9/11 Physics from Non-Experts

[Furcifer]

1. If you want to argue against FEMA (1/2 of Bazant's PE), NIST (references Culver) and McGuire et al. Did you miss this?

3. What do you mean by zone B?

1. Well I should say "a currently correct mass" as there is no "correct mass" as of this moment. I believe it is being contested as we speak

3. Fig. 1 i) The buffer zone between the upper and lower sections.

 

[GregoryUrich]

Yes, I understand you take issue with the 500,000 #. However, what I am asking is what is the number (or %) that they use to represent the upper portion in their work (expecting some # < 500,000/100%).

I did a quick approx using their scaling and got around 52 x 10^6 kg for wtc1 as I mentioned above.

 

[GregoryUrich]

1. Well I should say "a currently correct mass" as there is no "correct mass" as of this moment. I believe it is being contested as we speak

3. Fig. 1 i) The buffer zone between the upper and lower sections.

Does the buffer zone have it's own COR? I thought the COR was the ratio of the relative approach velocity to the relative separation velocity for two objects.

 

[rwguinn]

There are already many highly regarded researchers presenting work supporting gravity driven collapse. Since most people here are in agreement with this work, why would they need to reproduce it. For example, here is the latest from Bazant et al.:

http://www.civil.northwestern.edu/p...se - What Did & Did Not Cause It - 5-2007.pdf

It's true, that it is easier to dissect and pick apart someone elses work than to create your own model. Nonetheless, the people here for the most part are knowledgable and provide valid criticism. They are not always correct (see my previous post) but they are focused on evidence and proper physics.<snip>.

What you don't understand is that to Chriswgood, Models are not equations and numbers.

This is a model--by his lights.

 

[Furcifer]

Does the buffer zone have it's own COR? I thought the COR was the ratio of the relative approach velocity to the relative separation velocity for two objects.

It is, but remember the separation velocity will depend on the material properties, geometry and even the approach velocity of the colliding objects.

The best way I can think of to describe this is such: Imagine you have two identical pieces of silly putty colliding. At very slow speeds the collision will be inelastic, and they stick together. At higher speeds the collision will be elastic. Thus the COR will be 0-unity (1) for different approach velocities of identical materials.

 

[Arkan_Wolfshade]

I did a quick approx using their scaling and got around 52 x 10^6 kg for wtc1 as I mentioned above.

Ah, copy. Thank you for clarifying.

Okay, so they are saying that the top is 57,000 short tons of the total 500,000 short tons in the tower, or ~11%.

Compare this with the following:

http://en.wikipedia.org/wiki/World_Trade_Center
Height (m) 417
Height (ft) 1,368
Stories 110
http://www.house.gov/science/hot/wtc/wtc-report/WTC_ch2.pdf Section
2.2.1.1
American Airlines Flight 11 struck the north face of WTC 1 approximately between the 94th and
98th floors
2.2.1.5
Construction of WTC 1 resulted in the storage of more than 4x10^11 joules of potential energy over the
1,368-foot height of the structure. Of this, approximately 8x10^9 joules of potential energy were stored in the
upper part of the structure, above the impact floors, relative to the lowest point of impact.
2.2.2.1
United Airlines Flight 175 struck the south face of WTC 2 approximately between the 78th and 84th
floors.
For WTC 1, the top 12 floors of the tower translates into 8x10^9 joules of the total 4x10^11 joules. So, the top ~10.9% of WTC 1 contained ~2% of the entire PE of WTC 1. Extrapolating this on to WTC 2 (since the above mentioned report does not specify the amount PE contained above the WTC 2 impact point) we get the following:
WTC 2 => top 26 floors => ~23.6% of WTC 2.
If ~10.9% of WTC 1 translates into 8x10^9 joules PE
Then ~23.6% of WTC 2 translates into N joules PE
Therefore 10.9/8*10^9 = 23.6/N
=> 10.9*N/8*10^9 = 23.6
=> 10.9*N = 23.6*(8*10^9)
=> N = 23.6*(8*10^9)/10.9
=> N = 173[00000000]=> N = 17.3*10^9 joules PE
=> ~34.7% of the entire PE of WTC 2

http://arkanwolfshade.spaces.live.com/blog/cns!9E151F6EB6C7A35D!304.entry
bolding mine for the relevant part.

 

[rwguinn]

Ah, copy. Thank you for clarifying.

Okay, so they are saying that the top is 57,000 short tons of the total 500,000 short tons in the tower, or ~11%.

Compare this with the following:
http://arkanwolfshade.spaces.live.com/blog/cns!9E151F6EB6C7A35D!304.entry
bolding mine for the relevant part.

Ok, I am not following this.
The total energy was 4x10^11 J--this I can follow. MGH.
Of the top floors, the PE is calculated only for the distance of the damaged floors--the 1-2 floors with significant damage from the crash--or about 7-8m--because that is how much energy the can release falling 1-2 stories.
The first part of the wiki entry states that (the part you bolded), but the remainder of the article looks like a class project in obfuscation...

 

[GregoryUrich]

Core empty space as promised

I have finally done a calculation of empty space (no floor) and area with no permanent live load in the core.

I have sampled floors and approximated areas for elevators and shafts in the following way.

First I calculated the exact sizes for everything on one entire floor based on the numbers in the architectural drawings.

On all floors elevators were one of three sizes. Two of these sizes were very similar so I have used the smaller and simply counted large and small elevators. This was done on a number of representative floors roughly equidistant from the middle (floor 56). These numbers are given and averaged for the building (floors 1-110).

The exact sizes of shafts appeared to be grouped into three groups of which I took the average size for each. Then I simply counted the number of small, medium, and large shaft size on the representative floors. I have ignored miniscule shafts and columns.

Corridor, elevator lobby, and stair space was calculated from the numbers on the representative floors. These areas have no significant permanent live load and as long as loads due to people are accounted for elsewhere it will not affect the total mass. I have not included restrooms but there is essentially no permanent live load for them either.

With all the criticisms of my calculation, no one has pointed out that I overestimated floor concrete by 8,000 tons and the live loads in the core by a factor of nearly 1.8 or 6,400 tons.

Of course there are other things in the core like partitions, cables, pipes, and elevator stuff. Has anyone seen any better info on this stuff in the NIST reports (or elsewhere) other than the original design documents?

 

[Arkan_Wolfshade]

Ok, I am not following this.
The total energy was 4x10^11 J--this I can follow. MGH.
Of the top floors, the PE is calculated only for the distance of the damaged floors--the 1-2 floors with significant damage from the crash--or about 7-8m--because that is how much energy the can release falling 1-2 stories.
The first part of the wiki entry states that (the part you bolded), but the remainder of the article looks like a class project in obfuscation...

The wiki portion is only for the height of the tower. The bolded portion is from the pdf (http://www.house.gov/science/hot/wtc/wtc-report/WTC_ch2.pdf). The rest is working out the equivalent value for WTC1, as the pdf only addresses WTC2.

 

[GregoryUrich]

Ah, copy. Thank you for clarifying.

Okay, so they are saying that the top is 57,000 short tons of the total 500,000 short tons in the tower, or ~11%.

Compare this with the following:
http://arkanwolfshade.spaces.live.com/blog/cns!9E151F6EB6C7A35D!304.entry
bolding mine for the relevant part.

That's the problem with the 500,000 short tons total weight. Bazant says the total PE is more than 8 x 10^11 Joules, which fits in better with the mass they use.

 

[Arkan_Wolfshade]

That's the problem with the 500,000 short tons total weight. Bazant says the total PE is more than 8 x 10^11 Joules, which fits in better with the mass they use.

To make sure I am following you, please review my rewording of your statement and let me know if it is consistent, "Bazant says the total PE is more than 8x10^11 joules. This number, that is greater than 8x10^11 joules, fits better with their choice of 500,000 short tons in their calculations."

 

[GregoryUrich]

Ok, I am not following this.
The total energy was 4x10^11 J--this I can follow. MGH.
Of the top floors, the PE is calculated only for the distance of the damaged floors--the 1-2 floors with significant damage from the crash--or about 7-8m--because that is how much energy the can release falling 1-2 stories.
The first part of the wiki entry states that (the part you bolded), but the remainder of the article looks like a class project in obfuscation...

I think they mean total PE relative to a fixed point, not only the part that would be converted to KE if it fell some distance h. To visualize, put the upper part on the ground and calculate the total PE relative to ground.

 

[GregoryUrich]

To make sure I am following you, please review my rewording of your statement and let me know if it is consistent, "Bazant says the total PE is more than 8x10^11 joules. This number, that is greater than 8x10^11 joules, fits better with their choice of 500,000 short tons in their calculations."

The total PE value you cited is from FEMA I believe (4x10^11 Joules).

So yes, the 500,000 tons fits better with a total PE of more than 8x10^11 Joules.

 

[Arkan_Wolfshade]

The total PE value you cited is from FEMA I believe (4x10^11 Joules). This number just doesn't fit with the 500,000 tons value unless one assumes the building was extremely top heavy.

So yes the 500,000 tons fits with a total PE of more than 8x10^11 Joules.

Dammit Congress! *shakes fist* I need to update that entry. PDF is now located: http://www.fema.gov/rebuild/mat/wtcstudy.shtm
Ch.2 is http://www.fema.gov/pdf/library/fema403_ch2.pdf

How is the top ~10.9% of the structure accounting for ~2% of the PE top heavy?

 

[Furcifer]

Of course there are other things in the core like partitions, cables, pipes, and elevator stuff. Has anyone seen any better info on this stuff in the NIST reports (or elsewhere) other than the original design documents?

NO. To be perfectly honest with you Greg, every time I come across a reference to loads they appear to be much less than you are using. At least in the NIST report.

 

[GregoryUrich]

Dammit Congress! *shakes fist* I need to update that entry. PDF is now located: http://www.fema.gov/rebuild/mat/wtcstudy.shtm
Ch.2 is http://www.fema.gov/pdf/library/fema403_ch2.pdf

How is the top ~10.9% of the structure accounting for ~2% of the PE top heavy?

I think you are mixing apples and oranges here. Your 2% value is relative to the 96th floor (approximately) while the total PE is relative to the ground. The PE of the top section relative to the ground based on the Bazant weight for the top section is around 180x10^9 Joules or around 23% of the total PE.
Here I use the average height above ground for the top part:

52x10^6 kg x 9.801m/s^2 x 361m = approx 180x10^9 Joules

I think I confused things worse with my last statement which was incorrect.

Anyway, for FEMAs PE to be correct, the top couldn't weigh more than around 21,000 short tons.

 

[GregoryUrich]

NO. To be perfectly honest with you Greg, every time I come across a reference to loads they appear to be much less than you are using. At least in the NIST report.

Thanks for you candor. Honesty is a rare commodity.

 

[pomeroo]

Thanks for you candor. Honesty is a rare commodity.

While we're on the subject of honesty, can we all agree that when the curtain is mercifully brought down on these 25-plus pages of tedium, your conclusion will be that every demolition expert in the world is wrong and agents of a mathematically-impossible conspiracy blew up the Twin Towers?

By definition, honesty is never found in conspiracy liars.

 

[Belz...]

Thanks for you candor. Honesty is a rare commodity.

Indeed.

 

[Furcifer]

Thanks for you candor. Honesty is a rare commodity.

That being said there is still a wide discrepancy as to what the actual loads were.

I have also looked through Bazant/Verdure paper and found that they really give no justification for assuming rigid bodies, other than the simplification. I still believe the physics of my justification is sound. However, I believe a more accurate model can and most probably will be presented that incorporates "crush up and crush down" during the collapse. The reason for it is obvious, the video evidence for at least one tower is to the contrary. I think you will be disappointed, in that, a more detailed and complete model will not significantly change the fact that the KE of the upper section was an order of magnitude greater than the floor below could withstand.