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Bending moment of beam

  1. Jun 15, 2009 #1
    Hi,

    I have the equation:

    f/y=M/I

    And y = d/2; I = bd^3/13

    However i have been trying for ages to try and get this equation in terms of d. Can anyone help me/ give advice as to how?

    Thanks
     
  2. jcsd
  3. Jun 15, 2009 #2
    i've got to:

    2f/12M = d/bd^3

    How do i collect the d's now?
     
  4. Jun 15, 2009 #3
    is this correct?

    d = cube.root(12M/2fb)
     
  5. Jun 15, 2009 #4

    PhanthomJay

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    The I of a rectangle is bd^3/12, you may have a typo. The rest is algebraic substitution. Is that where your problem lies...in the algebra?
     
  6. Jun 15, 2009 #5
    yeah, i did use bd^3/12 when working out to find d.

    I think my above solution is correct, just need someone to check
     
  7. Jun 15, 2009 #6
    M = 45Nm
    f = 240x10^6
    b = 16mm

    Im trying to find d.

    I used the forumla:
    f/y = M/I

    re-arranged to find d:
    d = cube.root(12M/2fb)

    Put my values in and got an answer of:
    d = 0.041m

    Is this correct?
     
  8. Jun 15, 2009 #7

    PhanthomJay

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    No. You have a 'd' in the numerator and a 'd^3' in the denominator. 2f/12M = d/bd^3. That's the same as 2f/12M = 1/bd^2
     
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