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The use of concrete with traditional reinforcement pose the problem of finding ways to increase the crack resistance, impact strength, frost resistance and other characteristics, which in turn depend on the strength properties of the material. One of the solution is the use of dispersion reinforced concrete steel fiber concrete (with short steel fibers of 30-50mm). The combination of rigid fibers with significant strength reserves and the concrete could increase the crack resistance of the matrix and other strength characteristics. The paper presents the results of theoretical studies of the reinforcement percentage effect on the stress-strain state of the rectangular cross-section elements of steel fiber reinforced concrete (SFRC) in bending from at repeated loads with levels of application η = 0.5 and η = 0.7 . It is found that the limit deformations of the SFRC cross-section in bending is recommended to calculate using a polynomial function, which gives the greatest convergence between the true values and approximations in comparison with the logarithmic and exponential functions.

Abstract. The objective of this work is analysing of the calculating results of theoretical values of the beam flexure by the Ukrainian National Standard, European Standard and by the experimental data of concrete beams testing.The results of the experimental investigations of flexures of the reinforced concrete beams are shown. The theoretical comparison of the flexures of the reinforced concrete beams according to the Ukrainian National Standard and European Standard is done. It was proved that the flexures by these methods have an identical convergence with experimental data. The algorithm for determining deformations of materials at the known bending moments by using the method of simple iteration or method of successive approximations is proposed. The solution of this problem allows practical use of the National Standard and European Standard for calculating flexures. Analyzing of the experimental flexure and the calculated value is showed; the significant difference can be explained by the empirical coefficient.

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