Layman's terms please! Tower collapse issue

[einsteen]

Yes, NIST refers to this as "The Kink." It is strongly implied that this occurred after collapse initiation (but only just). Search for it in NCSTAR1-5A and NCSTAR1-6.

From studying videos I also would say that it happened after the top block dropped a few stories.

 

[einsteen]

Heiwa, this is something you've been consistently wrong about all along. All that is needed to start a collapse is enough force to start things moving. The weight of the top of the tower is a force. When enough support members have been severed and weakened to no longer exert an upward force equal to the weight they have to support, f = ma will take over.

Myriad,

This is exactly the difficulty of collapse initiation. If you look at the problem in 1d and use F=Ma you need to explain the initial movement, if you assume there is no initial movement (or a small constant movement) the netto force is zero. Only a fraction of the core columns were destroyed and due to heat weakening they still are able to provide a huge force (what we see because the whole top section was standing for an hour). At a certain moment in time it starts moving, implying a>0, implying a netto force, implying that the columns no longer can provide the static force. I believe that the perimeter columns are never able to keep the mass of the top section in the air (the NIST also says that a floor is able to take 10 times its mass, which is related) which is also consistent with the behaviour of those perimeter columns during collapse. But what happened with the core ? Since a 1d model cannot explain it the tilting of the top section then must play a key role, because I'm almost sure that a 1d model cannot explain it.

 

[Alferd_Packer]

One more time.


Heiwa, have you ever seen this formula before?

I'll give you a hint.

E is the Young's modulus of the column material.
I is the area moment of inertia of the column cross-section
I'll let you figure out the other terms

 

[X]

Myriad,

This is exactly the difficulty of collapse initiation. If you look at the problem in 1d and use F=Ma you need to explain the initial movement,

Very well. Let's do so. This wil be a very simple back-of-the-envelope sort of analysis.
To start with, let's figure out what "F" is.
"F" is the net external force on the upper block. It is the force which causes the upper block to move.

if you assume there is no initial movement (or a small constant movement) the net force is zero.

Correct. And for the net force to be zero (thus ma = 0), the weight of the upper block must be supproted by the structure below.
From this, we can deduce that F = mg - F_columns
Therefore, F = ma becomes:
mg - F_columns = ma
(positive is downards, F_columns is the support provided by the columns, equal to mg until the columns reach a critical scenario of heat weakening/impact damage that they can no longer provide full load bearing capacity.)

Only a fraction of the core columns were destroyed and due to heat weakening they still are able to provide a huge force (what we see because the whole top section was standing for an hour).

I think you make a poor assumption here.
You say: "Only a fraction of the core columns were destroyed and due to heat weakening".
Would you agree the following statement is perhaps more accurate?:
"Only a fraction of the core columns were destroyed by the aircraft impact, and more were subject to heat weakening and unsusual loading from the fires and sagging floor trusses."

At a certain moment in time it starts moving, implying a>0, implying a net force, implying that the columns no longer can provide the static force.

Correct. We can assume the weight (mg) would not change appreciably (ejected debris and people jumping (One of the most chilling things about the day, in my opinions, that they would do so. Tragic.) would not subtract a noticable amount of mass from the upper block.
This does indeed imply that the columns have reached that critical level I referenced earlier. This ciritical level is defined as:
F_columns < mg

I believe that the perimeter columns are never able to keep the mass of the top section in the air (the NIST also says that a floor is able to take 10 times its mass, which is related) which is also consistent with the behaviour of those perimeter columns during collapse. But what happened with the core ? Since a 1d model cannot explain it the tilting of the top section then must play a key role, because I'm almost sure that a 1d model cannot explain it.

The tilting is a natural consequence of the fact that is was not a 1 dimensional event.
You could get a better idea by modelling it in 2 dimensions, and seeing how, if the core columns on one side get damages, that section of coplumns will fail before the undamaged section as the load in that area becomes greated than the columns can support. This will result in the uper block having unbalanced forces. The side without sufficient support will go down, while the side with suport will remain, until the situation gets to the point where the re-distributed loads (no longer axial to the columns) overwhelms the columns ability to hold up the upper block. This situations is complicated. The load will be shifting and re-adjusting as columns fail. And as more fail, the load on the remaining ones becomes greater, making them more likely to fail. AAlso, the loads on the remaining collumns will be transmitting through an angled connection, due to the block's angulation, which is not ideal for columns, and can result in them failing before a critical axial load is reached.

 

[Heiwa]

Hiewa, I have been following this thread and I must say I do find your theory somewhat " out there" but hey you are entitled it.

From what I gather you seem to base your entire agrument on your belief that the upper portion of the tower did not impact the lower portion.It seems you are agruing that the entire upper portion above the impact zone completly disintegrates before any such an impact took take.

OK, it as been pointed out to you that the "upper block" weighted in at some 30,000 tons. Can you please tell me how much explosive power would be needed to produce such a complete disintegration?

Equally so can you also tell me, once the complete disintegation of the upper portion has happened how much explosives would be needed to stage the rest of the top down demolision?

Thank you.

According videos of WTC1 the upper block above the initiation zone (floors 94-97) does not impact the lower structure below.
According videos the upper block telescopes into itself (becomes shorter) while the columns at the initiation zone are still intact. These observations are described in my article. Free fall of the upper block and an impact between the upper block and anything below is not seen either.

I have no idea what made the upper block disintegrate before the destruction of the lower structure. According Nist, Bazant, Seffen & Co the upper block is supposed to be rigid, of uniform density and intact ... and 100% aligned with the structure below all the time ... in order to drive a gravity collapse of the lower structure after an initial impact followed by many other impacts.

It is only the PE/KE of the intact upper block that is available to drive the gravity collapse (avalanche) and if the upper block is not intact (and of uniform density) ... and disappears ... it cannot drive any gravity collapse to the ground.

The rubble produced by the upper block PE/KE in the lower structure evidently does not contribute to the gravity collapse! Agree? It just flies out and drops to the ground. Small pieces.

In my article I assume free fall/impact of the upper block - initiation as per Nist is assumed correct (even if my model test shows the opposite http://heiwaco.tripod.com/nist1.htm#6 ) - and find that they will produce a bump, elastic compression of the lower structure ... and that's it. OK, there may be some plastic local deformation but hardly columns being ripped apart. So the collapse would stop after hitting the uppermost storey of the upper block. All PE/KE is consumed then! End of collapse!

But not according Nist & Co. Because the strain energy of the uppermost storey structure of the lower structure and all the columns down to ground was too small they suggest without any calculations (everything was destroyed in the uppermost storey), the whole process is repeated with a new impact on the next floor below, etc.

But all this assumes that the upper block is still there ... intact ... to drive the collapse like a hammer, repeatedly hammering the lower structure into pieces. If it is not there ... there is no gravity collapse. And the upper block - the hammer - is definitely not there.

One reason why the upper block is not there is that is not rigid, not of uniform density and to put it bluntly, all 33 000 tons of it should then behave like a bale of wool!

And if there is any 'initiation' = failures of structure in the 4000 m² large initiation/fire zone, it will be gentle and the upper block should just land on the lower structure. No impact! All the failed, actually deformed, columns in between would ensure that the force of the mass above would be transmitted to the structure below one way or another (that I can describe). Equilibrium would be reinstated. No hammer hitting!

In the article I suggest Nist, Bazant, Seffen redo their calculations with a flexible, non-rigid, non-uniform density upper block (that does not disappear) and see what happens then! Evidently no global collapse - the upper block will really be shaken at the 'impact' ... and that's it. No big deal.

Small car hitting stationary big truck.

 

[Dave Rogers]

According videos the upper block telescopes into itself (becomes shorter) while the columns at the initiation zone are still intact. These observations are described in my article.

Heiwa, I've pointed this out before: The initiation zone is, by definition, the zone in which the collapse initiated. A region in which the columns are still intact, while a region above it is telescoping into itself, is not, by definition, the initiation zone. Your statement quoted above is therefore nonsense.

Dave

 

[Heiwa]

One more time.


Heiwa, have you ever seen this formula before?

[qimg]http://www.efunda.com/formulae/solid_mechanics/columns/images/Fcr.gif[/qimg]

I'll give you a hint.

E is the Young's modulus of the column material.
I is the area moment of inertia of the column cross-section
I'll let you figure out the other terms

Of course! I use it in my article to describe the columns, but use stresses, not forces (you have to divide the Force with the cross area - . The buckling stress > yield = no buckling. Only yielding. And the yielding will be of the crumple up, type. The columns used and supported by spandrels and beams (and to less extent floors) cannot bucklebend due to gravity.

 

[stateofgrace]

According videos of WTC1 the upper block above the initiation zone (floors 94-97) does not impact the lower structure below.
According videos the upper block telescopes into itself (becomes shorter) while the columns at the initiation zone are still intact. These observations are described in my article. Free fall of the upper block and an impact between the upper block and anything below is not seen either.

I have no idea what made the upper block disintegrate before the destruction of the lower structure. According Nist, Bazant, Seffen & Co the upper block is supposed to be rigid, of uniform density and intact ... and 100% aligned with the structure below all the time ... in order to drive a gravity collapse of the lower structure after an initial impact followed by many other impacts.

It is only the PE/KE of the intact upper block that is available to drive the gravity collapse (avalanche) and if the upper block is not intact (and of uniform density) ... and disappears ... it cannot drive any gravity collapse to the ground.

The rubble produced by the upper block PE/KE in the lower structure evidently does not contribute to the gravity collapse! Agree? It just flies out and drops to the ground. Small pieces.

In my article I assume free fall/impact of the upper block - initiation as per Nist is assumed correct (even if my model test shows the opposite http://heiwaco.tripod.com/nist1.htm#6 ) - and find that they will produce a bump, elastic compression of the lower structure ... and that's it. OK, there may be some plastic local deformation but hardly columns being ripped apart. So the collapse would stop after hitting the uppermost storey of the upper block. All PE/KE is consumed then! End of collapse!

But not according Nist & Co. Because the strain energy of the uppermost storey structure of the lower structure and all the columns down to ground was too small they suggest without any calculations (everything was destroyed in the uppermost storey), the whole process is repeated with a new impact on the next floor below, etc.

But all this assumes that the upper block is still there ... intact ... to drive the collapse like a hammer, repeatedly hammering the lower structure into pieces. If it is not there ... there is no gravity collapse. And the upper block - the hammer - is definitely not there.

One reason why the upper block is not there is that is not rigid, not of uniform density and to put it bluntly, all 33 000 tons of it should then behave like a bale of wool!

And if there is any 'initiation' = failures of structure in the 4000 m² large initiation/fire zone, it will be gentle and the upper block should just land on the lower structure. No impact! All the failed, actually deformed, columns in between would ensure that the force of the mass above would be transmitted to the structure below one way or another (that I can describe). Equilibrium would be reinstated. No hammer hitting!

In the article I suggest Nist, Bazant, Seffen redo their calculations with a flexible, non-rigid, non-uniform density upper block (that does not disappear) and see what happens then! Evidently no global collapse - the upper block will really be shaken at the 'impact' ... and that's it. No big deal.

Small car hitting stationary big truck.

Yes, very good,Hiewa but this is not what I asked you.

Please respond to the questions I asked.

Thank you.

 

[Alferd_Packer]

Of course! I use it in my article to describe the columns, but use stresses, not forces (you have to divide the Force with the cross area - . The buckling stress > yield = no buckling. Only yielding. And the yielding will be of the crumple up, type. The columns used and supported by spandrels and beams (and to less extent floors) cannot bucklebend due to gravity.

What beams are you talking about?

What pinned the exterior columns in place from in and out movement?
The spandrels only pinned them from side to side.

 

[Heiwa]

Heiwa

It's time to come clean, mate.

You haven't *actually* studied building structures, have you?

Tell the truth. We'll respect you for it.

Actually, when I started steel structural analysis 1965 (in shipbuilding) every member was supposed to be a beam with a web and flanges or a tube or a box or a pillar ... like a static building on land. So the structures were all 3-D beam structures - only the loads applied a little different. Same courses for civil engineers and shipbuilding engineers. Only later some 'beams' were replaced with real stiffened plate members, but then you needed a computer to calculate what happened. But you got a good feel using 3-D beam models where the loads ended up and what forces and bending moments were produced and what the the stresses were and how to avoid buckling. With beams and pillars, no problem with buckling. Stiffened plate fields would buckle under testing ... and soon we found out why.

You have not read my CV, have you? I am a structural steel man. No wooden JREF greenhorn.

 

[Dave Rogers]

It is only the PE/KE of the intact upper block that is available to drive the gravity collapse (avalanche) and if the upper block is not intact (and of uniform density) ... and disappears ... it cannot drive any gravity collapse to the ground.

Well, yes, if it disappeared it wouldn't be able to drive a gravity collapse. However, it doesn't disappear. Your error here is one of the more collossally stupid standard truther errors, that if an object is broken it loses its mass. It doesn't.

The rubble produced by the upper block PE/KE in the lower structure evidently does not contribute to the gravity collapse! Agree? It just flies out and drops to the ground. Small pieces.

Disagree. You can't quantify the amount of dust and debris expelled simply from photographs. There's no evidence that a significant amount of concrete was broken into dust in the early stages of the collapse, and good reason to believe it wasn't. There's evidence of some perimeter column trees being ejected in the earlier stages of collapse, but these appear to be from the lower block. There's no evidence of core column sections or any part of the hat truss being ejected in the early stages of collapse, nor is it in any way feasible that they might have been. Therefore, the majority of the mass of the upper section is available to transfer PE to KE to fracture energy. Your burning desire to handwave away anything that disagrees with your insane theories has no basis in reality.

Dave

 

[rwguinn]

Well, yes, if it disappeared it wouldn't be able to drive a gravity collapse. However, it doesn't disappear. Your error here is one of the more collossally stupid standard truther errors, that if an object is broken it loses its mass. It doesn't.

Let's not tell him that the PE of the lower portionof the building is pretty important, too--because it translates into strain energy that the non-disapearing mass of the upper portion's KE adds to.

Disagree. You can't quantify the amount of dust and debris expelled simply from photographs. There's no evidence that a significant amount of concrete was broken into dust in the early stages of the collapse, and good reason to believe it wasn't. There's evidence of some perimeter column trees being ejected in the earlier stages of collapse, but these appear to be from the lower block. There's no evidence of core column sections or any part of the hat truss being ejected in the early stages of collapse, nor is it in any way feasible that they might have been. Therefore, the majority of the mass of the upper section is available to transfer PE to KE to fracture energy. Your burning desire to handwave away anything that disagrees with your insane theories has no basis in reality.

Dave

Reality is for folks who can't handle chemical enhancement?

 

[einsteen]

Heiwa, I've pointed this out before: The initiation zone is, by definition, the zone in which the collapse initiated. A region in which the columns are still intact, while a region above it is telescoping into itself, is not, by definition, the initiation zone. Your statement quoted above is therefore nonsense.

Dave

Unless he is able to prove that it started not at the weakest part of the building.

ps. correction: then that is still the initiation zone, but a more suspicious one...

 

[Dave Rogers]

Unless he is able to prove that it started not at the weakest part of the building.

He's not saying that. He's saying that the collapse didn't initiate in the collapse initiation zone. If you want to prove that, go ahead and try, but defending obviously self-contradictory statements by misrepresenting them is pointless and irrelevant.

Dave

ETA: Missed your ETA. So you admit he's contradicting himself?

 

[Newtons Bit]

So I posted a fairly lengthy rebuttal to the introduction of Heiwa's "paper". And he ignores it. Should I be suprised? Or should I chalk this up to the typical truther mentality of asking for criticism, ignoring it when it arrives, and then pretending that there has been none?

 

[einsteen]

He's not saying that. He's saying that the collapse didn't initiate in the collapse initiation zone. If you want to prove that, go ahead and try, but defending obviously self-contradictory statements by misrepresenting them is pointless and irrelevant.

Dave

ETA: Missed your ETA. So you admit he's contradicting himself?

ETA means ? I'm normally a nitpicker but with things like this you have to read between the lines. I think he means that the top section compacts above the stories that are first expected to fail.

 

[Heiwa]

1. No, it completely disproves your point. You said it fell OUTSIDE. Stop trying to squirm away and admit that you made a small goof.

2. This is complete B.S. The upper block does not disintegrate. It is heavily damaged, but so is the upper floors of the lower block, imagine! And then it travels inside of the tower and causing more damage to the floors below.



From your paper


3. False. The upper block obviously falls at NEAR free-fall, otherwise we wouldn't have seen it fall. You can't say something didn't happen when there's video recording that it did.



4. Inaccurate. You cannot take the entire cross-section of the tower and the entire load and say all columns were below a certain stress. This is because columns near severed and damaged columns are primary to resolving the loss of nearby strength. Furthermore, this ignores simple concepts such as a cantilever (ONE example) developing after a column is severed/damaged. This will multiply the vertical loads, easily overloading columns.



5. False, the floors are necessary to provide bracing against buckling.



6. WTF. Obviously there is no stress in a column just above a cut. But the force that used to exist in that column has to be TRANSFERED SOMEWHERE ELSE. And it will not do that in a pure vertical fashion. You cannot understand the simple fact that the vertical forces will apply more than just a compressive force to the structure. This is BASIC statics.



7. Strawman. No one ever said that the columns failed simultaneously. Nor is this implied by the phyiscal evidence. The fact that both towers leaned noticeably during collapse shows that the towers collapsed linearly (roughly) from one side to another. This makes sense from how the tower actually resists core column failures.



8. WTF? The upper block wasn't lowered, it collapsed. That's the entire point. Dynamic forces are much higher than static forces. That's why we design framing below corridors for 100psf live load, even though they will never expierence that amount of load statically. They will expierence something close to that dynamically.

These are the first six of your paragraphs. They are all complete crap. I'm just going to randomly select a few more.



9. Complete crap. I recommend you do a little research rather than relying on your own "opinion".



10. Uneducated in engineering. The column will buckle before 100%, energy is absorbed when the column rotated about a plastic hinge (buckling), and THEN there will be a small amount of energy in rupture. Buckling is not the same rupture strain energy.



11. The floors are necessary to support the columns, otherwise they will just fall over and outwards (which is what happened) under smallish forces.

12. You also seem to be of the opinion that the entire upper block should disintegrate. But that doesn't make any sense. If the upper block can disintegrate from the striking the lower block, shouldn't the lower block (made of the same material, same craptacular uniform density measurement that you use) also be able to take damage from the upper block? You can't have it both ways.

Now then, you said something about calculations in your paper. The only thing I saw was inaccurately calculating weight and compressive stresses. Was there something else that I missed?

Thanks for the peep review:

1. The photo of WTC2 shows the upper block inclined outside the lower structure and, logically, cannot drop on the lower structure (it will contine to incline and slide off). In fact it disappears completely soon after.

2. The upper block is supposed to be rigid and intact. It is not supposed to be damage before initiation. My point is that the upper block of WTC1 disintegrates 3-4 seconds before initiation, which is not explained.

3. The upper block of WTC1 is not NEAR free falling on the lower structure below the initiation zone. It telescopes into itself, while the structure in the initiation zone is intact! Just look at the bottom of the upper block - floor 97.

4. No, the static stresses in the load bearing columns prior collapse are >20% yield in the walls and <30% yield in the core. Calculations are given in the paper.

5. Still, the floor is not a primary load bearing part. Clear from the article. It only transmit a load on the floor to the column. Remove all floors and no loads are transmitted to the columns, the latter then only being stressed by their own weight <3% of yield. Buckling is then prevented by the spandrels/beams and the other walls. Service floors are different with strong beams connecting perimeter/core.

6. The columns of the upper block are interconnected with spandrels/beams at every floor that will transmit the load on the cut column to the other columns. Remember that 38 wall columns were cut 100+ minutes earlier and nothing happened.

7. For an upper block to free fall vertically and impact all columns of the structure below simultaneously, evidently all the remaining supports must be removed at the same time. If the upper block tilts or gets inclined because the supports do not fail simultaneusly, the impact cross area of the upper block is also inclined = no instantaeous impact! Compare 1 above.

8. I know the upper block was not lowered. It collapsed into itself before it started the move down into the initiation zone.

9. Reference link is British authorities. At 500°C only yield stress is reduced, say 20%.

10. It is more likely that the energy will slip off the relevant structure (vertical column) and do no harm whatsoever. Read the complete paragraph.

11. No, the floors only there to transmit load on the floor to the columns. Remove the floor (and the load) and the column will still stand (thanks to spandrels and beams - and extra structure at the service floors).

12. You do not know what a gravity driven collapse is, do you?. You need KE for that and it can only be provided by an intact, rigid, uniform density upper block that remains intact, rigid, with uniform density during the whole destruction of the lower structure. The upper block is the only part that can provide KE during the alleged global collapse. The lower structure does not add any extra KE to the collapse or contribute to the collapse - it is being destroyed (lack of strain energy according NIST).

Actually, the upper block, intact, rigid and of uniform at start of collapse, should according to Bazant's and Seffen's theories remain INTACT after the global collapse ... on top of all rubble the upper block has produced of the lower structure. Nothing could destroy a rigid block of uniform density - not even the final impact with the ground forgetting that the rubble is there to dampen the final impact.

But thanks anyway for your input!

 

[Alferd_Packer]

Once again

What beams were attached to the exterior columns?

What strucutral element prevented the in and out movment of the exterior columns?

 

[tsig]

Actually, when I started steel structural analysis 1965 (in shipbuilding) every member was supposed to be a beam with a web and flanges or a tube or a box or a pillar ... like a static building on land. So the structures were all 3-D beam structures - only the loads applied a little different. Same courses for civil engineers and shipbuilding engineers. Only later some 'beams' were replaced with real stiffened plate members, but then you needed a computer to calculate what happened. But you got a good feel using 3-D beam models where the loads ended up and what forces and bending moments were produced and what the the stresses were and how to avoid buckling. With beams and pillars, no problem with buckling. Stiffened plate fields would buckle under testing ... and soon we found out why.

You have not read my CV, have you? I am a structural steel man. No wooden JREF greenhorn.

Oh man, leaving us on the edge of our seats like.... that.

It's just so woodenly greenhorn.

 

[tsig]

So I posted a fairly lengthy rebuttal to the introduction of Heiwa's "paper". And he ignores it. Should I be suprised? Or should I chalk this up to the typical truther mentality of asking for criticism, ignoring it when it arrives, and then pretending that there has been none?

Then quote mining you to prove the opposite of what you said.