yurtini, starshade, noah’s tarp and other simple geometries

[scmodstyle]

I drive a honda civic so I'm in the process of designing a shade structure where every piece must be under 5 ft in length. My first design had been this horrible cornucopia looking thing which became narrow and extremely low the farther back you get. The main design element are two 13 ft tall diamond shaped towers which I've completed the rough carpentry on already. So whatever the final shade structure design is, it's probably going to use the diamond towers.

22.png

Then I stumbled across the "noah's tarp" geometry which a quick sketchup study revealed would provide far more headspace and work well with my existing towers. Ideally if I went with a noah's tarp concept I'd like to find a way to add walls on two sides. Any ideas on how to do that? I may just have to build the thing and then figure out how to add a few walls once I'm staring at it in my back yard LOL.

11.png

Another geometry I think the tower might work for is a starshade or yurtini. One of my diamond towers could easily act as the central pole. Here's the yurtini

Yurtini-1.jpg

Today was the first time I heard of the yurtini which utilizes a novel concept of adding a compression ring to the roof which creates more usable head space than a traditional starshade. As far as I can tell only Mountain Hard Wear sells anything like this so it wouldn't surprise me if they have a patent on the compression ring concept. Erection instructions are posted online but the vagueness surpasses even Ikea http://demandware.edgesuite.net/aacw_pr ... urtini.pdf

Does anyone have experience with this concept or does it go by any other names?

-Dan

[delle]

Dang. There's a whole great thread around here on how to add a ring to a Northpole Shade.... Someplace.

Makes it much like your second design and its really easy and cheap.

Fuck me if I know where we left it tho......

[GreyCoyote]

They are pretty, but I worry (a lot) about wind. Thoughts?

[scmodstyle]

They are pretty, but I worry (a lot) about wind. Thoughts?

The cornucopia does look a bit like a giant wind scoop or funnel if pointed in the wrong direction, I think that's one of multiple reasons I'm revisiting the design. If a case can be made that the other designs are unsound I'd love to hear it.

The Noah's tarp design is structurally sound because every member is working in either perfect compression or tension. The diamond towers are composed entirely of triangles which is the most fundamentally strong shape - as my structural engineering teachers told me, if your frame design can be reduced to a series of triangles then it's probably sound.

Tie-downs I use are the ratcheting kind used in trucks rated at 700lbs and stakes are 18" long.

What DOES worry me is monkey huts that rely on bending a non-structural material (PVC) that's not designed to be bent and subjecting it to UV light which causes PVC to break down. Or pop up car shade canopies that aren't braced-frames but rather act like moment-frames. It's those designs that will bend-flex-break in the wind that concern me. A design where every member is already in compression/tension and won't wiggle doesn't worry me.

[Dr. Pyro]

This is why I stay in an RV.

[lucky420]

ohhh so that's the reason Doc!

[Elliot]

Dang. There's a whole great thread around here on how to add a ring to a Northpole Shade.... Someplace.

Makes it much like your second design and its really easy and cheap.

Fuck me if I know where we left it tho......

Try Copilot602's post on this page:

viewtopic.php?f=277&t=33810&start=60

[Eric]

What DOES worry me is monkey huts that rely on bending a non-structural material (PVC) that's not designed to be bent and subjecting it to UV light which causes PVC to break down. Or pop up car shade canopies that aren't braced-frames but rather act like moment-frames. It's those designs that will bend-flex-break in the wind that concern me. A design where every member is already in compression/tension and won't wiggle doesn't worry me.

Yes, but those monkey huts have been playa tested for years (they were already common when I started attending in '03), have (mostly) held up under the worst weather the playa can throw at them, and have become a staple structure at Burning Man for a reason. They work. Period.

All the engineering that looks so good & makes so much sense on a computer still has to get tested under real conditions, and I'd rather trust a structure that has been proven to work than a structure designed by a person who has only been once, and in a fairly mild year at that (once the Gate opened). That's not a personal slam, your idea might work brilliantly, it's just that it's unproven.

[scmodstyle]

your idea might work brilliantly, it's just that it's unproven.

I suppose that's part of what I like, coming up with ideas at home and then taking them out and see how they work. Course that tune could change if in '14 the roof blows away and a tower falls over landing on my car windshield

BTW huge thanks Elliot for tracking down the thread on compression rings.

[GreyCoyote]

Schmodstyle: The problem I have with your triangles is they do not attempt to approach an equilateral triangle. The equilateral is the holy grail of load-spreading designs. Cough-up a few of these puppies, assemble them properly, and you've got a hell of a strong design with minimal material. An equilateral triangle is a fooking anvil. But yours are a very asymmetric (isosceles) triangle, unbraced in the ordinary limb, which is the weakest of all triangles. Lots of unrestrained deformation possible in those, so I worry for it. (Put it this way, I wouldn't want to be downwind of any of these designs in a 70 mph dust storm).

Please note this isn't a personal slam, just a review of the whole concept of Triangulation 101. And if your stuff works, well, more power to ya! I just don't want to see you all bright-eyed and bushy-tailed putting this stuff up only to get hit in the crotch with a dose of Playa Reality. That would really suck.

Understand that things BREAK on the playa. Relationships. Plans. Structures. Schedules. You name it, the playa kicks its ass and laughs at our attempts to "beat it". It's just part of the game. And of course the engineering literature is replete with lots of examples of not-so-efficient triangles that *should* have worked, but failed spectacularly when Reality came knocking.

Personally, I'd CAD that sucker up and see what it does under real-world loads. Not the usual single, static, unitary loads, but those dynamic and combinatorial loads with a healthy twisting/torsional moment you could expect to see in a playa-sized blow. See where it deforms, where and when it fails, and then make your choice based on that.

If your triangular supports pass muster, definitely post about it. There are other folks treading the same waters you are (small car/limited space) who would appreciate the benefit of your insights, and may be able to replicate your structure to good ends.

[Elliot]

That kind of search does not need to take much time. I simply used Google and typed in "ePlaya Northpole ring". The top answer showed four or five similar threads, and the third one was it.

[theCryptofishist]

Schmodstyle: The problem I have with your triangles is they do not attempt to approach an equilateral triangle. The equilateral is the holy grail of load-spreading designs. Cough-up a few of these puppies, assemble them properly, and you've got a hell of a strong design with minimal material. An equilateral triangle is a fooking anvil. But yours are a very asymmetric (isosceles) triangle, unbraced in the ordinary limb, which is the weakest of all triangles. Lots of unrestrained deformation possible in those, so I worry for it.

This is a job for Needlessly Pedantic Fish!
I think you might mean scalene (oh, what a fishy word!) triangle. I'd say that isosceles triangles are reasonable symmetric...

[GreyCoyote]

Fishy, dahling:
The diagram of his pole supports are not composed of scalene triangles. The components are isosceles. To wit:

• Equilateral = 3 equal length sides

• Isosceles = 2 equal length sides

• Scalene = no equal length sides.

FWIW, a symmetrical triangle in engineering parlance is one where all sides are the same length (ie, symmetric), and form an equilateral triangle. When extended from 2D space into 3D space it's a tetrahedron, the simplest of the Platonic solids. And when extended into 4D space, we call it a "bad headache".

So, neener-neener-neener! I'm more pedantic than you are! (Insert raspberry with wiggling moose-antlers here. hehehe).

Oh my god, I sound like BBadger with all those italics!

[scmodstyle]

You guys rock for giving me things to consider. I'm also thinking about a little something like this, it would be much harder for the wind to get up underneath on first glance AND give me those walls I'd kinda like. http://blog.naver.com/PostView.nhn?blog ... 0174193449

MSR_Pavilion_tarp_tent_12-16_p.shelter,moss_dana_design,parawing_outfitter_wing2.jpg

[cosmic-honey]

The playa-tested monkey hut can be made using 5ft long pieces connected with 1-2ft long pieces of PVC. That's what we're planning on using (we are short on car space, too).

[theCryptofishist]

Ah, I'm more of a biologist. Bilateral is totally symmetry to me.

Or those damn ink blots.

[trilobyte]

For what it's worth...your concern about the impact of UV on the plastic for a monkey hut is completely valid if you're using parts that have seen several years' use on the playa. So long as you're not using old and weathered materials, any hut you build should perform on a similar level to the thousands of others that have worked successfully in the past. The main downside I'd see out of the cool structure in your last post is that the angled sides kind of limit the amount of walking around space you'd have underneath. You could use the shorter end of the sides for storage or something, so it's not like the space would be completely wasted...it's just something to consider.

[TT120]

If that last structure was open at both ends, it would probably work ok. If not, it would become an oven fit for baking cookies, lots of cookies, by about 9:00am.

It's cool to try different designs to see if they work in the desert but it would be smart to have some kind of backup shade plan if the original idea fails.

[GreyCoyote]

Schmodstyle: Just for grins, I dusted-off a program I used to play with and did a quick-and-dirty run of your triangle-pillar-module-thingies. A few thoughts, in no particular order.

1). The weak point in the design is the splice-type couplers located at shoulder height. These are kind of a nightmare.
2). Any twisting axially causes deformation and rapid failure.
3). The very top piece triangles (at least the way I defined it) does nothing structural.

Suggestions:
1). That flat, triangular spacer/brace (colored red in your diagram) you put in at the top to connect the three struts should be duplicated again at the couplers located at shoulder height. This single change dramatically stabilized the entire thing in all dimensions and loading configurations. The structure became much more resistant to buckling, especially when presented with a cantilever-type load from the top.

2). Switch your "splice-type" couplers to metal collars (ie, use a 12-inch section of fence-post tubing, EMT, or similar). This gives support all around the outside of the members. I would turn the ends of your struts down a bit so they are cylindrical in cross-section and are a slip-fit into the couplers. A couple of small carriage bolts will keep them securely in place. I didn't model this, but it's clear they'd be a step-up from strap-type connectors, and are likely to be faster to assemble on-playa.

3). Run a cable from the very top apex, through the middle spacers, to the bottom apex. Put a turnbuckle in-line. After you assemble and raise everything, tighten this down a bit. NOT a lot. Compressively loading the structure will help to stiffen it up. This would also makes the very top a semi-structural component.

4). Connect the tops of each triangle-pillar-module-thingie together with a cable. This lets each pillar share toppling loads with its neighbor. Makes a bitchin' place to hang a banner too.

5). Don't load these pillars from the edges (ie, don't attach your fabric to the uprights or to the edges of the red spacer plates). Instead, run a cable from the center of your red plate. The reason is this structure hates twisting loads. If you pull on it from the edges, it will twist. Bit of you pull from the center, it wont twist at all, and the resulting stresses will be more evenly shared by all three vertical members.

So, for whatever it's worth, there ya go. Keep in mind I didn't have the time or the inclination to do a really workman-like job, so YMMV. But at least it gives you something to noodle on. Perhaps others will chime-in with additional suggestions.

I really like the idea of you trying to make something big, elegant and bulletproof, yet still fits in a Honda.

[Captain Goddammit]

This is why I stay in an RV.

I dunno about you guys but I'm gonna keep doing what the doctor says.

[mosquito]

FWIW, I wanna hear how this has progressed and how it performs! )