Physics Of 9/11 Events - Part 3, continued from: 9/11 Events- New thread

Is your model compatible with an E1 value that drops by an order of magnitude as the collapse progresses, or isn't it?

Do you mean the rail car? While you can make the different cars weigh different amounts, I don't see any very good way to change the Velcro (maybe different sizes would work).

But why do you ask?

Considering that the column segment is no longer anchored on its lower end due to the plane impact, what secures it to be so deformed by the collapse? It seems possible that the column is driven down by the collapse to a point where the lower end (2ft. from the splice) becomes wedged securely enough to be deformed by the collapse, but limits the leverage on the splice.

I should have been clearer. The energy transferred through the wTC frame into the ground may have been very inefficiently converted into seismic activity. When you hit a nail into concrete, bending it slightly, where does the energy go? I believe most of it goes into concrete. But if, say, 45% of that energy is dissipated as a wave which attenuates 90% within 10 feet, and if 45% goes into fracturing (chipping the concrete), and if 5% goes into deforming the nail, and if only the remaining 5% goes into wave phenomena associated with earthquakes, then I'd call that rather inefficient into seismic activity.

What makes me think so? I've already written about this twice. What does Figure 6d) tell you? And with what degree of confidence can you state whatever opinion you may have?

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This post has been edited by David B. Benson on Jun 11 2007, 12:54 AM

My confidence first. I took a one-quarter geology course from Bob Sharp in 1961. It made me into a life-long amateur geologist. Of course, seismology was a substantial part of the lectures. Beno Gutenberg invited groups of students in the class to his house for dinner. He had his own seismograph occupying a significant portion of his modest house.

In the last 1.5 years, I've renewed and updated what I previously knew about seismology. I know enough, then, not to try to seriously interpret seismograph records without the use of all three directions, not just one, and with appropriate spectral filters.

However, the main thing to say is that there is no obvious initial P wave, so it is not an earthquake nor the result of an underground explosion. Being superficial, no S-wave is to be expected. So these records must be surface waves, some mixture of Love waves and Rayleigh waves. The surface waves are the slowest and the two types do not propagate at the quite the same speed.

Also, the bedrock is anisotropically elastic, so after the surface waves finally arrive from a sudden seismic event, the waves continue for some time before dissipating.

Finally, there is no Figure 6d. You mean Figure 6b. I try not to read too much into it. The text pushes the interpretation fairly hard. I prefer relying on the audio portion of videos, but that data came along too late for this paper.

I don't see 'constant' seismic input. What we know is that exterior wall sections fell down in free fall. So we see some waves from that. Then the main arrival, which gives a stronger signal. The rest of the record is useless regarding further interpretation.

This post has been edited by David B. Benson on Jun 11 2007, 02:09 AM

Because if your model is incompatible with a rapidly decreasing E1, and yet that is what the seismic record tells us, then your model is wrong.

To put it into an acceptable context for you, it could have taken less than 200 lbs of explosives if they had been used.

Thank you Dr Benson,

It would be my expectation that the difference in the initial acceleration rate from changing the block size would be smaller if the excess mass at the top was considered. That would make the weight of one lower storey less significant in comparison with the whole weight of the block. (Your "even" quialifier must have meant "one way or another")

Would it be correct to expect, also, that considering the crush-up of a few stories above the failure zone taking place concurrently with the initial crush-down phase would also make little difference? That would be because while the upper block would be shortening, the dynamic load on the B-Zone would be reduced somewhat in proportion, and this would slow the initial acceleration of the crush-down front in a way that compensates for the reduction of the upper block?

This post has been edited by Pierre-Normand on Jun 11 2007, 06:27 AM

If I could venture a guess about this, consider the load-displacement diagram represented as Fig.3 in Bazant and Verdure.

The first high strain-rate impact produced the initial buckling away from the splice, as you mention, and thus produced a geometry that is represented past the u_c point in the diagram. That is, at that point, the load displacement ratio is already much reduced, being situated past the normal peak (F_0) of the elastic response from axial-loading. So, subsequent buckling occurring during the collapse and/or while the column hits the rubble pile would have occurred under reduced load and taken place at the locations of the already established plastic hinges.

(IOW, only before the onset of plastic buckling, and before the formation of hinges, can stress from axial loading be spread more or less uniformly (I suppose) among the column length such that weaker splices are liable to fail first.)

"among the column length"

*Along* the column length...

a hammer that bounces back vibrates like crazy.
i've mentioned how energy can be dissipated in vibrations before.

when you drive a nail in with one blow, the hammer doesn't vibrate hardly at all. it feels good. i put a tongue and groove wood roof on a double arena in the 80's. ah, the joys of simplicity. hands on work like that is not different than being in a lab, if you're applying the same thought processes.

oh right. cymbals and gongs are a good example of where the energy goes. it phase cancels itself out by bouncing back and forth within the (highly elastic) medium.

hey.
sorry. i see you're on top of your game, here. just want to remind you that mass is the key. most of the energy goes into the more movable object, as it is the path of least resistance.

given that bedrock is pretty stiff/elastic that is, and efficient at not deforming. mud would be the opposite, and would absorb the energy through a multitude of tiny momentum transfers, each generating some heat.

in the case of the towers, that means, that energy not being dissipated into the earth, is dissipating in momentum transfers of the highly elastic, non-deformed steel.

in other words, it bounces back up into the falling material more than it transfers into the bedrock.

vibration is an energy sink that is being completely ignored, imo.

i'm out on a limb with this post, but i'm fairly confident i'm on the right track.

This post has been edited by newton on Jun 11 2007, 08:04 AM

more than 50% of married couples screw around on their significant other.

I hope you realize that what you're describing is exactly what I've described several times already.

The shock waves traveling through the structure travel at the speed of sound in steel, 20,000fps.

Compressive waves (P-waves) go through the structure at/near the speed of sound in steel, transverse waves (S-waves) go through more slowly, as the building structure is less-stiff in the transverse mode. Hence, when a structural member fails under load, that load gets transmitted to ground level at 20,000fps as a P-wave, but the S-wave goes much slower, but would also die out much slower as well. (Here is where a good FEA model would come in handy.)

The compressive wave travels through the structure like a wave through a waveguide, and when the wave hits the basement, the basement would act as an impedance mismatch, causing the wave to reflect back into the structure. The impedance mismatch of tower:basement happens before the basement:foundation, so the tower:basement mismatch limits the amount of energy that could be dissipated into the mud below the "bathtub".

You are correct in observing that the rubble at the crush zone would absorb most of the energy of the impulse (contributing to cominution). That, plus the other contents of the building that don't match the impedance of the structure, which also includes people getting knocked off their feet, and 50-ton presses getting bounced off their bases.

And guess what that would sound like to people inside the structure? A loud BANG!, followed by rumbling and the floor swaying back and forth.

Think the average observer inside the building would understand this phenomenon well enough to recognize that the source of the BANG!s aren't explosives, but are caused by structural members failing under load? Or would the average guy hear BANG! and say "It sounded like a BOMB went off!", and then we end up with 300 pages of this stuff, including self-righteous white-supremist revolutionary rhetoric advocating Revolution and anarchy.

Yeesh! I wish more people took high school physics.

This post has been edited by wcelliott on Jun 11 2007, 08:48 AM