Is a reduced slip joint length acceptable as per 222 G- addendum 2?

Discussion in 'Design, Development and Standards Discussions' started by George, Oct 31, 2011.

  1. George

    George Friend of the Community

    Does TIA-22-G addendum 2 clause 13.3.5 allow a reduced overlap length to be accepted?

    We have a cse for the 30 metre height Monopole, with three slip joints, one joint is actually only 80 % of the length as per the design drawing.

    Is this acceptable?

  2. J. Tinsley

    J. Tinsley Industry Observer

    Typically the install drawings show minimum and maximum allowable slip. Do you have the install drawings?
  3. George

    George Friend of the Community

    The installation drawings show a slip length of 1750 MM. (attached)
    Actual slip length at site after erection and "settling down" is 1405 MM.
    [We had made a reference mark before erection and measured from the same mark after erection.]

    This was done because of the reason that there was a slight "out of shape" noticed at this particular section (as a result of carelessness during unloading of the section). There is a small gap visible at the joint after erection (pic attached).



    Attached Files:

  4. J. Tinsley

    J. Tinsley Industry Observer

    Hi George,

    I have delivered probably a 1000 poles and dealt all kinds of problems associated with them, egg shaped sections, wrong anchors, warped anchor circles, poor installation, step tabs in the way of the slip, etc.

    We would need to look at the analysis data to make an accurate determination whether that slip is strong enough in that area. I reviewed your situation with our Design Engineer, first impression is it should be fine. There is a "gray" area in slippage, and you are probably close to the minimum allowable based on our design standards. It looks like the pole is designed for at least two carriers in high wind zone, so with the initial carrier loading this should be fine until the pole settles in. Any installation on the pole will help it settle in aswell.

    I would expect the pole to settle in over time especially if it is located in an area with a good temperature changes. The steel in the pole expands and contracts rather drastically, so it will "walk" itself down over time. The gap should close in as well.

    This is a super heavy 30 meter pole. Must be a high wind area, tropical, or wind turbine application.

    I don't see any jack nuts.

    Has the manufacturer commented on the situation? They should be willing to help as well
  5. Clifford Bryan

    Clifford Bryan Industry Observer

    I was also going to ask if the manufacturer has commented on this situation? That should be the first place to ask.
  6. J. Tinsley

    J. Tinsley Industry Observer

    I am thinking from the drawings this probably isn't a domestic supplier maybe the issue. It's my understanding from our Engineering department the TIA calls for 1.5 x diameter for the minimum slip.
  7. George

    George Friend of the Community

    We rechecked the slip joint length attained after one week and found out that the tower had "slided /settled" gradually by ~100mm!!. The analysis /calculations was submitted by the manufacturer and was satisfactory with the current slip length of 1505mm.
    It is still lesser that the specified 1.5 times dia 1092 =1638 mm by 133 mm. However based on the analysis and the fact that the tower is settling and will attain this slip length gradually.

    Ref to the earlier remarks- The Tower is built in UAE, for communication (cellphone operator). There are no jacknuts for the slipjoints.
  8. Jason Fortier

    Jason Fortier Industry Observer

    Yes J.

    In 222G: Tubular Pole Structures
    The design length of a slip type splice shall not be less than 1.5 times the inside width of the base of the upper section. The inside width shall be measured between flats for polygonal cross sections.

    In addendum two it says: Installed slip splices with lengths less than 67% of their design splice lengths shall require reinforcement.
  9. J. Tinsley

    J. Tinsley Industry Observer

    Thanks Jason. That's great George! I am sure it will settle in fine. That pole is extremely heavy for its height, it will be fine. I sure it would pass analysis as it is. Tell them not to paint the slip area in the future will help.

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