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Need help with more indepth beam theory?

  1. Mar 2, 2015 #1
    I have a project for a class and our goal is to design a beam using 1018 steel to achieve a certain deflection under one load and not fail under an even larger load.

    The design I have come up with is very similar to a cantilever beam, but is has a variable cross section. I have used the Euler-Bernoulli beam theory to find the proper dimension to minimize the volume and achieve the goals. I then built my design in ANSYS and my deflection values varied GREATLY. With beam theory I was getting about 3.655 inch deflection, ANSYS was giving me about a .031 inch deflection. That is all under a 60 lbf load

    Is there a more elaborate beam theory or more correct one that I could use?

    Attached is a pdf of my work in MathCAD and picture of my ANSYS model if that would help.

    Attached Files:

  2. jcsd
  3. Mar 3, 2015 #2


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    It's not clear, from what I can piece together from your attachments, that you need a new beam theory, you just need to make sure the beam theories you are using have been applied correctly.

    Why have you used only 60 ksi for Young's Modulus (E)? E for steel is going to be on the order of 30,000 ksi.

    In the quantity M / EI , you must use consistent units. If M is in inch-lbs, then I must be in in4 and E must be in lbs / in2, not ksi.

    One other thing to check is to make sure the tangent function in MathCAD accepts degrees as arguments.
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