This relationship explains how a transverse shear force V (which
acts vertically in our beam) can create the need for additional strengthening in
the horizontal direction.
Recall that ΔM/Δx = V, the transverse shear force. Wherever there is a transverse shear force V, bending stress resultants in portions of the beam will be unbalanced and additional shear force acting in the longitudinal direction will be needed to satisfy equilibrium.