Strengthening of concrete beams by CFRP considering initial state

The object of research is the bearing capacity of normal sections of bendable reinforced concrete structures, reinforced in the tensile zone with high-strength carbon fiber-reinforced plastic materials. The purpose of research is to analytically obtain the most universal and accurate dependence for determining the limiting bending moment of elements reinforced in a tensile zone with carbon fiber-reinforced plastic materials, taking into account their initial state before strengthening during failure of the concrete compressed zone. The objectives of research are: analytically obtaining the dependence for the height of the compressed zone of concrete in the section in the limit state after strengthening, taking into account the initial stress state; comparison of the load-bearing capacity obtained taking into account the presented dependencies, according to the dependencies adopted in the current regulatory documents, as well as according to the nonlinear deformation model. Method. The work adopted the basic techniques used in the modern theory of strength of concrete and reinforced concrete, as well as in the mechanics of anisotropic deformable solids. Results. The obtained analytical expressions for determining the limiting bending moment perceived by normal sections of reinforced concrete elements reinforced with carbon fiber-reinforced plastic materials in the tensile zone make it possible to consider the initial stress-strain state and the degree of its influence on the strength of such elements. A reasonable refinement of the analytical dependencies of the normative approach makes it possible to achieve good convergence with the results of calculations using a nonlinear deformation model. The proposed analytical dependencies make it possible to determine the actual strength of normal sections of reinforced bending elements, considering the initial stress-strain state without the need for complex iterative calculations.