The classical bending theory of beams, based on Bernoulli's
hypothesis that the plane normal cross sections of a beam remain
plane and normal to the deflected centroidal axis of the beam during
deflection, ignores the deformation caused by shear forces. When a
column buckles, however, the axial load causes not only bending
moments in the cross sections, but also shear forces. This is particularly
so in castellated columns because the web is flexible in shear. The
deformations due to shear forces in castellated columns can be taken
into account by using either the generalized form of the classical
bending theory called Timoshenko beam theory