(4) 10x10 or (1) 20x20 Tarp?

[Capt. RON]

Normally I run (4) 10x10 Silver tarps on an EMT frame, but I'm mulling over using a single 20x20 to speed up set up time and reduce the number of bungee balls.
How big of a comprise will I be making in terms of wind stability?

[Dr. Dust]

pressure = force/area

The wind pressure is a constant value, so if you multiply area by four, the force absorbed by the larger 20x20 tarp will be about FOUR TIMES greater than the force absorbed by a 10x10 tarp.

One good dust storm will rip your rebar out of the ground if too much force is working against it. Personally, I would go with the 10x10s just for the peace of mind.

[Zhust]

... (4) 10x10 Silver tarps ... a single 20x20 ...

... the force absorbed by the larger 20x20 tarp will be about FOUR TIMES greater than the force absorbed by a 10x10 tarp ...

Umm...

[TomServo]

How about 2x 10'x20' carports? But, if you already have the 10x10's, I'd say use em! What size is the EMT? Have thought about using fence tubing, with the crimped ends, so that one leg is not 7 feet actual, but two smaller pieces. Wish I could find a tool that does that to regular conduit!

[ygmir]

... (4) 10x10 Silver tarps ... a single 20x20 ...

... the force absorbed by the larger 20x20 tarp will be about FOUR TIMES greater than the force absorbed by a 10x10 tarp ...

Umm...

indeed.

that said:
what about leaving some gap between, to allow some pressure through? or I see folks cutting flaps to relieve pressure.

[TomServo]

20x20 is NOT a lot of area. I love how burner's prepare for a moon launch! But, it's the playa..and YES, I have experienced the worst in BM history... just use whatever is most convenient! They both sound just fine!

[shykat]

I have 2 20 x 20 and they work just fine.... Go for it...

[mudpuppy000]

I have 2 20 x 20 and they work just fine.... Go for it...

Any issues with it flapping in the center, or having the crossbars of the EMT frame rubbing holes in it?

[shykat]

I have 2 20 x 20 and they work just fine.... Go for it...

Any issues with it flapping in the center, or having the crossbars of the EMT frame rubbing holes in it?

I get the trap really taught no flapping whats so ever and no holes from rubbing in the 3 years i've used this set up. The only issues i have had is the grommets tearing out (maybe 2 to 4 a year) and having to reenforce them.

I use 1 in. emt and a peaked roof. I cut the sides to 6 1/2 ft and the peak is 8 1/2 feet. I have built it as one 20 x 40 ft shelter and as 2 separate 20 x 20, both with good results.

[some seeing eye]

10x10 or shadecloth. Do the wind load math. Especially with EMT which has poor structural specs - it is not designed for that. And poly tarps are not designed for grommet tear out forces at Gerlach NV wind design code. Then do the risk $ math. Clear choice.

[mudpuppy000]

Good point... Less stress on the grommets and EMT, not to mention the "venting" in the center.

[cullen]

I'd go with the 10x10 simply because they are easier to deal with. Both putting up and in the wind.

[CornMan]

At FurrBall, I used the 20x30 peaked canopy with a single 20x03 silver tarp. It was 90 degrees, but it was really hot under the canopy. I plan on using the double layer of mesh on the peak and 10x10 on the lower sections. That is by far the coolest option I have experienced.

[trilobyte]

I use 20x20 and 20x30 tarps without any issue, though I have a couple people helping with setup. I wouldn't try to attach in really heavy winds, and when you do attach start in the corner where the wind is coming from.

[gibson_]

pressure = force/area

One good dust storm will rip your rebar out of the ground if too much force is working against it. Personally, I would go with the 10x10s just for the peace of mind.

This is wrong. Maybe if you're using 6" of rebar pounded into the ground wrong, but if you have any idea what you're doing, nothing is going to rip your rebar out of the ground. Your guy lines will fail long before that happens.

And if you have designed your structure properly, all this means is that you're going to lose a tarp, not that you're going to have a structure go hurt somebody.

I award you no points, and may god have mercy on your soul.

[gibson_]

I suppose I should explain the right way of doing it instead of just being a dick.


Pound 18" (I actually use two feet, but that's overkill) of rebar into the ground at a 45 degree angle such that any force imparted upon it will be applied perpendicular to the rebar. It shouldn't be trying to pull the rebar out, it should be trying to push it sideways through the ground.

Use 550 paracord.

Don't attach your tarp to your structure, attach it to the ground. This way, if there is a strong wind, it's going to be tossing a few pounds of tarp around, not a few hundred pounds of conduit.

If you *do* attach your tarp to your structure, do it with something that can either be easily taken off (scrammed!), or something that will break with considerably less force than your guy lines. This way, if your guy lines fail, your tarp will rip off of your structure, and your structure won't kill anybody.

Just...plan for things to fail in a predictable way if they fail.

[trilobyte]

Or use no rebar at all - I hate the stuff. My structures can withstand anything the playa can throw at it - I use a mix of hurricane stakes (on the left in the pic below) for the corners and then 10 inch nail spikes (at right) at the footpad of each vertical post.

[gibson_]

Trilo, are those "hurrican stakes" just angle iron? (I can't tell from the photo).

Yeah, angle iron is better than rebar, and ground screws (these: http://www.w8ji.com/images/towers/Guys/screwandbust.jpg) are even better.

But I think grounds screws are probably overkill for anything other than the HUGE stuff.

(By the way, I think I'm going to do an EMT structure just like yours this year. Do you guy down your inner pieces, or just the ones at the edges?)

[trilobyte]

Not really angle iron, there are a few grooves in there.

I'd only use guy lines at the corners. When I did a 20x50 structure a few years back (with a medium peak roof to accomodate a dome in one end) I did guy lines halfway down the length of the structure, but that was both an unusual piece and an unusual year. What I've evolved to doing over the last couple years is to run additional conduit along the ground between the hurricane stakes at the side. I then connect the conduit to the stake with a ball bungee, and then secure the side tarps to the conduit using more ball bungees instead of nail spikes. There's a lot less wear and tear on the side tarps that way, and having tension on the tarps means less flapping in the middle of the night.

[gibson_]

Do you have many pictures of that?

[BBadger]

I don't like bungees for those more rigid structures. Break out some rope and do some proper rigging for those EMT frames. Save the bungees balls for more flimsy structures such as monkey huts where it'll hold the PVC in place.

It's soooo easy. You buy some cheap rope at your department store, then just loop through the grommets to your frame. No need for a bag of dusty, stretched out, expensive bungee balls that need to be double-wrapped to not pop off. No stress points wrecking that single bungee/grommet on your tarp. You get superior load distribution, and it's easy to setup as well as take down and take home.

[trilobyte]

Gibson, I believe there are photos in a shade structure thread elsewhere on the site.

Bbadger, thanks for the laugh. You continue to do it your way for your theme camp and installations, and I'll stick to mine for my stuff. In 9 years I don't think any of the bungees on any of the structures I've built has ever had to be replaced because it got stretched out, and of the tarps tarps that have been replaced, none of them has been because a connection point with a bungee has failed. When I've purchased additional gear, it's because I'm building additional stuff.

[BBadger]

Trilo, I actually wasn't even addressing your post (I had skipped to the bottom after reading a few), but while on the subject I had a different experience: I had bungeed a canopy on a carport and during the week a few of the grommets were stretching the material so much at those bungee points that I had to put some reinforcing tape around the zone to prevent it from coming loose. Later, I had to cut some flaps in the canopy to alleviate the wind load. Now, mind, this was with some silvered canopy I bought thinking that it'd be better than the one that the carport (it wasn't); so I'm guessing that this was more the fault of the cheap tarp than the bungees. Still, the bungees were often quite stretched, usually because the force would get concentrated on a specific grommet rather than causing the other grommets to also feel the force.

The following year I found that rigging guide and tried it out on the carport again -- this time we also used the canopy that came with the carport. Compared to the bungees, the canopy went up very quickly and was easier to fit onto the frame than the bungees because we could tighten the sides together, rather than fight bungees on different sides as they were looped. No problems with stretching or winds either, as the entire rigging redistributes the load "automatically". The placement of the camp, with respect to winds, was probably also a factor as we weren't on a corner of a block like the previous year. Still, I found the running rigging worked better and went up faster than the bungees; I also think it's a superior rigging solution as well. Takedown was also very fast: just untie and yank, or just cut if you're feeling lazy.

To each is own though.

Also, my statement about the bungees being expensive is not correct: they're really not that expensive in bags of 25 for $9.