the issues of strength and deformability of reinforced concrete floors during punching remain insufficiently studied at present, despite the available publications in the technical literature. This article presents the results of experimental studies on punching of fragments of conjugation of flat reinforced concrete monolithic slabs with a column under dynamic loading. The purpose of these studies was to obtain experimental data on the stress-strain state of a fragment of a monolithic floor during dynamic punching with varying thickness and class of concrete, to reveal the failure patterns of experimental samples, and to obtain new experimental data. A setup for dynamic testing is described. Comparison of breaking load for specimens tested under dynamic loading with breaking load for specimens tested for static load is presented. The angles of inclination of the punching shear pyramid under static and dynamic loading are indicated.

Introduction. The issues of strength and deformability of reinforced concrete floors during punching remain insufficiently studied at present, despite the numerous publications in the technical literature. This article presents the results of experimental studies of the punching shear strength of fragments of conjugation of flat reinforced concrete monolithic slabs with a column under static loading. The purpose of these studies was to obtain experimental data on the stress-strain state of a fragment of a monolithic floor during static punching and to develop a spatial model based on the finite element method with subsequent numerical studies. Materials and methods. Experimental studies were carried out on a test bench. The characteristics of prototypes are given: dimensions, reinforcement, class of concrete and reinforcement. A test setup is described. For the numerical simulation of the slab-column interface, the ATENA software package was used, which allows for physically and geometrically nonlinear calculations of reinforced concrete structures, taking into account the real work of the materials used to create experimental models. Results. Comparison of the results for the breaking load, obtained during the experiment, with the results of numerical modeling by the finite element method and with the results of calculations using the methods of SP 63.13330.2018 and Eurocode 2. The diagrams of the distribution of deformations in reinforcement and concrete, breaking loads and patterns of distribution of cracks in the samples are obtained. Conclusions. The analysis of experimental and numerical studies made it possible to formulate the conditions for the pun­ching shear strength of flat slabs with longitudinal reinforcement and to give recommendations on the strength calculation under central loading.

Modern domestic calculation methods and developed countries for determining the bearing capacity of monolithic reinforced concrete slabs for punching do not fully take into account all factors of design solutions and operating conditions. The available design provisions are made for the static operation of structures and there are no recommendations for taking into account the features of the dynamic impact on the overlap and the nature of the work of the node interfaces. The accepted empirical assumptions of the calculation, based on numerous experimental data, do not take into account the features of the stress-strain state of the coupling of the overlap with the column during destruction according to the punching scheme. This is due to the lack of computational models in which all the acting internal forces ensuring the resistance of the interface to penetration would be considered comprehensively. The complexity of the problem is due to the fact that the sections of the nodal interface are in an inhomogeneous stressed state. The stress-strain state of plates for punching under dynamic load is currently little studied. This article proposes a method for determining the bearing capacity of a symmetrical nodal coupling of a column with an overlap for punching under static and short-term dynamic loading. The proposed design model of the punching strength is based on the following prerequisites: the resistance to punching of a monolithic reinforced floor consists of the shear resistance along the surface of the reduced punching pyramid formed by the height of the compressed concrete zone; the strength of the concrete shear resistance increases due to volumetric compressive forces on the surface of the reduced punching pyramid; the angle of inclination of the faces of the punching pyramid depends on the loading speed. The obtained theoretical dependences are applicable under static and dynamic loading and are in satisfactory agreement with experimental data.