Key facts to remember about transverse shear stress in beams

1. Shear force arises in regions of varying bending moments.

2. In these regions, the imbalance of moments leads to an imbalance of resultant horizontal forces over portions of the beam cross section.

3. Since all portions of a beam must be in equilibrium, horizontal shear stresses develop to counter the resultant horizontal forces produced by the bending moments.

4. At any given location along the span of a beam, the shear stress magnitude varies throughout the cross section. The magnitude varies with distance from the neutral surface.

5. Shear stress always occurs on pairs of orthogonal planes. If a shear stress exists on a horizontal plane, an equal magnitude shear stress also exists on a vertical plane.