The paper deals with the torsional rigidity of homogenous and orthotropic beam with rectangular cross section. The torsional rigidity of the considered beam is defined in the framework of the Saint-Venant theory of uniform torsion. Exact and approximate solutions are given to the determination of the torsional rigidity. The shape of cross section is determined which gives maximum value of the torsional rigidity for a given cross-sectional area. The dependence of torsional rigidity as a function of the ratio shear moduli of beam is also studied.

The paper deals with the torsional rigidity of homogenous and orthotropic beam with rectangular cross section. The torsional rigidity of the considered beam is defined in the framework of the Saint-Venant theory of uniform torsion. Exact and approximate solutions are given to the determination of the torsional rigidity. The shape of cross section is determined which gives maximum value of the torsional rigidity for a given cross-sectional area. The dependence of torsional rigidity as a function of the ratio shear moduli of beam is also studied.