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Homework Help: Internal Forces on a Truss (Again!)

  1. Jul 12, 2015 #1
    1. The problem statement, all variables and given/known data

    Hello, in the attached file shows a picture of the problem I need to resolve. The question asks to calculate the internal force in the member BC. There is a pin support located at joint A and D, which is not shown in my diagram, and it is also symmetrical, which makes things slightly easier.

    2. Relevant equations

    See attached file.

    3. The attempt at a solution

    I calculated the forces in the y direction using the equilibrium equation, and then calculated the angle between member AE and AB using basic trigonometry to be 26.57 degrees. I then resolved the internal forces in members AE and AB. However, I am unable to determine what else I can do with resolving further internal forces in this structure. For all other joints, there are at least 2 unknown forces, for which I am unable to determine any other internal forces. What should be my next approach? Thanks, forum.

    Attached Files:

    • IMG.pdf
      File size:
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  2. jcsd
  3. Jul 12, 2015 #2


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    You have an error in getting FAB.
    You changed the cosine back into the sine .

    Also, can you clarify?
    Is member EB perpendicular to member AG ?
  4. Jul 12, 2015 #3
    Thank you, silly mistake there. And I'm not entirely sure, the question doesn't specify, but I'm assuming it is.
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