Khmil R. Stress-strain state and remaining resource of reinforced concrete structures reinforced under load

The dissertation is devoted to the research of reinforced concrete bending and compressed-bending structures, which are strengthened by increasing the cross section of reinforcement or reinforcement and concrete at one time under loading. In the first section analysis of stress-strain state of reinforced concrete structures, methods of forecasting (estimating) remaining resource of strengthened structures in operating conditions are presented. In addition, the reliability analysis of strengthened reinforced concrete structures, the state of the calculation of the actual reliability of the elements after reinforcement. The development of methods and programs for experimental research of reinforced concrete bending and compressed-bending elements, reinforcement of which is performed by the most common methods, namely increasing the cross section of reinforcement, reinforcement and concrete (clamp) are develped. The presence of the load on the structure allows us to simulate the operation of the strengthened structure in accordance with the actual operating conditions and the device of the reinforcement. The third section presents the results of experimental research of bending and compressed-bending reinforced concrete elements: not strengthened and strengthened with additional reinforcement and additional reinforcement and concrete both (reinforced concrete jacket) with and without preloading during strengthening. On the example the strengthening method by making of reinforced concrete jacket, as the most difficult to perform and as a general case of strengthening of reinforced concrete structures by increasing the cross section, some results were presented. The fourth section presents calculation methods of remaining strengthened reinforced concrete structures bearing capacity. An important difference between the calculation of the force model from code of DSTU B V.3.1-2: 2016 from the deformation model of calculation by DSTU B V.2.6-156: 2010 is that it does not allow to estimate the stress-strain state of the structure at any cross section layer and any stages but only in the limit state. The fifth section describes the computer modeling of strengthened r/c beams in the application software, which were developed by the finite element method (FEM). Algorithms for creating a geometrical and physical model, a loading model of strengthened structure, which would reflect the real conditions of their operation and reinforcement, are proposed. The sixth section presents the results of development and testing of the proposed methods, as well as analysis of the obtained values of qualitative and quantitative indicators of reliability – reliability index β of bending and compressed-bending structures, strengthened by increasing the cross section of reinforcement, both reinforcement and concrete under load. The level of load acting at the time of strengthening is considered as an additional random value. Based on the analysis of the obtained values of reliability indexes β and probability of failure-free operation P(β) the approaches to determining the remaining resource of reinforced structures are proposed.