Explain the Moment of resistance?

Sol.: The two equal and unlike parallel forces, the lines of action of which are not same, form couple. The resultant compressive force (P_C) because of compressive stresses on one side of neutral layer (or neutral axis) is equal to the resultant tensile force (P_t) because of tensile stresses on the other side of it. So these 2 resultant forces form a couple, and moment of couple is equal and opposite of the bending moment at section where the couple acts. This moment is called as moment of resistance (M.R.).

So, the moment of resistance (M.R.) at any section of beam can be defined as moment of the couple, formed by longitudinal internal forces of opposite nature and of equal magnitude, set up at the section on either side of neutral axis because of bending.

In the magnitude moment of resistance of any section of beam is equal to bending moment at that section of it.