Experimental studies of reinforced concrete structures in the "HPP supporting piers – powerhouse headwall" system strengthened with prestressed basalt composite reinforcement. Part I

Introduction. With long-term operation of head run-of-river powerhouses of hydroelectric power plants (HPP), technical changes occur that lead to a decrease in operational properties in reinforced concrete structures. To substantiate a new nanotechnology for strengthening long-term operated hydraulic structures based on the use of prestressed reinforcement from nanomaterials (BFRP), a set of experimental studies with elements of computational studies was carried out, taking into account the characteristic features of reinforced concrete structures of HPPs. Methods and materials. Experimental studies were carried out on the basis of reinforced concrete models of hydraulic structures "HPP supporting piers – powerhouse headwall" (scale M 1:25), which were manufactured and tested for static impact; after which they were strengthened with external reinforcement made of prestressed BFRP nanomaterial, with rebars installed in two directions: along and across the flow. A 3D finite element model of a run-of-river HPP powerhouse was developed to analyze its stress-strain state (SSS), taking into account seismic actions of more than 8 points (MSK scale) within the framework of the dynamical theory. Results. As a result of experimental studies of reinforced concrete models of hydraulic structures "hydroelectric power plant piers – headwall of the HPP powerhouse", the nature of crack formation, the width of crack opening and inter-block construction joints were determined, which were recorded in magnitude higher in non-strengthened reinforced concrete experimental models than in models strengthened with prestressed basalt composite reinforcement. In experimental reinforced concrete models under the acting loads, tensile stresses in the steel reinforcement in the area of the interface of the piers and the headwall were determined, which almost reached the value corresponding to the yield strength. In the article, calculations of the run-of-river HPP powerhouse were performed using the dynamic theory of calculation under the action of seismic loads of more than 8 points (MSK scale). At the same time, deformations of the structure and stresses in its elements in different periods of time (in seconds) were obtained, counting from the beginning of the seismic action. Discussion. It was obtained that the new technology of strengthening using reinforcement made of BFRP nanomaterial across and along the river flow leads to a decrease in tensile stresses in steel horizontal reinforcement across the flow in the headwall and in piers by more than 1.5 times with redistribution to basalt composite reinforcement. In case of seismic actions, the operation of the above structures will be more complex and the parameters of this work must be determined by calculations, taking into account all factors that will allow to study and ensure longterm safe operation of HPP structures. To achieve this goal, it is necessary to develop a 3D mathematical model of experimental reinforced concrete structures and verify it using a set of experimental data obtained. Further, the verified mathematical model can be used to calculate the SSS of the HPP powerhouse under the action of a set of loads and influences: static, hydraulic, temperature, seismic. Conclusion. On the basis of a set of experimental and computational studies of experimental reinforced concrete models "HPP supporting piers – powerhouse headwall", strengthened with prestressed basalt composite reinforcement, nanotechnology for strengthening reinforced concrete structures of long-term operated hydraulic structures based on the use of prestressed reinforcement from nanomaterials (BFRP) was substantiated, including the load-bearing capacity, displacement, width of opening of inter-block construction joints and cracks, deformations of steel and basalt composite reinforcement depending on the method of strengthening of reinforced concrete structures by external reinforcement.