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Thread: Question about pipe in concrete

  1. #1
    Associate Engineer
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    Question about pipe in concrete

    I am building a ground mount solar array in my yard. It will be 16 panels and IronRidge racking with a foundation of six 3" schedule 40 galvanized steel pipes in concrete. The plans from the manufacturer show the steel pipes 2/3 of the hole depth. I called for an inspection before pouring concrete and the inspector was good with everything except that I have the pipes deeper in a few holes so there would be about 4" of concrete under the ends.

    I Thought it was an interesting question (enough for me to join an engineering forum) but is the 1/3 hole depth concrete under the pipe as or more critical than the 2/3 hole depth for the pipe? He seems sort of hung up on having me dig deeper under the hanging posts get more concrete under them.

    I can see it for a pole barn or other weighty structure, but I will have about 2000 pounds total held up on 6 poles set in almost 1 1/2 yards of concrete. (holes were dug with an 18" auger to a depth of 42 to 48")

  2. #2
    Administrator Kelly Bramble's Avatar
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    I'm a little confused with your explanation.

    I do wonder if there is a code that overrides the manufacturer requirements and is being enforced by the inspector?

    You should have a "why" explanation from the inspector...
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
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    Hi Kelly, thanks for the reply.

    He saw drawings in the instruction manual for the racking that shows the posts going 2/3 depth into the holes and seems to want to interpret it literally. He said he thought the 1/3 was necessary for support of the system, but I see it as 2/3 of the hole depth (as a minimum) for the post for shear strength. I'm not an engineer, and I doubt he is either, so I thought I'd ask somebody who really knows.

  4. #4
    Administrator Kelly Bramble's Avatar
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    I suspect that intent may have been that 1/3 of hole is to ensure drainage from the pipe due to condensation or water entering from the top.

    When placing posts in my part of the world it is wise to put gravel / rocks at the bottom of the hole to ensure drainage.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  5. #5
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    OK, a picture is worth a thousand words, right? Poles are capped for crossmember attachment, so there is no drainage issue. He saw this photo (with no dimensions) in the instruction manual. Here is my drawing that I turned in for the permit and a couple extra photos.

    I can't upload photos for some reason, so here are links:


    https://photos.google.com/share/AF1Q...VxWkdYOWdINklB

    I put them in an album. Hopefully this link works.
    Last edited by hammergrips; 09-15-2020 at 08:24 PM.

  6. #6
    Associate Engineer
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    Dimension for photo upload is 1200x0??

    Doesn't look like my links are working either.

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