In this thesis, the topic of torsion action on straight rods is covered. Expressions were derived to calculate the stresses and deformations generated by the torsion action, and the procedure for solving statically undefined tasks when the element is loaded with torsion moment is explained. The topic covers the application of this theoretical knowledge to the sizing of reinforced concrete beams subjected to torsion action and its combined action with bending, by longitudinal and transverse force. The calculation of torsion reinforcement and the method of reinforcement of beams by torsion reinforcement are explained. Check of the limit state of usability of a reinforced concrete beam loaded with torsion action is also included. The method of determining the twist angle as the corresponding deformation is explained, and it differs depending on the duration of action. Derived expressions for the twist angle are used in the example of console deflection determination task. An example of sizing a reinforced concrete beam loaded with a combination of the torsion moment action, bending and transverse forces has been solved. The last chapter of the paper gives a conclusion on the torsion action and the importance of structures calculation on its action.