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Reaction at the pinned support

  1. Jan 11, 2017 #1
    1. The problem statement, all variables and given/known data
    The modulus of elasticity of each member is E = 20kN/(mm^2) and the cross section of each member is 1000(mm^2) , except member EB and EC is 40(mm^2) , determine :
    a) The vertical displacement at joint C
    b) The horizontal dispalcemnet at joint C

    at A , it's a pinned support , so there must be 2 reactions , right ?

    2. Relevant equations


    3. The attempt at a solution
    Why the author showed one reaction( horizontal reaction) only ? Is it wrong ?
     

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  2. jcsd
  3. Jan 12, 2017 #2

    haruspex

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    Suppose there is a vertical reaction. What do the force and moment sums tell you?
     
  4. Jan 12, 2017 #3
    what do you mean ? Can you please explain further?
     
  5. Jan 12, 2017 #4

    haruspex

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    You can determine the horizontal force at A easily. Take moments about D. What do you deduce about the vertical reaction at A?
     
  6. Jan 12, 2017 #5
    what do you mean ? Can you please explain further?
     
  7. Jan 12, 2017 #6
    what do you mean ? Can you please explain further?
     
  8. Jan 12, 2017 #7
    what do you mean ? Can you please explain further?
     
  9. Jan 12, 2017 #8
    The vertical reaction at A create clockwise moment about D
     
  10. Jan 12, 2017 #9

    haruspex

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    Yes, but write the equations. First, find the horizontal force at A. Then take moments about D to find the vertical force.
     
  11. Jan 12, 2017 #10
    HA = 20kN to the left . moment about D = VA(2) -20(1) = 0 , VA = 10kN(upwards) , is it correct ?
     
  12. Jan 12, 2017 #11

    haruspex

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    The equation must include moments due to all the forces, including those at B.
     
  13. Jan 12, 2017 #12
    moment about D = -20(1) +VA(2) -20(1)+20(2) = 0 , Thus VA = 0 ?
     
  14. Jan 12, 2017 #13

    haruspex

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    Right.
     
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