Abstract. The joints ensure the joint performance of the load carrying structural systems and they are the most responsible and important elements. Keyed joints are widely used in construction. They are characterized by an increased resistance to shear. On these grounds the structural concepts of keyed joints need further improvement. The article presents the research results of experimental test pieces five series in the form of single keys and one-keyed joints. Those samples have been tested in Poltava National Technical Yuriy Kondratyuk University. Follow strength factors have been varied: geometric parameters of joints (depth, height, width) and their ratio; angle of support surface (rectangular, trapezoidal and triangular key); level of compression; reinforcement (quality of reinforcement and the nature of its location); jointing width. The samples were made of heavy-weight, expanded clay and fibre concrete. The experiments program includes influence study both of one of these factors and their combinations. The deformations, nature of failure, the ultimate load have been studied. Structural parameters of keyed joints which ensure the efficient behaviour have been installed.

The connections ensure teamwork under the load of buildings and structures bearing elements. Joints distraction leads to a change in the structures support conditions and their design schemes. Keyed joints are the most effective under significant shear force action because they have high shear resistance. This makes it necessary to further improve their design solutions. In the article the experimental study results of multikeyed joints two series are presented. The joint models were tested in the department laboratory of reinforced concrete and stone structures and resistance of materials Poltava National Technical Yuri Kondratyuk University. The keyed profile (key’s depth to height ratio and load application surface angle), reinforcement (quantity of reinforcement and its location character), seam width, keys number were varied in experiments. Heavy-weight concrete, expanded clay concrete and polypropylene fiber concrete were used for the samples manufacture. In experiments the influence of one of listed factors and their combinations for bearing capacity were studied. The concrete and reinforcement strains, distraction character, the failure load were studied. The influence degree analysis of the factors determining the strength was carried out. The design joints parameters that correspond to maximum strength were determined.

Abstract. The two-dimensional concrete elements under the action of one-sided central crushing often occurs. For them, the strength problems are solved on the basis of the concrete ideal plasticity theory variational method with application of discontinuous velocities functions. The method takes into account the influence on concrete elements strength the compressive strength and tensile strength of concrete. It also takes the ratio of a sample height to the crushing platform length and friction coefficient between a surface of element and a load punch if it′s necessary. The results of experimental researches were confirmed the assumed in the theoretical solution the kinematical schemes of elements failure. Higher convergence of theoretical strength with tested is received. The calculation sequence of the concrete element under one-sided central crushing is described. The joint calculation of all factors that determine the strength opens the possibility of more accurate assessment and improvement on its basis of structural solutions of concrete elements under the local compressive load.

The usage aspects of ideal plasticity theory for concrete and reinforced concrete are investigated. The plastic deformation is considered to be localized n thin layers on the failure plane which divides the element into rigid parts. The variation method is used and the solutions in discontinuous functions are received. The functional of virtual velocities principle is investigated to stationary condition, the minimal capability of plastic deformation is found with which the solid changes into the mechanism. The limit and realization criterion of concrete failure under shear are set. The reinforcement influence on the element load-carrying capacity is taken into account.

The necessity of creating a general methodology for concrete and reinforced concrete elements strength calculation under the shear is established. Three failure cases of reinforced concrete corbels under the shear are considered. The solutions of problems of corbels strength with failure along the whole section, close to the normal, in the compressed zone under an inclined crack and within the compressed inclined strip are given. A variational method in the plasticity theory, the virtual velocities principle and the characteristic lines method are used for concrete and reinforced concrete elements calculations. In the ultimate state, concrete is considered as a rigid-plastic body. The shear is realized in case when the plastic deformation is localized in the compressed zone. The calculating ultimate load results for different failure cases are given. Such a design scheme is implemented, in which the console strength is minimal. This corresponds to the minimum of power of plastic deformation in concrete compressed zone. Reinforced concrete corbels calculation engineering methods are offered. The elements obtaining effective constructive decisions direction based on the plasticity theory use is determined.