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Number of total reactions in a structure

  1. Jan 12, 2017 #1
    1. The problem statement, all variables and given/known data
    In the example A , Why the author stated the total reactions = 9 only ? How to determine the total reactions for this type of questions ?

    2. Relevant equations


    3. The attempt at a solution
    we can see that there is a total of 3 reactions (vertical , horizontal and moment) at the cut of the 4 parts , right (circled part) , and 3 reactions below . So , the total reactions is 4x3 + 3 = 15.
     

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  2. jcsd
  3. Jan 12, 2017 #2
    When ever you have a closed loop as in this frame, you cut it, and you count the set of internal reactions (only once) as reaction forces.

    Looking at the loop we get a total of 3+3 reactions (note that the internal reactions of AD and DA are the same and we do not count them as 6 , but 3 unique ones)
    Looking at the supports , one is a pin ∴ 2 reactions and the other is a roller ∴ 1 reaction.

    In conclusion, we have 3+3+2+1 =9 reactions
     
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