"The force which tends to make the top and bottom flanges or fibres of a beam move parallel to one another. The web of the beam resists the shear force, which is at its greatest at the ends of the beam next to where it rests on its supports."

A shear load is a force that causes shear stress when applied to a structural element. Shear stress, which is a force per unit area, occurs in the plane perpendicular to normal stress; it is created when two planes of the same object are trying to slide past one another. Engineers need to calculate the shear load on structures to make sure they don’t experience mechanical failure. Too high a load can cause materials to yield or permanently deform.

Cantilever beam with shear forces |

Normal stresses occur when a material is put into tension or compression. In this case, both applied forces are along the same axis. If the forces are applied along different axes, there will be shear stresses in addition to any normal stresses. A square element of the material will experience forces that tend to skew it into a parallelogram. The average shear stress in a material is equal to the shear load divided by the cross-sectional area in question.