Karavan B. Stress-strain state of reinforced concrete arches made of high-strength concrete and improvement of the methodology for their calculation

For the first time, the operation of six double-hinged reinforced concrete arches made of high-strength quick-hardening concrete was experimentally studied, which made it possible to investigate the peculiarities of the stress-strain state of the belt sections and the nature of deflections and cracks development under single and repeated (low-cycle) short-term static and repeated impact loads. For the prototypes of the arches, we constructed diagrams of the dependence of "load - concrete deformation", "load - reinforcement deformation", "load - tensile force", "load - deflection", "load - displacement of supports", and diagrams of the dependence of crack opening width and the number of cracks in the arch belt on the load. The deformation diagrams and mechanical characteristics of high-strength quick-setting concrete at the age of 1 day and 28 days are presented. New experimental data on the stress-strain state of two-hinged reinforced concrete arches with and without tie-in under single and repeated short-term loads of varying intensity were obtained. A numerical experiment was carried out, i.e., calculations of experimental arches were performed in «LIRA» and «ANSYS» using the finite element method, and the data of the numerical experiment were compared with experimental studies of arches. An improved methodology for calculating the strength of normal sections and the stress-strain state of two-hinged reinforced concrete arches based on design standards, experimental data, and numerical experiments. The first section is devoted to a review of works covering the state of experimental and theoretical research on reinforced concrete arches, in particular: the scope of application of reinforced concrete arch structures in construction; general information about arches, loads on them, static calculation of double-hinged arches; stress-strain state and calculation of the bearing capacity of sections of double-hinged arches; review of experimental studies of reinforced concrete double-hinged arches. The chapter provides an overview of scientific papers on the results of experimental studies of high-strength rapidly hardening heavy concrete, as well as a brief review of studies on the resistance of concrete under low-cycle repeated loads. The second section presents the scope of experimental studies with the number of samples and their characteristics. The design of the prototypes and the process of their manufacture are described, the materials and their main physical and mechanical characteristics are specified. The test methodology for the experimental arches is described in detail, test schemes with the placement of measuring devices and their loading modes are shown. The principle of operation of the installation for dynamic testing of the arch is shown and described. The section presents the fracture criteria for the experimental arch specimens and concludes with the results. The third section presents the results of experimental studies of reinforced concrete double-hinged arches with and without tie-in from high-strength quick-setting concrete of classes C60, C80, and C90, in particular, their operation and stress-strain state under the action of a static single load to failure, under the action of a static low-cycle repeated load of η = (0.16...0.8) Fu, and under dynamic loading. As a result of the test, new experimental data were obtained on the stages and cycles of arch loading, namely: relative compressive and tensile strains of concrete and reinforcing steel in the cross-sections of the arch belt, relative tensile strains of the tie-in, values of the spacing and displacement of supports, deflections of the belt, the moment of crack formation and the nature of crack development in the belt, and the width of crack opening. Dependencies and diagrams were constructed based on these experimental values. The peculiarities of work under load and the nature of the failure of each experimental arch are described in detail, their bearing capacity and the load at which the failure criteria were reached are determined. The fourth section presents the results of a numerical experiment on the calculation of experimental two-hinged reinforced concrete arches under a single short-term load using the finite element method in the «LIRA» and «ANSYS» software packages; the data obtained from the numerical experiment were compared with the data obtained from the results of the experimental study of the arches. The scientific and applied provisions for calculating the strength of normal sections and the stress-strain state of two hinged reinforced concrete arches based on the deformation model and simplified calculation in accordance with current design standards using experimental data and the results of a numerical experiment have been improved.