In 2003 when our cheap shit pop-up shade structure from REI was whirled instantly into a ball of lousy plastic and shards of stabby aluminum, it occurred to us that we needed something slightly better. But where to find such a thing? We sought out help using the intertubes whereby we found a previous burners' experience to swipe from. Alas, I kept lousy notes and do not have this person(s) name or intertube earl.
2007 was the third time we used this thing, and found a nasty problem: the infamous Wednesday afternoon 70 mph windstorm hit the structure at a 45 degree angle, got inside, and lifted the hut off the rebar. We saved it only by hanging onto the top horizontal bar as human dead weight.
In 2008 we solved that, and it hasn't been a problem since. Rather than rope tiedowns at the open ends, we used braided nylon cargo ratchet straps at each end, anchored in one or two rebar with welded washers. Setup consists of pulling those tight enough to make the hut squat slightly. Now the worst-case 45 degree wind causes the hut to squat down, and dump the air. I'm sure there's still an upper limit but we've not it found it yet.
2012 will be it's 8th year; reports are that it's very windy and dusty. The last few years have been surprisingly calm so soon enough we expect another "design test" windstorm. Check back in 2013 to see how this fared!
The thing is made out of a bunch (you count 'em) of 10-foot one-inch white PVC pipe, with one length of 1-1/2" chopped into foot long pieces for use as couplers. There is actual cleverness in the structure. The parts list includes:
For 2011 we had to replace the outer skin tarp; it was starting to moop. Then 2012 it got lost, somehow, and i bought yet another one.
For 2012 the floor tarp was replaced, it mooped in 2011.
In 2012 the PVC pipes show a set curvature (they did after the first year) but all remain supple enough to reuse, still. Except for one which was stored so that sunlight got on one end, and that end cracked when I dragged it out. I then tested the others by whacking them with a rebar. No others cracked.
The pictures tell the story. (Or if it doesn't, tough luck, that's all you get.) Here's the high points, if they aren't obvious from the photos.
The rebar locates the hoops, and does a fair, but not adequate, job of holding the structure down to the earth. Anywhere but the playa they would be more than enough!
The slip couplers hold absolutely, and have never moved around. There's no need for pins, through-bolts, etc. Friction is sufficient, yes, even on the playa. In fact, the major reason for failure in PVC structures are weak points caused by stress at drilled holes and metal pins! With the slip couplers, stress is distributed evenly over much area.
The bicycle inner tube rubber bands are a major structural design point; they tighten under stress and distribute load, and allow the structure to flex such that load is distributed over the skin, the hoops and other rubber bands. (Rigid bolts and pins concentrate force on a small area.)
It is an important optimization that the rebar that the hoops fit over pass through grommets in the floor tarp. This does two things; one, it holds the floor tarp down, and two, it makes the hoops be in a perfectly rectangular shape and spacing with no measurement or other effort. it does mean you have to use thin rebar, but that's easy. Note that the photos below were taken in different years, and someof the older photos show the rebar not in the floor tarp grommets.
We've found that simple spring clamps are the ideal way to affix the outer skin to the hoop frame. The 18-foot wide outer skin is too wide for the hoop structure; but just wrap it in and affix with the spring clamps. This are also a major source of fail-safe; a severe wind can pull the skin out from under the clamp, which immediately relieves wind load. Usually only a couple in one corner come out and that corner flaps until you reclamp it. The redundancy of the other clamps keeps the rest of the skin in place.
