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Finding the unknown forces at two supporting pins

  1. Nov 23, 2011 #1
    1. The problem statement, all variables and given/known data

    In a simple truss where P = 8 kip, find the unknown forces D_x, D_y, C_x, and C_y then determine the average normal stress in each member.

    Description of truss:

    I cannot copy an image due to the source it is coming from, so here is my attempt at a description

    A triangle with arms AB (going up and to the right (5 feet)), BD (going down and to the right(5 feet)), and DA (going to the left connecting back with A (8 feet)). Member BE cutting straight down the middle of the triangle (3 feet). Member BC parallel with member ED and equal length of 4 feet. Pins at C and D. The force P is applied downward at point A and the force 0.75P is applied downward at point E.

    2. Relevant equations

    3. The attempt at a solution

    I know that in a 2D problem you can only have three unknowns to find the forces. I am able to find C_x and D_x to be 29.3 kip (D_x in the negative x direction), but cannot remember how to find the y values.

    Attached Files:

    Last edited: Nov 23, 2011
  2. jcsd
  3. Nov 23, 2011 #2
    I am having difficulty downloading the attachament.
  4. Nov 23, 2011 #3
    I went ahead and made a rough sketch on paint
  5. Nov 23, 2011 #4


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    ptguard1: The force in truss members is always axial. Therefore, you know C_y = 0.
  6. Nov 26, 2011 #5
    What do you mean by an axial force?
  7. Nov 26, 2011 #6


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    ptguard1: The direction of the resultant (i.e., total) force in each truss member is always along the longitudinal centerline of each truss member. A force along the longitudinal centerline of a member is called an axial force.
  8. Nov 27, 2011 #7
    I just discovered that I actually didn't need to find the forces at each pin in order to solve the overall problem, but thank you for the information.
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