Experimental research programme of complex stressed nodes of reinforced concrete structures

Introduction. In recent years, a number of experimental and a significant number of numerical studies have been conducted to study the resistance mechanisms of reinforced concrete building frames both under design loads and under emergency and special emergency impacts. The relevance of such studies is determined by both the need to assess the deformation and destruction of such structural systems as a whole and by a fragmentary study of frame and wall units containing both pure bending zones and transverse bending zones in the presence and absence of longitudinal forces. The stress-strain state and the coordinates of the points of formation of spatial cracks in the structures of such fragments remain poorly understood, together with the unexplored effects that arise when the continuity of reinforced concrete is violated. Materials and methods. When developing the volume of experimental studies, special attention was paid to such modelling of frame and wall nodes that would not distort the stress-strain state of the studied zones with local application of load, would simplify the study of mating nodes (statically determinate fragments of nodes) to the maximum and at the same time allow for the evaluation of the redistribution of forces in statically indeterminate systems taking into account the flexibility of nodes and the real picture of crack formation. Results. The justification of the adopted design solutions of experimental reinforced concrete structures of nodes was completed and a programme and methodology for conducting research on the considered types of nodal connections of frame systems was developed, which allows for the development of a test scheme for the experimental identification of the features of the actual operation of the specified type of structures. Conclusions. A programme and methodology of experimental research were developed to study the characteristics of crack formation, deformation and destruction of reinforced concrete frame structures, taking into account the different nature of their stress-strain state. Particular attention is paid to determining rotation angles, assessing the deformability and flexibility of nodes, as well as deflections, patterns of formation, development and opening of cracks, as well as deformation of concrete in complex stressed areas of reinforced concrete structures.