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Shear Force and Moment Diagrams

  • Thread starter TyErd
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  • #1
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Homework Statement


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.


Homework Equations


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


The Attempt at a Solution



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

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Answers and Replies

  • #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.
 
  • #3
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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?
 
  • #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.
 
  • #5
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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?
 

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  • #6
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im pretty sure the shear diagram is right, isnt it??
 
  • #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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