Wind loading on a big box shade structure - ideas

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CptSparkles
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Wind loading on a big box shade structure - ideas

Post by CptSparkles » Tue Jan 07, 2014 3:55 pm

Good day all,

I'm slowly prepping for 2014, just getting my thoughts in line while I wait for tickets. Last year, I went with a group of friends and we (they) had a 20x20 daytime shade structure that could be fully enclosed with some nicely stitched cloth for when there was a dust storm (hexayurts hiding behind in the picture unseen). Here's a pic:

Image

Basically, during the day, we kept it open, and it provided nice shade. In the evening, we could close it up for privacy, or if it got really dusty, we could 'batton down the hatches' and really keep the dust down. Next time, I'd like to do something similar, but smaller, and bluntly, more wind-hardy. We didn't really get any big windstorms in 2013 (unless you came early) as I understand it, and neither did 2012. Maybe next year? Time to plan!

The structure had feet, and each foot had a rebar stake in it as I've seen done for some EMT structures. I'm afraid, however, that in 70mph winds and the thing would have collapsed or flown. 2x4's and 4'x4' sailing down the 8 o'clock avenue would have been bad. And so too, would be my idea, as I want to make a 10'x10' version, but put plywood on the top. Can you imagine that going for a sail? Yeah, lets not. Also, right next to the structure in the picture above, you can see Cpt Sparkles Fortress of Solitude... it's a 4'x'4'x8' box, fully insulated (1.5" Rmax), with 2x2 framing and a door, figjam evap cooler. Very sturdy, and it's low enough to the ground that it wasn't going to go anywhere (being next to a truck would help too).

So, here's my idea: For 2 people, a 10'x10' shade structure, 8-10' tall, plywood on the top, 2'x2' opening for a ladder, some simple railings, etc, and there's a penut gallery on top. I want the shower up top also because then it's easy to run the water right back into a greywater barrel (Not for exhibtion purposes, but so as to not have to mess with an evap system, ugh that was gross...) Shower would probably take up ~3'x3' or so. I would *love* to have the 'downstairs' fully enclosed, openable for air, sealable for keeping the dust down (worst case though, the FOS/box can be a retreat point), and enclosing on the sides also provides some vital sideways shade. I can park my truck under one corner and use the truck as an anchor too... cut one leg short so it's in the middle of the truck bed... The Fortress of solitude would go under the shade structure. I consider this vital so that I can sleep in. The FOS stayed nice and cool as long as it got some shade.

Around the edges I have considered: silver tarp; silver tarp with U pieces cut to allow airflow*; shade netting (dust reduction?) ; Just leaving it open (no side shade, dust) ; Angled walls (larger footprint, trying to be nice and not take up TOO much realestate) ; Cloth like what the group used last year ; angle the sides, reduce the top to 8'x8' or smaller?

So. Thoughts? What am I missing? What kind of wind loads should I expect to be able to handle(and am I right in assuming the previous structure could have easily become a sail?) If I fully enclose it with silver tarp, can I expect to reasonably secure it, be able to unsecure it for air, and have it and the structure secure enough so that the whole thing doesn't become flying death travelling down the road at 70+mph?

Thanks!

*I haven't seen any good tutorials on cutting (silver) tarp so it doesn't rip, just some vague descriptions.
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Canoe
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Re: Wind loading on a big box shade structure - ideas

Post by Canoe » Tue Jan 07, 2014 10:27 pm

Most successful playa structures tend to have features that allow the wind to flow around or through them, so the load from wind pressure is minimized. If you're wanting to seal up against dust: first, good luck; secondly, it will need to provide flow over/around it and/or be very very strong. Having some flex makes some structures survive.
Take a long look at what has been proven to work on the playa. There's tons of threads to read. Search.

As to wind loads:
Canoe wrote:
GreyCoyote wrote:Easy design point: 70 mph winds sustained for 5 mins, and 50 mph winds for hours. These are straight-line winds with a lift overall hitting at any point on the compass. The occasional macrocell with 80 mph down bursts. Vortex winds with center velocity of 90+ mph.
But note that surrounding structures can result in higher wind pressure on your structure than you would expect from a given wind speed. As in, a simple 75 mph wind on a 160 sq.ft. profile can range from a simple 2,250 lbs. to a 4,500 lbs. load.
For a simple ballpark number, a 75 mph wind can provide from ~14 lbs to ~28 lbs per square foot. So for a 4' x 8' sheet of plywood, that's from ~450 lbs to ~900 lbs.
A ten foot long sail, eight feet high, for 80 square feet, can catch ~1,120 lbs to ~2,240 lbs from 75 mph winds.

Happy thread reading!
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CptSparkles
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Re: Wind loading on a big box shade structure - ideas

Post by CptSparkles » Tue Jan 07, 2014 10:49 pm

Holy crap thats a lot... though I shouldn't be too surprised I suppose. I've been going through threads, haven't found what I'm looking for yet though... but that gives me a good rough idea of the wind loading. I'm more and more thinking of a 12' x 12' base, 8' high, and an 8' x 8' top area, more than enough area as a penut gallery.

I should also state, though, that keeping the dust 'out' is relative. This last year when we closed down the flaps when the wind picked up and had a good dust cloud coming our way, it really did a lot to keep the dust down, and made it quite comfortable inside. I could never really take pictures inside the structure at night, as there were always latent dust particles causing backscatter. Shade cloth, I would assume, would do *zero* to keep the dust down, not even act as a 1% filter.

If there's a good thread somewhere on cutting U-shaped slots in a tarp and reinforcing them so they don't rip under high winds, I'm all ears. Haven't found it yet in all my reading over the last month. I saw shade structures this year where people use silver tarps for shade, but they have regular U patterns cut in... I haven't been able to find anything here or with google about the best way to cut them so they don't rip...
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Re: Wind loading on a big box shade structure - ideas

Post by A-RockLeFrench » Wed Jan 08, 2014 9:26 am

I'd think that gorilla tape would work well for reinforcing cut tarps. One idea is a heated stencil cutting tool, similar to a wood burner, a small heated metal point for melting through plastics would melt through a tarp possibly sealing the plastic threads together so they don't fray.

https://www.google.com/shopping/product ... MMBEKYrMAM

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Canoe
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Re: Wind loading on a big box shade structure - ideas

Post by Canoe » Wed Jan 08, 2014 10:27 am

A-RockLeFrench wrote:I'd think that gorilla tape would work well for reinforcing cut tarps.
Some people have good luck with Gorilla Tape, others don't (be it a tape strength failure or the adhesion lets go in the heat, or perhaps the surface was too dusty or greasy - fingerprints, or the release agent on a foam board). Gorilla Tape will not publish their product testing data. The little bits that have leaked out make the tape appear to be good. Some reports have Gorilla Tape coming out around 48 lbs compared to the 220 lbs Bi-Filament tape strength, which is actually quite good (on par with Pro-Gaff 48 lbs, better than 3M 8979N duct tape at 36 lbs), and some reports believe the adhesive strength is on par with that bi-filament, but others claim it's around half that adhesion. But we don't know if those Gorilla Tape numbers are true or not. Without Gorilla publishing product data, and their testing method, ... who really knows.

With good on-playa reports and bad on-playa reports, Gorilla Tape has to fall into YRMV.

If Gorilla Tape is as good as the scarce reports suggest, then:
3" wide tape:
  • a good regular duct tape breaks around 108 lbs,
  • Gorilla Tape (and ProGraff 48) breaks at 144 lbs,
  • 220 Bi-filament breaks at 660 lbs.
4" wide tape:
  • a good regular duct tape breaks around 144 lbs,
  • Gorilla Tape (and ProGraff 48) breaks at 192 lbs,
  • 220 Bi-filament breaks at 880 lbs.
The 6" wide 220 Bi-filament tape breaks at 1,320 lbs.

Here's what one of the most popular hexayurt bi-filament tapes (220 lbs) can do
viewtopic.php?f=277&t=65276p955761#p955761

Image
Video games are giving kids unrealistic expectations on how many swords they can carry.
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CptSparkles
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Re: Wind loading on a big box shade structure - ideas

Post by CptSparkles » Wed Jan 08, 2014 6:58 pm

It sounds like maybe some earth augers are in order. Best results I've seen so far seem to be pre-drilling a 1/2 inch hole to give the auger room to dig down into the hardpack that's 4-10" below the surface, and can hold craploads of weight. 4 of those in, plus bolts for the side tarps at an angle maybe...

ideas ideas ideas ideas crap I haven't gotten any work done today.... :P
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garyt
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Re: Wind loading on a big box shade structure - ideas

Post by garyt » Thu May 08, 2014 2:34 am

Cpt Sparkles, I can't see the picture you posted. If I understand your description correctly, I'm inclined to build something similar but with cardboard boxes all around and on top instead. Could you re-share picture or PM to me? I am worried about the wind as well since its a cube. I was thinking of keeping it at 7' high and have a 8' emt shade structure over it with camo netting all round to cut wind/light.

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CptSparkles
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Re: Wind loading on a big box shade structure - ideas

Post by CptSparkles » Fri May 16, 2014 8:05 am

Sorry, looks like I deleted the picture when I was cleaning up a webserver. I put it back up. The picture itself isn't very descriptive. The entire idea for mine was to use plywood so that you could sit on top of it and have a peanut gallery.

Due to cost and transportation reasons though, I'm probably going to go with a monkeyhut overhead instead, the shade structure the camp is doing this year is going to be pretty damned cool, and we're going to re-use part of the old one for the kitchen.
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Re: Wind loading on a big box shade structure - ideas

Post by mdmf007 » Wed May 21, 2014 7:13 pm

heres a handy sail area calculator

http://www.sailingcourse.com/keelboat/r ... d_load.htm

1 square foot at 75kt = 24 lbs per square foot sail force.
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