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Calculations for Tent Poles
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 Liam de la Bedoyere (liambedoyere) - F Calculations for Tent Poles on 03/07/2012 11:06:00 MST Hi everyoneMy name is Liam and I am designing a small 2 man tent for a project but I need to show some math calculations showing how much stress and strain there is on my tent poles. I assume that it depends on the length and the angles that they are at but if anyone has some suggestions or accurate equations that you think would help me I would be very much appreciative.Liam
 Ben H. (bzhayes) - F Locale: So. California How mathimatical are you? on 03/07/2012 15:44:54 MST I haven't looked at this stuff since I was an undergrad, but this is the beam equation:Most undergrad textbooks assume small deflections so the bottom right side of the equation is neglected. Unfortunately, a tent pole does not undergo small deflections, so most standard solutions can't be used. Hopefully someone else around here has more experience and can give you a better answer. If you don't get a better answer and the above equation does not scare you too much, then let me know and we can try to move forward.
 Kevin Beeden (captain_paranoia) - F Locale: UK stressed membrane on 03/08/2012 11:49:12 MST > Unfortunately, a tent pole does not undergo small deflections, so most standard solutions can't be used.Not only that, but it's supporting a stressed membrane (assuming it's a flexi-pole, geodesic tent), which adds to the problem of trying to identify the bent pole shape and loading.Having figured out that I couldn't figure out what the pole shape ought to be, I gave up analytical methods of designing tent panels, and went empirical...If the OP figures out the maths, please post a thread on it; it would be very welcome...
 Ben H. (bzhayes) - F Locale: So. California Thought about this some more... on 03/08/2012 14:40:15 MST I thought about this some more. I was spending a lot of time thinking about boundary conditions that should be used to solve the equation. Then it struck me, most tents have a series of clips or sleeves that constrain the pole to a design shape. What force is applied? It is exactly the correct force to get the designed shape. The force isn't your known quantity, but... shape is! Now look at the equation I posted... it is also in terms of shape. If you have a graphical representation of the shape of you tent pole, you can numerically differentiate, plug it into the above equation, and solve for the applied moment. OP, let me know if this makes any sense to you or you need additional help.
 Kevin Beeden (captain_paranoia) - F Locale: UK boundary conditions on 03/09/2012 07:41:32 MST > I was spending a lot of time thinking about boundary conditions that should be used to solve the equation. Then it struck me, most tents have a series of clips or sleeves that constrain the pole to a design shape.Yes, that was the way I'd thought of attacking a numerical solution to tent design, using some form of simulated annealing of a fabric mesh, based on the boundary conditions (be they a set of fixed pole anchor points, pole lengths, and fabric stresses (including catenary edges for the panels)). I'd got to the point of thinking about modelling a fabric as a mesh of cells, each comprised of four rigid, fixed length elements (representing the warp and weft fibres) joined flexibly at the corners, with springs across the corners (representing the bias movement of the fabric). Then I got distracted by something shiny...
 Daryl and Daryl (lyrad1) - MLife Locale: Pacific Northwest, USA, Earth Then I got distracted by something shiny on 03/09/2012 09:00:35 MST "Then I got distracted by something shiny"I finally found part of this discussion that I could understand.
 Ben H. (bzhayes) - F Locale: So. California Re: Thought about this some more... on 03/14/2012 16:55:03 MDT Ok, this is what happens when you ask a nerd a question. I made a little write-up on how to calculate maximum stress on a tent pole. A note about engineering analysis. I am a mechanical engineer but I am not a structural engineer. I am confident in this analysis but I do not have the back ground to suggest what kind of safety factors need to be applied for design purposes. This only calculates the static load (i.e. with the tent set-up in you garage). In actual use (wind load, bending the poles to set-up the tent, or falling on your tent in the middle of the night after a pee run) can significantly increase the load a tent pole will see. Let me know if you have any questions.
 Peter Nielsen (alpineclimber247) - F Locale: Pacific NorthWest You would be surprised. on 03/15/2012 15:08:00 MDT I have a buddy that use to work for cascade designs and we were just talking about tent design the other day. I was very surprised to find out that there is very little design calculations done on tents. most of the design is based on experience of what works and testing.
 Jennifer D (jenniferd) - F Calculations for Tent Poles on 03/26/2012 08:55:06 MDT I'm working on a similar project but need to figure out if my structure will fail under different load conditions. My tent is a hexagonal dome consisting of 3 semi-circular aluminum rods. The loading conditions i'm considering are: a uniform snow load, a non-uniform wind/snow load, and a wind only load. If anyone has any suggestions on how to do this analysis with hand calculations it would be very much appreciated! I should state that a major assumption is that the frame will support the loading and as a preliminary assessment, I can neglect support from the fabric.Thanks in advance,Jennifer
 David Drake (DavidDrake) - F Locale: North Idaho Re: Calculations for Tent Poles on 03/26/2012 10:25:47 MDT Both the OP and the last poster might want to look at this:http://www.backpackinglight.com/cgi-bin/backpackinglight/storm_resistance_ultralight_shelters_part_1_intro.htmlGood stuff for background, and I believe is available to non-members.Edit: Checked again, and it is subscription-only. However, there are extensive forum comments on the article they are available without subscription. Edited by DavidDrake on 03/26/2012 10:32:38 MDT.
 Ben H. (bzhayes) - F Locale: So. California Re: Calculations for Tent Poles on 03/26/2012 10:40:20 MDT Jennifer, I don't mean to be nosy, but what is your background? Did you understand the analysis I presented and could you perform it? I can try to help you but I need to know where you are at.
 Tim Zen (asdzxc57) - F Locale: MI Re: Re: Calculations for Tent Poles on 03/26/2012 13:22:13 MDT Don't forget buckling. Ignore the finite deflection as it just changes the loading which you are estimating. Can you analyze something simple like a flat tarp on two poles?
 Jennifer D (jenniferd) - F Calculations for Tent Poles on 03/26/2012 22:48:22 MDT Ben, I'm a materials engineering student so structural engineering is not my expertise. However, I think I did make sense of the method you presented. I divided one arched rod into 16 points and used the equations you presented to determine the bending stresses at each joint as a result of it taking the shape I defined. In my case, I'm using semi-circular rods so the equation was SQRT(r2 - (x-r)2). Since the resulting maximum stress value (which occurred at the apex of the arch) is less than the maximum tensile stress of aluminum i've concluded that the rod can take the shape of the arch and will not fail due to bending. In reality, the rods are 16 individual segments press-fit together, however i'm pretty sure in the above analysis I consider the arch to be one uniform rod. If I design each rod to be slightly pre-bent, this further alleviates the stresses.I'm not sure how to determine whether the entire frame (3 crossing arches) will fail under each loading condition I mentioned. I don't have access/knowledge to FEA software, so i'm trying to come up with a valid way of assessing the structure using hand calculations. I've been looking for calculations for arches and think these would qualify as two pinned (two hinged) which are indeterminate. This further complicates my analysis.Hope you could lead me in the right direction.Thanks for your response!Jennifer