He connection of rebar of concrete structures by looping rebars with the formation of the joint core was developed at the beginning of the last century, but it has not been actively used due to the complexity of the work and the lack of calculation methods. The article presents a review of the history of the creation, practical application, national and foreign scientific research of the loop joints of rebar in concrete structures. The article describes advantages and disadvantages of such joints, gives brief information about the main parameters of the joints and the principle of operation. Suggestions for the directions of further study of the looped joints of reinforcing bars operation are presented, the goals for full-scale and numerical experimental research aimed at the development of calculation and design methods of looped joints for their further wider introduction into the construction practice are set.

The results of determining the probabilistic parameters of the strength characteristics of concrete in the control of cubic strength and tensile strength, as well as the probabilistic parameters of the distribution of the concrete deformation modulus are presented. The influence of stochastic inhomogeneity of concrete on the reduced moment of inertia of a reinforced concrete section has been evaluated, and the probabilistic parameters of the distribution of the initial bending stiffness of the beam have been obtained. The influence of the statistical nature of concrete strength on the height of the compressed zone of concrete and the elastic-plastic section modulus of the beam was evaluated, and the probabilistic parameters of the distribution of the moment of normal cracking were obtained. The probability of formation of normal cracks in the foundation beam is determined for the cases of control of the cubic strength of concrete and the tensile strength of concrete. The characteristics of the distribution of the length of zones with cracks in a foundation beam loaded with a number of concentrated random forces are obtained for the cases of controlling the cubic strength of concrete and the tensile strength of concrete, which opens up the possibility of solving the equation of beam bending on an elastic foundation with piecewise constant stiffness in a closed form .

The article provides a model of "internal stresses" for concrete matrix of reinforced concrete structures from dislocations, microcracks to macrocracks. The energy theory on the surface of the sphere and the definition of the integral for the mean square value of tangential stresses from plasticity theory are used. An alternative to the general model of the "eight" in the form of a paraboloid from the summation of the volume sectors, levels - radii for the matrix of sliding planes (including octahedral and pure shear) is developed. In the environment of different materials, the model is constructed based on the structure of crystals and dislocations from microcracks to macrocracks, and its working assumptions are formulated. The important principle for displacement (deformation) processes of summation and reduction of relaxing stresses from the stress-strain diagram of concrete is taken into account. The internal total stresses at the rupture of the "figure of eight" (of two contour rings) are obtained for combinations of tetrahedrons or layers-strips from the tangle-paraboloid. The lower boundaries of concrete micro-cracking depend on stresses (deformations), growth rate, energy in crack advancement for a prism or a standard "figure of eight". Displacements from shear, opening widths and crack development heights are obtained from the criteria and connecting parameters in a "representative" volume of concrete. As a result, the dilatation moduli for the stages of the stress-strain state of reinforced concrete are determined, and the equality for the second stage and the dual console elements from the fracture mechanics are obtained.

The study of wood with reduced physical and mechanical characteristics, including wood exposed to fire, is an important step towards economical and rational environmental management. Fires cause changes in the physical and mechanical properties of wood: moisture content, density and strength. Conducted tests for static bending, compression and tension along the fibers. Decrease in density and strength in fire-prone wood occurs along the entire height of the trunk. The following pattern is observed: in the butt part, the density is higher than in the middle part. The decrease in strength in the middle and butt parts is: in compression along the fibers 15-18%; when stretched along the fibers up to 24%. The highest loss of strength occurred in tests for static bending: in the top part up to 42%, in the middle part up to 29%, in the buttom part up to 23%. The smallest decrease in strength in all tests occurred in samples taken from the buttom.

During the reconstruction, or upon expiration of the service life, as well as after external impact, reinforced concrete structures require examination and verification calculations. The most modern and accurate calculations are based on diagram methods. Existing diagrams of concrete deformation are focused on designing new structures and are not adapted to the concretes that have changed their strength and deformation properties over time or because of external influences. The main parameter describing the deformability of concrete is the secant modulus ratio. A technique for determining the secant modulus ratio is proposed in this arctical. The technique is based on using the exponential concrete deformation model. The obtained secant modulus ratio can be used for the widely adopted description of the concrete deformation diagram. The technique is illustrated on a specific example. The proposed technique significantly expands the application range of diagram methods and extend them to concrete after long-term operation or external impact.

The analytical solution of the problem of sound and vibration passage through structures and joints requires determining the elastic-dissipative properties of structural and sealing materials of translucent structures: the dynamic modulus of elasticity and loss factor. In this paper, the parameters of the dynamic modulus of elasticity and loss coefficient of some well-known building materials are investigated and experimentally established in comparison with previously obtained data from other authors. To automate and accurately measure the coefficient of dynamic characteristics of materials, a measurement technique was used, using Zetlab software and measuring equipment. When measuring the dynamic modulus of elasticity of sealing materials, LDS measuring equipment was used. The refined values obtained for the dynamic modulus of elasticity and the loss factor of materials allow them to be used in vibroacoustic calculations of translucent structures.

The article is devoted to the problem of arranging through openings in the stone vaults of reconstructed building structures. The need for such openings arises in connection with the use of new communication and engineering systems in opening cases and laying, for example, elevators, plumbing equipment, water supply systems, ventilation, etc. An analysis is made of the severity of the state of a stone wall with a rectangular and checked openings, as well as a study of anisotropy the strength of the stone lining on its bearing capacity in the presence of openings. It is noted that the use of the device of openings is possible with a compromise between the requirements of the project, the allowable sizes, shapes and locations of openings in the vaults, and the likelihood of their use. For this purpose, a detailed analysis of the complex acute condition of the vaults using modern software systems is required. In this case, special attention should be paid to minimizing tensile strains that cause cracks, especially at the corners of rectangular openings. There are cases associated with the detection of violations in difficult conditions of the stress state of blood coagulation in the presence of openings. Use examples of the practical implementation of through openings in the main cylindrical and cross stone vaults with a detailed analysis of their state of sharpness, as well as a study of the bearing capacity. It is emphasized that the most common manifestations of openings are minor tense sections of vaults, for example, stripping due to the proximity of walls under them. The elimination of vaults weakened by openings is analyzed. Preference is given to their reinforcement or reinforcement using reinforced concrete belts. Technological aspects of making openings are discussed. Attention is also drawn to monitoring the progress of openings.

A large number of theoretical and experimental studies confirms the classical resistance models introduced into standards. However, in modern conditions of rapid improvement of materials and technologies, new original design forms are increasingly being used, for which calculation models have not been established or do not have sufficient confirmation. To overcome these difficulties and due to the high cost of testing, numerical methods of analysis (modeling, simulations) of the behavior of building structures or a separate structural element are becoming increasingly widespread. However, the implementation of the design of steel structures based on numerical models is primarily constrained by the lack of unified approaches to development. There are no verified recommendations on the assignment of parameters of the numerical model, such as the description of steel deformation diagrams, recommendations on the assignment of the dimensions of the final elements, recommendations on the assignment of the shape and values of imperfections, etc. The second important problem is the lack of a safety format and the values of partial factors. The article substantiates the areas of application of the design method based on numerical resistance models, systematizes the factors affecting the uncertainty of the resistance and formulates the necessary stages of development of the design method based on numerical resistance models.

In the construction industry, buildings that provide themselves with energy are increasingly appearing. The article discusses the formative capabilities of the kinematic system, presents lattices and the three-dimensional shapes obtained from them. Special attention is paid to the cylindrical surface, its geometric immutability is ensured by the rigidity of the contour and the spatial shape of the surface of the central part. The authors of the article proposed a public building based on a transformable frame - it is a quick-erect and lightweight spatial structure that will meet the three main requirements of modernity: energy conservation, eco-nomicity and environmental friendliness. Have created a three-dimensional model of the structure, viewed in two states: before construction (flat rectilinear lattice) and after construction. The selection of enclosing structures based on thermal engineering calculations was carried out, and solar panels are used as additional panels. The color scheme of the facades is proposed. The light openings are triangular in shape on the side facade and trapezoidal with triangular at the ends of the building. This solution is due to maintaining the rhythm of structures and sandwich panels. installation of additional internal supports. The absence of internal supports in the building provides freedom in planning issues. To generate an alternative type of energy and save money, solar panels are installed on the building so as not to violate the general concept of facades.

An approach to numerical simulation of the stress-strain state of reinforced concrete square columns with various types of initial imperfections is considered. Their ultimate bearing capacity is determined taking into account the possible dynamic additional loading by the longitudinal force and the bending moment. For research, a numerical model is used that describes the design of the column with volumetric elements for concrete and rod elements for the reinforcing cage. Initial imperfections are modeled by physical removal of elements, unzipping of elements, unzipping with the possibility of subsequent stitching by nonlinear bonds that simulate gaps and adhesion at the interface between media. Numerical analysis was carried out in a dynamic formulation according to an implicit scheme based on the direct method, the solution of a nonlinear problem was performed using the Newton-Raphson method with a discrepancy in the value of nodal forces. The degree of influence of initial imperfections associated with deviations of geometry and damage to the material on the bearing capacity of compressed-bent elements under emergency impact has been established. It is shown that for structures with an increased level of responsibility, it is advisable when designing to provide for an additional margin of safety for additionally loaded columns in frame structures within 10%.

The substantiation of the modes of static-dynamic loading of the operated reinforced concrete frames of multi-storey buildings under the out-of-design impact in the form of sudden removal of individual load-bearing elements is presented. Based on the theory of plasticity of concrete and reinforced concrete by G.A. Geniev, analytical dependences are constructed to determine the parameters of the static-dynamic deformation diagram of concrete under various modes of static loading and sequential dynamic loading. The advantage of the obtained refined variant of concrete deformation is that it contains two important parameters that take into account the influence of the loading speed and the level of static loading on the complex stress-strain state of concrete. Numerical studies have shown that the limiting static-dynamic strength of concrete under dynamic loading depends on the level of the initial stress state under static loading of concrete, from which dynamic loading is carried out to the limit state. The numerical analysis carried out using the model under consideration also confirmed the results of experimental studies that microcracking in concrete under static loading does not begin with a certain stress level, but practically from the moment of the beginning of concrete loading. The results obtained are of interest for solving applied problems related to the problem of survivability, protection of buildings and structures from progressive collapse, in particular when determining the criteria for the strength of concrete under special stress.

To prevent premature wear and reduce the bearing capacity of reinforced concrete slabs, it is necessary to conduct a timely examination of their technical condition with the determination of the causes of defects with their subsequent elimination. At present, GOST 31937, which regulates the inspection rules, does not contain quantitative values of the technical condition criteria, according to which it is possible to assign a category of the technical condition of structures, including within the framework of a visual inspection. To identify the frequency of occurrence of defects associated with corrosion of reinforcement in reinforced concrete slabs of buildings and structures, as well as to determine the causes of their occurrence, 738 archival survey reports of TsNIIPromzdaniy JSC were considered. An analysis of previous surveys showed that defects caused by corrosion of reinforcement are among the most common and require more detailed instructions on the designation of the category of technical condition of structures. To develop criteria for the technical condition of reinforced concrete slabs with defects resulting from reinforcement corrosion, a calculation analysis of the effect of reinforcement corrosion on the bearing capacity was performed, the effect of corrosion products on the formation of longitudinal and transverse cracks, experimental data, and the requirements of regulatory documents were considered.

The tasks related to the expansion of the raw material base in the production of porous aggregates for lightweight concrete with minimal energy consumption are becoming more and more urgent every year. As part of these studies, issues related to the production of porous aggregates for lightweight concrete that can withstand higher loads without compromising quality due to the presence of a crystalline structure of interpore partitions are considered. The material has low water absorption compared to expanded clay, which indicates the ability to maintain its thermal performance over time, and has an almost unlimited service life. The purpose of this study is to obtain foam-glass-crystalline porous aggregates for lightweight concrete using the technology of low-temperature foaming. The object of the study was technogenic production waste containing silica and aluminosilicate components as the main component (slag, TPP ash, enrichment tailings). Research results: the resulting porous fillers are characterized by high physical and mechanical properties: density 200-220 kg/m3; strength 3.1-4.0 MPa; thermal conductivity 0.07 - 0.1 W / (moS); water absorption 1-2%. Samples of light aggregates are characterized by a high degree of uniformity of the pore structure and preferred for strength and thermal conductivity pore sizes up to 1.2 mm and an interpore wall of 50 μm.