PSI - Issue 81

Yuriy Panchuk et al. / Procedia Structural Integrity 81 (2026) 509–513

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commonly used elements of modern building structures due to their combination of high strength and reliability (Babych et al. (2019); Karalar et al. (2022); Korniychuk et al. (2024); Sarhan and Al-Zwainy (2025); Deng et al. (2021); Hansapinyo et al. (2021)). Compared to timber structures, metal structures, and other composite materials, reinforced concrete is characterised by high durability and fire resistance (Do et al. (2018); Rybak et al. (2025); Iskhakov et al. (2023); Pan et al. (2025); Kononchuk et al. (2022); Parneta et al. (2024)). In addition, reinforced concrete structures demonstrate good resistance to environmental influences and various corrosion processes. On the other hand, the use of mixed reinforcement allows for a more rational redistribution of stresses within the cross-section and more efficient utilisation of materials.

Nomenclature 

reinforcement ratio, %

prism compressive strength of concrete, MPa initial modulus of elasticity of concrete, MPa

f b,prism

E b0

E b modulus of elasticity of concrete, MPa f bt,prism prism tensile strength of concrete, MPa λ R plasticity coefficient η load level ε sp

relative strains of prestressed reinforcement, mm/mm relative strains of non-prestressed reinforcement, mm/mm relative strains of compressed concrete, mm/mm

ε s ε b ε bt K p M u

relative strains of tensile concrete, mm/mm mixed reinforcement coefficient load-bearing capacity of the beam, kNm height of the compressed concrete zone, cm

х

f

beam deflection, mm crack width, mm

a crc

The aim of this study is to perform experimental investigations of rectangular reinforced concrete beams with mixed reinforcement under a single short-term loading and to identify the specific features of the structural behaviour of such flexural elements. 2. Methods of experimental research Under factory conditions, two reinforced concrete beams with mixed reinforcement and dimensions of 100 × 100 × 2000 mm were manufactured in accordance with the applicable standards (Eurocode 2:2004; DBN B.2.6-98:2009). The concrete hardened at a temperature of 18-20 0C. The concrete class was C20/25. The cubic strength of the concrete was 32.1 MPa. The test beams were reinforced with prestressed reinforcement of class A-IIIv with a diameter of 12 mm (  02 = 850.7 MPa;  spu = 895.0 MPa; E sp = 1.95 × 10 ⁵ MPa) and non-prestressed reinforcement of class A-III with a diameter of 10 mm (  y = 556.9 MPa;  su = 708.9 MPa; E s = 2.01 × 10 ⁵ MPa). The non-prestressed reinforcement was placed in the midspan and terminated in accordance with the bending moment diagram. Strengthening of the A-IIIv prestressed reinforcement was carried out with fixation of both prestressing forces and reinforcement strains. The support zones of the beams were reinforced with flat reinforcement cages made of wire of class Vr-I with a diameter of 5 mm. Wire meshes of the same class were installed at the beam ends to prevent possible local crushing of concrete due to prestressing forces after release of the reinforcement. The total reinforcement ratio of the beams was μ = 1.15%. The mixed reinforcement coefficient was K p = 0.686. In total, two beams were manufactured and tested under a single static load applied until failure. The beams were fabricated in steel moulds with mechanical tensioning of the prestressed reinforcement against rigid abutments. The stress-strain state of the beams during the release of the prestressed reinforcement from the form stops onto the concrete was determined by the results of measurements of the deformations of the prestressed and unprestressed reinforcement over time. The deformations of the working reinforcement in the middle of the span were measured by two strain gauges glued to the unprestressed reinforcement and four strain gauges placed on the prestressed reinforcement with a base of 20 mm. To determine the possible slipping of the prestressed reinforcement at the ends of the beams, clock-type indicators with a division value of 0.01 mm were installed. After the development of all prestress losses, the stress in the prestressed reinforcement was 642.5 MPa. Beam testing was performed according to the “pure bending” sc heme at an age of 240-330 days in order to exclude time dependent changes in concrete properties (Eurocode 2:2004; DBN B.2.6-98:2009). The tests were conducted under laboratory conditions. Concentrated forces were applied at the third points of the span with a constant loading rate, in increments equal to 10% of the expected ultimate load. The magnitude of the applied load was determined using a dynamometer. To measure strains in the midspan section of the beams, strain gauges were bonded to the concrete on both sides along the height of the specimen with a gauge length of 50 mm. Strain gauges with a gauge length of 20 mm were installed on both prestressed and