Reality Believer
Muse
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Another thought. A vertical billiard ball analogy is a bad parallel. Billiard balls transmit momentum as solid objects. The WTC's were 75% airspace. Very squishy.
New guy here: Questions for official hypothesis
- Thread starter Sizzler
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Hokulele:
I'm having a hard time getting my head around the collapse fall time.
a more direct question.
Does the fall time directly depend on the compounding of the floors? Such that, if the compounding hadn't happened, it would have greatly changed the collapse?
I'm having a hard time getting my head around the collapse fall time.
a more direct question.
Does the fall time directly depend on the compounding of the floors? Such that, if the compounding hadn't happened, it would have greatly changed the collapse?
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Gravy
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The compounding (pancaking) is caused by the entire falling mass above. If the lower portion were, for example, a solid block of steel, and you dropped the upper (office building portion) on it, the upper portion would disintegrate and mostly fall to the ground around the lower. I'm sure you can see why that's a bad analogy for the collapses, though. The floor connections and framing were very weak relative to the falling mass above.
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Hokulele
Deleterious Slab of Damnation
Meh, that is kind of going back to what greatly changed means. I would have to go back over the Bazant paper, but I believe that there was enough mass in the top blocks alone to doom the towers. However, that is greatly simplifying the problem, and doesn't actually address what happened very well. I know another poster (R.Mackey) has described the Fallacy of the Single Cause that many people on both sides of the debate commit, although more on the CT side.
I am not sure exactly why you find compounding such a compelling issue (is this something that was brought up on another site or something?), but the mass of the floors as their support was destroyed was under the influence of gravity, so you really cannot subtract it from the equations.
So the speed of the collapse depends on the compounding of the floors, right?
If compounding had not occurred, the collapse wouldn't have gone all the way to the ground?
Gravy
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If a floor (and the columns to which it was connected) were strong enough to arrest the collapse, it would arrest the collapse.
Meh, that is kind of going back to what greatly changed means. I would have to go back over the Bazant paper, but I believe that there was enough mass in the top blocks alone to doom the towers. However, that is greatly simplifying the problem, and doesn't actually address what happened very well. I know another poster (R.Mackey) has described the Fallacy of the Single Cause that many people on both sides of the debate commit, although more on the CT side.
I am not sure exactly why you find compounding such a compelling issue (is this something that was brought up on another site or something?), but the mass of the floors as their support was destroyed was under the influence of gravity, so you really cannot subtract it from the equations.
The problem is that as the floors collapse, they need to compound in such a way that they are a single body of weight. I picture that being a uniform collapse, straight down into the footprint of the building.
When I watch certain videos, a lot of the buildings mass is falling outside of the footprint.
Can someone help me with this issue.
Hokulele
Deleterious Slab of Damnation
Ah, I see what you are asking here. Most of this is answered in the first Bazant paper in the list Gravy posted. This is a direct link to that paper, but it is in PDF format so you will need a reader to access this paper. Some of it is technical, but the abstract and conclusion should be pretty clear even if you do not have a physics background. I would recommend giving this the once over and then asking specific questions you may have based on this.
Gravy
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Much of what's falling outside the footprint is the exterior columns that are being pushed aside by the falling mass. That mass is pounding the floors from their connections, destroying the core columns, etc. By that time, the collapse has reached a terrific speed. Again, the collapse will continue to the ground after it goes a few feet, not to mention a few hundred feet.
Note the height of the top of the building in the before and after below. That's a couple of hundred million pounds that's fallen 150-200 feet, and adding to its mass as it goes.
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Hokulele
Deleterious Slab of Damnation
Cool, any time.
I have to sign off now and get some sleep, but do post any questions you may still have as there are plenty of people on this forum who can answer even better than I.
(Although I am enjoying getting the jump on most of Gravy's answers. Eat my posting dust sucka!
)gumboot
lorcutus.tolere
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This is actually a very good question, that I think has been brushed over. Has anyone actually taken video of the collapses and calculated the propagating speed of the collapse? Did it actually accelerate (obviously it initially accelerated) and if so, was the acceleration constant, or did it slow, or did it increase?
This would be quite interesting information to have, although I'll be the first one to point out that producing such information would be very difficult and quite possibly impossible given the video evidence we have, and the margin of error would be significant.
-Gumboot
The speed of the collapse depends on the compounding of the floors.
However certain videos show a lot of the buildings mass falls outside of the footprint and not compounding.
So I am curious about that effect and how it was taken into consideration when analyzing the collapse.
i was directed to the bazant paper.
he says realisitic K value is between .05 to .5
What do these values represent in terms of percent of mass falling out of the footprint?
However certain videos show a lot of the buildings mass falls outside of the footprint and not compounding.
So I am curious about that effect and how it was taken into consideration when analyzing the collapse.
i was directed to the bazant paper.
he says realisitic K value is between .05 to .5
What do these values represent in terms of percent of mass falling out of the footprint?
Gravy
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Yes, it accelerates to over 100 mph. I was going to post links to scenes in my latest video, but it's apparently been deleted.
Gravy
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Properly, it depends mostly on the resistance of the structure below. Think of the pancaking as a symptom of the collapse, not the cause.
Define "a lot." What constitutes this mass? As you can see from my photos above, and in videos, at first most of what is ejected is smoke and lower-density material like insulation and gypsum (which comprised the majority of the WTC dust), along with some aluminum cladding. No doubt some concrete is pulverized early on also. As you can see in the photos above, no major structural steel has visibly left the footprint, as it will later in the collapse. Since the structure was not designed to have 200 million pounds dropped on it, the building must collapse.
To which paper are you referring? Do you mean the calculations of mass shedding in the Bazant, Le, et al paper?
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gumboot
lorcutus.tolere
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Yes but under "zero resistance" conditions, a falling body would exceed 100 MPH in 4.5 seconds. Obviously the mass had to accelerate at some point because it was initially stationary. I'm more curious as to any change in the rate of acceleration throughout the collapse.
Of course, I have strong doubts that such data could be reliably gathered, but I think it would be interesting... what would it mean, for example, if the mass' rate of acceleration decreased gradually throughout the collapse, from 9.8m/s2 at initiation?
-Gumboot
Gravy
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For one, it would make saying "klunkity-klunk, klunkity-klunk" much harder!
I'm off to bed.
yes.
He says .05 to .5 are realistic boundries.
But what do this numbers represent in terms of actual mass percent falling outside the footprint, and thus not contributing to the increasing mass of the falling section?
Gravy
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I'm not off to be yet. Had a bunch of emails and PMs to answer.
I'm not looking at the paper now, but those numbers represent a range of mass shedding (outside the footprint) from 5% to 50%, which would be in line with the seismic and video records. The paper shows how the collapse times would be affected by lower and higher numbers within that range for each tower. Interesting stuff, and somewhat counterintuitive, at least to me.
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