Several existing theories of elastic rods that take into account shear
effects are classified. Then, a new model for the influence of sheari
ng force, based on simple shear of finite amount, is proposed. The pro
perties of the model are examined on the stability problem for a heavy
elastic rod. It is shown that the rod may exhibit sub- and super-crit
ical bifurcation patterns at the trivial equilibrium configuration. A
comparison is made between the results for the critical load of the ro
d predicted by the new and the three different existing models.