structural engineering

[jsimms]

Wondering if any of you folks can recommend a structural engineer who is knowledgable about windloading , tip over forces, and other factors relative to sculptural forms?

Thanks
John

[G. Murdoch]

Good Morning,

I would ask Merlion.

Graham

[Merlion]

I am a retired mechanical engineer who had worked on the structural strengths of fabricated steel structures. But I am half way around the world from where you are which means I can't take up your job, nor recommend anybody near where you are.

On the other hand, perhaps you can explain what specifically are your problems, and if possible show photos.

[F.C. White]

Any Civil Engineering firm would gladly help you out, they're very knowledgable and qualified in this regard. I occasionally have need to design artwork for structural criteria and seismic load considerations. Typically, if you're good at drafting a decent layout of what you're working on, covering all the bases such as size (height, width, material, estimated weight, etc), they can do their calculations based upon your input and give you their seal of approval with an hour's worth of billing. I generally get charged near $100 for this service (whatever their minimal billing rate is for design consultation). If you know of any drafters they may know of an engineer who'd give you a bit of a break on such costs, too.

Good Luck.

[ironman]

Hey John, I got a solution!
Just build it, put it out on your property and watch it sway back and forth in the wind!
You'll find out pretty quickly if it's well engineered or not.
Have a nice day,
Jeff

[jsimms]

Thanks Jeff.........

I've tried that, but the neighbors got a little bummed about their squashed dogs. At least my dogs knew better than to get too close.
john

[jsimms]

Thanks F.C......

I think my stuff gets a little more complicated, though I admit I haven't run it by an engineer. I've always trusted my instinct and seat of the pants engineering abilities, but these folks want a real engineer to pass on it. Me too for the comfort level, as I'd hate to see people getting squashed. Its an 8' cube mounted on an apex complete with bearings to allow it to revolve. Lots of dynamic going on here! see image

John

[jsimms]

here's another image which shows the piece better

[Merlion]

If you said each side is 8', the whole cube would be pretty heavy, and it would catch the wind. In that case, they are right in asking for a professional engineer's opinion.

The support column has to be strong enough not to buckle, and to be able to take the additional bending force due to wind.

The top part of this column would be inserted into the cube, which I understand is allowed to rotate. There is sufficient length for this insertion. The distance from the top apex to the bottom apex is 2x8 = 16'. So this insertion length would be at least 4'. This would call for two rolling bearings, one on top and one below. As the cube is heavy, the one at the bottom would be one that can take both radial as well as axial loads.

[jsimms]

Thanks Merlion,

That was very helpful! The weight would be 1100 pounds in .120" aluminum.
I would likely use an 8" alumium tube with 1/2" wall as the shaft, which would allow pretty beefy radial tapered bearings.

Thanks again!
John

[Merlion]

The weight would be 1100 pounds in .120" aluminum.
I would likely use an 8" alumium tube with 1/2" wall as the shaft

As the whole thing is free standing on the shaft. Whether this flagpole like shaft is strong enough depends very much on how tall it is.

[Merlion]

Hi John. Any further development with building this large cube on a flagpole artwork ?

[jsimms]

There are three of us in the running for the commission, with artist presentation on May 1 and notice of award on May 15.

Actually Merlion, in my drawing I had not trimmed the base stem, so it appeared to be on a flagpole. The stem of the sculpture will only be 4' tall with the bearing assembly at the 3' level.



I did run it by a mechanical engineer, and he saw no realistic chance for failure as long as the base foundation was such as to resist tipover. My plans now are to do it in in .093 Titanium

Thanks for your help!
John

[iron ant]

Titanium,I new jewlers were hot on it,but fabing it in sheets sounds really high doller.What type of gas and rod do you tig it with,or is it seamed and soderd?Never worked with it,or even sceen the materials.Can you explain more without giving trade secrets of course........................m3

[Merlion]

Actually Merlion, in my drawing I had not trimmed the base stem, so it appeared to be on a flagpole. The stem of the sculpture will only be 4' tall with the bearing assembly at the 3' level.

Just to give my 2 cents of comments. Why not plan to install it higher up? It attracts more attention. It avoids the temptation for people especially children to spin the heavy cube around which can be dangerous.

[jsimms]

You're right, Merlion! The cube would be much more exciting mounted high. See Imploding Octahedron below with a 5' tall base.. I guess I was overly concerned about tipover or bending forces, but if I mounted it on a 10' pipe base, it should be plenty strong. Thanks for the wake-up!

As for the titanium, iron ant, it is expensive, up to $30/#, but I've got some good connections. (in titanium, an 8' cube will weigh almost 1000#)

And yes, it is very tricky to weld. Tig with argon. It embrittles very quickly if just a touch of oxygen gets to it. Best to use jury-rigged shields to contain the argon shielding gas. The pros use an argon filled glove-box or chamber. I haven't figured out yet how many inches of tig weld, but guessing about 600 inches.
John

[Merlion]

Oh, the final shape is not quite the same as your earlier design. If you would allow another differing view from me, I like the original design better. On the latter, all edges and surfaces are not horizontal, and no vertical viewing edges go from top to bottom.

By the way, why do you install the cube on bearings. Is it supposed to be turned by people viewing it?

The shape is well balanced. Does it still turn with the wind?

[Araich]

I have seen a few kinetic works on posts like this, and the weak point has always been the post to the ground. Vibrations from the rotating mass above have fractured the welds.

Titanium! My mouth is watering...

[iron ant]

John,,

still facinated about titanium.Sounds like just a draft in the shop will screaw things up.Would you say it welds more like Aluminum,stainless,bronze.or non of the above.Will you powder caot,or use automotive paint?Good luck and I hope you bag the job...IA

[jsimms]

Actually Merlion, the shape is virtually identical. Both are cubes mounted on an axis. The difference is in how the 6 faces roll/slope inwards to the cubic void at the center. If you have a high speed connection, I would be happy to forward an animation of the new piece revolving. (digitally). Did you view the movie of the original on my site below?

As to the titanium, I would use it from a strength/weight ratio. Strength of steel, weight of aluminum. Also, it quickly forms a protective oxide coating, so is needs no further finish.

As I lay in bed last night, I off hand figured more like 150 feet of weld! Yikes!

Interestingly Araich, I have had no problems with bearings, as all motion is smoothly axial. virtually zero slack

see below with 6' stem

john