The connection of rebar of concrete structures by looping rebars with the formation of the joint core was developed at the beginning of the last century, but it has not been actively used due to the complexity of the work and the lack of calculation methods. The article presents a review of the history of the creation, practical application, national and foreign scientific research of the loop joints of rebar in concrete structures. The article describes advantages and disadvantages of such joints, gives brief information about the main parameters of the joints and the principle of operation. Suggestions for the directions of further study of the looped joints of reinforcing bars operation are presented, the goals for full-scale and numerical experimental research aimed at the development of calculation and design methods of looped joints for their further wider introduction into the construction practice are set.

The article describes the statement of a problem of research of the stress-strain state of reinforced concrete monolithic structures with loop joints of rebar using the finite element method. A review of plastic damaged concrete model, a description of its basic parameters and their selection by the example of the problem of verification of mathematical material model by the results of full-scale tests of concrete prism and beam with a loop joint over a static load have been presented. The detailed description of the model parameters, diagrams of concrete and reinforcement state, including stress-strain diagrams with regard to the models features, as well as graphs comparing the experimental and numerical research of a concrete prism and a bendable reinforced concrete beam with a loop joint, including a model of concrete, and reinforcement model are presented. The results of numerical calculations obtained stresses in the reinforcement of 514 MPa, which is close to those resulting from the full-scale experiment of 550 MPa (Fig. 8). The value of deflection when the failure load in the experiment was 16.7 mm, in the FE model it was 18.07 mm.