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Internal forces in members of structure

  1. Mar 26, 2013 #1
    what are the internal force in the hinged member 1-4?

    Attached Files:

  2. jcsd
  3. Mar 29, 2013 #2
    Interesting problem.

    I've attached an image that illustrate my thoughts on how to go about solving it.

    I'm assuming the beam is "rigid" and the bars all have the same "stiffness."

    Take a look at the image.

    Finding the bar forces in the first step is trivial, as the structure is symmetric.

    Once you've found the bar forces from step 1 and the bar forces from step 2 (based on my attached image), you can sum them to arrive at your solution.

    I drew a red arrow pointing at the second step in the process, which I think needs further explanation. You may find example #2 useful on this website: http://utsv.net/mechanics-of-materials/2-statically-indeterminate-structure-axial

    Hope that helps

    Attached Files:

    • PF.png
      File size:
      16 KB
  4. Mar 29, 2013 #3
    tx alot I'll try it
  5. Mar 29, 2013 #4
    dear afreiden,
    I've tried the clue that you've given me
    I found N1=0,6P N2=0,3P N3=0,03P N4=0,07P
    but the answer should be N1=0,4P N2=0,3P N3=0,2P N4=0,1P (according to the writer)
    the writer said use the force method or displacement method or
    the matrix stiffness method, any idea?
  6. Mar 29, 2013 #5
    Show us your work and we can help. Your answer immediately looks wrong to me since I'd expect the forces to be larger in the rods that are nearer to the point of load application. In the author's solution this is indeed the case.
  7. Mar 31, 2013 #6
    please find attached on how I got to that answer

    Attached Files:

  8. Apr 1, 2013 #7
    Your equation that you wrote at the top right of your page (I think it might be labeled (1) ) is definitely wrong.

    In general, I see several procedural mistakes.

    In step 1, all bar forces should be the same.

    In step 2:
    What is your value of "M" ?
    How did you determine that N1=2N2? (I expect to see some axial deformation equations)
    Do you understand how I was able to draw that triangle?

    Your triangle at the bottom of your page does not make physical sense.
  9. Apr 1, 2013 #8
    can you show me how to get to the right answer than?
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