The article deals with the case when a concentrated force is applied to the web of a prestressed beam. The preliminary shear stresses do not affect the stress state in the middle of the beam span. However, preliminary normal stresses will act over the entire height of the wall and affect the distribution of the zone of local stresses and the stress state of the web. Determination of stresses in a beam is based on the beam theory of S.P. Timoshenko. The article presents a system of equivalent forces on the edges of the wall and the equation of normal stresses in the cross section of a prestressed beam. Compared to a conventional beam, prestressing reduces normal stresses from concentrated forces.

Keywords: thin-walled structure, steel beam, I-beam cross-section, prestressing, local stresses, local effect, Saint-Venant principle, Timoshenko SP beam theory, Karman's solution, Fourier integral, stress function

The article analyzes the results of experimental studies of prestressed steel I-beams. Presented specific features of the stressed and deformed states of welded steel beams, prestressed by wall stretching and bending of the initial T-element. In the first method, the prestressing in the beam was created by mechanical stretching of the wall on a special stand. In the second method, the T-piece is loaded by external forces applied to the T-bar plate until normal stresses appear at the bottom point of the wall, equal to the design resistance of low-carbon steel, then the second belt plate is welded to the T-piece element. The results of a numerical experiment with these beams, carried out in the SP LIRA, are considered. Presented a comparative assessment of the results of numerical and full-scale tests of prestressed I-beams a similar section with bimetallic beams without prestressing.

Keywords: web stretching, T-beam bending, section asymmetry, numerical experiment, test stand, stress, bearing capacity, beam rigidity, bending deformation, local stability