In order to find out the vertical displacement of C of the beam shown in Figure 4.16(a), apply a unit load as shown in Figure 4.16(b).

The internal virtual work is considered mainly due to bending and caused due to internal moments under going the rotation due to the applied loading. (internal virtual work done by shearing forces and axial forces is small in comparison to the bending moments and hence ignored). Since the where is the moment due to applied loading, the Eq. (4.12) for the displacement of C will take a shape of

The basic steps to be followed for finding the displacement or slope of a beams and frames are summarized as

1. Compute the bending moment (i.e. ) due to applied external forces.
2. Compute the bending moment (i.e. ) due to unit load applied in the direction of required displacement or slope.
3. Compute the integral over the entire members of the beam or frame which will provide the desired displacement.
4. The bending moment shall be taken as positive if sagging and negative if hogging (in case of beams).
5. The positive implies that the desired displacement is in the direction of applied unit load and negative quantity will indicate that the desired displacement is in the opposite direction of the applied unit load.