IMPROVED JOINTS OF REINFORCED CONCRETE ELEMENTS IN PRECAST-AND-CAST-IN-PLACE CONSTRUCTION BASED ON DESTRUCTION MECHANICS

Systematic theoretical and experimental studies of the keyed joints of concrete and reinforced concrete elements have been carried out at PoltNTU over the recent thirty years that made it possible to formulate recommendations for their design and to improve the existing design solutions of joints. The keyed joints have higher bearing capacity. The method for calculating the strength of the joints is proposed. This method is based on the theory of concrete plasticity, the variational method and the principle of virtual velocities. It considers the stage of destruction and takes into account the full set of influence factors. The research takes into account the influence of the following factors on the joints strength: the ratio of the key depth to its height; compression level; the intensity of reinforcement and the nature of the reinforcement location. The keys of a rectangular profile of circular cross section are considered, which are formed in the voids of the slabs at their ends surface when girders concreting. For their reinforcement, a spatial cage in the form of a hollow cylinder is proposed. The results of experimental verification of the quantitative and qualitative influence on the joints strength of these factors are presented. The boundaries of the efficiency of reinforcement intensity, the degree of compression are determined, the optimal ratio of the depth of the key to its height is accepted. The design features of the joints of multi-hollow floor slabs (roofs) with a monolithic girder and between themselves in a precast-cast-in-place frame structural system, with wall panels in large-panel houses, as well as joints of wall panels on flexible loops in large-panel buildings, are taken into account. Examples of improved structural solutions for connecting elements of modern load-bearing systems based on the specifics of their work are given