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Stand PLan, What size stock for load/span ?

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  • Stand PLan, What size stock for load/span ?

    I am building a two shelf stand to hold two fish tanks, 75 Gallon on the lower shelf and 40 Gallon on the top shelf, This will be about 24" X 6" and about 44" tall. I need the lower shelf to support up to 700 lbs and the top shelf to support 350 lbs. I was going to use square tubing but I need about 60 ft and angle iron is about 1/2 the price. Was trying to find a calculator for load/span/size but had no luck so far.

    I was thinking 1 1/4 or 1 1/2 angle 1/8 or 3/16 I would like the top to span the 5 1/2 or 6 feet, the lower shelf I could put extra feet on to lessen the load.

    What are your thoughts on size and thickness for this project?
    Thanks for the help. Mark Click image for larger version

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    Last edited by mbrady4him; 07-06-2011, 04:34 PM.

  • #2

    The two shelves will be made out of laminated MDF.

    Thanks again for your help

    I will be welding with a Lincoln 175 Plus with Argon tank, this will be the first project with this welder, last welder was a Century 115V Flux core. Can't wait to try this one out.
    Last edited by mbrady4him; 07-06-2011, 04:35 PM.


    • #3
      Beam deflection formula


      Here are links to a site which will help you figure out how much deflection will occur depending on the shape and size of your horizontal members.

      The first link gives you the formula for a single load centered between 2 supported ends.

      The other links give you the details on how to calculate the moment of inertia for steel angle or square steel tubing.

      While the formulas look daunting, you only need to calculate the moment of inertia for the shape (angle or square) you are using.

      Then plug this value into the bending formula.

      Your use of MDF shelves will help distribute the load but please add their weight to the load calculations.

      Good luck
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      • #4
        For that design you will want something with moment of inertia of 1 in^4 or higher. To get angle iron that stiff you need something like a 3 x 3 x 3/16 at 3.7 pounds per foot.

        A 3 x 1.5 x 1/8 rectangular tube would work also at 3.5 pounds per foot. (Note that you would use this with the 3 inch dimension vertical)

        You don't need so many cross pieces so long as the tank is sitting on the stringers. That will save some material.


        • #5
          Just and FYI, the moment of inertia is basically the inertia around an imaginary line where the material stress is zero. When you bend something, parts of it compress, other parts stretch (in your case, the top compresses and the bottom stretches).

          Anyway, if you make the top out of sheet metal - say 16 gauge or thicker, it will could add to the moment of inertia. Better seam weld it if you really want it to help. (stitch welding too complicated to model).

          Recommend you hit your local college used book store and grab a book on "strengths and materials". You will refer to often and most actually have tables in the back for things like I-beams and regular steel pieces (normal shapes). Most of the math involved is easy - besides, you always err on the safe side.... Next size up in steel etc.
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