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4' fiberglass military surplus masts- wind load?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC8PJS, Dec 3, 2009.

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  1. KC8PJS

    KC8PJS Ham Member

    It has come to my attention that in order to erect antenna supports around my city lot I must submit a City building permit. The permit is only to prove that the structure I erect will be able to withstand the "typical" maximum wind for the region. This is a safety issue, so the supports don't fall and hurt someone. The building department is not requiring approval to install an antenna in general.
    So, I would like to use the 4' sections of military fiberglass mast. They are 1-7/8" outer diameter with a wall thickness of 0.110", and do have the stiffening rings. The catch is, I cannot find any sort of recommended stacking height or wind load specifications. Does anybody have this sort of information, or know where to find it?
    I would like to stack 5-6 sections tall to hold a single 18AWG wire loop (80 meters). The bottom section would be slid over a 6' t-post sunk into the ground. The mast will also be attached to the top of my 4x4" (4') fence post with angle iron, and steel muffler clamps. This will place 4-5 sections above the fence. While I don't plan to guy it, the loop wire itself will help the top of the mast from whipping about.
    Any help in calculating wind load and such would be greatly appreciated!! 73's
     
  2. KB9MZ

    KB9MZ Ham Member

    No problem at all. The aluminum poles fit inside the fibre glass poles also so you could go half and half so you have fibre glass where the loop is positioned
     
  3. AE5JU

    AE5JU Ham Member

    You can buy guy rings for the fiberglass poles.

    Rather that fit them together on the ground and try to raise the assembled mast, I would suggest you get some help, and put it together vertically. As you lift the mast, another person fits a section into the bottom.

    I don't go more than 5 up.

    There are aluminum mast pieces the same size, and will interchange with the fiberglass.

    Check this out, the new club Field Day antenna I just finished last month. 75, 40, 20 meters, and 17 and 15 with a tuner.

    The guys ARE the antenna.

    [​IMG]


    Stacking height: The poles are 48" long, but the plug end is 4", so you actually get 44" per section.

    I would suggest using the aluminum pieces for the lower half, at least, and just 1 or 2 fiberglass sections at the top.

    The plastic rings about the socket end break off. Put a radiator hose clamp on the end and that will help prevent the end from cracking.
     
    Last edited: Dec 4, 2009
  4. K4TBX

    K4TBX Ham Member

    nobody read the op ????
     
  5. K4PP

    K4PP Ham Member

  6. K4SAV

    K4SAV Ham Member

    Are you sure you need a permit to put up a pole? I wonder what they are going to inspect. Most permits require supporting documentation, either manufacturers data or engineering stamped data. I hope you don't need that. I thought I read somewhere that those fiberglass masts were originally intended for use as tent supports. If that is the case, it is not likely there will be data to support its use as an antenna mast, and you sure don't want to pay an engineer to generate it.

    Most structures also have set-back requirements. Where is you fence located? If you use a fence pole as a support they will probably want to inspect the concrete frame (if it has concrete) for the pole before you pour it (checked against the documentation), which means you have probably already violated the permit requirements. Normal fence poles would not quality as antenna mast supports.

    The reference listed by K4PRP shows about what you would need to survive 80 mph winds, and you are at least in a 70 mph wind area. Notice that the diameter of that mast is 2.36 inches and it requires guys at three levels.

    You didn't give any information on how the antenna wires would be attached, but I think it is unlikely that this would support a horizontal 80 meter loop, unguyed. What supports the other ends? Are you going to use 4 of these?

    You had better recheck the requirements for a permit.

    Jerry, K4SAV
     
  7. K6OK

    K6OK Ham Member

    KC8JPS: Back to your question...

    wind load per Uniform Bldg Code in lbs per sq ft: 0.00256 x V^2 where V is wind in mph

    at 100 mph, load = 25.6 lbs per sq ft

    24 ft high x 2-in dia pole = 4 square ft area presented to the wind

    distributed wind load = 102.4 pounds

    must use a factor of safety, typically 3. Assume design load of 310 pounds. This should be enough to include the point load at the top from the wire antenna.

    For a freestanding pole, unguyed, must consider two possibilities: pole will snap and buckle at the base; or, the soil will fail and allow the whole thing to become uprooted.

    For the pole buckling question: stress at the bottom of the pole will be s = WL/2Z, where W=load, L=length, and Z=section modulus. Section mod for a pipe is
    (pi x (OD^4 - ID^4)) / (32 x OD). Fiberglass has a crosswise flex strength of 10,000 psi (http://www.k-mac-plastics.net/data sheets/fiberglass_technical_data.htm).

    For the soil question (depth of embedment): you might try

    http://www.enercalc.com/sel58_help/index.html?footing.htm

    this calculator has a 45-day free trial. Calculates foundation strength of a pole embedded in soil.

    Good luck and 73...
     
  8. AE5JU

    AE5JU Ham Member


    Yes, and I suggest guying.
     
  9. AC0GR

    AC0GR Ham Member

    Must have missed this part....

    He needs hard specs to submit for his permit, not anecdotal 'It worked for me' stories.
     
  10. AE5JU

    AE5JU Ham Member

    Well, all I have is anecdotal. Sorry, the eBay sellers of these fiberglass masts aren't big on engineering specs. :D

    But the fiberglass poles are good for handling force straight down, but not side forces.

    And without guying, I don't think it's going to work out well for him. The aluminum poles would be a lot better.

    So not specs, just that I've actually used these things.
     
  11. KC8PJS

    KC8PJS Ham Member

    K6VAR, THANK YOU! That helped greatly.

    I cannot guy the poles because in order to have the linear length for 275' of wire I am using my side yard fences, located on the edges of my city lot. This means any guys would be in my neighbors' yards. That's a no go! I could use diagonal support bars if needed, but no wires.

    The antenna wire is attached with muffler clamps and a metal ring, so wire is free floating.

    K4SAV, they are not inspecting anything. The building department sent me a letter mandating a permit be submitted, so I think I need one. They are ONLY worried about the wind load, not that there is an antenna or support pole. Believe it or not, the loop is up and standing. Thus, why the neighbors called. The poles have a bit of a bend by the top due to slight wiggle room at junctions, but it's working so far. And no guy wires.
     
  12. W0DV

    W0DV XML Subscriber

    I purchased a bag of 12 from ebay last fall. I am using 10 of them to support a G5RV. Also, on the top is a VHF/UHF vertical antenna. The G5RV doubles as guy wires. I installed a 3rd guy rope on the top. Then, about half way down there is a guy ring I installed and there are 3 guy ropes installed there. So far, it has survived winds in excess of 50 mph. I'm not worried about it.

    I wasn't aware I would have to apply for a permit for just a pole?
     
  13. K6OK

    K6OK Ham Member

    KC8PJS -- You're welcome, glad to help. For the wiggling pole junctions, you might be able to drill a hole and put in self-tapping metal screws, maybe 3 per junction at 120 degrees from each other. I'd use stainless.
     
  14. K4SAV

    K4SAV Ham Member

    Sounds like your neighbors reported to the building department that you installed an antenna mast. The building department probably doesn't know exactly what it is. If they consider it to be an antenna support structure that requires a permit, it's unlikely that you will be able to come up with the data they need, and for sure you will be in violation of the set-back requirement.

    You had better find out if you are really required to obtain a permit for that pole(s). If so, you are probably going to have to take it down.

    I have never heard of a city issuing a permit for an antenna structure and then not doing any inspections.

    Jerry, K4SAV
     
  15. KG6LMY

    KG6LMY Ham Member

    And here I thought my use of a speaker stand as a base for my 2 meter copper j-pole and to hold the top of the dipole was unique. Stuck two stacked and clamped chain link fence top poles in it and bam! 26 ft tower to clamp it to. (I added the original speaker pole on top for the extra height, was not sure about using the fence poles all the way to 37+ feet)

     
  16. KC8PJS

    KC8PJS Ham Member

    Permit Submitted

    Hey guys,
    So I submitted my permit to the city about two weeks ago. They called the next day and requested a copy of my FCC license to attach to it. I sent it, and have not heard anything from them since. I did catch them watching the poles from their city vehicle parked on the street a week or so ago when we had 50MPH winds come through. No creaking, no breaking. Some sway, but it's fiberglass, and I can handle that. All in all, I am pretty happy with them.

    And as far as permit approval? Either way works for me. The letter I got from the city said I had to APPLY for a permit by said date, not have an approval. If it gets lost on somebody's desk, fine with me. If they approve it, fine with me. If they reject it, I build it bigger and stronger..say 40' Rohn towers in the back corners of the lot. That will make my neighbors happy :eek:

    For the person that talked about setback, the city didn't seem to have a problem with the poles attached to my fence (on property line). What setback requirement is normal? The only thing I have found searching google is house setback requirements, which don't apply as far as I can tell.
     
  17. K6OK

    K6OK Ham Member

  18. KC8PJS

    KC8PJS Ham Member

    Pictures will be coming

    Jim,
    I will get some pics of the poles up tomorrow morning to the thread, as it will be dark by the time I get off work today. My mother-in-law, who we have kept up to date, came to the house yesterday and wanted to see the famous poles. When she saw them, she asked "That's it? That's what they have been whining about?". Glad to see she is on my side...come to think of it, she has plenty of land outside the city.....:)
     
  19. KC8PJS

    KC8PJS Ham Member

  20. K6OK

    K6OK Ham Member

    Thanks for sharing the photos. What's all the white stuff on the ground? I was born and raised in California, so I'm not used to seeing that :) Anyway, I like your loop installation, seems like you've made the most of your space available.

    FWIW I agree with your XYL's Mom, that's what they are complaining about? Big deal.

    If your neighbors or the county inspector continue to give you grief about your poles, then you could say you'd have to consider something like this instead:

    http://xrl.us/bgqvxc

    I didn't take the photo but he happens to be about 5 miles north of me. I don't know why but the guy wire tied to the tree stake in the front yard cracks me up :)

    Good luck and Merry Christmas,

    Jim K6VAR
     
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