Shear force and bending moment diagram:
How can you draw a shear force and bending moment diagram.
Sol.: In these diagrams, the Shear Force or bending moment are represented by ordinates while the length of the beam represents abscissa. The following are important points for drawing shear force and bending moment diagrams:
1. Consider left or right side of portion of the section.
2. Add the forces normal to the beam on one of the portion. If right portion of section is chosen, force on right portion acting downwards is positive while force acting upwards is negative.
3. If the left portion of the section is chosen, a force on left portion acting upwards is positive while force acting downwards is negative.
4. The positive value of shear force and bending moment are plotted above the base line, and negative value below the base line.
5. The Shear Force diagram will increase or decrease suddenly that is by a vertical straight line at a section where there is a vertical point load.
6. In drawing Shear Force and bending moment diagrams no scale is to be chosen, but the diagrams should be proportionate.
7. For drawing Shear Force and bending moment diagrams, the reaction of the right end support of a beam need not be determined. If however, reactions are wanted particularly, both the reactions are to be determined.
8. The Shear force between any two vertical loads will remain constant. Hence the Shear Force diagram will be horizontal. The bending moment the diagram is inclined between these two loads.
9. For UDL Shear Force diagram will be inclined straight line and the bending moment 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.
11. The bending moment is highest at the section where Shear Force changes its sign.
12. In case of overhanging beam, the maximum bending moment will be least possible when negative max. Bending moment is equal to the negative maximum Bending moment.
13. If not mentioned particularly, self weight of the beam is to be neglected.
14. Section line is draw between that points on which load acts.