Intermediate Dome Building

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Intermediate Dome Building

Postby P690 » Wed Jul 29, 2009 6:16 pm

Not a noob, but still have some questions about dome-building.

Here's the chase: I want to build a dome for my camp's communal shade structure, and I need to decide what EMT thickness to use: 3/4" or 1"? The plan is for a 3V, 22-24' foot diameter dome. I understand, having been closely involved in building a 3V nearly spherical dome (15' diameter) that 3/4" conduit is pretty strong, and should survive playa harshness and allow climbing near vertices. But I want our dome to have a few hammocks hanging, and if possible to be pretty climbable.

The question I have is whether 1" is enough of an upgrade to merit the extra cost (nearly 2x!). If the strut strength scales with area, then a 1" dome should be 70% stronger than a 3/4" dome. A 1.5" dome would be 300% stronger.

Would we be able to climb all over a 1" dome, stepping in the middle of struts? If we had the appropriate fabric, could we create an upper floor suspended like a trampoline?

The negatives of the 1" are the obvious ones: cost, cargo space, and cargo weight.

Also, will we need a ladder to build a 24' diameter dome? And I mean need.

Thoughts on covering: we may do a real cover, but I'm also idly considering cutting our cover, whatever it may be, into strips about the width of the strut lengths and just weaving it through the dome structure. This should keep it well attached. This would, of course, provide only shade and wind protection, doing little to nothing about dust and rain. But it seems workable. Comments?
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Postby stargeezer » Wed Jul 29, 2009 7:21 pm

I can't help on the strength question, but on the size, you can make your dome 23' 10 1/2" with a minimum of scrap. As for needing a ladder, it would be very difficult without one unless you can build from the top down and lift the dome as you go. I would suggest building this at home so you know the requirements.
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Postby P690 » Wed Jul 29, 2009 8:43 pm

Thanks for the comments. I'm concerned with other design factors.

Another question: how do you do the entrance in a 3V? Just take out a triangle? Do you something special with it? I've seen Disco Dave's modification to make a door, but I'm hoping for something simpler.
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Postby Burp! » Thu Jul 30, 2009 12:41 pm

Image
This is how we do it, just remove one bar to make a diamond shape door
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Answer to strength question?

Postby erosissa » Wed Nov 25, 2009 7:22 pm

Hey there! I'm wondering if you got an answer to your strength question or what you ended up doing and how it turned out. I'm looking at a 4V , 16' radius dome, and I'm wondering what size EMT to look at to make the thing climbable and suitable for hanging people from.
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Postby robotland » Mon Nov 30, 2009 6:30 am

That middle-of-the-strut stepping thing is a real killer- If you COULD just stay to the ends, you'd be fine to use 3/4" for your domes- ANY that have been mentioned so far in this thread! Here's something to think about: You can REINFORCE some "trouble areas" without having to use 1" conduit throughout. I've beefed up select struts by sliding pieces of 1" scrap OVER the 3/4" strut pieces, which has to be done BEFORE squishing both ends. Or, fasten a piece of 2x2" or 2x4" lumber to the strut using pipe clamps and screws. (One towards each end and another in the middle should do you, unless the strut is over 5' long!) This "splints" the conduit, and the wood will flex but prevent the steel from overbending. Best results are where you can secure the wood to the TOP of the strut where it'll take load from little climbing monkeys, and this can be a bit tricky since the clamps will allow the wood to rotate even if they're nice and tight. Drill a hole, and zipstrip the splint to a nearby vertex for added stability. This is also how you can fasten a deck onto your dome- Splint the five topmost radial struts of your dome and add plywood triangles! (Reinforce 'em unless it's a small dome...I can help with that if you give me design specs.)
FOR HAMMOCKS: Instead of bolts, use EYEBOLTS. This is one reason why I use 3/8" hardware on ALL of my domes- 3/8" is a common eyebolt size! Thet also have long threaded sections, which can help with those last few stubborn connections that need to be "cranked in". Then just hang your hammocks from the eyebolts with a couple of carabiners! (The giant ones from Harbor Freight are personal faves.) A WARNING about hammocks: If you fasten them loosely to the struts without anchoring them at vertices, they can slide to the middle of the strut where they can overload and bend said strut...causing problems. (I just stupidly did this last year at Lakes Of Fire.)
The cover-made-of-wrapped-strips idea is interesting...I like to use long, thin silver tarps (made for wrapping woodpiles) for the bottom areas so there are a minimum of breaks, and then smallish (8'x10' or so) tarps "up in the wind", secured mostly with zipstrips and spring clamps. (Clamps offer lots of quick flexibilty, enable you to try out a fit without tying, and in a huge windload will release the tarp without tearing it.)
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