This article describes strengthening normal cross-section of reinforced concrete beams with prestressed reinforcement under load. The samples of RC beam with 2100 mm. length, 100 mm width, and 200 mm height was tested. As beam’s tension reinforcement A500C Ø12 mm rebar was chosen. A240C Ø8 mm rebar was chosen as compressed reinforcement. Transverse reinforcement – A240C Ø8 mm rebar located in the supporting area with step 50–100 mm. Class of the concrete was C32/40. The beams were tested for a pure flexure. The load was added using the hydraulic cell in the thirds of the span. The beams were strengthened using two non- prestressed or prestressed reinforcing bars A500C Ø12 mm. Reinforcing bars were connected with the main beam reinforcement by means of welding using reinforcing bars Ø28 mm. The beams of three series were tested: two beams of the BO series and two beams strengthened with the non-prestressed reinforcing bars at 0,5Mu and two beams strengthened with the prestressed reinforcing bars at 0,5Mcr. All tested beams were destroyed in the central zone. The beams of BO series were destroyed after to the onset of the flow of the beam’s longitudinal reinforcement and with further chipping of the compressive zone of the concrete. The beams of BR and BRR series were destroyed after the flow of the additional prestressed reinforcing bars, further flow of the main reinforcing bars and the destruction of the compressive zone of the concrete. After the tests there is an increase in strength of the reinforced of the beams for 89% and 93%.

1. Du J., Liu X. Experimental study of RC continuous beams strengthened by external prestressing. INNOVATION& SUSTAINABILITY OF MODERN RAILWAY PROCEEDINGS OF ISMR, Beijing, 2008. pp. 221–227. 2. Kim S., Yang K., Byun H., Ashour A. Tests of reinforced concrete beams strengthened with wire rope units. ENGINEERING STRUCTURE, Kwangju, 2007, Vol. 29, pp 2711–2722. 3. Minelli F., Plizzari G., Cairns J. Flexure and shear behavior class of RC beams strengthened by external reinforcement. CONCRETE REPAIR, REHABILITATION AND RETROFITTINGII, Cape Town, 2009, P. 377–378. 4. Rymar Ya. V. Mitsnist’ ta deformatyvnist’ zalizobetonnykh balok, pidsylenykh pid navantazhennyam naroshchuvannyam armatury: Avtoref. dys. … kand. tekhn. nauk: 05.23.01 [Strength and deformability of the reinforced concrete beams, strengthened by the reinforcing bars under load]. Lviv, 2010. – 22 p. 6. Boiarchuk B. A. Mitsnist’, trishchynostiykist’ ta deformatyvnist’ zalizobetonnykh konstruktsiy pry riznykh sposobakh pidsylennya roztyahnutoyi zony. Avtoref. dys. na zdobuttya nauk. stupenya kand. tekhn. nauk: 05.23.01 [Strength, crack resistance and deformability of reinforced concrete structures with different methods of strengthening the stretched zone]. – Lutsk, 2003. – 157 p.