• Quick note - the problem with Youtube videos not embedding on the forum appears to have been fixed, thanks to ZiprHead. If you do still see problems let me know.

9/11 Physics from Non-Experts

GregoryUrich said:
Augustine is suggesting that I adjust the stiffness of the lower section based on less weight above. I can calculate the stiffness (which Bazant already did and I have not questioned), but should I manipulate it?
Click to expand...

I am suggesting no such thing. Reread. Bluntly I am telling you there is no way you can come up with a magnification factor of 0.3. Stiffness is unrelated to "actual weight" above, it is a function of "design weight". It will not vary based on relative occupancy of floors.
 
GregoryUrich said:
I don't see how I can adjust the stiffness. The stiffness is the stiffness based on the structure, so essentially more damage would be done to the upper part?
Click to expand...

Stop getting ahead of yourself. You are immediately jumping to "damage" without comprehending the formula.
 
Augustine said:
I am suggesting no such thing. Reread. Bluntly I am telling you there is no way you can come up with a magnification factor of 0.3. Stiffness is unrelated to "actual weight" above, it is a function of "design weight". It will not vary based on relative occupancy of floors.
Click to expand...

Sorry, I thought you meant I should reduce the stiffness. I'll recalculate.
 
Apollo20 said:
Gregory Urich:

I think the "whitepaper" you are looking for is by Blanchard
Click to expand...
If that's the case, it's an estimate based on reviewing photos, with no detailed analysis or calculation, and it doesn't attempt to account for (for example) the amount of debris in sublevels or how much debris was ejected long after progressive collapse became inevitable.

Edit: ah, I didn't see that you had linked to it while I was posting. Note 3body's comment below.
 
Last edited:
3bodyproblem said:
This paper does not indicate, as i suspected, whether the mass ejected before or after contributing to the collapse though Greg. You still need to determine what critical mass remained within the footprint during the collapse and contributed to the KE available to destroy a lower floor.
Click to expand...

At each impact/buckle (or even continuosly) mass is ejected during the entire collapse. Before or after makes only a small difference as the mass is no longer available to drive further buckling. Then there's the energy associated with the lateral velocity.

Actually, I think the 95% number is an overestimate. Blanchard doesn't say this number comes from cleanup statistics but rather from satellite pictures which makes the margin of error high unless they are topographical with a margin of for altitude error less than 1 ft. I have seen topographical images somewhere but nowhere near the resolution required.

I think actual the percentage expelled is more likely between 50-80%. I have no idea how to try and establish a better number.

Regarding how much mass stay within the footprint, I believe the expulsion ramped up during the entire collapse which raises another scaling issues. Also there appear to be sprikes at the mechanical floors which one would expect due to the stronger floors. What do you think?
 
Newtons Bit said:
Well, he supposedly already has the mass of them, it should be trivial to get a cross-sectional area.
Click to expand...

Yeah--I thought about that afterit was toolate toedit.
It'll be conservative, but won't make much difference, given the energy levels available.
And GregoryUrich:
Mass has nothing to do with stiffness, except that area*length=volume, and since real materials have density, volume*density=mass.
 
GregoryUrich said:
At each impact/buckle (or even continuosly) mass is ejected during the entire collapse. Before or after makes only a small difference as the mass is no longer available to drive further buckling. Then there's the energy associated with the lateral velocity.

Actually, I think the 95% number is an overestimate. Blanchard doesn't say this number comes from cleanup statistics but rather from satellite pictures which makes the margin of error high unless they are topographical with a margin of for altitude error less than 1 ft. I have seen topographical images somewhere but nowhere near the resolution required.

I think actual the percentage expelled is more likely between 50-80%. I have no idea how to try and establish a better number.

Regarding how much mass stay within the footprint, I believe the expulsion ramped up during the entire collapse which raises another scaling issues. Also there appear to be sprikes at the mechanical floors which one would expect due to the stronger floors. What do you think?
Click to expand...



Try F=ma.

Works every time.
 
GregoryUrich said:
Regarding how much mass stay within the footprint, I believe the expulsion ramped up during the entire collapse which raises another scaling issues.
Click to expand...
Scaling? Acceleration due to gravity.

Also there appear to be sprikes at the mechanical floors which one would expect due to the stronger floors. What do you think?
Click to expand...
I don't know what you mean. There were puffs of debris from the mechanical floors before the falling mass reached them, which would be expected because those floors had vents to the outside.
 
GregoryUrich said:
Actually, I think the 95% number is an overestimate. Blanchard doesn't say this number comes from cleanup statistics but rather from satellite pictures which makes the margin of error high unless they are topographical with a margin of for altitude error less than 1 ft. I have seen topographical images somewhere but nowhere near the resolution required.

I think actual the percentage expelled is more likely between 50-80%. I have no idea how to try and establish a better number.

Regarding how much mass stay within the footprint, I believe the expulsion ramped up during the entire collapse which raises another scaling issues. Also there appear to be sprikes at the mechanical floors which one would expect due to the stronger floors. What do you think?
Click to expand...

I think that number is fair. However, it is my contention that the exterior walls did little else than retain the falling mass within the footprint, providing little to no support. I beleive this is supported by close inspection of the videos. I also would note that a substantial portion of the core remained free standing and did not contribute to the KE of the collapse mechanism.

http://www.youtube.com/watch?v=ACbFfqFap2M&mode=related&search=

note 1:36 2:28 and 3:12 of the above video

(for the most part it appears the core was behind the collapse wave in both towers). This means the upper crumbling mass and impacted floors were the only available KE. In my personal model of the collapse, the only significant figure is the energy required to separate the floor trusses from the core and exterior columns which would remain essentially constant for the duration of the collapse. Hence the steady progression of the collapse noted by many. As the crumbling mass built up within the footprint the horizontal forces on the exterior columns "peeled" them away from the core and outside the footprint. The ability of the exterior columns to retain mass inside the footprint would be proportional to their thickness and rigidity not to mention inertial mass. Thus, most of the upper crumbling section, most of the floors, a small potion of the core and a small portion of the exterior remained in the footprint during the collapse.
 
3bodyproblem said:
I think that number is fair. However, it is my contention that the exterior walls did little else than retain the falling mass within the footprint, providing little to no support. I beleive this is supported by close inspection of the videos. I also would note that a substantial portion of the core remained free standing and did not contribute to the KE of the collapse mechanism.

http://www.youtube.com/watch?v=ACbFfqFap2M&mode=related&search=

note 1:36 2:28 and 3:12 of the above video

(for the most part it appears the core was behind the collapse wave in both towers). This means the upper crumbling mass and impacted floors were the only available KE. In my personal model of the collapse, the only significant figure is the energy required to separate the floor trusses from the core and exterior columns which would remain essentially constant for the duration of the collapse. Hence the steady progression of the collapse noted by many. As the crumbling mass built up within the footprint the horizontal forces on the exterior columns "peeled" them away from the core and outside the footprint. The ability of the exterior columns to retain mass inside the footprint would be proportional to their thickness and rigidity not to mention inertial mass. Thus, most of the upper crumbling section, most of the floors, a small potion of the core and a small portion of the exterior remained in the footprint during the collapse.
Click to expand...

gravity buldings are designed to resist it>
 
Gravy said:
Scaling? Acceleration due to gravity.

I don't know what you mean. There were puffs of debris from the mechanical floors before the falling mass reached them, which would be expected because those floors had vents to the outside.
Click to expand...

By scaling (I don't have a better term) I mean that in order to model the ejected debris, one would need to increase the amount for each floor or buckle/impact.

By spikes I mean irregularities in the scaling function. From the videos it looks like the amount of debris ejected at the mechanical floors increases dramatically.
 
3bodyproblem said:
I think that number is fair. However, it is my contention that the exterior walls did little else than retain the falling mass within the footprint, providing little to no support. I beleive this is supported by close inspection of the videos. I also would note that a substantial portion of the core remained free standing and did not contribute to the KE of the collapse mechanism.

http://www.youtube.com/watch?v=ACbFfqFap2M&mode=related&search=

note 1:36 2:28 and 3:12 of the above video

(for the most part it appears the core was behind the collapse wave in both towers). This means the upper crumbling mass and impacted floors were the only available KE. In my personal model of the collapse, the only significant figure is the energy required to separate the floor trusses from the core and exterior columns which would remain essentially constant for the duration of the collapse. Hence the steady progression of the collapse noted by many. As the crumbling mass built up within the footprint the horizontal forces on the exterior columns "peeled" them away from the core and outside the footprint. The ability of the exterior columns to retain mass inside the footprint would be proportional to their thickness and rigidity not to mention inertial mass. Thus, most of the upper crumbling section, most of the floors, a small potion of the core and a small portion of the exterior remained in the footprint during the collapse.
Click to expand...

I'm not sure I agree. The combined mass of most of the floors (would include the live loads) and the upper section would be around 50% of the total mass. Another problem is that if all that mass precedes the core collapse, that there would be very little mass to drive the core collapse. The core by itself would be one of the strongest buildings ever built with the exception of resistance to lateral forces, of which we have none.

I don't say I know the collapse sequence but your explanation seems improbable.

I've watched videos with the "spire" from wtc1 a number of times. It appears to me that it is some small portion of the core (e.g. 5-9 columns). I have seen a fairly clear photo of it.

Some interesting photos of wtc2 show what appears to be the entire bottom half of the core standing (I'm not sure how long it stood). What I can't figure out is that, if the intact part of the core was standing for a period of time, why it fell later with no extreme forces acting on it.
 
GregoryUrich said:
I'm not sure I agree. The combined mass of most of the floors (would include the live loads) and the upper section would be around 50% of the total mass. Another problem is that if all that mass precedes the core collapse, that there would be very little mass to drive the core collapse. The core by itself would be one of the strongest buildings ever built with the exception of resistance to lateral forces, of which we have none.

I don't say I know the collapse sequence but your explanation seems improbable.

I've watched videos with the "spire" from wtc1 a number of times. It appears to me that it is some small portion of the core (e.g. 5-9 columns). I have seen a fairly clear photo of it.

Some interesting photos of wtc2 show what appears to be the entire bottom half of the core standing (I'm not sure how long it stood). What I can't figure out is that, if the intact part of the core was standing for a period of time, why it fell later with no extreme forces acting on it.
Click to expand...
Define "Extreme force"
I suggest you look up "Creep load" , buckling, and column stability if you're having trouble with the core collapsing post-event.
Ejection of mass--even 50% mass ejection (which I consider very high) onlyreduces the available energy by 50%. There was much more than 200% energy budget during the collapse.

And I want to know how it is you can see through all the dust to determine
... it looks like the amount of debris ejected at the mechanical floors increases dramatically.
Click to expand...
Define dramatically--and show us how you determined this.
 
Greg,

You had 8 supposed issues with Bazant's paper. Currently you are bogged down on one, debris ejection, where your sole reference is one paper in which, for my own part, I believe the author chose some rather unclear wording. I do not believe that Mr. Blanchard (or anyone) asserts that 95% of the mass of the towers fell outside the footprint of the towers. If anyone would like to contact Mr. Blanchard, assuming that he corrects his meaning, do you have any other sources? Any other estimates?

(Also, you may want to ponder the fact that horizontally "peeling" away the exterior columns actually consumes less energy than plastically crushing them.)
 
Augustine said:
I am suggesting no such thing. Reread. Bluntly I am telling you there is no way you can come up with a magnification factor of 0.3. Stiffness is unrelated to "actual weight" above, it is a function of "design weight". It will not vary based on relative occupancy of floors.
Click to expand...

OK, I recalculated and got a magnification factor of 18.2 with no safety factor.

Here is an interesting question though. What is the smallest mass you can drop from 3.7 m onto the structure in question and still have a global collapse?

I get 62,754 kg or 4% of the mass of a single floor (floor 95 = 1,583,000 kg by my calculation). Something is amiss in Bazantland!

Edit: I forgot the plastic work. This will just exceed the load capacity.
 
Last edited:
rwguinn said:
Define "Extreme force"
I suggest you look up "Creep load" , buckling, and column stability if you're having trouble with the core collapsing post-event.
Ejection of mass--even 50% mass ejection (which I consider very high) onlyreduces the available energy by 50%. There was much more than 200% energy budget during the collapse.

And I want to know how it is you can see through all the dust to determine
Define dramatically--and show us how you determined this.
Click to expand...

I was suggesting to 3Body that 95% debris ejection as proposed by Blanchard seems like too much and wouldn't fit his scenario.

Extreme force was overkill actually. The only force acting on the core at that point was gravity.

I said it looks like...

So sue me.
 
Augustine said:
Greg,

You had 8 supposed issues with Bazant's paper. Currently you are bogged down on one, debris ejection, where your sole reference is one paper in which, for my own part, I believe the author chose some rather unclear wording. I do not believe that Mr. Blanchard (or anyone) asserts that 95% of the mass of the towers fell outside the footprint of the towers. If anyone would like to contact Mr. Blanchard, assuming that he corrects his meaning, do you have any other sources? Any other estimates?

(Also, you may want to ponder the fact that horizontally "peeling" away the exterior columns actually consumes less energy than plastically crushing them.)
Click to expand...

I don't see how this can mean anything else:

Blanchard: A review of all photographic images clearly shows about 95% of falling debris being forced away from the footprint of the structure...

Concluding:... These facts indicate that a relatively small amount of structural support debris actually landed straight down in the towers foot prints...
Click to expand...

Anyway, I reject this claim.
 
You must log in or register to reply here.

Back
Top Bottom