9/11 Physics from Non-Experts

[Apollo20]

Does this mean that the calculations I have seen about the safety of nuclear reactors in the event of an aircraft impact are all suspect too?

I worked in the nuclear industry and my company claimed to be very SURE about what it told the regulatory bodies...

 

[gumboot]

Does this mean that the calculations I have seen about the safety of nuclear reactors in the event of an aircraft impact are all suspect too?

I worked in the nuclear industry and my company claimed to be very SURE about what it told the regulatory bodies...

That's a bit different. They test the materials for those by actually flying aircraft into them...



-Gumboot

 

[rwguinn]

That's a bit different. They test the materials for those by actually flying aircraft into them...



-Gumboot

yeah-
I once saw the remains of a spill of what they call "concrete" used in those things. I'm not sure they ever got it all up...Jackhammers hardly touch it, even without all the rebar.

 

[babazaroni]

Or did the perpetrators just get lucky?

Lucky or not does not matter. Four hijacked airliners, three smoking icons, and 500+ dead would have been enough to incite a war. The towers did not have to collapse and only a small portion of the Pentagon was destroyed.

 

[Newtons Bit]

My office just finished the design of a sled that would send jets into concrete walls. It was paid for by the japanese so that they could see if their new reactor protection was good enough. They're actually testing tens of millions of dollars of structures to failure.

 

[Furcifer]

Then you should be able to confirm that, averaged over the total floor area, an actual load equal to 25% of design load is pretty normal. If not, I have to assume you are a bricklayer.

Scathing. And you're wrong. 50% of design load is "normal" at the time of construction And, you know what they say about assuming...

 

[Furcifer]

I think you are correct regarding the outside dimensions of the columns, but I don't see plate thickness anywhere in the diagram.

I wasn't suggesting that the outer dimensions taper but the plate thickness does. In fact the exterior columns have the same outer dimensions all the way up after the 7th floor.

What would make sense is starting with the strongest grade lowest in the building and varying the grade to retain a symetrical joint up until the weakest grade and then changing the plate thickness and starting over with the strongest grade.

If I remember correctly, they didn't use alot of different grades in the core.

We builders are very lazy, and hate change. They didn't use very many grades of steel in the core. You should readjust your calculations to reflect this.

 

[GregoryUrich]

We builders are very lazy, and hate change. They didn't use very many grades of steel in the core. You should readjust your calculations to reflect this.

Doesn't seem like you read what I wrote. I just said "...they didn't use alot of different grades in the core".

Anyway you can't deny the need for scaling the strength. The loads at the bottom are 279,000 tons, in the middle around 100,000 tons, at the top 10,000 tons or less.

I have used the weakest steel in my calculation which has the highest density per unit strength.

 

[tsig]

Doesn't seem like you read what I wrote. I just said "...they didn't use alot of different grades in the core".

Anyway you can't deny the need for scaling the strength. The loads at the bottom are 279,000 tons, in the middle around 100,000 tons, at the top 10,000 tons or less.

I have used the weakest steel in my calculation which has the highest density per unit strength.

You are the weakest link.

 

[Furcifer]

Doesn't seem like you read what I wrote. I just said "...they didn't use alot of different grades in the core".

Anyway you can't deny the need for scaling the strength. The loads at the bottom are 279,000 tons, in the middle around 100,000 tons, at the top 10,000 tons or less.

I have used the weakest steel in my calculation which has the highest density per unit strength.

I am beginning to think you are just debating for debates sake. They didn't use very many grades of steel in the core, YOU DID. The effect of scaling the loads linearly does just that.
Buildings DO NOT SCALE LINEARLY, but i do agree you can't deny the need for scaling. The core dimensions remained constant until the 66th floor. If you think they scaled the steel while maintaining these dimensions you are sadly mistaken. Adding complexity is a sure recipe for disaster on a construction site. K.I.S.S.
"I have used the weakest steel in my calculation which has the highest density per unit strength" Are you kidding me? The density of steel varies by 0.5% for all grades including exotic stainless steels. I would challenge you to find a 0.1% density variance in any construction grade steel. This is just another good attempt a subterfuge Greg. Stick with me, listen, don't make rude comments (i happen to be Italian, your brick layer comment was mere coincidence I hope) and we will get to the correct conclusions about the WTC mass.

 

[Newtons Bit]

3bodyproblem: I suggest you read the FEMA and NIST structural repots (not damage) and learn more about the construction of the building. The grade of steel that they used for the plates varied from 42 to 100ksi. This is mostly for the box columns and spandrels. On one floor, different spandrels had different strengths. When I first saw that I thought they were crazy, but the columns came pre-fabbed with spandrels. While you can't trust the guy in the field to get it right, you CAN trust the shop to get it right.

The wide-flanges in the core were PROBABLY A36 (36ksi) steel, but I can't be sure of it.


Steel is 490 pounds per cubic foot. The grade doesn't change this. A36 would have a higher density per unit strength, but that's kind of a silly way to measure things.

 

[rwguinn]

3bodyproblem: I suggest you read the FEMA and NIST structural repots (not damage) and learn more about the construction of the building. The grade of steel that they used for the plates varied from 42 to 100ksi. This is mostly for the box columns and spandrels. On one floor, different spandrels had different strengths. When I first saw that I thought they were crazy, but the columns came pre-fabbed with spandrels. While you can't trust the guy in the field to get it right, you CAN trust the shop to get it right.

The wide-flanges in the core were PROBABLY A36 (36ksi) steel, but I can't be sure of it.


Steel is 490 pounds per cubic foot. The grade doesn't change this. A36 would have a higher density per unit strength, but that's kind of a silly way to measure things.

Is that what GregoryUrich has been stating? No wonder it went by me. "density per unit strength"?
Never heard it stated that way. If you use that criterion, why not go with 7050-T8451 Aluminum? 60KSI yield, a little over 1/3 the weight.
Oh--wait--we'd need to use 3 times as much, since the sway at the top might disconcert a few folks--stiffness is a factor...

 

[Newtons Bit]

That and designing a material that has a stress-strain curve that resembles a parabola is a bitch anyways. Give me a straight line or give me death!

 

[R.Mackey]

3bodyproblem: I suggest you read the FEMA and NIST structural repots (not damage) and learn more about the construction of the building. The grade of steel that they used for the plates varied from 42 to 100ksi. This is mostly for the box columns and spandrels. On one floor, different spandrels had different strengths. When I first saw that I thought they were crazy, but the columns came pre-fabbed with spandrels. While you can't trust the guy in the field to get it right, you CAN trust the shop to get it right.

The wide-flanges in the core were PROBABLY A36 (36ksi) steel, but I can't be sure of it.


Steel is 490 pounds per cubic foot. The grade doesn't change this. A36 would have a higher density per unit strength, but that's kind of a silly way to measure things.

For what it's worth, the core contained primarily A36 steel. Here's NIST NCSTAR1-1, page xxxvii:

Hidden within the building, the core columns were thicker and larger on the lower floors. Thus, core columns used fewer grades of steel. The box columns were either 36 ksi or 42 ksi. Core wide flange columns were one of four grades, yield strengths ranging from 36 ksi to 50 ksi, but most (approximately 90 percent) were primarily 36 ksi or 42 ksi steel.

This is in sharp contrast to the perimeter columns, which were spec'd for 14 different grades all the way up to 100ksi, but in practice used only 12, with one high-strength alloy being substituted for three different specifications that it met or exceeded. This was, of course, to retain the same exterior dimensions all the way up the building, in addition to column wall thickness which did eventually begin tapering as well. Spandrels were also spec'd for 12 different grades in similar fashion.

It should be pointed out, though, that while the dimensions of any particular column remained the same for some distance (some columns changing from box to wide-flange as low as Floor Seven, others not making the switch until Floor 95 in the case of Columns 801 and 803, as seen in NIST NCSTAR1-1A Fig. 2-12 on Page 27), the core was massively cross-braced below Floor 7 to add stability where the perimeter was thinner (the "trees" where one column below supported three above). In this respect, the core was heaviest on the lower floors.

 

[rwguinn]

That and designing a material that has a stress-strain curve that resembles a parabola is a bitch anyways. Give me a straight line or give me death!

That's the trouble with you young whippersnappers--always looking for the easy way out!

 

[Furcifer]

Newtons Bit: Saying "Hey I used the heaviest steel i could find" is hardly a concession. I'm not sure if reading more of the NIST report will help change my mind on that? Or are you saying the density could have varied in a linear fashion because the columns were built using various grades of steel on the ground, while maintaining the dimensions? I think you mean on the exterior, not on the core right? We were discussing the core. It hasn't been my experience to to taper a core gradually, nor have i seen any reference to this in the NIST report. If you have such a reference please send it to me, i have been looking hi and low.

 

[GregoryUrich]

No offence intended

I am beginning to think you are just debating for debates sake. They didn't use very many grades of steel in the core, YOU DID. The effect of scaling the loads linearly does just that.
Buildings DO NOT SCALE LINEARLY, but i do agree you can't deny the need for scaling. The core dimensions remained constant until the 66th floor. If you think they scaled the steel while maintaining these dimensions you are sadly mistaken. Adding complexity is a sure recipe for disaster on a construction site. K.I.S.S.
"I have used the weakest steel in my calculation which has the highest density per unit strength" Are you kidding me? The density of steel varies by 0.5% for all grades including exotic stainless steels. I would challenge you to find a 0.1% density variance in any construction grade steel. This is just another good attempt a subterfuge Greg. Stick with me, listen, don't make rude comments (i happen to be Italian, your brick layer comment was mere coincidence I hope) and we will get to the correct conclusions about the WTC mass.

I hope you will forgive my dig, but that was pretty minor compared to what others have said to/about me here. I thought I was just keeping with the forum's culture. Definitely not an attack on your heritage either, I had no idea you are Italian. No offence intended to the manual trades either, just that they would likely know less about design than say a structural engineer.

The lowest core perimeter columns had 3 parallel 7" plates and dimensions 24" x 52". If you look at the photos of debris you will find the same dimensions without the center plate and what appears to be 1-2" plate thickness. Where did these come from? If you require photos I can find them but I haven't yet given false data. I am convinced the plate thickness was scaled just like in the exterior columns. That they would use the same grade and thickness over 66 floors is just preposterous!

 

[GregoryUrich]

Heaviest steel

Newtons Bit: Saying "Hey I used the heaviest steel i could find" is hardly a concession. I'm not sure if reading more of the NIST report will help change my mind on that? Or are you saying the density could have varied in a linear fashion because the columns were built using various grades of steel on the ground, while maintaining the dimensions? I think you mean on the exterior, not on the core right? We were discussing the core. It hasn't been my experience to to taper a core gradually, nor have i seen any reference to this in the NIST report. If you have such a reference please send it to me, i have been looking hi and low.

I used A36 steel as referenced in NIST, I mistakenly wrote A35 in my paper due to fat fingers. This I will also correct.

 

[Furcifer]

No, i am not accusing you of giving false data. (which is refreshing departure from usual "truther" tactic) But I am accusing you of manipulating the data to such a degree as it has become unreasonable, at least for me and my experience.
And preposterous? I don't know about that. Has anyone ever measured the last piece of core standing in the videos? It would appear to have been considerably stronger that the rest wouldn't you agree? I wouldn't hesitate to assert that it was probably about the height of the fist change in the core construction.

 

[Furcifer]

No offense taken