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Three pinned arch/ beams

  1. Jun 18, 2011 #1
    1. The problem statement, all variables and given/known data

    This is a series of beams pinned together at A, B, C
    Find reactions at a b c

    2. Relevant equations

    Sum of moments at B has to = 0, sum of Fx = 0, sum of Fy = 0

    3. The attempt at a solution
    Sum of moments about A, anti clockwise +ve
    2(-16) + 8Cy -4Cx = 0

    considering section BC
    sum of momeents about B
    4*-25 + 4Cy -8Cx= 0

    solving ffor Cx = 61.33

    I've been staring at this question all day, it has literally stopped making any sense.
  2. jcsd
  3. Jun 18, 2011 #2
  4. Jun 20, 2011 #3


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    Science Advisor
    Homework Helper
    Gold Member

    These equations are both correct
    You didn't solve the 2 equations correctly.
    Redo the algebra. Cx will come out negative , meaning you assumed the wrong direction for Cx. After finding Cy from these equations, use the other relevant equilibrium equations to solve for the support reactions Ax and Ay, and the internal forces Bx and By at B.
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