In these diagrams, the shear force or bending moment are represented by ordinates whereas the length of the beam represents abscissa.
The following are the important points for drawing shear force and bending moment diagrams:
Consider the left or right side of the portion of the section.
Add the forces (including reaction) normal to the beam on one of the portion. If right portion of the section is chosen, a force on the right portion acting downwards is positive while force acting upwards is negative.
If the left portion of the section is chosen, a force on the left portion acting upwards is positive while force acting downwards is negative.
The +ive value of shear force and bending moment are plotted above the base line, and -ive value below the base line.
The *.F. diagram will increase or decrease suddenly i.e. by a vertical straight line at a section where there is a vertical point load.
In drawing *.F. and B.M. diagrams no scale is to be chosen, but diagrams should be proportionate sketches.
For drawing *.F. and B.M. diagrams, the reaction of the right end support of a beam need not be determined. If however, reactions are wanted specifically, both the reactions are to be determined.
The Shear force between any two vertical loads will remain constant. Hence the *.F. diagram will be horizontal. The B.M. diagram will be inclined between these two loads.
For UDL *.F. diagram will be inclined straight line and the B.M. diagram will be curve. 10. The bending moment at the two supports of a simply supported beam and at the free end of a cantilever will be zero.
The B.M. is maximum at the section where *.F. changes its sign.
In case of overhanging beam, the maximum B.M. will be least possible when +ive max. B.M. is equal to the -ive max. B.M.
If not otherwise mentioned specifically, self-weight of the beam is to be neglected.
Section line is draw between that points on which load acts.
Numerical Problems Based on Simply supported beam
