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  1. #1
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    Jun 2014
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    Default Vertical column calculation for shelves



    First post, hope I'm it's not in the wrong subforum.

    I'm curious to know how to calculate the width and depth for the vertical column that will hold the shelves. Material i would use is pine wood. Most of us got used to measure by experience (or simply ask at the shop), but i'm curious about the math that's going on behind. Can anyone point me into actual equations of this particular problem?

    The goal is to have vertical column that will not bend or swing under full capacity load, particularly not when new things are inserted on shelves i.e. to have a sturdy feel all the time.

    Each shelf would carry roughly 30lbs of weight (this includes its own weight). Total of 13 shelves would be used, so that's 390 lbs under total load, or 97,5 lbs per column. Column height is 79". Each shelf is tightened by 8 screws. Shop owner told me to use 2x4" for columns. When i asked him how did he calculated that, he couldn't answer. Well, i'm curious to know...

    Thanks!

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  3. #2
    Join Date
    Feb 2003
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    back in Alberta for a while
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    Default

    there's no simple answer

    under axial loading, your 45kg per column (post) can be accommodated by a ridiculously skinny section.
    Periodically engineering schools set bridge or tower challenges (think support a house brick 1/2 m above the ground) which are typically won with structures made of spaghetti.

    How small your columns can be is primarily related to the type of connection between the shelf and the column and the stiffness of your shelves.
    it's most likely that the limiting design parameter for the columns will be how the shelves are connected to them.
    regards from Alberta, Canada

    ian

  4. #3
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    Default

    Thank you for help! I will try a few other designs and eventually ask a few more questions.

  5. #4
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    Default

    Can not help with your question but I will welcome you to the forum.

    It is an interesting question.

  6. #5
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    Queensland
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    Default

    I can't really answer your question but just an observation - it would also depend on how the shelves are attached to the uprights as well as the length you are trying to bridge.

    If they are butt joined and only the screws are doing the holding then I could foresee the vertical shear forces being a problem - if the shelves are inlet into the vertical [and how deeply] this would be a great improvement or if support blocks were added under each shelf then the load capacity would be increased.

    As has been said, an interesting problem.

    By the way, welcome to the forum.

    Regards,
    Bob

  7. #6
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    back in Alberta for a while
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    In terms of Steven's original question, the critical constraint is the buckling load of the column -- ie the axial load at which the support bends and collapses.
    Given the properties of wood, for the load Steven mentions, a 5 x 5 mm section with straight grain will be stiff enough, as would a section possibly as small as 3 x 3 mm.

    HOWEVER a 5 x 5 mm section won't be "meaty" enough to contain the fasteners needed to tie the shelves to the uprights.
    So the design limitation is not the axial load on the "Column" per see but the TYPE of connection used to attach the shelf to the column -- or vice versa. The "solution" to this issue depends heavily on the design of the shelves.

    a stiff torsion box shelf could be attached to a very light upright that passed through a suitable hole on the torsion box and was secured against movement with wedges. Constructing such a joint would require very precise joinery.
    regards from Alberta, Canada

    ian

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