A special limit state of reinforced concrete frameswith laterally reinforced nodes in the case of emergency impacts

Introduction. The increasing number of domestic and foreign publications on structural safety and survivability of buildings and structures evidences a great interest in the study of the problem of protecting bearing systems from progressive collapse. The relevance of these studies is determined by the ongoing rise in the number of man-induced, natural and terrorist impacts on buildings and structures. In this regard, the decisive factor is the expansion of experimental and theoretical studies, focused on ensuring the required level of survivability of bearing systems under such special impacts and, respectively, developing methods for protection from progressive collapse. Materials and methods. This work presents new results of experimental studies on models of a fragment of a multi-storied building made of monolithic reinforced concrete, whose nodes, connecting the girder and the column, are reinforced with laterally reinforced meshes designed to resist operational static loads and a special emergency impact caused by the failure of one ground-floor column in the framework. Results. The article presents the results of experimental and theoretical studies on the stress-strain state and crack resistance of reinforced concrete frames or fragments of multi-storied frameworks of buildings, made of monolithic reinforced concrete. Nodes of these buildings are laterally reinforced. The data on force-induced resistance of structures were obtained for cases of the static operational loading of a structure and special emergency impacts caused by the instantaneous withdrawal of one column on the ground floor. A comparative analysis of the pace of cracking, crack development and opening is made. The co-authors have made a benchmark assessment of parameters of limit and beyond-the-limit states, as well as elements of structural systems, having nodes with/without laterally reinforced meshes. Conclusions. The co-authors have identified the nature of actual deformation and destruction of elements in the bearing system, whose nodes are laterally reinforced. The co-authors have experimentally identified the principal properties of structural elements to allow for a more rigorous assessment of deformability and the bearing capacity of the effect produced by the lateral reinforcement on the resistance of structural systems in beyond-the-limit states.