The Detective]

3. Not really - but sometimes I get useful info. That's one reason I participate at JREF. Main reason is to educate the masses.

I see. Well, personally I'm going to continue to trust the expert opinion here, but that's only because I'm not an expert myself... so I have no choice. But good luck with your goals.

 

[tfk]

Heiwa,

I asked you a question several pages back.

Why do you think that the crush zone always occurred on the top floor of the part that you call "segment C", (i.e., the lower block) and not down somewhere between that point & the ground?

tk

 

[Heiwa]

How many lies are you going to tell this time, Heiwa?



Why post things that can be seen to be false simply by watching the video? Firstly, there weren't any explosives used. Secondly, anyone who actually counts the storeys can see that the bottom part has six floors, so does the top part, and it's floors 7-9 that are removed. So you're lying about the process.



Part C is six floors, and part A six floors, and we can expect that the lower floors are more strongly constructed than the upper, in order to bear the greater dead loads. So you're lying about the top block being larger than the bottom block.



And you're not even French.

Edited by Gaspode: 

Edited for civility

Dave

They also used hydraulic aids to shift the upper part sideways so it would crush down the lower part (to minimize the use of explosives) in this destruction of a reinforced concrete bldg.

http://www.dailymotion.com/video/x17lks_demolition-tour-abc-balzac-vitry_news

See also how the top of the upper part at Vitry, like at WTC 7, remains more or less intact during the controlled demolition and drops free fall while the lower part is getting crushed.

No such upper part is visible at WTC 1 and 2.

We French are really clever .

 

[Architect]

No. I've just posted a detailed explanation of why the actual safety factor is not 3, including facts/figures. You have blindly stated "FoS>3" without any explanation. Please clarify, in detail, how you arrived at this figure.

I've checked your paper and I can see nothing which would approximate to a meaningful explanation of how you sensibly arrive at "FoS>3". Please provide this material.

 

[Grizzly Bear]

They also used hydraulic aids to shift the upper part sideways so it would crush down the lower part (to minimize the use of explosives) in this destruction of a reinforced concrete bldg.

http://www.dailymotion.com/video/x17lks_demolition-tour-abc-balzac-vitry_news

See also how the top of the upper part at Vitry, like at WTC 7, remains more or less intact during the controlled demolition and drops free fall while the lower part is getting crushed.

No such upper part is visible at WTC 1 and 2.

We French are really clever .

So now instead of arguing that you cannot destroy an object using a piece of itself you're contending that there was now no mass pushing down on the collapse front in the first place because you could not see a mass through the dust?

I somehow doubt having an intact section is all that relevant if the mass is sufficient to cause the successive failure of additional floors.

 

[Heiwa]

I've checked your paper and I can see nothing which would approximate to a meaningful explanation of how you sensibly arrive at "FoS>3". Please provide this material.

Check http://heiwaco.tripod.com/nist0.htm#3 - it is all there!

 

[Heiwa]

So now instead of arguing that you cannot destroy an object using a piece of itself you're contending that there was now no mass pushing down on the collapse front in the first place because you could not see a mass through the dust?

I somehow doubt having an intact section is all that relevant if the mass is sufficient to cause the successive failure of additional floors.

Sorry, the subject is that steel structures cannot globally collapse due to gravity alone. OK, subject is extended to that you cannot destroy a structure dropping a part of it on itself, e.g. top of WTC 1 on lower part of WTC 1. At Vitry a big top part of a concrete structure is dropped on a smaller part of it by suddenly removing an intermediate part in between by hydraulics and explosives and the lower, smaller part is destroyed as expected.

I find the Vitry demolition interesting as you can see the upper part free falling for 1.5 seconds through the removed, intermediate section ... and during that time the upper part is intact, as expected.
Then, at contact upper/lower parts of course the lower, smaller part is crushed down, while the upper part is also destroyed crushed up at the interface.

As the upper part is bigger than the lower part, evidently the lower, smaller part is destroyed completely first. Finally what remains of the upper part is destroyed when it hits ground because the ground is stronger than the upper part.

It is all in accordance with what I have always stated.

You could of course at Vitry have removed say floors 0-3 and arranged floors 4-12 to drop against ground and then floors 4-12 would be destroyed as the ground was stronger or not a similar structure of what was dropped on it so the ground remained intact. You follow? No! OK, wrap a wet towel around you head and try again.

 

[Architect]

Check http://heiwaco.tripod.com/nist0.htm#3 - it is all there!

I'm sorry, but that statement is simply not true. What you actually say on the linked page is:

The above is a clear indication how the Towers were originally built by serious architects and engineers in the 1960's. Compressive static stresses in the primary structure columns were less than 1/3 of the yield stress of the steel before (obviously) ... and after serious damage (not so obvious but shown here)! The buckling stress of the column is virtually the same as the yield stress as the columns were arranged with spandrels. One reason why the static stresses were so low was that the designers had no access to computers to optimize (slender down) the construction. Manual calculations were done and to be on the safe side you added steel and built strong! And steel was quite cheap at that time. And US steel was good quality. The assumed yield stress 248 MPa was probably much higher in reality. NIST never checked the yield stress of the steel from the initiation zone in the rubble!

There was therefore plenty redundancy. A plane may crash into the bird cage and nothing happens. A big fire may break out and nothing happens. Why? Because the normal compressive stress in the supporting vertical structure is so low and if any column breaks or buckles, its load is transmitted to adjacent columns via the spandrels and the stress in adjacent columns increase a little. No global collapse is possible under any circumstances.

Evidently the columns got stronger (thicker plates, steel with higher yield stress) further down when the 'mass above' increases, but it is certain that the compressive stresses in the Towers never exceed 1/3 of the yield stress. Same applies for the buckling stresses.

What I see there are several sweeping generalisations and broad statements, but nothing that actually backs up you assertion of "FoS>3" anywhere.

Let's take a look again at how this item was put to you:

NIST tested the steel recovered from WTC (which in itself is of interest, as CTers usually claim it was all whisked away to China with unseemly haste). NIST NCS STAR 1-3D (http://www.fire.nist.gov/bfrlpubs/fire05/PDF/f05158.pdf) confirms a range of actual values:

- Core webs ranged from as low as 31.1 to 41.9 ksi, ie. 86 to 116% of specificed strength.

- Core flanges ranged from 32.4 to a high 53.4 ksi, ie. 90 to 146% of specified strength.

Setting to one side the 31.1 and 32.4 ksi results, inasmuch as a small proportion of columns below failure point are unlikely to lead to any wider problem, let's take the lower maximum of 116% specified value.

Now, the NIST Demand to Capacity Ratios (DCR) are based upon specified strengths and NIST themselves note that there is effectively spare capacity up to actual (but varying) yield point/strength.

Core columns in WTC typically had a Demand to Capacity Ratio (DCR) of 0.83, ie a safety factor of 1/0.83=1.20. Now let's assume assume that the steel has an additional 16% beyond minimum yield value. This would reduce the DCR to 1.16/.83=1.4.

In other words we could increase the loads in these areas by up to 40% before yield point was reached and plastic (permanent) deformation begins. Of course this figure has lots of variables - most of the steel webs did not have such a high yield factor, some areas had DCRs well in excess of 0.83, and so on.

What we don't do is then add any significant additional allowance for tensile strength because (a) yield failure is already occuring and (b) gravity loads will be compressive, not tensile.

As I frequently mention, one thing we also have to appreciate is that the structure of WTC is complex; in addition to dead and live loads, it will be dealing with (for example) transverse and shear loadings from the wind. There will be a degree of torsion due to differential loading. And so on. We would therefore have to look at the exact steelwork design in considerable detail before we could determine a safety factor for each. That's why engineers earn a lot of cash, and why complex modelling software was developed.

Nevertheless it is clear that the actual capacity of the core is not going to be anything like 400% or 4:1 before irreversible damage and failure begin to occur.

But in any event the above calculations all assume an intact core, and we know from the various NIST studies and eyewitness evidence that the cores suffered damage - around a third. This will obviously have reduced loadbearing capacity still further, and a simple pro-rata reduction of (say) 30% is likely to be wrong because the damage is concentrated in localised areas and hence these areas will be susceptible to accelerated failure under loads.

Now, Heiwa, can you produce similar calcs and figures to back up the "FoS>3" position you've adopted, or is it as substantial as your structural calculations?

 

[rwguinn]

I don't understand why truthers think the crush should be symetrical to begin with. The impact force may be equal and opposite, but gravity is not. If you add up all of the forces at play, gravity is adding to the downward force on the lower block, but it's in the opposite direction of the upward force on the upper block. It's not a symetrical situation.

Nice try, but no cigar
"The rest of the story" is that the force applied by the falling part of the building to the next lower floor is in excess of that required to remove (obliterate, do away with, etc) the resisting force of that lower, non-moving, intact at the time, floor of the building.
In a static case (nothing is moving), the SUM of all forces = 0. This occurs when the building is standing there, undamaged.
In a dynamic case (i.e., things are moving) the SUM of all forces = M*a. In this case, a=g

 

[twinstead]

Sorry, the subject is that steel structures cannot globally collapse due to gravity alone.

And, sorry, you have been shown to be horribly wrong about that to my satisfaction, and to the satisfaction of just about everybody I have shown this thread to. You know, real life people. People whom I KNOW know what they are talking about. Either every single person who has even the smallest expertise in the subject is wrong, and you are right, or you are wrong. Hmmmm. What to think. What to think.

So. You have the ability to argue an untenable point forever. Congratulations. When you are wrong but still like to debate it's a great skill to have.

 

[Heiwa]

I'm sorry, but that statement is simply not true. What you actually say on the linked page is:



What I see there are several sweeping generalisations and broad statements, but nothing that actually backs up you assertion of "FoS>3" anywhere.

Let's take a look again at how this item was put to you:

NIST tested the steel recovered from WTC (which in itself is of interest, as CTers usually claim it was all whisked away to China with unseemly haste). NIST NCS STAR 1-3D (http://www.fire.nist.gov/bfrlpubs/fire05/PDF/f05158.pdf) confirms a range of actual values:

- Core webs ranged from as low as 31.1 to 41.9 ksi, ie. 86 to 116% of specificed strength.

- Core flanges ranged from 32.4 to a high 53.4 ksi, ie. 90 to 146% of specified strength.

Setting to one side the 31.1 and 32.4 ksi results, inasmuch as a small proportion of columns below failure point are unlikely to lead to any wider problem, let's take the lower maximum of 116% specified value.

Now, the NIST Demand to Capacity Ratios (DCR) are based upon specified strengths and NIST themselves note that there is effectively spare capacity up to actual (but varying) yield point/strength.

Core columns in WTC typically had a Demand to Capacity Ratio (DCR) of 0.83, ie a safety factor of 1/0.83=1.20. Now let's assume assume that the steel has an additional 16% beyond minimum yield value. This would reduce the DCR to 1.16/.83=1.4.

In other words we could increase the loads in these areas by up to 40% before yield point was reached and plastic (permanent) deformation begins. Of course this figure has lots of variables - most of the steel webs did not have such a high yield factor, some areas had DCRs well in excess of 0.83, and so on.

What we don't do is then add any significant additional allowance for tensile strength because (a) yield failure is already occuring and (b) gravity loads will be compressive, not tensile.

As I frequently mention, one thing we also have to appreciate is that the structure of WTC is complex; in addition to dead and live loads, it will be dealing with (for example) transverse and shear loadings from the wind. There will be a degree of torsion due to differential loading. And so on. We would therefore have to look at the exact steelwork design in considerable detail before we could determine a safety factor for each. That's why engineers earn a lot of cash, and why complex modelling software was developed.

Nevertheless it is clear that the actual capacity of the core is not going to be anything like 400% or 4:1 before irreversible damage and failure begin to occur.

But in any event the above calculations all assume an intact core, and we know from the various NIST studies and eyewitness evidence that the cores suffered damage - around a third. This will obviously have reduced loadbearing capacity still further, and a simple pro-rata reduction of (say) 30% is likely to be wrong because the damage is concentrated in localised areas and hence these areas will be susceptible to accelerated failure under loads.

Now, Heiwa, can you produce similar calcs and figures to back up the "FoS>3" position you've adopted, or is it as substantial as your structural calculations?

Sorry Architect. You are simply talking nonsense. The dimensions of the core columns and the whole core structure with horizontal and sloping beams as taken from the drawing clearly indicate that its elements could in fact carry 300% of the static (dead and live) loads applied. Reason for this is the redundancy required, e.g. if one primary element, a column, would fail for some reason; bad material or workmanship, misalignment or similar hidden defects or due local fire or some other mishap (elevator exploding, etc). Then the other parts would carry the load and for that FoS=3 is a requirement.
Same goes for the perimeter structure. We could all see that the big hole in the north wall, 60% of the columns broken, floors disconnected, etc, and nothing really happened to the structure! Reason - redundancy and a built in factor of safety, FoS>4 for the walls with regard to static loads. NIST actually explained that - yes, you could remove 60% of a wall and the stresses in the remaining walls increased a little due to load distribution (i.e. redundancy).
Re testing steel - the steel of WTC 1 was tested before installation in the 60's and with a little effort you should be able to find the records.
Actually, the whole NIST WTC 1/2 report - 10,000+ pages, is a failure as it does not analyse what failures the fires could produce and what the consequences would be, e.g. some other failures and then ... arrest. NIST's only conclusion that potential energy released exceeded the strain energy that could be absorbed by the structure is absurd. All described with proper documentation at http://heiwaco.tripod.com/nist3.htm .

But topic is of course that steel structures cannot globally collapse due to gravity alone. It never happens. Local failures yes, structural parts may drop off and get smashed when hitting hard ground but global collapse - sorry, no!

 

[Gravy]

I find the Vitry demolition interesting as you can see the upper part free falling for 1.5 seconds through the removed, intermediate section ... and during that time the upper part is intact, as expected.
Then, at contact upper/lower parts of course the lower, smaller part is crushed down, while the upper part is also destroyed crushed up at the interface.

A "free-fall" of the upper (smaller) portion of 1.5 seconds is sufficient to destroy this building, yet you claim that one of the Twin Towers wouldn't be destroyed if 30 stories of it were dropped on the lower section from a height of two miles. Please explain why you believe this to be so. Show your math.