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Homework Help: Mechanics of Materials: Statically Indeterminate Problems

  1. Mar 3, 2017 #1
    1. The problem statement, all variables and given/known data
    Hi! So my question isn't really about a specific problem, but more of when to use which method.
    I'm having trouble knowing when to use the method of super position, the force method, or just being able to go straight into just writing the equilibrium equation and the compatibility relation.

    2. Relevant equations
    δ = (F*L)/(A*E)

    3. The attempt at a solution
    For example, in the problem I attached I originally just summed the forces in the x direction and then wrote out my compatibility relation:

    FEF - 2FAB = 80 kN (Because of symmetry let FAB = FCD

    δAB = δEF

    And then I just solved for my forces using these two equations. But this was incorrect, I don't understand why this doesn't work (The solution I looked at used the method of super position). The total deformation between the two rigid walls should be zero, right? Shouldn't the compression in rods AB and CD equal the expansion in rod EF?

    Thanks for any help!

    Attached Files:

  2. jcsd
  3. Mar 3, 2017 #2


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  4. Mar 3, 2017 #3
    Thanks so much!! I can't believe I made that mistake. So just to clarify, you can pretty much use whichever method as long as you are careful?
  5. Mar 4, 2017 #4


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    Yes, use the method that is easier for you , they all lead to the same result.
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