Polygonal Tubular members

Discussion in 'Design, Development and Standards Discussions' started by david cohen, Jun 7, 2008.

  1. david cohen

    david cohen Friend of the Community

    I'm a structural engineer, and I was wondering if anybody knows about the real advantages that the polygonal sections has on the circular section (on monopoles), the difference of cost by manufacturing polygonal section is cheaper than circular sections .
    According to the TIA-222 F (in rev G they omitted the 4-8 table) the rounds sections are really stronger than polygonal , so that is almost equivalent regarding the two reasons (cost and strength).
    Do you have any other reasons to choose polygonal sections instead of round ones ?
    Thanks
  2. Bob Hardee

    Bob Hardee Friend of the Community

    David,

    I'm not a structural engineer, but having worked with them in the industry, especially in Florida, it seems to me that another big advantage the round sections have is less wind resistance than anything with any part having a flat face to the wind.

    Bob Hardee
  3. Mike  Plahovinsak

    Mike Plahovinsak Friend of the Community

    Round sections have their advantages to certain heights and special applications, however, when you require fabricating a heavy duty pole, it is cost effective to design a tapered, polygon-type pole.

    Straight, pipe-section poles tend to waste steel near the top where stresses are low, and the additional cost of fabricating flange connections usually drive costs up.
  4. Chas  Wagner

    Chas Wagner Industry Observer

    David,
    It looks like you've had some time to consider your options since your post and the other replies. If you are still up in the air, consider future loading cases as a factor also. As you know, the dynamics of the bolted connection on a step taper pole will be a challenge to overcome when reinforcement comes into the picture.

    Slip joint poles are more easily modified and it seems we have a lot of new loading coming. Think about what would be involved to increase a bolt diameter on a flanged pole with interior bolt flanges like the lowers on a Central.
  5. John Bridge

    John Bridge Friend of the Community

    I was a past monopole erector with only a couple of round poles under my belt, but up to 50 of the polygonal-taper-sleeve type. (from now on, referred as "PTS" type.

    From an installer's point of view, here are some differences:
    1. Installing new handholes in a round pole (in the field) is more expensive than poly.

    2. Erectors/climbers don't feel safe having to go inside a round pole (if designed as such) to make the sectional connections.

    3. PTS connections require no hardware or tools (bolted take a lot of time and possible to loose hardware or drop).

    4. PTS poles should be 'jacked' down during installation, but rarely done. The pole is left to settle over time. That is why someone always has to go back several times to tighten the safety climb cable, and also why feeder coax at the base of the pole lower with the sections settling (can possibly damage the feeders).

    5. When using clamp-on collar style compression mounts for platforms or sector frames, round poles are much easier to set orientation, as polygonal force incremental adjustments. This isn't a show stopper though.

    6. Things seem to get hung-up more during hoisting operations (inside round poles), especially when lowering (your load line, decommissioned or damage feeders, etc..).

    7. Inside diameters of round poles (at the top) seem to be smaller than PTS at top. Not good. Need all the space you can get up top.

    8. I think I remember round pole section weights being heavier too. More weight means bigger machine (crane).

    9. PTS poles can be a pain in the butt to line up (orientation) during erection ops (some poles have tight tolerances), especially during light winds when they don't want to sit still. Round is faster to set in place, but still takes longer.

    10. Somewhat rare, but PTS poles can be bent out of shape on the ends and will cause havoc during erection ops. Smart crews inspect/measure before any rigging. There are different fairly simple ways to (temp) get the end into shape.

    *** ALL antenna mast pipes MUST be easily adjustable for plumbness in the direction I would call 'forward/backward' not from side to side. There are different designs that allow an installer to adjust (without shimming or bending) to an incremental change. THIS IS CRITICAL to insure the best antenna downtilt settings. There is one primary purpose for those poles and towers: to hold antennas up in the air. Having to deal with mast pipes that can easily be plumbed is 'bad'. That goes for any antenna mount.

    Off the soap-box now. Thanks all, John.
  6. Narain Sarshar

    Narain Sarshar Industry Observer

    You don't see too many round sections going up any more. It would be logical that it is a cost factor as well as the difficulty to beef up a round pole. All of the things you mention are related to the cost of construction and carriers typically expect the same pricing whether it is a flanged round or slip joint.
  7. Simon Weisman

    Simon Weisman Industry Observer

    It looks as if people think that circular sections have to be cylindrical and have flange connections only, while polygonal cross section poles will always be tapered and have a slip joint.

    This is not always true. You can have other options. It is just that there are not many shops that can manufacture tapered poles of circular cross section. It is also possible to have slip connections on non-tapered poles. You see, the root of engineering is ingenuity, not beaurocracy.

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