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Homework Help: Finding dimensions of a beam using shear, moment, and moment of Inertia

  1. Apr 1, 2010 #1
    1. The problem statement, all variables and given/known data


    2. Relevant equations

    Moment of Inertia equation: I=(1/12)bh^3
    Stress and Strain equations: Sigma= -(M*c)/I Tao = (V*Q)/(I*t)

    3. The attempt at a solution

    I know I need to use shear and moment diagrams to find the max moment so I can use the Stress diagram to find the Moment of Inertia to find the dimensions of the cross section, but I can't figure out how to get started. Any help would be great. Thank you.
  2. jcsd
  3. Apr 1, 2010 #2


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    Wouldn't you want to start by setting sigma in your equation equal to the given allowable bending stress? Give it a try.
  4. Apr 2, 2010 #3
    Can you draw a loading diagram for the cantilever you think has the most stress? Do you know a definition of bending moment that will enable you to draw the bending moment diagram?
  5. Apr 4, 2010 #4
    I am using the weight density to find the weight distribution over the entire area and then treating that as a simply supported beam. Will this work?
  6. Apr 5, 2010 #5
    If it is a simply supported beam, rather than a cantilever (as it says in the question !) where are the two supports?
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