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Thread: Rule of thumb for drilling holes in I beam flange

  1. #1

    Rule of thumb for drilling holes in I beam flange

    I am aware that there are general rules of thumb regarding the size and placement of holes in beams.
    The question was presented to me today:

    Is there a general rule of thumb regarding size and placement of holes in the flange (not the web) of an steel I beam?

    Here is the application: around christmas time, a rigger buddy wants to drill a half inch hole in the flange of a vertical I beam column. He will place an eye bolt through the new hole, and using standard rigging hardware, suspend 300-400 lbs. of electrical / audio / lighting / fiber cable.

    Something along the lines of this:

    Comments?
    Last edited by daleacyr; 10-23-2019 at 08:20 PM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    I should think not less than 1.5D hole edge to edge distance and 2D hole edge to flange edge minimum.

    AISC structural steel design specifications defines industry standards for building.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Thanks Kelly.
    I've been wandering around the AISC for a day or so.

    Referring to the attached drawing:

    In a horizontal beam, the lines of force, compression and tension make sense to me.
    And so, it makes sense that holes (generally, lots of exceptions) will go in the neutral axis,
    since the fibers are neither in compression or tension.

    What I don't know, is how do the lines of force run in a column?
    Where is the neutral axis? Or does the concept not exist in a column?

    Conversely, can I put a hole pretty much anywhere (respecting edge clearance) in a column?

  4. #4
    Administrator Kelly Bramble's Avatar
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    Yes, always put cutouts and/or hole features on or nearest possible the neutral plane relative to peak loading.

    If you have a basement that's how conduits, electrical wire, plumbing should be on your floor joists. Also, if possible, hole flange patterns or applied loading should be symmetrical about the neutral plane of any structural member.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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