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Author Topic: Seattle Space Needle in Iron  (Read 1061 times)
Patron Zero
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« on: May 12, 2015, 07:28:59 pm »

I've always been a fan of the Seattle Space Needle for it's graceful lines and other aesthetics, mind it achieves such through it's reinforced concrete construction.

That said, would there have been room in a different setting for this tower had it's composition been more like Gustave Eiffel's iron structure ?



« Last Edit: May 12, 2015, 07:31:14 pm by Patron Zero » Logged

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« Reply #1 on: May 13, 2015, 02:03:29 am »

If I may give you my perspective in this, I'm an aerospace engineer, and not necessarily a structural engineer, but I know enough about structures to offer myself when I apply for jobs...

The thing with the Space Needle is that it shows some late 20th C knowledge that was missing back when Maurice Koechlin and Émile Nougier designed the structure for Gustave Eiffel's tower.

The theory in particular is a material efficiency analysis (minimizing the amount of mass of a structure) which states that a single fat column (think elephant legs) is the most efficient way to carry a heavy compressing load, while an infinite series of strings would be the most efficient way to carry a tensile load (ie hanging the top "saucer" of the Space Needle from an imaginary ceiling).  This is due to way the forces are distributed during loading ( along the center of a column in compression VS along the surface  of cables in tensile loads).  This knowledge was not available back then.

Instead more fundamental knowledge about materials was applied. More like using the general knowledge that steel is a tension-compression symmetric material (same strength in tension and compression).

Nougier and Koechlin used very standard engineering mechanics of materials science and designed a tower made of Trusses.  A Truss is a structure made of linear elements which crisscross to make triangular cells. The triangular arrangement ensures that forces (tension or compression) "flow" right along the axis of each of the linear elements in the structure, thus minimizing the load, as opposed to a Frame, where not only do you have tension and compression, but also bending, torsion, etc.

So early steel structures tend to be trusses, and riveted ones at that, because welding was not reliable or easy enough.

Could they have made a Space Needle?  Perhaps, but you need a mathematician using a Babbage engine to make this discovery...  Perhaps something that looks like the needle, but made of trusses...
« Last Edit: May 13, 2015, 05:45:34 am by J. Wilhelm » Logged

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« Reply #2 on: May 13, 2015, 02:24:57 am »

What about making the Needle's "legs" of steel trusswork but surrounding a single concrete central column? Something like a pillar with flying buttresses.
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« Reply #3 on: May 13, 2015, 07:02:35 am »

What about making the Needle's "legs" of steel trusswork but surrounding a single concrete central column? Something like a pillar with flying buttresses.

The needle, if you look carefully is a very simplified truss above the "waist" of the tower, and it's also a very simplified truss below the waist.

What this "waist" does is minimize the diameter of each of the legs (think about it if you were to have 6 straight columns holding the sauce, these would have to be much thicker than what you see.  Exactly how thick depends on something called Euler's Column Stability theorem, which basically describes the maximum load you can impose on a column without having it buckle as a function of height.  The longer the column, actually the weaker (more susceptible to bending/buckling) a column is. So when you create a truss of columns you are reducing the length of the "columns and therefore are more stable and can be thinner.

So, yes,  perhaps have the legs be made of trusses then tie the trusses at the waist with a central compressive-ideal material Having a single column in the center would be very heavy, but the column would be made much thinner by the buttressing effect (again Euler's theorem applied to the central column).  Still, a very cavalier design for the era if they didn't understand the weight advantage of the central "waist."  They basically would rely on the general thought of "trussing the trusses and the column."

Perhaps using a square cross section and  of a 3 or six-sided geometry. Think of two Eiffel Towers sitting on top of one another.

Something like this:

I think they would arrive at a similar design using Euler's Column Stability Theorem and understanding the use of a composite truss with a compressive-ideal material in thet part of the truss where they only have compressive forces - but I'm not sure if they'd envision the advantage mathematically maybe by chance calculation.

Eiffel's Needle
(Not necessarily in correct proportions - just the idea)



« Last Edit: May 13, 2015, 07:11:59 am by J. Wilhelm » Logged
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« Reply #4 on: May 13, 2015, 07:37:40 am »

Somehow it needed this... Grin

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« Reply #5 on: May 13, 2015, 08:06:13 am »

Somehow it needed this... Grin



Damn, beat me to it.
Although, wasn't Eiffel's original used as a mooring mast?
The Empire State Building was.

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« Reply #6 on: May 13, 2015, 11:58:48 am »

1. Maybe at some point, but it was not originally intended to.
2. An open structure such as the Eiffel Tower would allow such things, but ironically, the Empire State building, which did have a provision for airship mooring added to the original design, would have winds hitting it and shooting up the side of the building, making it impracticably dangerous. Plus, of course, the idea of boarding by a narrow plank so high above the street, wind or no wind, soon put paid to that.
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« Reply #7 on: May 22, 2015, 05:57:24 pm »

Quote from: J. Wilhelm   
[center
Eiffel's Needle[/center]
(Not necessarily in correct proportions - just the idea)

     

That's very close to what I was envisioning, nice interpretation !
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« Reply #8 on: May 22, 2015, 07:59:13 pm »

Quote from: J. Wilhelm   
[center
Eiffel's Needle[/center]
(Not necessarily in correct proportions - just the idea)

     

That's very close to what I was envisioning, nice interpretation !
Not far off what I had pictured, as well.
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« Reply #9 on: May 23, 2015, 01:31:26 pm »

A lattice design might also be worth looking at

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« Reply #10 on: May 26, 2015, 10:09:17 am »

A lattice design might also be worth looking at




I'm not sure.  A pure metallic lattice-truss is basically what the Eiffel Tower is, save the floor sections.  The problem is the weight to strength ratio of the structure, and arguably Koechlin and Nougier felt they were already pushing the limit. A larger third floor, would mean a much heavier structure in the lower segments, than the Eiffel already is, so even if I design a conical truss structure it'd be heavier than the Eiffel Eiffel Tower or about the same if the third floor is kept small.  How you go about making such a large top floor is what the engineers needed to solve to make something that looks like the needle

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« Reply #11 on: May 29, 2015, 12:31:06 am »

I'm wondering if such an iron structure could have a 'practical' application as either lightning collector or wireless-telegraph tower ?

Mind even if the restaurant level does not rotate, the view would remain quite spectacular wherever such a tower was erected.
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« Reply #12 on: May 29, 2015, 02:01:38 am »

I'm wondering if such an iron structure could have a 'practical' application as either lightning collector or wireless-telegraph tower ?

Mind even if the restaurant level does not rotate, the view would remain quite spectacular wherever such a tower was erected.

Oh you can bet on it.  That's a large investment to make for the era.  Almost undoubtedly it would have to be justified with a function.  Observation, meteorological, radio, all of the above...
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« Reply #13 on: May 30, 2015, 12:25:50 am »

I'm also wondering on the feasibility of using it as a tourist attraction.  Tourism as we know it stared very slowly in the 19th C. If I'm not mistaken. The world fairs became tourist attractions, and also if I remember sone of the technological displays on the Paris 1899 Expo  Universelle, like the elevated moving sidewalk could be considered tourist attractions.  Certainly the Eiffel Tower became one.
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