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Thread: HELP!!!! - Basic Statics Question

  1. #1
    Associate Engineer
    Join Date
    Oct 2013

    HELP!!!! - Basic Statics Question

    Ok Everyone, I'm in DIRE NEED OF HELP....

    .... as I've been out of practice now for a while - though I'm sure this is an easy problem to solve. Please see attached free body diagram.

    Need to find reactions, R1, R2, R3 to support a 185 lb load as per the attached. I have done summation of forces R1 + R2 + R3 - 185 = 0 and summation of Moments about R1=0. What's my 3rd equation?!?!?!?
    Attached Files Attached Files

  2. #2
    Technical Fellow Kelly_Bramble's Avatar
    Join Date
    Feb 2011
    Bold Springs, GA
    Sum of Forces = 0 = R1 - 185# + R2 + R3

    185# = R1 + R2 + R3

    R1 = R2 + R3 - 185#



    Sum of Moments about 185# = 0 = -13(R1) + 10(R2) + 25(R3)


    Substitute and solve for R1, R2 and R3


  3. #3
    Technical Fellow jboggs's Avatar
    Join Date
    Mar 2011
    Myrtle Beach, SC
    But from what I see it looks like R2 and R3 are sharing the load. The actual load at each point is going to depend on the stiffness of the beam and could range from zero to the full load based on its position.

  4. #4
    it's statically indeterminate, you have more unknowns than equations... it can be solved but it's not as straightforward as you'd expect. There are several methods for solving statically indeterminate problems, the most popular one is probably the moment distribution method.

    Just as an FYI, most structures in the real world are statically indeterminate. They can be solved by hand but depending on the degree of indeterminacy it can take a very long time. In these cases computers are very useful.

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