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In current economic trends, changes in construction using are required. It usually leads to changes in value and type of the working load on building structures, with the requirement to rate the technical state and replace or strengthen the elements. An important aspect of determining the residual bearing capacity of damaged bending reinforced concrete elements is the research concerning the influence of difference defects and damages on the change of strength and deformability. In the article main types of damages and defects, methods of studies of damaged reinforced concrete elements and the expediency of usage of this elements are described. However, most methods are suitable only for certain defects and damages due to the large complexity of calculations and the consideration of multifactoriality. Significant complexity of a single method for calculating damaged elements depends on the possible changing stress strain state of an element in combination with certain defects and damages, the presence of a non-complete separation where during loading or alteration of the damaged element the fractions become included in the work, reinforced concrete is the composite material which carrying complexity in calculating the joint work of its components.

In the building industry, it is a frequent cause of damage to elements at different stages: during transportation, operation, installation, etc. Since replacing an element is not always possible due to various circumstances, it entails significant financial losses, logistics, and others. For this reason, the expediency of studying the effect of damage on the bearing capacity of reinforced concrete elements is growing. This effect is dependent on its type and has significant variability. In the case of the combination of the defect and damage in reinforced concrete elements, the complexity of the research of this element increases significantly. In this article is discussed: a review of damaged reinforced concrete elements; researching the influence of the damage and additional factors on the element; developed testing methodology for bending reinforced concrete elements with damage to concrete in a compressed zone with insufficient reinforcement, when performing damage to the action of the load and during the action of the load, is presented; the influence on the deformability and bearing capacity of the variability of damage on the sample with insufficient reinforcement is reflected, taking into account the factor of change in the load at which the damage is performed; a comparison is made of the dependence of the change in the actual height of the compressed zone on the change in the load on the elements; implementation of conclusions on the result of the study.

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Abstract. The tendency to use buildings and structures for new purposes is growing every year, which leads to the need to change constructive solutions. In such cases, during inspections, there is a need to analyze the bearing capacity of damaged structures. Damage can occur at various stages of the use of an element in construction: transported, installation, operation, and others. For this period, according to the current standards, the residual bearing capacity is determined by the method of the equivalent element. Thus, the strength of the reduced cross-section is determined (the damaged part is folded back). This calculation excludes from the consideration the zones that perceive the loads, but are located in plane damage. Currently, studies of the effect of damage on the residual strength of elements are constantly increasing, taking into account their expediency. Research is more focused on typical elements such as beams and columns. The compositional properties of reinforced concrete elements significantly increase the number of factors that must be taken into account when performing experimental and theoretical studies in this area. The damage itself, depending on their type and characteristics, has a different effect on the strength of the element. There is also a need to take into account additional variations in external influences on the element in addition to damage, such as: change in the load level, the presence of defects, change in the design scheme of the element due to external factors and others. Thus, the priority is, first of all, the study of idealized injuries, with the subsequent use of this base of developments for the study of this damage with additional factors. This article discusses: research on damaged reinforced concrete elements in Ukraine and abroad; the developed test methodology for bending reinforced concrete elements of rectangular cross-section with damage to concrete in a compressed zone with insufficient reinforcement, with variability in changing the width of damage of 20 and 80 mm with a height of damage of 30 mm is presented; the influence of variability of damage in research specimens with insufficient reinforcement on deformability and bearing capacity is reflected; the influence of damage variability on the change in the real height of the compressed zone from the load level is considered; implementation of conclusions on the result of the study.