THE STUDY OF LEVEL FORMATION AND DISCLOSURE OF NORMAL CRACKS IN REINFORCED CONCRETE ELEMENTS

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This article is devoted to the study of the main patterns of normal cracks multilevel formation in reinforced concrete elements and structures. A critical analysis of the latest publications related to the theme of these studies is carried out. The classification is carried out and the main shortcomings of the known works on the four identified areas of research are identified. The most important elements of the method of reinforced concrete beams experimental research are developed and briefly described. The main characteristics of the prototypes, the conditions for their manufacture and storage are given. The most important results of testing reinforced concrete beams, concerning the main parameters and characteristics of level formation and crack disclosure are highlighted. It was confirmed that the process of normal cracks formation is indeed multilevel and is accompanied by a gradual disruption of the bond between reinforcement and concrete. According to the results of experimental studies, it has been established that in the real design of bending reinforced concrete elements, when calculating their crack resistance, it is possible to restrict oneself to only 2 levels of normal cracking. The calculation of the step and normal cracks opening width in beams research was carried out according to the real multilevel and traditional "one-level" schemes of their formation. These calculations were carried out according to the author's general and simplified methods, according to a method that uses a linear function of the average adhesion stresses of reinforcement with concrete, according to the methods of current domestic and European standards and building rules. Their statistical comparison with the experimental studies results confirmed the effectiveness of those calculation methods in which the crack formation step is directly related to the basic laws and parameters of reinforcement to concrete adhesion. The results of this comparison showed that the author's general method, based on the use of a nonlinear function of the reinforcement with concrete average adhesion stresses, turned out to be the most accurate. Keywords: reinforced concrete, elements, adhesion, reinforcement, cracks, levels of formation, step, width.