Originally posted by Seymour Butz
Who says that they don't know?
Um...they do. Read your article. It's right under the portion you quoted.
wtcmodel.wikidot.com...
Regarding the thickness of the steel used inthe perimeter columns, the NIST document makes the following statements:
Perimeter columns in the upper stories were typically fabricated of lighter gauge steel, most commonly 0.25 in (6.35 mm) …
In contrast to the upper stories, in the lower stories, the perimeter column flanges were as thick as 3 in. (76 mm) and typically made of lower
strength steels.
Fourteen grades of steel were used in the construction of the perimeter columns with minimum yield strengths of 36, 42, 45, 46, 50, 55, 60, 65, 70,
75, 80, 85, 90, and 100 ksi. No further information is given on the transition points in the columns from one thickness to another and one grade of
steel to another.
Let's see what NIST really says.
wtc.nist.gov...
Go to page 9 where they talk about the perimeter columns.
I can't find where it says the "In contrast to...." part. But, I just read the perimeter column part and it doesn't say that. Maybe further on
in the NIST report?
I will admit that I was unaware that the thickness of the columns decreased. That is what gauge is. Thickness not strength. So, having higher
strength steel at the top, they were able to lower the thickness at the top. This would make sense because they wouldn't be as big and heavy
(gravity load/dead load). Which points out a huge flaw for Bazant et al. who want to take the mass of the top of the building by dividing the entire
tower by the number of floors. Since those floors on top were not as heavy as the ones at the bottom, their entire premise of calculating energy by
using that mass figure would be way off. Thanks NIST.
But, onto what they say. So, the lower floors were made of weaker steel but a little bit thicker. The top portion was made of thinner steel but
stronger.
It would be nice to know what the balance is and where it occurs. Meaning, how can you claim bsbray's analysis is false when you don't know if
there is a balance and maybe the use of stronger steel would cause the top portion to actually be stronger or as strong or almost as strong? Even
though it has thinner webs. We don't. Without proper calculations, we don't know this.
The only thing you can say with accuracy is that the transition points aren't given in that doc. That's all.
Because they don't know where they occur. And they admit it in the wiki article. NIST is very hush-hush about the finer details like this.
So, now that you know that the ext columns had 1/4" steel, and the base had steel up to 3" thick, do you still think that bsbray's comment
still holds water?
Possibly, here's why.
Say the 3" steel was A-36 steel. A-36 meaning that it's strength is 36 ksi (kips per square inch) or 36,000 pounds per square inch.
A 3" x 1" steel plate of A-36 steel can hold 108 kips or 108,000 pounds.
Now, let's say the 1/4 inch piece has a strength of 432 ksi (arbitrary number just to make this work).
This 1/4" x 1" steel plate can also hold 108 kips.
See why the structural documentation is needed? And possibly why it's hidden?
In my view, it would defy all logic to continue to talk about "moments" when the core columns displayed thinner walls AND sizes due to
decreased loads.
I thought we were talking about the perimeter columns?
It would be absurd to me that now that you know that the ext columns were in fact different to claim uncertainty about whether or not the ext
columns at the impact zones were "able to carry about as much weight as those that held up the whole damn thing down at the base."
It would be absurd for me to think that anyone would claim anything pro or con. As we still don't even know how the damn thing was built. And yes,
the areas of every single member makes a difference. When talking about "moments", "moment" of inertia, failure, strength, and anything else that
deals with engineering.
