Hey taff I need your help Please =]

[Andres Roquete]

I'm building an "art car" for burning man. I need to build a dome on a base vehicle that is 20 feet wide at its widest point by 28 feet long. this makes the dome an oval instead of a perfect circle at the base. I want to know if it's possible to to make this happen without compromising the stability of the dome. If it is is there a way to figure out the measurements of each piece.

here are a few pictures of the base vehicle with a stretched dome on it, not sure if that would work which is why I've come to you for help.

Any help is greatly appreciated.

[Blair Wolfram]

 On the topic of mobile domes, here is a preliminary outline for a geodesic Airstream trailer. The dome has to be elongated to contain any volume if the vehicle width is limited to a standard 104" highway width.

Brrr

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Blair F. Wolfram
Founder, Dome Inc.

thedo...@domeincorporated.com

http://www.hurricanedomes.com

888-DOME-INC or 612-333-3663

[TaffGoch]

Andres,

Do you plan to skin with rigid panels? If so, using planar intersections is going to be more reliable than "stick building" the model (using struts to define the shape.)

_____________________________

Your question about stability -- If you are NOT using triangles, it won't be stable (always the first rule, in any construction.) The triangles don't have to be physical frames, as a pent or hex frame that is intimately attached to a rigid panel exhibits multiple triangles (latent within the panel, of course.) Note that this is not unique to domes. It's true of conventional (box) house construction, too.

Now, if your panels aren't rigid enough, then a hex/pent construction will be compromised. If you were planning to skin it with fabric, for instance, then the hex/pent frame is going to require strong triangular gussets at the nodes (or some such similar reinforcement.) Thin metal skin won't help as much as you'd expect. 

Diagonal tension cables can produce rigidity, if employed such that tension/compression forces are evenly spread. It's the "hot spots," of high tension or compression, where structural integrity is compromised and breakage propogates. You have to be careful, with tension cables. If you employ tension cables across the face of a hexagon, for example, and the planarity of the hexagon is not secured, then the panel will, obviously, be subject to collapse by folding. (Try it, with dowels and rubber bands.) Even with such tensegrity compression and tension elements, 3D triangulation is REQUIRED.

All in all, just keep in mind that 3D triangulation should be your objective. If you can't see the physical or latent (triangulated) force-distribution elements in a region of your design, then consider that a potential weak spot.

Also, you need to ensure that your "ground" plane -- the physical frame upon which the dome is anchored -- is also rigid. If you've ever built a model dome of cardboard, then you'll know that geodesic frames/shells are rigid only if they encompass a complete sphere, or the truncation/ground plane is sufficiently rigid. In fact, it's my recommendation that you build a scaled-down shell out of cardstock, and see how and where it flexes.

_____________________

Regarding measurements of each piece, that's what the SketchUp model can provide. As long as the virtual 3D model is "full-size" (i.e., not "to scale,") then you can simply take all your measurements; linear and angular, directly from the model.

-Taff

[TaffGoch]

Andres,

Let's break down the geometry, a little, and consider gravitational forces on just the top elements:

What happens when you push down on the top pentagon (assuming the pentagon, itself, is inflexible)?

How would you rectify?

-Taff

[Andres Roquete]

Hey Taff thanks a lot for the help.

Let me start by saying it will be a no climbing dome. The plan is to leave the frame all open and run LED strips on each piece. there will also be 4 light weight color changing LED lamps hanging from the frame as well. All in all there isn't going to be much weight on the structure but I'm wondering if it'll even be strong enough to support itself.

I wasn't planing on skinning it at all, but did think about throwing fabric over it to create shade when needed. I like the gussets at the nodes idea as reinforcement.

As for the base it encompasses the complete area. But the base isn't 100% rigid since it'll be placed on a walkway frame that sticks out 5 feet from the original structure. When standing at the edge it tends to bend down very slightly.

Is it a problem that i stretched the dome to an oval/egg shape?will it stand?

- And for the question:

the pentagon collapses.

rectify it by placing triangular gussets at the base of each bar?

bare with me here not too familiar with this stuff =/

Thanks a bunch
A.

[TaffGoch]

Employ tension cables, to prevent the spread of the legs:

Forces on small triangular corner gussets would be extreme, leading to node failure (unless the gussets are large enough to resist the loading forces.)

So, how about further down?

Spreading will also occur. To rectify, more cabling:

Note that this tension-cable solution is exclusively for downward forces, and won't help for lateral forces, due to wind or sideways g-forces in a curve. (If there is no paneling/fabric, serving a "sails," wind shouldn't be much of a factor.)

The "levels" below the two depicted above will require similar tension support, to prevent spread & collapse.

__________________

The bottom line:  A hex/pent frame is NOT stable, all by itself. It WILL collapse. It needs some kind of triangulation, whether solid struts to combat compression forces, or cables to account for tension forces.

Elongating the frame, to the mild degree depicted in your initial post, isn't going to detrimentally affect the strength of the frame to any degree of concern. The real problem is the lack of triangular load-bearing support, as described above.

-Taff

[Andres Roquete]

Great I see what you mean.

Would you mind showing me how you would place the solid struts to reinforce the hex/pent?

would you recommend doing a geodesic dome instead ? if so is it possible to elongate it like that?

Thanks again,
A.

[TaffGoch]

Andres,

Personally, I would, indeed, choose a triangulated geodesic dome. Even though you state that it is not to be climbed on, it will be difficult to prevent people from resisting their natural inclination to do so. Also, it may be handy to permit climbing, by your own crew, for stringing wires, adjustments, etc.

Elongating a triangulated geodesic dome presents no additional challenges, compared to a hex/pent dome, while removing the structural loading deficiencies presented by hex/pent geometry.

-Taff

[Andres Roquete]

Ok Taff thanks for your input it was exactly what I feared.

Now another problem that I have its that second small platform it gets in the way of the dome. I see that there is a way to  brake the dome with out compromising the stability of it but I'm not sure how to do it. I found a model but it doesn't look like it was built correctly. I'm attaching a pic of it.

I hardly know my way around google sketch up and I really need help with this project.

Can I commission you to build a dome that fits correctly and works on the base vehicle I crated? I need something created by someone who knows what they are doing. And you seem to be the right guy.

Please please please bless me with your help. how much would you charge for something like this?

[Paul Kranz]

Andres:

Have you thought of fewer triangles like the DoggiDome?

Paul sends...

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Very high regards,

 

Paul sends...

ReviveTheFlame.com

[Andres Roquete]

Hey Paul,

Thanks for the suggestion but Im trying to create a "Turtle shell" and the shape of the doggie dome isn't round enough.

[TaffGoch]

Andres,

If you rotate the icosahedron, so that an edge (rather than a vertex) is directed upward, then you achieve an orientation that exhibits right/left, fore/aft symmetry. This will reduce complexity, during design & construction.

Here, I depict a 3v example. Note the orientation of the edges in the 2 "parent" icosahedra, on the left:

It should be apparent that, after "stretching," left/right & fore/aft reflection symmetry is maintained.

I've attached the SketchUp model, for your exploration.

-Taff

[Paul Kranz]

My first attempt at the DoggiDome, circa 1982

On Thu, Jan 30, 2014 at 2:26 PM, Andres Roquete <andresr...@gmail.com> wrote:

Hey Paul,

Thanks for the suggestion but Im trying to create a "Turtle shell" and the shape of the doggie dome isn't round enough.

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