The aim of the research - to investigate the behavior of thin-walled beam I-section loaded with bending and torsion using theoretical, numerical, and experimental approaches. In this paper, the main criteria for consideration of the different methods of analysis is the geometric characteristic of the section. The results obtained by the finite element method, the numerical method, as well as experimental data are compared. The analysis by finite element method by considering an additional degree of freedom at a node to include the restrained torsion and the dimension of the stiffness matrix is thus 14×14. The results of the calculation according to this theory are compared with the numerical solution obtained using finite element software, and with the results of the experiment. The I-beam section subject to bending with torsion is considered. The deformations, strain, and stress distributions of open thin-walled structures subjected to bending and torsion are presented using experimental methods. The comparative results for the angle of twisting, deformations, and normal stresses in the frame element subjected to combined loading are displayed graphically. To evaluate the results, a theoretical, numerical, and experimental investigation of I-beam behavior under bending and restrained torsion was carried out. As a result of the comparison, it was revealed that the results obtained according to the refined theory proposed by the authors have good convergence with experimental data and are also quite close to the values obtained using commercial software.