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Homework Help: Unusual problem for my course and struggling

  1. Jul 30, 2013 #1
    A boom AC is supported by a rectangular steel bar BD, and it is attached to a bracket at C by a high-strength steel pin. Assume that the pin at B is adequate to sustain the loading applied to it, and that the design critical components are the bar BD and the pin at C. The factor of safety against the failure of BD by yielding in uniaxial tension is 3.0. The factor of safety against a shear failure of the pin at C is 3.3. Determine the required:

    a) Thickness, t of the rectangular bar BD, whose width is b; and,

    b) Diameter, d, of the pin at C.

    known data

    P = 10 kN,
    L = 3 m,
    h = 2 m
    Bar BD: b = 25 mm,
    shear stress = 250 MPa
    Pin C: = 400 MPa

    Attached Files:

  2. jcsd
  3. Jul 30, 2013 #2


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  4. Jul 30, 2013 #3
    this is my efforts on this question i believe i have part a correct in this however i can't piece together how to do part b in it

    Attached Files:

  5. Jul 30, 2013 #4


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    Staff: Mentor

    That's fairly hard to read. We prefer that you type your work into the forum posts (preferably with Latex, but at least type in the equations). If you could take a closer picture of your figure (or scan it), that would be a help too. Thanks.
  6. Jul 30, 2013 #5
    hopefully these photos are clearer, i got an answer of 12mm for the thickness and cannot get a solution to part b

    Attached Files:

  7. Aug 7, 2013 #6
    The dimensions used in your answer don't match with the symbolic notation used in the question. You could try using the property that when a body is acted upon by three forces that are in equilibrium, then they must all meet at one point (otherwise there is a turning moment). You could use that property to determine the force on the hinge at C. Even if you don't do it that way, the method I suggest acts as a check on the method you do use.
  8. Aug 7, 2013 #7
    so my answer of 12mm was incorrect?
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