Chapter 11 - Torsion of Beams

Abstract

Torsion in beams arises generally from the action of shear loads, whose points of application do not coincide with the shear center of the beam section. The solution of torsion problems is complex particularly in the case of beams of solid section and arbitrary shape for which exact solutions do not exist. Empirical formulae are used that are conveniently expressed in terms of correction factors based on the geometry of a particular shape of cross section. The behavior of closed and open section beams under torsional loads is similar, in that they twist and develop internal shear stress systems. A pure torque applied to a beam section produces a closed, continuous shear stress system because the resultant of any other shear stress system would generally be a shear force unless the system was self-equilibrating. In a closed section beam the closed loop system of shear stresses is allowed to develop in a continuous path round the cross section, whereas in an open section beam it can only develop within the thickness of the walls.