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An approach to estimating the long-term strength of concrete in building structures in the calculation of reinforced concrete structures of buildings and structures of various types is proposed. The process of increasing the initial modulus of concrete deformations in time as a consequence of a certain physicochemical reaction of strength gain is considered. The function of the age of concrete is presented, taking into account the change in the modes of temperature effects during the period of hardening. It is shown that the entropy criterion of strength is more flexible compared to the criterion of the energy barrier of destruction. The application of the entropy strength criterion allows us to take into account the effect of temperature on the long-term strength of concrete.

The specific properties of deformation and failure of a reinforced concrete frame are investigated under sequential realization of arch and catenary action of beams after removal of the middle row column. Numerical modeling with the use of solid- and beam-type finite element models is performed for the purposes of the study. It was found that at the failure of the column of the second row the beam of the frame above the point of column removal transform to catenary structure, as evidenced by the relative deflection 1/29.8 (179 mm). The compressed concrete at the outer face of the corner column then collapsed, followed by the complete collapse of the frame. It is shown that the results of calculation performed with the use of the frame model based on solid finite elements were visually close to the results of numerical modeling with the use of bar finite element models before the onset of catenary action of the beams. For more correct modeling of reinforced concrete frame structures when catenary action of beams is realized in them. It is advisable to use specific modeling methods, such as accounting for additional rotations of sections at crack formation.

The article formulates proposals for improving the calculation methodology for punching. The methods in the current regulatory documents for assessing the tensile strength are based mainly on empirical dependencies obtained on the basis of numerous experimental studies. It should be noted that they give reliable results if certain design requirements are met (typical column sections). Along the interface line of the plate with a rectangular (square) column, supporting bending moments act in two orthogonal directions. The magnitude of these moments for the most common spans is large and, in an elastic setting, exceeds the span by two times. Taking into account the redistribution of forces and the most likely formation of cracks in the stretched zone, it can be argued that in the operational stage, the support sections of the plates have compressed and stretched zones. With such a stress-strain state, in the calculation scheme, when evaluating the tensile strength, the stretched part of the side surface of the “reduced” pyramid, bounded by the neutral axis along all faces, should be excluded. As a result, expressions are presented to determine the parameters of the reduced punching pyramid and the value of forces in concrete and reinforcement at the maximum bearing capacity stage.

The main directions of development of the theory of structural safety of buildings and structures have been formulated. A hierarchical approach to the assessment of structural safety of objects under corrosion damage from structural materials to structural system is proposed. Peculiarities of corrosion damageability of concrete of reinforced concrete structures are determined, mechanisms of force and corrosion effects and their influence on progressive destruction of structural systems of exploited buildings are analyzed.

The methodology of calculation of reinforced concrete frames of buildings for a special design situation caused by initial local failures, taking into account the violation of the continuity of the concrete matrix during crack formation, is proposed. The verification of the proposed methodology is carried out by comparing it with the results of experimental data for a U-shaped reinforced concrete frame with prestressing. The bending moments in the frame, determined by the proposed calculation method, are in practically complete agreement with the values found experimentally. As a result of cracking, there was a redistribution of bending moments in the beam of the frame: the moments in the structural nodes decreased by 148 % and increased in the span by 37.5 % compared to the results obtained using the traditional finite element method approach. On the basis of the results of the calculation of the reinforced concrete 3-storey frame by the proposed method, the increase of longitudinal tensile forces in the beam support sections above the zone of local failure at failure of the middle row column is revealed in comparison with the traditional approach to modeling. The revealed effect may lead to an increase in the influence of longitudinal bending for the outermost row column to which the beam is adjacent.

The article is devoted to the fatigue of bending reinforced concrete beams under reinforcement corrosion. The influence of lugs and rebar notches periodic profile in concrete under repetitive loads, which act as stress concentrators, leading to the appearance of fatigue cracks and to the reduction of fatigue strength, is considered.

The paper presents the results of experimental design of a cortex of the embedded stress sensor, which allows to determine stresses in the cross-section of large-scale laboratory monolithic structures made on the basis of mineral and polymer binders (concrete, gypsum, etc.). The objectives of the design were to develop a constructive solution of the stress sensor housing based on strain gauges, which has small dimensions, low manufacturing cost, as well as high resolution and stability of readings over the entire sensitivity area (stress up to 400 kgf/cm2).The stress sensor allows to determine the stress in laboratory structures with high accuracy, without significantly affecting the stress-strain state of the section at different stages of operation of the structural element.

There are a large number of works on a comprehensive assessment of the seismic resistance of buildings and structures. However, these studies, as a rule, do not take into account the random nature of the seismic impact, which is a pronounced non-stationary random process. An adequate assessment of the seismic resistance of buildings and structures is possible only on the basis of methods that allow taking into account the large variability of seismic impact parameters. The article presents a probabilistic method for calculating multi-storey reinforced concrete buildings designed in seismic regions, taking into account the interaction of a building with a non-linearly deformable foundation. The developed technique makes it possible to provide the required level of seismic resistance for the designed buildings based on the non-collapse criterion. As an ex-ample, the calculation of a multi-storey reinforced concrete building is considered. External seismic action is represented as a non-stationary random process. The external seismic action is considered as a non-stationary random process, which is obtained by multiplying the stationary random process by a deterministic envelope function. The parameters necessary for constructing the envelope and the stationary random process were obtained from the results of processing the available database of intense earthquakes. The stationary random process was generated by the shaping filter method. The impact parameters are based on the results of processing the available database of intense earthquakes. When modeling reinforced concrete structures, a concrete model is used with the function of damage accumulation under cyclic loads, as well as taking into ac-count the degradation of the strength and stiffness of the material during an intense earthquake. Accounting for the interaction of the building with the soil base is implemented using the SSI interface (Soil Structure Interaction). To prevent the influence of waves reflected from the boundaries of a limited ground massif, a PML layer (Perfectly Matched Layer) is used. The calculation was carried out using explicit methods for integrating the equations of motion on a computing cluster using parallel computing technology. The presented technique makes it possible to investigate the nature of the destruction of reinforced concrete structures during intense earthquakes and to identify zones with a deficiency in bearing capacity. The proposed probabilistic approach to modeling seismic impact as an implementation of a non-stationary random process with given parameters, together with taking into account the nonlinear deformation of the reinforced concrete structures of the building and foundation, allows you to control the level of reliability and design buildings with a given seismic resistance.

Existing composite floor design approaches require technical data on strength and ductility of shear connectors, which can be defined only by shear tests. The article discusses the failure modes of composite floor shear connection, made of powder-actuated shear connectors. The influence assessment of the main detailing parameters on the strength and deformability of shear connectors was executed. The database for analysis included the results of shear tests performed by both the authors and other researchers. According to the results of the study, the dependence of the strength and deformability of shear connectors on their height, orientation relative to the shear force vector, the strength of the concrete slab and the geometric parameters of the profiled flooring was estimated.

Reinforced concrete beams can experience local low concrete strength under certain conditions, for example, poor construction practices can cause problems such as concrete voids, surface cavities, block cracking, surface sinks and create areas of low concrete strength. This study presents the response of flexural hinge-supported reinforced concrete beams with different local areas of low concrete strength along the span. Modified models are adopted to describe the concrete properties and an ideal elastic-plastic model is adopted for the steel properties. The beam was divided into three main parts: one sensitive to bending moment, the second sensitive to shear, and the third sensitive to bond. The variables included two types of concrete strength and one reinforcement diameter. The results show that the most critical region with low concrete strength along the span of the beam is the confluence zone near the supports, which is reflected in the ductility of the load-deflection curves. A new generalized empirical model is developed to predict the effect of bearing capacity reduction from local low-strength concrete.

The main indicators of durability, which characterize the time of operation of the structure before the onset of an emergency condition, are the total service life and the remaining service life, the determination of which allows a more reasonable approach to the issue of planning current or major repairs in the building. The most common engineering techniques that allow predicting the remaining service life for reinforced concrete structures are considered: according to standard terms and analogous objects, according to external signs, based on changes in reserve coefficients and strength criteria. Their modifications are given for a number of techniques. Based on the results of the analysis of the methods, their main advantages and disadvantages were established. As a proposal to improve the existing approaches, a methodology is proposed in which the interval between visual examinations is taken for the remaining period of operation.

In the modern construction complex of the city of Moscow for the protection of buildings and structures from man-made vibration arising from the movement of trains of rail transportation (subway trains, railroad lines and trams). To protect buildings and structures from anthropogenic vibration arising from the movement of rail transport trains (subway trains, railroad lines and streetcars), Moscow uses layered rubber-metal vibration isolators [1]. Most often, to determine their static and dynamic characteristics, the finite element method (FEM) is used, which makes it possible to determine all components of the stress-strain state and frequencies of free oscillations in the loaded state practically for any structural forms of isolators. However, for the most popular software packages that implement FEM, the problem of optimizing the structural shape of the vibration isolator still requires significant time expenditures for multiple changes of the finite element mesh, repeated setting of boundary conditions and implementation of a series of calculations. Only some of the software packages implementing the FEM solve optimization problems of the shape of the product being calculated, most often it is related to foreign software products with universal functionality. Variation-difference method (VDM) is the closest to the finite element method (FEM) in terms of its computational capabilities. It is possible to create program modules that repeatedly and automatically solve three-dimensional problems of elasticity theory taking into account the changed geometry of the vibration isolator: the dimensions of the product, the location of perforations within the rubber layers, as well as the thickness of the rubber layer and other parameters important for obtaining an effective technical solution for vibration isolation of buildings. Further, the article describes the method of implementation of the variational-difference method (VDM) as applied to the solution of the problem of determining the components of the stress-strain state inside a three-dimensional layered vibration isolator with perforations of different sizes having different locations relative to the contour of the vibration isolator, i.e., the solution of the problem of optimizing the three-dimensional shape of the vibration isolator is given.

The stress-strain state of precast monolithic reinforced concrete shells from enlarged elements taking into account the installation conditions. The results of experimental-theoretical studies of precast monolithic reinforced concrete shells of complex geometry assembled from enlarged elements are given. The studies were carried out on full-scale composite shells 48x48 m and diameter 96m, its enlarged elements 3x18m and 3x24m as well as on the shell model on a scale of 1:10 and 1: 4. The stress-strain state of shells of a similar type was studied with different mounting and splitting designs. Recommendations are given on rational methods for the construction of shells from enlarged elements for public buildings.

The article presents a calculation of rubber-metal vibration isolators with five holes of different diameters using a software package that implements the finite element method. A comparative analysis of the Eigen frequencies of rubber-metal vibration isolators with five holes (one in the center, 4 symmetrically at the corners) and without holes is presented. Finite element models of a rubber-metal vibration isolator with and without holes are modeled, and their characteristics are analyzed. The results show that vibration isolators with several symmetrically located holes have several advantages in a number of parameters to vibration isolators without holes, and, therefore, can be used for vibration isolation of buildings, especially in the case of delayed installation of vibration protection.

This article outlines the main provisions in the design of an acoustic reverberation chamber, methods for modeling such objects in engineering and construction practice. A finite element model of an object is presented in the Midas FX software package. As a result of the calculation, it is possible to evaluate the components of the stress-strain state in concrete and in structural elements or on the contact surface, the effect of vibration loads on RAC structures, their interaction with the foundation and soil base, as well as analysis of the use of vibration isolators in the RAC foundation Based on the results of the analysis, recommendations are given for perform calculations of system elements, select design solutions.

The construction of a mathematical model based on the finite element method for determining the stress-strain state of a 25-storey reinforced concrete building on a multilayer deformable foundation is considered. The sensitivity of the physical and mechanical characteristics of the building and foundation material to the type of stress state, the development of plastic deformations in reinforcement, damage in the form of cracking, and induced heterogeneity are taken into account. The relations for nonlinear isotropic materials proposed in the frame-work of the theory of normalized stress spaces are taken as constitutive relations. A modification of a multilayer triangular hybrid finite element with five degrees of freedom in the node is formulated to describe the features of the mechanical behavior of building structures. A description is given of methods for modeling fictitious layers of an element corresponding to various variants of the stress-strain state of reinforced concrete. Quantitative estimates of the stress-strain state of the combined "building-base" system under the action of static loads of two types are obtained in the form of graphs of the dependence of dis-placements on the magnitude of the load in floor slabs and pylons. According to the results of the research, it was confirmed that taking into account "complicated" ones is necessary to obtain correct estimates of the stress-strain state of buildings.

The article discusses the issues of reliability for various types of failures of beam systems. A single-span bending beam is analyzed. The limit state functions for moment failure modes in the characteristic sections of the beam are determined. The ways of forming a plastic hinge for a beam are shown. The lower and upper limits of the beam reliability are calculated. Limit state functions corresponding to failure mechanisms are presented.

The article presents a brief analysis of the experience of developing standards for the design of reinforced concrete structures in the Republic of Belarus. The principles on the basis of which these norms were developed are considered. The advantages and disadvantages of using European design standards EN 1992-1-1 of various generations, as well as fib Model Codes are shown.

One of the main components of the economic development of the Russian Federation is the current trend in the development of the territories of the Far North and the Arctic. The need for such development is enshrined at the state level in various programs. Experiments on the study of the effect of negative temperatures on the operation of reinforcing steel show that with decreasing temperature, an increase in strength and modulus of elasticity is observed. At the same time, there are no unified recommendations on the deformation and strength properties of reinforcement for calculating reinforced concrete structures under conditions of low and ultra-low negative temperatures. RF standards do not take into account the influence of climatic (up to -70°C) and technological (up to -196°C) negative temperatures on the deformation and strength characteristics of reinforcing steel.The purpose of this work was to experimentally study the effect of negative temperatures (up to -196°C) on the deformation-strength properties of reinforcement, concrete and reinforced concrete rod elements. Concrete prisms 10x10x40 cm, samples of reinforcement of a periodic profile of class A400 and reinforced concrete prismatic rods with a section size of 12x18 cm and a reinforcement percentage of 1.45% were taken as prototypes. At the same time, the negative temperature of the tests varied. As a result of the studies carried out with centrally stretched reinforced concrete elements, it was found that lowering the temperature to -165°С leads to an in-crease in the cracking force by 162%; strength by 85%. Empirical dependencies are proposed to determine the deformation-strength characteristics of reinforcing steel, depending on the negative temperature.

In this article, the authors present the results of a study of unreinforced and reinforced stone vaulted ceilings, which included numerical and physical experiments. We have also developed our own constructive measures to strengthen stone vaulted ceilings, based on the introduction of composite flexible rods into the body of the luggage in optimal places and, in turn, allowing to increase the efficiency and safety of work. The article presents the process of creating a homogeneous and heterogeneous model, which made it technically possible to solve problems with modeling reinforcement in masonry.

This paper presents the history of the development of the method for calculating the crack resistance of reinforced concrete elements according to Soviet and modern design standards, which was based on the work of the Soviet and foreign scientists, such as: A.F. Loleit, V.I. Murashev, A.A. Gvozdev, S.A. Dmitriev, A. Clark, J. Monier and others. Also, the article discusses the currently updated calculation methods for the formation and opening of normal cracks according to domestic and foreign standards.

Analytical, computer and experimental modeling methods are applied in the study of seismic resistance and changing dynamic parameters of long-term loaded non-linearly deformed large-span spatial shell structures. Physically and geometrically nonlinear deformation models and computational algorithms for solving dynamic problems are proposed for estimating the stress-strain state of smooth and ribbed spatial systems with variable stiffness caused by damage accumulation and orthotropic structure reinforced by ribs. The possibility of using the proposed method of taking into account variable dynamic stiffness in calculations for solving problems of dynamic strength and stability of spatial large-span shells of unique buildings of complex geometry is shown.

The article deals with the issue of estimating the strength and stress-strain state of a reinforced concrete shell by the method of membrane theory and the theory of infinitesimal bending. A brief description of the methodology consists in the fact that the ground stress state of the shell is allocated to an independent problem, when, without introducing boundary effects, two of the four boundary conditions of the general moment theory are distinguished, which, together with the equations of the momentless theory, determine the ground stress state, and then boundary effects are superimposed. The equilibrium equations of the moment theory in forces and moments, geometric equations, components of tangential deformation and displacement, and the physical equations of state connecting them, expressing forces and moments through the components of deformation, are presented, since the characteristics of the stress-strain state of the shell depend not only on the variability of external influences and forces, but also on the length of the structure. The provisions laid down in the article shall be retained in the case of casings made of anisotropic material, provided that the presented elastic ratio is met. A system of equations of the generalized semi-membrane (semi-bending) state of an arbitrary shell of zero curvature, which determines the accuracy of this approach, is solved. The equations of the semi-torque theory for a circular cylindrical shell are presented, as well as describing the semi-membrane stress state of a long shell of zero curvature. The most important result of the study is the method of constructing integrals of the ground stress state of the shell based on the method of simple iterations, which expands the possibilities of the reliability theory, which makes it possible to build the foundations for the practical calculation of reinforced concrete shells according to the membrane theory and the theory of infinitesimal bending.

Most of the experimental investigations devoted to the study of the stress-strain state of bent reinforced concrete elements reinforced with carbon fiber-based polymer-composite materials have examined only unloaded beams or beams without preliminary cracks. However, reinforcement of real load-bearing structures is most often performed under load and taking into account previously occurring defects. At the same time, there are a limited number of systematic studies of the effect of preload on the bearing capacity of reinforced concrete beams reinforced with carbon fiber. This article presents a methodology for assessing the effect of the stress-strain state level of reinforcement on the bearing capacity and other parameters of the sections of bent reinforced concrete elements reinforced with carbon fiber, taking into account the physical nonlinearity of concrete and using real deformation diagrams, including reinforcement and reinforcement systems. On the basis of the developed method, numerical studies of the operation of reinforced concrete sections reinforced at various stages of SSS were performed. After analyzing the obtained data, we can conclude that the level of reinforcement load has a significant effect on the deformability, rigidity and strength of normal sections of reinforced concrete beams and the need to take this factor into account when calculating bending reinforced concrete elements. After analyzing the data obtained, we can conclude that the influence of the reinforcement load level on the deformability, rigidity and strength of normal sections of reinforced concrete beams and the need to take this factor into account when calculating bending reinforced concrete elements.

By present time significant experimental and theoretical material on concrete creep has been accumulated. At the same time, the known approaches to calculation of concrete and reinforced concrete structures with regard to creep are oriented mainly to solving problems with relatively simple geometry of the product. Moreover, there are no mechanic-mathematical models of hereditary type oriented to the finite-element method.The concept of modelling of long-term deformation of reinforced concrete structures in a three-dimensional statement, based on the use of the integral deformation modulus of concrete, does not allow one to carry out designing considering the technological prehistory. Therefore, the problem of developing a finite-element algorithm and corresponding software allowing the modelling of the volumetric stress-strain state of large-span prestressed reinforced concrete structures within the framework of the theory of hereditary aging is relevant.

In this study, a detailed analysis of the use of standardized deformation models is carried out to calculate the design characteristics of reinforced concrete elements, such as crack resistance. For theoretical verification of the values of the moment of cracking, calculation methods based on the use of a nonlinear deformation model are used.A theoretical study of cracking moment using a non-linear deformation model shows that the application of a two-line diagram of concrete deformation allows to obtain the most accurate values of cracking moment.

The article is devoted to the research of application of reinforcing steel of a new spiral profile for reinforcement of reinforced concrete constructions. The article presents the results of experimental studies of prism specimens with screw four-row reinforcement with diameters of 20 and 32 mm of class Av600P and concrete of classes B30 and B60 under static compression loading. The purpose of the research was to justify the introduction into practice of the construction of an innovative screw reinforcement profile, which will develop the ideas and principles that have become the basis for the widely used six-row A500SP profile, whose design solution (the absence of longitudinal ribs with the arrangement of transverse protrusions in four rows with the possible formation of a two-start screw thread by them) makes it possible to significantly increase the rejection minimum value of the Röhm criterion (fR ≥ 0.075), which characterizes and determines the strength and deformability of the adhesion of reinforcement to concrete, which determine the strength and crack resistance of reinforced concrete structures, and, consequently, their operational safety and reliability. The coupling joints of screw reinforcement can significantly speed up the process of reinforcing work at the construction site as a result of replacing labor-intensive and expensive welded joints. The results of the research showed the effectiveness of application of new screw reinforcement of the Av600P class for reinforcing compressed reinforced concrete elements made of concrete of classes B30÷B60 with coupling threaded contact, partially contact and non-contact butt joints of the reinforcement.

The work of a reinforced concrete beam resting on an elastic foundation is considered. The strength characteristics of the beam materials - concrete and reinforcement - are considered as random normally distributed quantities. The parameters of the distribution of the probability density of the initial stiffness of the beam, the moment of crack resistance of the beam under the control of the strength of concrete in compression and tension are obtained. The beam base is considered as statistically inhomogeneous elastic half-plane with the soil elasticity modulus taken as a quasi-stationary random function of depth. The load on the beam, its geometric parameters and the modulus of elasticity of the foundation soil are taken as deterministic values. The parameters of the density distribution of the probability of bending moments in a reinforced concrete beam lying on a stochastic half-plane, and the probability of the formation of normal cracks in it, are obtained for the case of controlling the strength of concrete only in compression and for the case of controlling the strength of concrete both in compression and in tension.

Currently, much attention is paid to the structural reliability and safety of buildings and structures, as well as the speed and quality of design and construction. The increase in these indicators is facilitated by the expansion of the use of information modelling technology through the integration of new calculation methods into the digital building model.The paper considers the design of structures of a single-storey frame industrial building using information modeling technology. The order of work in the programs “Tekla Structures” and “Crystal” is presented on specific examples. Conclusions are given about the advantages of using BIM technologies in the construction industry.

The problem of restoring reinforced concrete structures that have received dynamic impacts (emergency as a result of collisions with vehicles, damage as a result of dismantling nearby structures, explosive impacts) is quite an urgent issue. The current regulatory documents regarding the restoration and reinforcement of reinforced concrete structures do not fully correspond to the issues related to the results of dynamic impacts that have characteristic features. Also, the volume of published scientific papers on this topic is not sufficient and implies the need for further research. Nevertheless, to date, a certain amount of work has been carried out to restore such structures with subsequent tests and confirmation of the required level of reliability. The article considers the experience of restoring reinforced concrete structures of bridge spans that were damaged as a result of dynamic impact from vehicles - the result.

Some examples of failures of structures, buildings, where the lack of robustness was recognized, are analyzed. Several author’s definitions for robustness are presented and discussed. Special emphasis is given to the fact that define robustness as an intrinsic structural property and the other hand it as a property of the structure and its environment. Some related concepts are presented and discussed.The most important proposed measures for robustness are also present-ed including some illustration examples. Finally, a comparison between them is made and the respective shortcomings are identified. After anal-ysis of the robustness nature, a new structural oriented definition is pro-posed. Based on the highlighted shortcomings of the existing measures, in particular those related with the application to deteriorated structures, a conceptual framework for robustness assessment is proposed.

In the practice of modern construction, flexible centrally and eccentrically compressed reinforced concrete elements are becoming more common. In this regard, the relevance of studying their work and the mechanism of bearing capacity exhaustion increases. There are two directions in determining the bearing capacity of these elements: calculation for stability and calculation for strength. The loss of stability in a number of cases, obviously, can cause the destruction of not only centrally, but also eccentrically compressed rods with small eccentricities, since under certain conditions they can practically turn out to be close in their work. The stability of these eccentrically compressed rods is calculated by multiple integration. Such a calculation is especially laborious for reinforced concrete elements. This article is devoted to the study of the stability of centrally and eccentrically compressed reinforced concrete rods with small eccentricities, taking into account the creep of concrete. An eccentrically compressed rod with a small eccentricity of length l is replaced by a centrally compressed rod of length l0 so that the bending arrow includes the eccentricity. The numerical values of the rheological coefficients are determined from the boundary values of the reduced stiffness, which varies along the length of the rod. Complicated integration is replaced by the solution of the differential equation of the bent axis of the rod in the form of a sinusoid half-wave.

During the reconstruction, or upon expiration of the service life, as well as after external impact, reinforced concrete structures require examination and verification calculations. Existing diagrams of concrete deformation are focused on designing new structures and are not adapted to the concretes of the reconstructed structures.Using the exponential model of concrete deformation makes it possible to describe the resistance of concrete during reconstruction, including after repeated cyclic loading.A technique for creating an individual deformations model under cyclic load during the reconstruction is demonstrated on a specific example.

When performing structural calculations for dynamic loads including seismic impacts, the STARK ES software package allows to implement various damping models. In this paper, a comparative analysis of three types of the damping models used to increase the calculated seismic resistance of structures is carried out. These are the models of nonlinear viscous dampers, in which the reactive force depends non-linearly on the velocity of the rod movement, equivalent (for an energy dissipated) linear-viscous dampers and equivalent (for a maximum force and an energy dissipated) elastic – perfectly plastic elements. As an example, an analytical model of the structural system of a projected building on a site with a seismicity of more than 8th intensity level is used.

The paper considers the influence of various factors on the consumption of transverse reinforcement in the design of sections of linear bending reinforced concrete elements. The aim of the work is to determine the degree of influence of the pitch, diameter and class of transverse rods, as well as other factors, on the minimum consumption of clamps at various levels of loading of a linear bending element. The calculation and analytical method of research was used, based on the results of applying various diameters of transverse rods, reinforcement classes. The object of the study was a beam of rectangular cross section, in which the step of the clamps varied from the minimum to the maximum allowable standards, with a stepwise changing load. Research results. It has been established that the optimal longitudinal single reinforcement of the beam is achieved by applying a maximum force of 255 kN from the studied load range. When a concentrated force of less than 125 kN is applied to the beam, the transverse reinforcement is installed according to the design requirements. The most economical solution for reinforcing a beam with transverse bars is achieved with class A240 and a step of 0.235 m and 0.140 m, with an overrun of 0% and 6.9%, respectively. The use of transverse bars made of A500C class reinforcement, with the accepted beam parameters of 0.3×0.5 m, with single reinforcement, with the application of a force of 255 kN, is not advisable, since the assortment of reinforcing steels does not provide for diameters less than 10 mm. The dependencies and the levels of influence of the use of different pitches, diameters and classes of transverse rods, with a stepwise changing load, on the minimum consumption of transverse reinforcement in the design section of the beam are established. The presented work specifies the consumption of transverse reinforcement for its most economical use.

Ribbed ceilings in reinforced concrete, and more recently in steel-reinforced concrete and wood-concrete versions, occupy a significant place in the total volume of buildings and structures. An analysis of the regulatory and technical literature shows that in domestic and foreign sources, empirical dependencies are proposed for assigning the effective width of a T-section flange, which does not lead to economical and reliable design solutions.The purpose of the study is to determine the calculated effective width of a flange of a tee monolithic section or a composite section of a floor. Based on the analysis of the stress-strain state of a bent tee section, analytical ex-pressions are written and formulas are obtained for determining the design flange width.

The article provides an overview of the existing methods of early loading of monolithic structures. It is shown that keeping concrete up to standard strength without taking into account the stages of loading leads to a significant increase in the cost of work, especially in winter. Based on experimental studies, formulas are proposed for calculating the required strength by the moment of loading of monolithic foundations, walls, columns, ceilings. Instructions are given on the design of early loading technology. The results of full-scale tests of floors under conditions of early loading are given. The technology of tiered heat treatment of monolithic structures is described.

An analysis of the calculation methods found in the normative literature on strengthening reinforced concrete structures with composite materials arranged in the transverse direction by the method of wrapping structures showed that there is no calculation method for the second group of limit states.The Code of Rules 164.1325800.2014 does not consider options for strengthening flexible compressed reinforced concrete structures, with the arrangement of composite materials in the transverse direction, introducing restrictions to the dimensions of structures. However, our research suggests the opposite. In this paper, experimental values of deflections of reinforced concrete struts in the transverse direction by composite materials, characteristics and testing methods of prototypes are given. The results of the theoretical calculation of deflections are presented and, based on the comparison of experimental and theoretical values of deflections, an algorithm for calculating the second group of limit states was developed.

Approaches to assessment of stability of reinforced concrete columns in case of horizontal emergency impact have been investigated. For this purpose, finite-element modeling of the system in spatial formulation, calculation according to the deformed scheme in the scope of nonlinear static analysis and dynamic transient process have been implemented. When constructing the model, the hexahedral elements were used, working in accordance with the Drucker-Prager model for concrete, and the rebars deformed according to the Prandtl model were used to modelling the reinforcement.The impact action was considered as a short-term pulse of constant intensity. Dependence diagrams for critical force on various scenarios of emergency impacts on the column have been obtained. Results of researches can be used for an estimation of resistance to the progressive collapse of reinforced concrete structures at their variants design and optimization.

An estimated estimate of the long-term operation of a reinforced concrete beam on a ground base is presented, taking into account environmental and dynamic force effects. A method of dynamic calculation of reinforced concrete structures of structures of various types on a ground base operated in an aggressive environment is proposed, internal factors of rheological deformation are also taken into account, taking into account corrosion damage, reflecting their real work under the joint action of the load and the aggressive environment on the basis of the modern phenomenological theory of deformation of the elastic creeping body. It is shown that corrosion damage to reinforced concrete elements can affect the strength of the material, change the calculation schemes, redistribute forces in the cross-sections of the structure and disrupt the joint operation of concrete with reinforcement, as well as lead to other consequences that reduce the design time of operation of structures and other operational characteristics. The possibility of modeling the processes of deformation of reinforced concrete under conditions of long-term operation with a changing mode of action of an external load is shown. An example of the calculation of a reinforced concrete flexible foundation on a soil base is given for the considered service life and the presence of corrosion damage.

The impact of aggressive environments and, accordingly, the corrosion damage of concrete and reinforcing steel, the violation of adhesion between them in some areas lead to a change in the values of the limiting height of the compressed zone, which determine the plastic or brittle mechanism for the destruction of structures of reinforced concrete frame buildings. The purpose of the presented study was to assess the influence of the depth of corrosion damage on the ultimate height of the compressed zone of the section of eccentrically compressed elements of reinforced concrete frames of buildings, as well as to assess the bearing capacity of these elements. The article presents analytical dependences for estimating the limit value of the height of the compressed zone of the section of a corrosion-damaged reinforced concrete element of the building frame with a two-line approximation of the state diagram of concrete.It has been established that an increase in the depth of corrosion damage leads to a decrease in the height of the compressed section zone relative to the part of the working height of the section that retained the resource of force resistance, as well as to a decrease in the bearing capacity of eccentrically compressed reinforced concrete elements due to a decrease in the effective working height of the section and an increase in their flexibility. An increase in the flexibility of the elements leads to a decrease in the magnitude of the limiting longitudinal force perceived by eccentrically compressed reinforced concrete elements. At the same time, an increase in the relative depth of corrosion damage enhances this effect due to an increase in the effective flexibility of such elements compared to elements without damage.

Asymmetric arrangement in the plane of vertical bearing elements, ladders, stiffness elements is to the occurrence of eccentricity between center of rigidity and center of mass. Later, under the action of a horizontal load, torsion occurs in asymmetric load-bearing systems. This paper considers the resistance of multi-storey buildings during torsion caused by an asymmetric arrangement of vertical load-bearing objects.The object of the study was the carrier system of a residential monolithic multi storey building with an implicitly non-coinciding center of rigidity and center of mass. Numerical simulation for a horizontal load determined the stress-strain state of vertical reinforced concrete structures. The change in forces and displacements in the pylons during the torsion of a multi-storey building is obtained. The results of the analysis carried out can be used in the design of compressed and bending reinforced concrete structures subject to torsion.

The article discusses the features of the structure of concrete in a structure made using additive technology (3-D printing). The result of the formation of the structure when using the 3-D printing method is investigated. According to the results of experimental studies, the features of the formation of the concrete body of the structure performed using additive technology are revealed.The features of the concrete structure formed in the concrete body when using additive technology are established. The results obtained can be used in the development of methods for experimental studies of effective mechanical characteristics of concrete, as well as in studies to determine the coefficients of concrete working conditions in structures made using additive technology.

Civil defense structures are exposed to short-term dynamic loads of high intensity. In order to reduce dynamic forces and movements of structures, active methods of protection, which include yielding supports, have been increasingly used in recent years. In this paper, the assessment of the influence of the yielding of supports is carried out based on the results of the calculation of reinforced concrete beams on yielding supports under short-term dynamic loading. The work of the structure is considered in the conditionally elastic stage, and yielding supports in the elastic, plastic and hardening stages. Collapsible inserts of an annular profile are accepted as yielding supports. For reinforced concrete beams on yielding supports, the equation of motion, function and coefficient of dynamism are determined. It has been established that the use of elastic yielding supports can have both positive and negative effects on the operation of structures, which is expressed in the excess of forces and displacements of structures on elastic supports relative to elements on non-displaceable supports. When yielding supports are deformed in the elastic and plastic stages, there is a sharp decrease in the dynamic coefficient of beams, and, consequently, stresses and deformations in structures. The transition of yielding supports to the stage of hardening leads to a sharp increase in the dynamic coefficient of the structure.

Reinforced concrete structures can be exposed to aggressive environmental influences, which leads to a decrease in their bearing capacity during their service life. If a safety assessment of such structures is to be carried out in order to be able to continue in service, the main challenge would be to ensure that they can withstand future extreme loads over their intended lifetime with a level of reliability sufficient for safety.There are currently no methodologies for such an assessment.This methodology is proposed to facilitate quantitative assessments of the current and future structural reliability and load-bearing capacity of reinforced concrete structures. This methodology takes into account the random nature of past and future pressures, as well as degradation as a result of negative environmental factors.The time-dependent reliability and deterioration assessment of reinforced concrete structures provides the basis for determining the duration of safe operation.

The article considers the structure of regulatory documents for precast reinforced concrete structures. The directions of development of the regulatory framework by updating and developing standards (GOST and GOST R) for certain types of precast reinforced concrete structures are given. It is noted that the purpose of the development and updating of standards is to establish current technical requirements for precast reinforced concrete structures, due to changes in the regulatory framework for the design of reinforced concrete structures, in particular in SP 63.13330.2018 "SNiP 52-01-2003 Concrete and reinforced concrete structures. The main provisions", and the improvement of technological requirements. In recent years, JSC "Tsniipromzdaniy" has developed and updated more than 20 standards (GOST and GOST R) only by the Department of Structural Systems No. 1, in which a number of new provisions have been adjusted and developed based on the analysis of domestic and foreign regulatory framework, modern manufacturing and installation technologies. It is advisable to develop standards for individual structures taking into account the requirements given in the fundamental GOST 13015-2012 "Concrete and reinforced concrete products for construction. General technical requirements. Rules of acceptance, marking, transportation and storage". The structure of the standard standard for precast reinforced concrete structures is considered.