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Product moment of inertia of an inclined section of a beam

  1. Nov 20, 2009 #1
    Hi guys,

    I would like to derive the Ixy equation from simple integration and I can't seem to get the right answer (third equation down the picture). I seem to be able to derive Ixx and Iyy easily but product moment of area requires first moment of area to be calculated and I just don't know how to do that on an inclined section.

    Any help would be apprecited on this issue.

    Thank you.

    Attached Files:

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    • un1.JPG
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  2. jcsd
  3. Nov 20, 2009 #2


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    Welcome to PF!

    Hi emRage! Welcome to PF! :wink:

    Is the rod in the x-y plane? And what is t?

    ok, you need to prove that Ixy = L3t(sin2θ)/24.

    Show us the integral you have for this. :smile:
  4. Nov 20, 2009 #3
    This one I've figured out! :tongue:

    x = cos(theta) . s
    y = sin(theta) . s
    dA = ds . thickness
    limits for s = L/2 and -L/2

    Thanks anyway!
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