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Thread: Structural Member: Built Section Vs Solid Plate

  1. #1
    Associate Engineer
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    Structural Member: Built Section Vs Solid Plate

    I have two structural components that I am designing. One is basically a pad eye, the other is a pillow block for a shaft line. In both components my design calls for a single piece of heavy 3" plus thick plate. If I were to build these heavy plate sections from two 1.50" thick plates welded together, how does that change my structural design? Is there a difference in the two from a loading perspective?

    Both of these components will be welded to other members. With a built section for the pad eye, how should the "anchor" welds be considered? Normally, with a solid section weld calculations are the perimeter of the solid part. When you have two plates welded together this essentially leaves a seam between the two that will not be welded to the frame. OR am I over thinking this?

    As for the pillow block built section, only one piece of plate will be welded to the frame. The other half is hanging out in space but welded to the first piece. There will be a common bushing on the shaft at the built section. Is it accurate or grossly conservative to apply the full bearing load of the shaft to the entire built section, or only to one piece of plate within the built section?

    Ultimately, what load should the weld on the parting line of the built section be designed to withstand to prevent possible separation of the built section?

  2. #2
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    The answer your questions requires an engineering analysis which is impossible with the sketchy description you have provided. Hire a professional to perform said analysis.

  3. #3
    Lead Engineer Cake of Doom's Avatar
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    As no loads have been given, it's impossible to even guess what the welds will be subject to. If it's a compression load, the plates should be OK but the welds will be subject to bending and shear flow loads. Possibly more. Or is it in tension and you're worried about it pulling apart?

    Find yourself a local engineer that can put it through a FEA but you'll have to provide more information than in the OP.

  4. #4
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    Mods, please delete this post.

    If the best answer anyone can provide is "Go hire an Engineer" I'll search for answers else where. I really didn't think I needed to explain how a pad eye is loaded.

  5. #5
    Administrator Kelly Bramble's Avatar
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    Quote Originally Posted by jonathanslade7 View Post
    If I were to build these heavy plate sections from two 1.50" thick plates welded together, how does that change my structural design? Is there a difference in the two from a loading perspective?
    Yes, it is different. Solid vs welded on the perimeter will deflect differently depending on how it is loaded and the bearing is secured to the welded/solid pad.

    Slot + edge fillet welds could mitigate the differences - but with little information, who knows?

    Quote Originally Posted by jonathanslade7 View Post
    Ultimately, what load should the weld on the parting line of the built section be designed to withstand to prevent possible separation of the built section?
    Somebody would need a free body diagram of the loading, material specifications, bearing specifications, fastener specifications and installations + about fours hours assuming they the right software to do a complete analysis and provide feedback/direction.

    My general recommendation: Slot welds from the backside + perimeter fillet welds + through bolts on the pillow block is a reasonable suggestion with little information..

    To estimate stress applied to selected weld design see:

    https://www.engineersedge.com/weld_design_menu.shtml


    BTW,

    Mods, please delete this post.


    If the best answer anyone can provide is "Go hire an Engineer" I'll search for answers else where. I really didn't think I needed to explain how a pad eye is loaded.
    Nobody anywhere owes you answers you expect/demand and a little patience and professionaism in a busy world goes far.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

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