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Analysis of Structures (Method of Sections)

  1. Jun 28, 2011 #1
    1. The problem statement, all variables and given/known data
    Using the method of sections, determine the force in members BD, CD, and CE of the roof truss shown in the figure
    (the red line is the cutting plane and the green arrows are my assumed directions of the unknown forces)

    2. Relevant equations
    summation of moments=0
    summation of horizontal forces=0
    summation of vertical forces=0

    3. The attempt at a solution
    i assumed there's a reaction at F (upward), and since i didn't know its value i tried taking the moments at pt. F, N, O to make that reaction disappear. But so far, it doesn't seem like i'll be getting any unknown force anytime soon. please help! am i wrong with my assumption that there's a reaction at F? and also, i tried assuming that there's no reaction at F but i still can't find any unknown force at all.
    Last edited: Jun 28, 2011
  2. jcsd
  3. Jun 28, 2011 #2


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    The link to your diagram is broken.
  4. Jun 29, 2011 #3
    looks okay to me.
  5. Jun 29, 2011 #4


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    The reactions at A and F should be solved first, by looking at the entire truss and summing forces in x direction = 0 and summing moments about one of the reactions to get the other reaction, etc.
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