Some Calculations requested regarding why the towers upper portion did not slide off

[Furcifer]

Here's a challenge: build a vertical structure such that when you impact it from above with a sledge hammer, it collapses "floor by floor" with no visible damage below the impacted "floor".

[qimg]http://pharaqey.org/temp/PVC2.jpg[/qimg]

[qimg]http://pharaqey.org/temp/PVC3.jpg[/qimg]

No angled cuts allowed in the structure, and no cheating with wedges or anything (the sledge hammer has to come down vertically).
Can you see why this is problematic?

Jim Hoffman has a more involved challenge too if you are interested:
http://911research.wtc7.net/wtc/analysis/challenge.html

Arrgh, lozenge you need to make that thing look tapered. From what I remember from the Greg Urich debate, the ratio was 16:1 over the length. Like this:


/\

 

[lozenge124]

You don't understand how structures work. There is not 1 straw. There is 110 straws with 111 fingers. The straws vary from being large at the bottom to being smaller at the top. Each finger represents a floor, and this floor braces the straws against buckling. There is no buckling length over several floors. Each finger is a floor, it laterally braces the straw against buckling. The smallest straw will buckle first as it has the highest slenderness ratio. The force which causes the top-most straw to buckle is the same force the causes elastic strain energy in all the straws below. This buckling force is the peak force that the upper straw can transmit, and hence, this is the peak force that the straws below are subjected to. Ross has calculated the energy the lower columns absord (inaccurately I might add), and it is less than the energy required to completly fail the top most column.

These are good points, but again I have trouble seeing how the upper "straw" can be subjected to a force that makes it buckle while the straw directly below it - subjected to the same transmitted force - has zero damage. We see massive perimeter sections being blown out at terrific speeds, while the structure below looks pristine. It's this damage "gradient" that to me is counterintuitive.

In any case my basic point is this: the NIST "global collapse ensues" hand waving, the few Bazant/Greening papers, your and Gordon Ross's submissions to the journal of 911 studies are not enough material to adequately cover the mechanics of the WTC progressive collapse. The assumptions and simplifications required to make the math manageable are too broad. We need an FEA model to validate the theory that the collapses could have happened under the force of gravity alone.

 

[Furcifer]

These are good points, but again I have trouble seeing how the upper "straw" can be subjected to a force that makes it buckle while the straw directly below it - subjected to the same transmitted force - has zero damage. We see massive perimeter sections being blown out at terrific speeds, while the structure below looks pristine. It's this damage "gradient" that to me is counterintuitive.

In any case my basic point is this: the NIST "global collapse ensues" hand waving, the few Bazant/Greening papers, your and Gordon Ross's submissions to the journal of 911 studies are not enough material to adequately cover the mechanics of the WTC progressive collapse. The assumptions and simplifications required to make the math manageable are too broad. We need an FEA model to validate the theory that the collapses could have happened under the force of gravity alone.

That's a fair enough request. While I think the money could be better spent, the US government has spent money on worse, less productive projects. Unfortunately, being in the minority, the onus would be on you to come up with the funds and resources to do so. I can only offer you my knowledge and insight at this time

 

[William Rea]

I'm not sure about he rest of the "JREF'ers", but I agree with the notion that a volume of the upper section underwent progressive collapse as the lower section underwent progressive collapse. "Crushed together" for the first few seconds of collapse. I'm not sure what you hope to prove with this? At some point the upper section did get crushed, to treat it before , after or during the colpase of the lower does little to change the validity of the math involved. It just changes the density of the crushing front. I believe Bazant admits this in the BandV paper if I remember correctly.
What do you think it means Rev91?

Don't have a problem with that except that "crushing into each other" does not imply "impulse deceleration". I'd just like to see the data for the impulse deceleration and how many of the upper block floors could have become detached?

 

[William Rea]

Before during or after collapse initiation? My understanding is the the floors pulled the exterior inwards at the point of impact, and only at initiation. After that neither were "bowing", although one section would have forced the other out of the way during impact. Either way, you can have the upper section getting tucked behind the lower during ythe collapse. I'm not a big fan of that analysis myself, but it is a valid consideration for the first few (2?) seconds of the collapse. It's certainly not an outrageous claim, I've heard worse. Those guys put more effort into the analysis than I have, so if push came to shove I would yield to them. I'm just not feeling it.

My undestanding is that the sagging trusses in the lower block pulled the outer columns inwards and this is backed up by visual evidence. I believe this was put forward to support the sagging trusses theory.

I am talking prior to the collapse.

Have you tried getting two end tapered tubes of similar diameter to slide into each other?

 

[William Rea]

Uhh, no, they did. You see, to any engineer, all the information about how and why the collapse happened is why the building originally failed. It is the msiguided laypeople who yell "we want the truth!" who seem to think that what happened after the initial collapse has any bearing on building safety or responsibility of the engineer/owner/contractor.

There is no reason to investigate what happened after the initial collapse started. Studying the collapse prior to that can yield information that will further our undertanding of structural mechanics which can then be used to modify building codes. Which by the way, the study has already done. Most codes have already introduced new provisions based upon the NIST study.

Studying the collapse after it happened is a waste of money and would serve almost no purpose to furthering understanding of structural mechanics. The only thing it would do is appease the ignorant and bitter in the population for a few minutes before one in their ranks steps forward and says, "omg lol this is wrong!!21" and then we're right back where we started except that there's less money to fund actual real research that could save lives.

You might be right that the initiation is all that requires investigation in economic terms but actually, as people aren't we interested in what happened? I find your comment that we're just not interested in such an incredibly important event very curious.

 

[Newtons Bit]

These are good points, but again I have trouble seeing how the upper "straw" can be subjected to a force that makes it buckle while the straw directly below it - subjected to the same transmitted force - has zero damage. We see massive perimeter sections being blown out at terrific speeds, while the structure below looks pristine. It's this damage "gradient" that to me is counterintuitive.

In any case my basic point is this: the NIST "global collapse ensues" hand waving, the few Bazant/Greening papers, your and Gordon Ross's submissions to the journal of 911 studies are not enough material to adequately cover the mechanics of the WTC progressive collapse. The assumptions and simplifications required to make the math manageable are too broad. We need an FEA model to validate the theory that the collapses could have happened under the force of gravity alone.

It has to do with elastic strain. The upper column buckles at a certain force, below the plastic limit. The column below it is slightly larger. It does not buckle and stays in the elastic stress range. That column unloads most of that energy (in a dynamic manner) when the columns above go into post buckling bending as there is less and less vertical force applied to the lower columns.

This is not over simplification.

 

[Alt+F4]

I'm assuming of course that she says this weapon is in low Earth orbit. This raises its own problems since in LEO an object will not be spending very long over the same part of the Earth's surface.

Excellent point. A satellite in low earth orbit takes about 90 minutes to orbit the earth, so how was Dr. Judy's flying microwave oven able to hit WTC1 at 8:46am and then WTC2 only 15 minutes later, at 9:02?

In regard to WTC2, how was the evil conspirators able to perfectly coordinate the space based attack with the TV fakery and the mass brainwashing of the eyewitnesses?

 

[Corsair 115]

Excellent point. A satellite in low earth orbit takes about 90 minutes to orbit the earth, so how was Dr. Judy's flying microwave oven able to hit WTC1 at 8:46am and then WTC2 only 15 minutes later, at 9:02?

The counter would be to say the orbital weapon was in geostationary orbit, and thus stays over the same part of the Earth's surface all the time. The problem there is that geostationary orbit requires a much larger distance from the Earth; low Earth orbit is at an altitude between 124-1,240 miles but geostationary orbit is at an altitude of 22,300 miles. That's more some 18 times further away than the highest level of LEO. Being that much further away greatly complicates the aiming process as well as greatly increasing the power required by this supposed weapon.

 

[GlennB]

Excellent point. A satellite in low earth orbit takes about 90 minutes to orbit the earth, so how was Dr. Judy's flying microwave oven able to hit WTC1 at 8:46am and then WTC2 only 15 minutes later, at 9:02?
...

This is also a major hangup for that brand of moon hoax twoofers who maintain that the Apollo astronauts spent the entire mission in earth orbit, while maintaining "lunar direction", so as not to spook the tracking stations (although, given the angles involved, they would have been spooked anyway. But it's all b#llocks anyway, as we know).

It ain't physically possible to stay that low and go that slow.

 

[Furcifer]

My undestanding is that the sagging trusses in the lower block pulled the outer columns inwards and this is backed up by visual evidence. I believe this was put forward to support the sagging trusses theory.

I am talking prior to the collapse.

Have you tried getting two end tapered tubes of similar diameter to slide into each other?

Well like I said before, I'm not a big proponent of the "turtle" theory. In fact, two or three days before Jones released this paper to the public I made almost the same observations over at PhysOrg. By my observations most of the upper section, excluding possibly the truss hat, was commuted in the collapse, as is evident by the freestanding core. I fail to see how the solid upper section could have passed through the core undamaged at the point it becomes visible. There is some speculation that the tilt/deflection may have allowed this to occur. I feel however that the extent to which the tilt/deflection had to occur for this to happen is so great as to be unreasonable.

 

[einsteen]

It has to do with elastic strain. The upper column buckles at a certain force, below the plastic limit. The column below it is slightly larger. It does not buckle and stays in the elastic stress range. That column unloads most of that energy (in a dynamic manner) when the columns above go into post buckling bending as there is less and less vertical force applied to the lower columns.

This is not over simplification.

Wouldn't that imply an exponential strength ? That would certainly arrest the collapse.

 

[Furcifer]

Wouldn't that imply an exponential strength ? That would certainly arrest the collapse.

The steel thickness increased linearly, but the strength increased exponentially? I can see how that makes sense...

 

[einsteen]

For at least the third time, forget the scale model. All the properties scale differently with size, so a scale model will behave nothing like the full size building, and if the experimenters change the proportions of the model so it does behave like the full size building then you won't believe the results because they may have changed them so as to weaken the model too much.

Dave

Scale models are also used in wind tunnels, of course you are right that it is hard to scale the wtc, you should scale each floor's mass with the same factor, the energy values E1 with the same factor, gravity cannot be scaled, but the system is invariant as long as gh is constant, i.e. h the distance between the floors. You should place the model in a centrifuge. Furthermore you don't need a full building, a stepwise collapse of a few floors is enough proof for global collapse. Collapse initiation is no proof of global collapse, I have higher standards for a scientific proof.

 

[einsteen]

The steel thickness increased linearly, but the strength increased exponentially? I can see how that makes sense...

I was refering to the implications of Newton Bit's model, since you correctly understand that this could not be the case NB cannot explain the stepwise collapse (see Lozenge124's notes). Remember reaction force needed to crush a story. Folks the answer could be so extremely simple and it would explain everything.

 

[William Rea]

Well like I said before, I'm not a big proponent of the "turtle" theory. In fact, two or three days before Jones released this paper to the public I made almost the same observations over at PhysOrg. By my observations most of the upper section, excluding possibly the truss hat, was commuted in the collapse, as is evident by the freestanding core. I fail to see how the solid upper section could have passed through the core undamaged at the point it becomes visible. There is some speculation that the tilt/deflection may have allowed this to occur. I feel however that the extent to which the tilt/deflection had to occur for this to happen is so great as to be unreasonable.

Could you explain "turtle" theory for me please.

 

[Furcifer]

I was refering to the implications of Newton Bit's model, since you correctly understand that this could not be the case NB cannot explain the stepwise collapse (see Lozenge124's notes). Remember reaction force needed to crush a story. Folks the answer could be so extremely simple and it would explain everything.

I'm not sure how NB explains it, but I think it has a lot to do with the truss connections that failed prior to the application of this force. As hard as it may seem to believe, there is a good chance that the upper section did remain structurally sound for a period of time after initiation. At least relative to the lower section. If we are to believe the greening model, only a small amount of mass was needed to ensure progressive collapse (about 4 floors of mass). This accumulated mass, what's it called Zone B?, perhaps it did more of the damage to the lower part than you are assuming the upper part did?

 

[Furcifer]

Could you explain "turtle" theory for me please.

Lol, this idea that the upper section slipped in behind the lower section in the picture.

 

[William Rea]

Lol, this idea that the upper section slipped in behind the lower section in the picture.

OK, thanks for that. A whole language appears to be developing for this thing.

 

[Newtons Bit]

Wouldn't that imply an exponential strength ? That would certainly arrest the collapse.

How the heck did you come to that conclusion. Linear != exponential.