Shear & Bending Moment Diagrams

[skaterbasist]

I apologize for not using the template, but my question is more of a conceptual question than anything else.

The only thing so far that confuses me with Shear and Bending Moment Diagrams is when, in some cases, it is easier to approach the beam from the right side instead of the left.

When you do so, how does the graph change? Is it "mirrored"? If so, are both the shear & moment diagrams mirrored about the Y axis or X axis? Does it matter if the problem is cantilevered or simply supported in terms of the above asked question?

Thank you for any assistance. I have been stuck with this scenario in my head all day long.

 

[pongo38]

It's not so much right and left as - well, in a cantilever, if you start x=0 at the free end of the cantilever, you don't need to initially work out the reactions. If you are using the method of integration, the boundary conditions are easier to deal with at the free end than at the encastre end. However in a simply supported beam, it doesn't make much difference, because you really do need those reactions before you start the shear force or bending moment diagrams. A symmetrical beam will not necessarily have symmetrical V and M diagrams. One way for you to learn, after having covered basic cases, is to draw some symmetrical V and M diagrams, and work out what loading would have produced such diagrams.