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Shear Force and Moment Diagrams

  1. Aug 19, 2011 #1
    1. The problem statement, all variables and given/known data
    This cantilever confuses me so much. The negative point loads and negative distributed load. And is the other one that's -40kN/m moment/torque or something. My question is how do I do the shear force and bending moment diagrams of this. Am i suppose to redraw the diagram and make everything positive by changing the direction??? can i even do that especially with the distributed load?

    I don't really mind much for the numbers or anything its just the shape of the diagrams.
    I've attached the diagram of the cantilever beam.


    2. Relevant equations
    M=Fd where m=moment, f=force and d=perpendicular distance.


    3. The attempt at a solution

    i have attempted and attached it and so can anyone tell me if this looks right?
     

    Attached Files:

    Last edited: Aug 20, 2011
  2. jcsd
  3. Aug 20, 2011 #2

    SteamKing

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    You are confused because your problem diagram makes little sense. The applied torque should have units of kN-m, not kN/m; there is a difference. You also show an applied point load and an applied distributed load, both with negative magnitudes, yet each is drawn acting in opposite directions.

    If you can provide a scan of the original problem, that would go a long way in resolving these contradictions.
     
  4. Aug 20, 2011 #3
    Yeah i realize the difference between kn-m and kn/m,, silly mistake by me but about the distributed load and point load, that's how the question is given. that is the original problem. negative values. i know its confusing but this is what was given to us. i can just simply switch the directions and make the values a positive right? even the distributed load? can i switch the direction of the torque and make it a positive???

    is the shape of the bmd and sfd look right?
     
  5. Aug 20, 2011 #4

    SteamKing

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    Without getting into the problems with the applied loads, no, your shear and moment diagrams are not correct. At the free end of the cantilever (the left end), there are no applied loads. Therefore, the shear and bending moment at this end must be zero. A couple which is applied to the beam produces a jump discontinuity in the bending moment curve just like an applied point load force produces a jump discontinuity in the shear curve.
     
  6. Aug 20, 2011 #5
    i've redrawn the diagram and attached it, is this diagram equivalent to the original one?

    thats the diagram i used to draw the shear and moment diagrams. are both diagrams incorrect or just the moment?
     

    Attached Files:

  7. Aug 20, 2011 #6
    im pretty sure the shear diagram is right, isnt it??
     
  8. Aug 20, 2011 #7

    SteamKing

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    I don't see any calculations to determine the reactions at the wall. I also don't see any shear or moment diagrams for the revised beam.
     
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