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Having trouble calculating reaction forces for this truss.

  1. May 8, 2016 #1
    1. The problem statement, all variables and given/known data
    Calculate reaction forces for truss. Truss is attached in picture.

    2. Relevant equations

    ΣFx=o
    ΣFy=0
    ΣM about reaction point=0
    3. The attempt at a solution
    attached in picture
     

    Attached Files:

  2. jcsd
  3. May 9, 2016 #2

    SteamKing

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    Unfortunately, the attached images are almost entirely illegible. :frown:

    If you want some help, either write out your calculations or post better images. :wink:
     
  4. May 9, 2016 #3
    This truss is statically determinate now, and should be solvable, right? That is why I don't understand why I am having trouble solving for the support reactions.
     

    Attached Files:

  5. May 9, 2016 #4

    SteamKing

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    What makes you think this truss is statically determinate? You're still trying to calculate four reactions using only two equations of statics.
     
  6. May 9, 2016 #5
    I
    I have 4 equations Sum of forces in y direction and the
     
  7. May 9, 2016 #6

    SteamKing

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    Your last post came out garbled. Can you repeat?
     
  8. May 9, 2016 #7
    I have more than 2 equations, I have sum of forces in y and sum of moments about any of the supports. It is statically determinate because 2 (11 joints)=17 members+5 reactions. What do you mean by 2 equations of statics?
     
  9. May 9, 2016 #8

    SteamKing

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    You can write only one equation involving the sum of the forces and one equation summing the moments about one convenient reference point.

    You cannot write, for example, one moment equation where you sum moments about point A and another equation where you sum moments about point H.

    This beam is statically determinate:


    simple-beam-dist-load.png

    This beam is statically indeterminate:


    upload_2016-5-9_8-26-53.png

    Both beams are loaded in a similar fashion, except the latter beam requires an extra equation in addition to the equations of static equilibrium in order to solve for the reactions at the supports. In the case of the latter beam, we must know how the beam deflects under load, and we cannot calculate that unless we know some additional structural details beyond the spacing of the supports.
     
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