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Wind Stress on Cuben
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David Olsen
(oware)

Locale: Steptoe Butte
Re: Tested that one yet? on 01/16/2012 10:52:44 MST Print View

Daryl-

Have you pulled on that one yet to see where the failure occurs? I am guessing it will
be at the far end of the middle finger where the stitching ends.

Ron Bell
(mountainlaureldesigns) - F - M

Locale: USA
Re: Wind Stress On Cuben Tie-outs on 01/16/2012 12:28:52 MST Print View

Circling back to Ryan's main question in the OP:

" I'm wondering if any of you have any Field Experience that has resulted in stitching failure on tie-outs of Cuben tarps/shelters resulting from the stitching cutting the Cuben and ripping out in response to wind stress?"

It looks like almost no one has a direct Yes answer. -Not sure that that means...OK- maybe I do-

The one pic Ryan posted looked like a particularly poor design - Just a web loop lightly zig zag stitched to a unreinforced panel with an over size needle- a poor design you would expect to fail. But- I guess you do see it done that way sometimes. - I'm sure he picked that shot as only an example - but maybe there are more folks building cuben shelters that way than I know...I hope not...

I think what would be interesting is to see any Yes answers and then to note the construction design that failed and the conditions.

As a design note - the main things that would affect the strength of a side or middle panel tie-out are:
1: Amount of area reinforcement
2: The stitch technique

Using a few layers of bonded on reinforcements that are large enough - and at least one on each side- and then sew the web loop on with a bar tack, tight zigzag or even a simple box stitch pattern and it would probably be OK. - Reinforcement is the Key.

One note on any light weight shelter side panel tie-out:
They are there as an additional supplementary tie-out point. The main tie-outs ( corners, edges, etc) of the shelters should take the majority of the wind force first. Do not over tighten the side panels to change the shape of the shelter in an effort to add more internal room. If you do that then that one single point will get super-loaded in gusts and even a well designed and constructed tie-out can weaken. Using a short loop of bungee at those type points is also a good idea.

If your trip need is for each and every side panel tie-out to withstand certain and huge wind forces ( winter arctic expedition, etc) , you may need a custom shelter that is built from the 1.4oz or heavier style cuben material.

Edited by mountainlaureldesigns on 01/16/2012 14:10:43 MST.

David Olsen
(oware)

Locale: Steptoe Butte
Another take on sail making on 01/16/2012 13:01:07 MST Print View

Sailfish in the Kinetic Grand Championship.

Note the complex curves needed to reinforce the absurd and whimsical
Kinetic Sculpture 2009 Sailfish.

Ryan Jordan
(ryan) - BPL Staff - MLife

Locale: Greater Yellowstone
More Wind Stress Info on 01/18/2012 17:48:03 MST Print View

I have another goodie, I think I'll just bury it in this thread for now :)

How about knowing the tension forces at shelter stake out points in response to wind loading? Here's a graph of wind loads in a guyline in response to a 1-2 mph breeze for a guyline that was preloaded to 5.6 lb or so.

The x-axis is time from 0 to 8 minutes and the y-axis is guyline tension (lbf) from 5 at the bottom to 8.75 at the top.

guyline forces

Of course we don't care a lot about breezes, or these low forces. We care about real wind, and real tent stress. The graphs get pretty exciting even at 15mph winds on some of these tents.

When we combine this data with video, wind speed and direction, and real-time monitoring (data transfer from the sensors to a laptop), we get a really, really cool holistic picture of what's going on in a shelter in response to winds. Stay tuned for more - a lot more - in 2012 about this.

We're also using these sensors (combination load cell = force + accelerometer data) to evaluate load stability in backpacks and the real effects of trekking poles on reducing impact forces while walking. Gonna be a fun year :)

Edited by ryan on 01/18/2012 17:52:03 MST.

diego dean
(cfionthefly) - M
Re: More Wind Stress Info on 01/18/2012 17:57:28 MST Print View

This is why I will be renewing my membership. Was thinking that I probably wouldn't, but if you guys are willing to get involved with stuff like this, then I want to know all about it!