"Inside Job": Hidden energy in reports by Prof. Bazant, Dr. Greening and D. Thomas

reply to post by IrishWristwatch

If mass is not to accumulate, what then happens to it?

It doesn't get any more than it was before. No floor of the building had more mass above itself at any point in the collapse than it was able to hold up for three decades.

Uuuh, domino day, that scares the heck out of me. Defies the laws of nature, right? No. Putting up all the blocks (storing potential energy) goes into the energy balance. Or were the Towers made of domino blocks? Remember, remember... the day we started a war over a few domino blocks.

It's called cascading failure.

Experts should make up their minds already. Last week, Dr. Greening told me it's a disproportional collapse. NIST called it progressive collapse and gravitational collapse. This is science, not religion, we don't debate what it's called, it's about what happened. We could call it "pouff pouff" or "crumblification" and still talk about the same thing as long as we agree that 2+2=4.

Sufficient force can be applied to a member to cause it to fail without causing a loss in velocity. The acceleration must diminish, but the velocity need not.

I could agree, but Isaac Newton would be real angry at me.

Overload need only occur in the local region, ...

Correct.

...then failure propagates downward.

Non sequitur. You read Bazants papers too much.

When two vehicles collide head-on, does the rear bumper experience the same deformation as the front? Even if one of the cars is butted up against a wall? No.

That's right, they both just disintegrate until the rear number plate of the other one hits the wall and drops to the floor.

No, it did not accelerate all the way down. As I said above, terminal velocity has been measured for a good share of the leading progression.

Ever cared to calculate the resistive force of all floors below impact zone (that's an easy one, a=v/t and F=m*a) and compare it to the force exerted on the first floor below the upper block for three decades?

Something tells me I've not made a dent

You won't even leave a scratch on my firm belief that the laws of nature won't obey the scribblings of a thousand experts.

Let's stick to the math now, please. Please explain why in Fig. 3, a "typical load displacement diagram", m*g is much bigger than F_c for all 110 floors, and the case from Fig. 4b+c where F_c is bigger than m*g aren't even considered although that is the natural state all buildings are in.

Also, as you state that the process is an iterative one, please explain why there is the step missing after Equation 6 on page 4 in which the deformation energy should be substracted from the kinetic energy for the next iteration.

With this, please sum up all dF_a and dF_d, and multiply with 110 floor's u to compute the Energy needed for the crumblification of the towers. After that, please explain why Bazant makes no mention of this energy and insists that only 2.1GJ were input and sufficed to pouff pouff the building.

And then please explain who, what and why brought that energy into the building.

//edit: thank you! I always feel my english is miserable... I should have known better that "Impuls" is momentum as in "conversation of momentum" It gets even worse with unit conversions and when we write 2,105 GJ it's 2105 GJ in english so I have to remember that it's 2.105 GJ instead and so on, so sorry for any mistakes that are related to this and thank you for your understanding :-)

Originally posted by Akareyon
It doesn't get any more than it was before. No floor of the building had more mass above itself at any point in the collapse than it was able to hold up for three decades.

Of course mass is not created. Accumulation of debris mass. If the debris is not arrested, then it is in motion and possesses momentum. This is why accumulation of debris mass has a bearing, for it implies accumulation of momentum.

Uuuh, domino day, that scares the heck out of me. Defies the laws of nature, right? No. Putting up all the blocks (storing potential energy) goes into the energy balance.

Perhaps you can give me one reason why the statement "Putting all the blocks (storing potential energy) goes into the energy balance" does not apply to the towers. You think all that mass got up there for free? What happens to that potential energy as mass moves down?

Or were the Towers made of domino blocks? Remember, remember... the day we started a war over a few domino blocks.

You know what? I ****ing despise these wars, loss of freedom and all the rest. You want to change subjects or do you want to discuss the mechanics of collapse?

Experts should make up their minds already. Last week, Dr. Greening told me it's a disproportional collapse. NIST called it progressive collapse and gravitational collapse. This is science, not religion, we don't debate what it's called, it's about what happened.

Exactly. A rose is a rose. These are all legitimate terms and in some sense equivalent. Don't get so hung up on terminology.

I could agree, but Isaac Newton would be real angry at me.

I think you'd better check your understanding of elementary physics before you go invoking Newton. If a force Fc is sufficient to fail a component, it will fail when that force is applied, and will also (with action-reaction) impart that force on the object loading it. If the object applying gravity load is of mass m (-> load = mg), and the magnitude of mg is greater than Fc, the loading object will accelerate downward WHILE it fails the component. Fact. Newton's not angry at all, not even at you.

Non sequitur.

Hardly. If a vertical support fails, the support is gone or greatly diminished. Definition of failure, you understand. What happens to the load? Let me guess: you think it goes up, or perhaps hovers there. Sideways? Disappears? Uh no. It goes DOWN. Not a non-sequitur, it's the whole point. Newton is actually starting to get angry now.

Ever cared to calculate the resistive force of all floors below impact zone (that's an easy one, a=v/t and F=m*a) and compare it to the force exerted on the first floor below the upper block for three decades?

THAT is a non-sequitur, in case you weren't clear.

Let's stick to the math now, please. Please explain why in Fig. 3, a "typical load displacement diagram", m*g is much bigger than F_c for all 110 floors...

It's less than mg for reasons you already know and which you stated in your open letter. Buckling columns lose most of their capacity after a relatively small axial compression. Integrate that curve (with your eyes, roughly) to see that the average magnitude over the interval is Fc, and it's less than mg. It's the same all the way down because the demand to capacity ratio is essentially the same for all stories and the diagram is expressed in terms of load.

As to the rest, I'll refer to the paper and get back to you.

I assure you your English is not miserable, not at all.

Originally posted by Akareyon

With this, please sum up all dF_a and dF_d, and multiply with 110 floor's u to compute the Energy needed for the crumblification of the towers.

Okay. Now you sum up the change of potential energy you thought came for free in erecting the towers.

After that, please explain why Bazant makes no mention of this energy and insists that only 2.1GJ were input and sufficed to pouff pouff the building.

It's just like the finger pushing over the first domino. Did the finger need to supply all the energy up front to push over all the thousands of dominos? No, it did not. And a domino chain is horizontal propagation, orthogonal to the gravity force vector, unlike a collapse which is collinear with gravitational force. Other than that, same principle.

Exactly. A rose is a rose. These are all legitimate terms and in some sense equivalent. Don't get so hung up on terminology.

You are right, we should work this out together instead of fighting each other, that's why I proposed to stick to math.

Let me return to this:

The magnitude of the Maxwell line in that diagram is 39% of the load, or 13% of the peak capacity assumed by Bazant. It means the average resistive force provided by columns which are overloaded to full compaction is about 40% of the static load above.

The Maxwell line once was around 200%, if not even 300% (Bazant's peak capacity) of the load (Fig. 4c). If the load exceeds it upon impact from a 3.7m fall, (Fig. 3+4a), I'm fine with that. If it exceeds it for all 110 stories, something is seriously wrong. Either we apply Fig. 4a for the first impacted floor and proceed with Fig. 4b+c for the next 108 iterations, or we apply Fig. 4c for all 110 stories at once. What Bazant did is this: he applied Fig. 4a for the first impacted floor and assumed that therefor, the load must have been equally greater than the Maxwell lines for all other floors. That's non sequitur and results in a set of equation that presumes that the mass of more than three towers was put on the roof of the building or that someone pulled a string from beneath.

The potential energy has safely been stored for 30 years by that what Bazant calls strain energy, that is, even more energy that must be overcome to release the potential energy. Unlike domino blocks, where the force of impact is supposed to exceed the resisting force (Maxwell line bigger than expected "load", and the "toppling energy" smaller than the potential energy), the towers weren't supposed to go mechanical. Just think of the meticulous planning required to bring all domino blocks down. More often than not, something goes wrong. I've been building large towers made of unstable paper rings and extreme weights, Jenga towers and houses of cards before I did the math to understand what I'm talking about and I found it more challenging, if not even impossible without Lego Technik and mouse traps to build something that comes down from top to bottom than to build something that keeps upright. High structures tip, tilt and topple. If they go downwards like the machine of a thousand dominoes, somebody needs to put some huge effort into building this. So, even from this perspective and in your own words, there's no way to deny that the collapse needed to be planned, extremely well planned, and were not the result of some chaotic and random process (except if the universe tried to teach us two lessons about butterfly effects).

I'm sorry, I know what it feels like, I've been where you are now just a few weeks ago. But once you're through this, things will be fine :-)

Originally posted by Akareyon
High structures tip, tilt and topple. If they go downwards like the machine of a thousand dominoes, somebody needs to put some huge effort into building this. So, even from this perspective and in your own words, there's no way to deny that the collapse needed to be planned, extremely well planned, and were not the result of some chaotic and random process (except if the universe tried to teach us two lessons about butterfly effects).

How do you explain the Verinage demolition technique?

One very big difference between building something from Jenga blocks (or similar) or a skyscraper is that when a skyscraper is build the load capacity of the supports are chosen as weak as minimal required. When they are made stronger than required it means the cost increases.

reply to post by -PLB-

Sure. In a Vérinage, F_c is diminished on several floors, the collapse is decelerated on impact and Jenga blocks aren't connected by thousands of steel bolts. Please, let us not discuss the differences between a Vérinage, a tower of Jenga blocks and a 400m-500.000t-structure of steel and concrete all over again, at least not in a thread which is about the math in the papers by Professor Bazant and the other "experts" ;-)

Originally posted by Akareyon

I'm sorry, I know what it feels like, I've been where you are now just a few weeks ago. But once you're through this, things will be fine :-)

That's pretty funny, I was going to say something similar myself! With a few differences... I started looking at this about five years ago, spent quite a few hours over the span of a couple of years to digest the papers by Bazant et al, Seffen and Greening. I had the good fortune of being walked through a lot of the theoretical end by Greening and Benson themselves. I guess you assume I started from where you see me now and have been static until the present, but that's not the case. I originally had a great deal of skepticism about these papers but, after working through them, I now have only SOME skepticism (it would be nice to get beyond the basics in this discussion so I could share the remaining issues with you).

You see, I started out more like you, and ended up where I am. It's unlikely you're going to pull me back into the past, but you can always try

Originally posted by IrishWristwatch
You see, I started out more like you, and ended up where I am. It's unlikely you're going to pull me back into the past, but you can always try

Oh, I'm not trying to pull you back into the past, really not. I'm trying to push into a better future. If that means that I must rethink my judgement, that's okay for me, because it's not about me, but about truth and reality, freedom and peace. I won't feel hurt if logic, physics and math prove me wrong :-)

Originally posted by Akareyon
The Maxwell line once was around 200%, if not even 300% (Bazant's peak capacity) of the load (Fig. 4c). If the load exceeds it upon impact from a 3.7m fall, (Fig. 3+4a), I'm fine with that. If it exceeds it for all 110 stories, something is seriously wrong.

Indeed, something is wrong. Your interpretation of the single overload condition directly resulting in 110 overloads is not correct. At each story, the same situation exists. There is a momentary peak resistive force as each set of unbuckled columns is encountered. At each story, the only opportunity for arrest is that peak; if the peak is overcome, the resistance (of the buckling columns) drops to less than the imposed load and the mass descends further. Repeat, repeat, repeat...

This is why I described the process as iterative. One could argue that Bazant's scenario is an artificial one and that this is the only reason there is the illusion of story-sized mechanical transactions. After all, the columns go continuously end-to-end all the way to ground, and the columns themselves are in 3-story lengths. But, in fact, the storywise scenario described by Bazant is physically correct because the columns are pinned at every floor, core and perimeter. Therefore they are constrained to buckle in one story lengths (if they are to buckle at all). The alternative is that the lateral connections fail, and the columns buckle over a length greater than one story, but that requires LESS energy per unit length than a single story buckling (please see my posts on this page describing this aspect in more detail).

Either we apply Fig. 4a for the first impacted floor and proceed with Fig. 4b+c for the next 108 iterations, or we apply Fig. 4c for all 110 stories at once. What Bazant did is this: he applied Fig. 4a for the first impacted floor and assumed that therefor, the load must have been equally greater than the Maxwell lines for all other floors. That's non sequitur and results in a set of equation that presumes that the mass of more than three towers was put on the roof of the building or that someone pulled a string from beneath.

You misunderstand. Bazant applies figure 3 repeatedly for each story. Figures 4a-c depict the situations for different load-displacements, for comparison.

The potential energy has safely been stored for 30 years by that what Bazant calls strain energy, that is, even more energy that must be overcome to release the potential energy.

It does take energy to overcome the strain potential barrier - in an intact building. That's why an intact building remains... intact! But the towers were not intact at initiation, FOR WHATEVER REASON. I stress that point because in discussions with people who do believe the towers were demolished by some means other than impact+fire, they typically seem to think I'm arguing against demolition. I'm not. I'm not even arguing against a series of charges all the way down. I'm arguing that a series of charges all the way down were not necessary. But the essence of what I believe is that once the top was moving, the tower was indeed doomed. There's simply nothing capable of bringing it to rest, except the ground.

So, we consider that energy WAS added - if only via impact and fire but maybe also something else - to alter the intact configuration such that the top began to move. Once this happens, a number of other factors kick in. One is misalignment. Do you understand that if even the largest core columns displaced by only two feet in the minor axis, they can miss each other entirely? That's ZERO resistance from the vertical columns. An H-column rotated 90 degrees loses > 90% of its capacity at the contact interface with the column below, a box column not much better. It is true that St Venant's principle dictates deformation will redistribute the load to ensure the next interface down does not see any difference in loading, but it does not guarantee the column on top will survive.

Reaching post size limit. To be continued.

It's a good to take a couple of steps back at this point and do a reality check. Bazant did not analyze the scenario of reduced capacity resulting from the inevitable (and directly observable) misalignment I describe above. In reality, the perimeters on at least two faces practically missed each other entirely due to the tilt. On the other two faces, there is expected to be buckling in place which will result in significant misalignment. This was observed in video on the north face of WTC2, I'll dig up video if you like. Therefore, based solely on observation, we must eliminate an enormous fraction of total capacity from any realistic scenario, as the perimeter columns were misaligned from the onset of collapse. More important than the fraction of capacity lost is the fact that globally loads must be redistributed and, if there is no viable load path to emerge, things will keep moving.

EVERYONE needs to get over the idea that the towers could afford full, intact capacity all the way down in a messy collapse. Think about it: buildings are assembled with fairly precise alignment for a reason. The strength is as much in the geometry as the material. I'll also dig up for you a reference concerning a skyscraper in Manhattan (Citibank, as I recall) which received a multimillion dollar reinforcement of columns because it might have been undetectably out of plumb. The referee architect who demanded the modifications was none other than Leslie Robertson of WTC fame.

Still, Bazant does not work with this reduced capacity because he seeks to establish a boundary case most favorable for survival. So he artificially constrains the collapse to a perfectly axially aligned descent, so that the calculations can be run with the maximum theoretical capacity of the structure. When we argue Bazant, we are not arguing the towers, we're arguing an idealization. There is a relationship between them, of course, but there is no reason to expect full capacity to come into play; in fact, there is every reason not to when you can see columns were missed with your own eyes.

As long as we're clear on this, it should change the tone of discussion. At the very least, we always need to be clear on when we are referring to real towers versus the abstraction of Bazant. Bazant's point is, if the abstracted idealized system exhibits progressive collapse, so will the real (messy) system since it cannot afford the same resistance as the abstract.

Now I wish to go back to the abstract. Let's assume columns do remain in plumb, the impacts are perfect axial strikes, the columns are forced to buckle instead of weaker lateral connections failing and leaving them unsupported horizontally... all very obviously not the case if you look at videos... does it still collapse? Bazant says it does. And I agree.

One thing (and there's more than one) which is not optimistic towards survival is that Bazant assumes a full one story drop at freefall, unimpeded. That did not happen. Moreover, there was not empty space to drop through, even though most of the volume was empty space. The top initially descended very slowly in a creeping fashion. Creep has been detected at least 9.5 seconds prior to global initiation in WTC1, average acceleration about 0.05g. The capacity loss at initiation was not instantaneous. At global initiation, the perimeters can be observed to fail all the way around very rapidly. Then the top begins to descend at an average 0.6g (with some jolts). There is no first "impact" per se.

Does this mean the tower could have survived the initial creeping motion and found a new stable static equilibrium? I can say with very high confidence (but not certainty): no. The fact that it moved at all is indication of insufficient capacity of at least one story, which of necessity is deforming. Therefore there will be no viable load path between the intact sections above and below. But, for sake of discussion, let's assume there is perfect axial contact.

Applying this to Bazant's scenario, we can see that 0.6g over most of story has a lower impact speed (-> less momentum, less KE) than a freefall drop over an entire story. However, Bazant's calculations show that a freefall drop of 0.5m is enough to overload the lower story; this is considerably less speed than even the real descent. It's because the peak of the load displacement curve is so narrow for steel columns that it takes little momentum to climb over it and go down the other side. Once that happens, the resistance is less than mg, and the upper section accelerates downward through the remainder of the failing story.

This allows momentum to build for the next collision.

When I say Bazant's calculations indicate a freefall of 0.5m is more than enough to overload the next story down, I mean only the next story down - not the one after that, and so on, all the way down. If buckling occurs over one story, the story below that is still intact. Problem is, the upper section is in motion, and the same predicament is faced by the story below. If a free drop from 0.5m is enough, a drop of 0.6g through most of a story is also enough.

When I asked you to sum the gravitational potential energy change in erecting the towers, it was a hint that all that PE is lost when the tower descends, as it descends. There is no need to propagate the overload instantaneously through 110 (or 96 or 82) stories to ground.

1) the upper section drops through one failed story, losing PE and acquiring KE
2) the KE is sufficient to overload the next single story
3) go to step 1

That's really all there is to it. The failures and loss of PE occurs in a storywise fashion.

Some, most notably Gordon Ross, have claimed that the first "impact" is not with a single story, but rather a 110 story spring which has elastic response capable of absorbing the momentum and bouncing the upper section back up. I don't know if that sounds plausible or ridiculous to you, but it's ridiculous to me. I believe even Ross has backed off this assertion as of now. This notion is flawed because it presumes the entire lower section is a MASSLESS spring. The fact is, it is a coupled mass-spring system, and the most elementary principles dictate (and experiment confirms), the impact energy is dissipated primarily in the local region of the impact, and is attenuated greatly even a short distance away from this zone.

Think about two trains colliding head-on. It piles up in the front, at the collision point, doesn't it? The backs of the trains keep moving forward with their inertia, crushing the cars which keep arriving at the impact zone. Two trains colliding never result in an accordion formation simultaneously over the entire length. NEVER. Because it's a violation of physical law to do so.

This was my point earlier about the auto collision. I should have used trains for the analogy since they are much more the scale of size and mass of the towers than autos.

Energy IS dissipated at the crushing front of a plastic system. It's physical law, not a mere assumption which Bazant introduces. It has been shown true by theory, physical experiment, and numerical simulation. If you need to be convinced of this, I will bring out an embarrassing array of supporting references; otherwise, there's no point and I'll save us both the effort.

This is the point where I stop and ask you what you think, rather than going on endlessly with ponderous sh*t.

reply to post by Akareyon


IrishWristwatch is already replying to your comments on Bazants work and I think he is better at it than me. I have an engineering background, and I have no major issues with the Bazant papers. The main issue I have with it is that it describes a non-existing situation. He calculates the energy required for the columns to fail from compression, which is not what happened in the actual collapse. But it is the situation that is in favor of arrest, so it proves a gravity driven collapse is possible.

But still, figure 4 that was posted seems pretty clear to me. The energy is the integral of the force over distance, and Fc is the average force over that same distance, or in other words, energy divided by the distance. The instantaneous force is high at the places where connections and columns fail, and zero when nothing fails. So I disagree with the statement in the OP where it says that in that model a constant force of 31 times mg is used (or something along those lines).

Originally posted by -PLB-
I have an engineering background, and I have no major issues with the Bazant papers.

So you don't claim to be an electrical engineer anymore? Just an engineering background? What kind of engineer doesn't understand basic physics?

Originally posted by -PLB-
reply to post by bsbray11

 

I tried to explain to my fullest capacity, but I failed. So I am sorry I can't help you. Remember that I am an electrical engineer, I think you can better contact a structural engineer.

www.abovetopsecret.com...

Read through this thread folks, an engineer who couldn't answer basic physics questions? The lies never go away on ATS....

www.abovetopsecret.com...

Thank you for your kind assessment, -PLB-.

Originally posted by -PLB-
The main issue I have with it is that it describes a non-existing situation. He calculates the energy required for the columns to fail from compression, which is not what happened in the actual collapse.

Yes. It leaves us without an actual detailed model/mechanism of the collapse. A lot of people might feel it's unnecessary, but from an academic perspective it's quite interesting. There is also a school of thought (small in number) who feel that Bazant/NIST/et al effectively act to cover bad design and possibly also slipshod construction, unwittingly or otherwise. Because of the baggage associated with this subject, there's a tendency to lock down the study with Bazant as the final word - a curious incuriousity, if you will.

I don't think the architectural community, or public at large, should settle for the implied notion that collapse is inevitable for a skyscraper impacted by airliner, even at top speed. I don't wish to suggest there was any negligence - it was an extreme situation in which the buildings did stand long enough for many to get out - but i do think the open floor plan was a dubious idea at best, in a building of that height.

reply to post by ANOK


So according to your logic an electrical engineer does not have an engineering background. Right.

Those threads could indeed be a fun read for people who understand a bit of physics.

Click here to learn more about this warning.

reply to post by Akareyon



As you dont seem to understand how a falling mass can seem heavier here is a little calculator for you.

Use a 10 kg mass as an example the drop height for the 9/11 event was a floor height approx 3.6 mtrs the distance traveled after impact is difficult but since the truss seats sheared that supported the floor that is impossible to enter if we use the thickness of an angle seat (say 50mm or 0.050 mtr) that would give us an idea of the force.

A 10 kg weight is 100n rounded up so lets see what it would be after a 12ft 3.6 mtr fall. put the figs in.

www.livephysics.com...

so 10kg 3.6 mtr height 0.050 mtr travel . Answer is 7056 N or an impact force of 705.6 kg!!!!

From 10kg mass !!!!!! even if the travel distance was 0.2 mtrs its still 1764N or 176.4kg from a 10 kg mass.

SO now do you understand the forces of this type of event!

I have a lot burning on my chest, first of all: thank you.

Originally posted by IrishWristwatch
When I say Bazant's calculations indicate a freefall of 0.5m is more than enough to overload the next story down, I mean only the next story down - not the one after that, and so on, all the way down. If buckling occurs over one story, the story below that is still intact. Problem is, the upper section is in motion, and the same predicament is faced by the story below. If a free drop from 0.5m is enough, a drop of 0.6g through most of a story is also enough.

I absolutely agree with you. That's exactly what I'm trying to say. Please take Fig. 3 and a ruler and draw a new line for m*g. Attention! This is a different g, not the 0.6g you're referring to but the g we have to derive from the very first equation to calculate K from P_dyn from Eq. (1) in Bazant/Zhou, 2002 using the 0.6*g you mention. From that, we derive the new line between the Maxwell line and the old m*g (P_dyn). What does that mean for dF_d, W_c, dF_a, W_b and u_c? And what does THAT mean for the next iteration and the conditions in Eq (5) and (6) in (B/V '07)?

If it's iterative, we would take the output and make it input again for the next story, wouldn't we? Mass a little bit more, g'=g*0.6 (in Eq.(1) (B/Z '02)), from that derive m*g from Fig.3 (B/V '07) whis is a little less now, F_c stays just the same. No more K=3.7m*mass*9,81m/s² this time.

Where's my mistake?