Bending Moment Diagrams - UDLs

1. Apr 29, 2008

BrIDo

I'm ok with these simply supported beams, cantilever's and such.

Firstly, I'd like to state my understanding of bending moment diagrams and would appreciate if you can tell me if I'm going wrong somewhere:

Draw a line and mark the points where forces act on the line.

A_____B__________C__D

Take point A, and sum the torques acting to the right of that point.
At B, use the forces C and D.
Same as above for C.
D would be 0.

Regardless of whether these values are positive or negative, all we're interested in is the magnitude. Whether the moment diagram itself is positive or negative depends on the actual deflection of the beam (smiley face for positive).

Assuming the above is right, with a UDL.. I'm used to assuming the force it provides acts in the centre of it. Do I take a moment about this point? Do I used this force when calculating other moments?

One example of a bending moment diagram I've seen looked as though they took the moment at the point where the UDL ends.

Any help, much appreciated.

Do I take the moment about the po