Strength of Materials

4.4 BENDING MOMENT AND SHEAR FORCE

Bending moment at a section is defined as the algebraic sum of the moments about the section of all the forces (including the reaction) acting on the beam, either to the left or to the right of the section.

Shear force at a section in a beam is defined as the algebraic sum of all the forces including the reactions acting normal to the axis of the beam either to the left or to the right of the section.

4.4.1 Sign Convention

1. Bending Moment

Bending moment is said to be positive (sagging) moment at a section when it is acting in an anticlockwise (ACW) direction to the right and negative (hogging) moment when acting in a clockwise (CW) direction (Figure 4.14).

 

 

Fig. 4.14 Sign convention for bending moment. ...