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Elliott Wolin
(ewolin) - MLife

Locale: Hampton Roads, Virginia
Pyramid tent poles - buckling, stresses, shock absorbtion on 03/10/2011 11:10:29 MST Print View

I am building an 11' square pyramid tent and am going around in circles concerning designing the pole (nominally 90", but maybe as long as 102" to raise the pyramid for extra ventilation), probably since I've never used a pyramid tent before. Engineers or pyramid tent owners, please advise:

At first I thought that avoiding buckling was the main concern. Thus simply choosing a pole with the most material (aluminum) at the largest radius (actually one with the largest moment of inertia) would be best (for a given pole weight, of course).

Then I decided that buckling not only was not a primary concern, but that buckling was actually desirable. Under wind load the upwind tent wall would tend to flatten. If the pole buckled a bit it would allow the tent to spill wind more effectively, and would act as a shock absorber for sudden gusts, springing back when the wind load lessened. If it didn't buckle and bend a little the increased stresses in the wall fabric might lead to fabric failure. Now pole tensile strength becomes paramount. Also, smaller moments of inertia would allow the pole to bend more and be a better spring, but allowing too much bending might cause the pole to snap.

Finally I considered intermediate guys or stays. Adding guys to the center of the pole will stiffen it dramatically, but might increase fabric stresses under wind load. Maybe loose guys are the answer, rigged in such a was as to only take effect when the center of the pole bends beyond a certain amount, limiting the bend to that amount.

(I won't describe my forays into alternate materials, fiberglass and carbon fiber...)

The above is a clear case of over-analysis leading to analysis-paralysis!

Please advise on how to choose an aluminum center pole (carbon is probably way too expensive for me) that is both lightweight and able best handle wind loads and gusts.

Edited by ewolin on 03/10/2011 14:31:11 MST.

jerry adams
(retiredjerry) - MLife

Locale: Oregon and Washington
re on 03/10/2011 11:44:25 MST Print View

I have 9' square pyramid, 62" pole - .625 Easton Aluminum

I have always thought the pole was way overkill - thinking about switching to .490

.625 might work for your bigger tent - polesforyou.com

You could try it and see what happened

Like you said, when you push down on the pole, it tends to bow out in the middle and would break at some point. In my case the pole doesn't bow significantly but I think it would bow a lot before breaking.

Your tent may be stable enough with little more than 4 corner stakes. If you can set it up in the yard and wait for a windstorm you could see how it worked.

j lan
(justaddfuel) - F

Locale: MN
Re: Pyramid tent poles - buckling, stresses, shock absorbtion on 03/10/2011 11:45:11 MST Print View

I own an oware pyramid, 10x10 and use my trekking poles strapped together, i know many others here use the same. They flex some especially where they are overlapped, but as you found that is desirable, correct?

I also use the shaft from my kayak paddle or a stick, but my favorite is to tie off the top to an overhanging limb from the outside, so much space! Sometimes i will even run a line from tree to tree, then run a line over that. You will probably get some buckling in the wind, but that's why most pyramids have side tie outs as well.

Good luck!

Paul McLaughlin
(paul) - MLife
Re: Pyramid tent poles - buckling, stresses, shock absorbtion on 03/11/2011 21:57:39 MST Print View

I suspect that if you use a pole with enough flexibility to give a little, it will give so much that you'll have trouble getting a really tight pitch - and a tight pitch is key, in my experience. I have had a pole fail due to buckling under heavy wind load (one humongous gust on Shasta). That was my original Chouinard pole, and they replaced it under warranty. No problems with the fabric in that event, and I doubt you'd reach the point where fabric failure would be an issue unless you have something besides tent stakes to anchor to, as the load on the stakes gets pretty high
Just getting a tight pitch imposes a lot of load on the pole, and the only arrangement I can imagine that would have enough strength for that and yet still have some give would be if you used several smaller diameter poles together - but that would end up heavier than a single pole of larger diameter.
Ofcourse, if you use trekking poles and a coupling arrangement of some sort, and if the trekking poles have shock absorption, then that might work - although my tent instincts tell me that a rigid pole is going to be better.
One key thing is adjustablity. Unless you can adjust the length of the pole it is very hard to get a tight pitch, since the fabric stretch and the unevenness of the ground mean that you effectively need a slightly different length pole every time you set it up. My current pole adjusts in increments of about 3 1/2", and I find that is too much. Smaller increments, or infinite adjustability, is better. I also have an MSR Twin Peaks (kind of a double pyramid) and I use my flicklock poles with that, and the fine adjustment allows me to get a really nice tight pitch, and to tighten it once it stretches.

Ultra Magnus
(Ultra_Magnus) - F
Re: Pyramid tent poles - buckling, stresses, shock absorbtion on 03/18/2011 15:07:50 MDT Print View

Hello there- First post here...

I'm interested in your project because I've had the idea to built pretty much the same thing, an 11' square 'mid tent, with a sewn in 10' square bathtub floor. That should leave a comfortable 8' square sleeping area with halfway decent sitting room, with an approximate 1' perimeter for gear storage. I had envisioned attaching the bathtub floor to the test walls with about 12" of noseeum netting. I haven't figured out the door details yet- I don't want a 18" threshold to step into my tent, especially since I would be using it with children who would be tripping over it all the time. My plans (tentative) only call for a 78 - 84" pole, adjustable for venting/weather conditions, so buckling never really crossed my mind. I haven't decided if I'm going to go with a dedicated pole or trekking poles yet.

Storm proofing the door, I think, would be the next big challenge...

If you've made any progress, please post pics. I'd be very interested in seeing your work.

BM

Edited by Ultra_Magnus on 03/18/2011 16:09:56 MDT.