Mumbai university > MECH > SEM 3 > Strength Of Materials

Marks: 5M

Year: Dec 2013

A Bending Moment Diagram (B.M.D.) is a graph, which shows the variation of the bending moment along the length of a beam. The characteristics of this graph are as follows:

• The bending moment variation is linear between two sections where no load acts. Moment is a function of force and perpendicular distance. So, if there is no force acting, the bending moment is a function of only the distance and hence the variation of the bending moment here is linear. This variation is represented as a straight line on the B.M.D.

• Is a Uniformly Distributed Load acts between two sections; the variation of the B.M.D. of the beam is parabolic. This is represented as a parabolic curve on the B.M.D.

• If a Uniformly Varying Load acts between two sections; the variation of the B.M.D. of the beam is cubic. This is represented as a cubic curve on the B.M.D.

• If a couple is present at a section, the bending moment value changes from one value to another suddenly. This change is equal to the value of the couple. This is represented by a straight line on the B.M.D.

• The point on the bending moment diagram where the bending moment changes its sign and acquires a zero value is known as the ‘Point of Contra flexure’.

  The ‘Point of Contra flexure’ is also known as the ‘Point of Inflexion’. This point signifies the point of change of the bending patter in the beam