РОЗРАХУНКОВА МОДЕЛЬ ЗЧЕПЛЕННЯ У ЗАЛІЗОБЕТОНІ ЗА НАЯВНІСТЮ ДИСКРЕТНИХ ТРІЩИН

Abstract

The thesis is devoted to the development of computational models of coupling in reinforced concrete in the presence of discrete cracks in the nonlinear formulation and deformation effects, taking into account the descending branch of the deformation carried out on the basis of experimental and theoretical studies. An analytical model of the bond reinforcement with concrete consists of a system of nonlinear equations, two of which are first-order differential equations. The graphs of the distribution of relative longitudinal strains movements, forces in concrete and reinforcement bar, as well as tangential bond stresses in the contact zone of the reinforcement bars and concrete along the length of the bar, the longitudinal reinforcement stiffness crossing the discrete crack from the acting force and displacement in the reinforcement are obtained as a results of experiments. The proposed model allows to conduct the calculation of the crack opening width in bent, centrally-stretched, eccentrically-stretched elements of reinforced concrete structures taking into account the nonlinear work of reinforced concrete and the contact zone of concrete and reinforcement. The techniques and experimental studies of the bond reinforcement with concrete under the deformation effects were developed, taking into account the descending branch of the strain in a representative volume of concrete by the acting the central and eccentric tensile force were carried out. New experimental data have been obtained on the nature of the deformation of reinforcement and concrete when the reinforcing bar is pulled from concrete (into concrete) and shifted along a discrete crack, taking into account the descending branch of deformation, among which the graphs of the dependence of the measured displacements on the acting loads, the pattern of crack formation in time. The cracks opening width, the values of destructive forces and cracking forces, the types of failure under various force impacts are performed. The two bar and five flat finite-element models of the adhesion between reinforcing bar and concrete are developed and investigated in terms of the central extension of the reinforcement in concrete in the environment of the PC “LIRA-SAPR”, and differentiate in the way of modeling the contact of the reinforcement with concrete. On the basis of a comparative analysis of the results obtained with the FEM models and the proposed analytical model, the most reliable finite element models of the reinforcement coupling with concrete are selected. Recommendations are given for modeling the coupling of reinforcement to concrete by the finite element method. Numerical studies using the accumulated bank of experimental data to study the bond reinforcement with concrete in a wide range of anchoring length, which yielded a comparison of theoretical and experimental parameters for determining relative displacements with respect to the concrete reinforcement under the action of the engagement of forces and the external tensile force (the coefficient of variation in research accumulated sample not exceeding 11,432%).