The elastic theory of bending and the moment of inertia

We have already seen that bending plays a major part in structural behaviour and that this is caused by bending moments. We have also seen that to equilibrate moments, opposing moments are required. Figure 56 shows how a beam under bending stress has to react internally to produce these equilibrating moments. It was also explained above that deformation is indicative of the stresses involved. These stresses, which are the result of the elastic deformation, produce the forces required for equilibrium. Figure 91 shows a beam under load and its deformation at one section. We see that the greatest shortening occurs at the top causing compressive stresses, while the greatest lengthening occurs at the bottom causing tensile stresses.