Consider a homogeneous or inhomogeneous beam made of isotropic or orthotropic materials, with a linear central axis and a thin-walled cross-section (constant over the length of its longitudinal axis) of any form. Up until now, in order to calculate the fundamental cross-section parameters, the shear rigidity, the torsion stiffness and the shear stresses of this beam caused by torsion and flexure, it has been necessary to use a complex three-dimensional calculation with the help of the finite elements method (FEM). Due to this, special line elements are developed in this thesis, with which the numerical determination of warpages of the above mentioned beam is possible. Further, the shear stress distribution, the shear and torsion stiffness and the shear centre can be determined. In order to calculate these parameters, only knowledge of the material properties and the cross-sectional geometry is necessary and not that of longitudinal stretching of the beam. This is possible because the three-dimensional problem can be transferred into a two-dimensional one. This calculation model determines numerically the unknown cross-sectional deformation taking into account the analytically known deformation in the cross-sectional level as well as the known stress dependency in the longitudinal direction of the beam using FEM.