The results of calculating a reinforced concrete beam on an elastic statistically inhomogeneous foundation after the formation of cracks in concrete are presented. The compliance coefficients of the base are considered as random stationary functions, and the load is assumed to be a random non-stationary function of the x coordinate. Strength parameters of concrete are taken as random Gaussian values. The distribution parameters are given for both the initial bending stiffness of a reinforced concrete beam and the stiffness of the beam after cracking, as a function of the random cube strength of concrete. The parameters of the distribution densities of the deflections of the beam before the formation of cracks in it, as well as after the formation of cracks, are determined. For an approximate solution of the differential equation for the bending of a reinforced concrete beam after the formation of cracks, the variational principle of stationarity of additional energy (the Castigliano functional) is used. This makes it possible to determine the probabilistic characteristics of the distribution of the equivalent constant stiffness of the beam, the probabilistic parameters of the distribution of beam deflections after cracking, as well as the total differential law of the distribution of deflections in a beam on an elastic foundation in an arbitrary section of the beam. The probability of occurrence of the limiting state in the form of exceeding the value of the deflections of the beam, the limiting standard value of the deflections, taking into account the possible formation of cracks in the beam, has been determined.

The article presents the results of a comparative analysis of the axial tensile strength of masonry made of autoclaved cellular concrete blocks with cement mortars of various grades and polyurethane adhesive compositions of various manufacturers. The tests were carried out on prototypes made of two cubes of 150x150x150 mm glued together. As cellular concrete, blocks of autoclaved hardening of the compressive strength class B1.5, B2.5, B3.5 were used. M200 and M300 cement mortars, "Tytan Professional”, "Technonicol", "Bonolit" and “KUDO” foamed polyurethane glues were used as a binder. The experiment was performed in the Laboratory of the Department of Reinforced Concrete and Masonry Structures of the Moscow State University of Civil Engineering. On the basis of the experiment, the values of the increase in the strength of the masonry under axial tension were obtained depending on the binder.

The method of experimental and numerical studies of reinforced concrete frame structures with crossbars reinforced with inclined rods under special influences is given. The main objective of these studies was to determine the nature of deformation, cracking and destruction of such structures under special impact caused by the sudden removal of one of the structures and, as a consequence, the redistribution of force flows in them. To increase the survivability and protection of the studied structural system from progressive collapse, with a quantitative and qualitative change in the forces in its elements, it is proposed to install transverse reinforcement from inclined reinforcing rods in two mutually perpendicular directions on the supporting sections of the frame system crossbars. The parameters of such reinforcement and the parameters embedded in the design model of the frame structure under consideration for static loading at the first stage and dynamic loading at the second stage are determined by numerical modeling using the Ansys software package. On this basis, the justification of the adopted design decisions of frame structures for the development of a program for conducting experimental studies of such structures under special influences was carried out.

For buildings of historical development of cities, as well as architectural dominants of urban and rural settlements, the architectural attractiveness of buildings is often created by erecting external load-bearing brick walls, including multilayer ones, as well as curtain external walls with a finishing layer of facing bricks. When designing building envelopes, as well as in the process of researching and assessing the technical condition of building envelopes, it becomes necessary to calculate (assess) the bearing capacity of external walls, to assess their durability. The object of research is the bearing capacity and durability of the outer walls of buildings.
A review of domestic and foreign scientific and technical literature has been carried out. He showed that the overwhelming majority of scientific publications concern the choice of constructive solutions for walls, the purpose and use of new building technologies and materials, their technical characteristics, as well as the assessment of the energy efficiency of the proposed constructive solutions for external walls.
Examples of defects in the outer layer of multilayer bearing walls of brick buildings and recommendations for ensuring the durability of the front layer of a brick wall are given. The requirements of the current building codes for calculating the bearing capacity of multilayer brick walls are considered. An example of calculating an eccentrically compressed multilayer brick wall with equivalent calculated cross-section is given. In order to simplify the calculation of the bearing capacity, it is proposed to use computer programs to determine the geometric characteristics of the equivalent calculated cross-section. In particular, for a short-term application of loads to determine the stresses and analyze the stress state of the equivalent calculated cross-section of the wall, an example of using the program, the constructor of sections PK LIRA-SAPR, is given. It is shown that it is necessary to consider the distribution of stresses over the section under short-term and long-term loading in the design of multilayer brick walls.

When constructing a stress-strain compression diagram for concrete with indirect reinforcement within the framework of the theory of limit state design, it is necessary to assign the strength values of materials with the required security. To do this, a transition is made from average strength value obtained from the results of experiments to reduced characteristic compressive strength and the design value of strength. In view of this, a contradiction arises due to the fact that initially the formulas for determining the deformations corresponding to the top of the compression diagram were obtained for experimental value of strength, and in the calculations of structures it is proposed to use reduced characteristic compressive strength and the design value of strength, which can lead to incorrect results. The article compares the calculated values of strains with experimental data and notes a significant overestimation when calculating by the characteristic compressive strength and the design value of strength.

The article provides the analysis of the causes of damage in the masonry of historical buildings after their restoration. It has been established that the use of mortars of an increased grade and, accordingly, stiffness during repairs of historical masonry leads to an increase in tensile stresses in bricks under temperature and humidity effects. The reasoning behind the use of such mortars is to increase the strength and durability of the restored areas of historical masonry. The results of numerical simulation show that the masonry mortar must be sufficiently strong in compression and, at the same time, sufficiently plastic. It is shown that the use of hard mortars based on a cement binder, compared with plastic mortars based on a lime binder, on average doubles the value of normal tensile stresses at a temperature difference ΔТ=+100С.. This effect is much higher when stones swell due to their moisture. According to the results, for restoration work with brickwork, one should use mortars in accordance with the technology corresponding to this historical period, i.e., lime with additives that were identified during laboratory tests of samples taken from historical masonry. Low-grade mineral solutions with a low modulus of elasticity are preferable. It increases the crack resistance of the masonry under temperature and humidity effects. The article also shows that improper jointing of masonry joints facilitates the destruction of masonry. It happens when areas of accumulation of rainwater are formed, leading to increased wetting of stones in areas of direct impact of rainfall.

The relationship between the maximum deflections W0 from a static uniformly distributed load q and the fundamental frequency of natural transverse vibrations ω of a round isotropic plate of variable thickness according to the law of a square parabola with a thickening in the center under homogeneous conditions of support along the outer contour, depending on the ratio of the thickness of the plate in the center to the thickness along the edge, is considered.According to the results of the study, graphs of the dependence of the maximum deflection and the frequency of natural vibrations of the plate on the ratio t2/ t1 are constructed. It is shown that for round plates of linearly variable thickness at t2/t1≤1.1, the coefficient K with an accuracy of 5.29% coincides with the analytical coefficient for round plates of constant thickness

The article presents the author's approach to determining the weight of indicators of the technical condition of buildings and structures, which allows solving the problem of increasing the reliability and effectiveness of assessing their real readiness for use for their intended purpose. The implementation of this approach is based on the experience of solving practical problems in assessing the technical condition of buildings and structures, when the weight of their indicators cannot be directly measured. In this case, it is proposed to use expert ranking methods to determine it and direct evaluation. The effectiveness of their use largely depends on it depends on the competence of evaluating experts and the consistency of their opinions on the issues under study, which are established by determining the coefficients of awareness and argumentation of experts and step-by-step solution of research tasks based on the use of the rank correlation method. A distinctive aspect of the described approach to assessing the weight of indicators of the technical condition of buildings and structures is the establishment of a criterion for determining their importance for solving the tasks set, as well as uniform rules for measuring them. The proposed procedure for assessing the weight of the investigated problems has been successfully tested during the survey of protective structures of the executive authorities of the Russian Federation. It can be recommended to determine a reliable assessment of the technical condition of buildings and structures for various purposes.

An analysis of the experimental studies presented in the scientific literature indicates that the strength and deformability of fiber-reinforced concrete under dynamic additional loading may depend on the initial level of stresses caused by a preliminarily applied static load. In this regard, the purpose of this study was to build improved models of fiber-reinforced concrete deformation of operated fiber-reinforced concrete structures of bearing systems of buildings and structures during their dynamic additional loading, taking into account the nonlinearly elastic law of material deformation at the stage of loading with a static load, as well as changes in the parameters of viscous resistance during loading. As a model of the force resistance of fiber-reinforced concrete of loaded fiber-reinforced concrete structures during their dynamic additional loading caused by an emergency situation, the Kelvin-Voigt model for an elastic-viscous body was adopted. On the basis of the adopted model, an analytical solution of the differential equation of uniaxial compression of fiber-reinforced concrete was obtained under its single dynamic additional loading from an arbitrary level of initial stresses acting in it from a previously applied static load. A step-iterative approach to determining the parameters of state diagrams of fiber-reinforced concrete under static-dynamic loading conditions is proposed. An analysis of the obtained dependences between stresses and strains shows that an increase in the level of initial stresses acting in a compressed concrete element at the moment a dynamic load is applied to it leads to a decrease in the dynamic strength of concrete with the same impact parameters.

The reliability of the design characteristics of any design is influenced by both the operating load and the wear of the material itself due to environmental influences. This article provides a probabilistic assessment of reinforced concrete elements exposed to chlorine penetration. A freely supported reinforced concrete slab was used for the study. Well-known techniques developed by many authors were included in the mathematical model of the loss of the bearing capacity of reinforcement under corrosion.
Uncertainties in strength and applied load were fully accounted for using the probabilistic method. The limit state function of the bearing capacity of a reinforced concrete bending slab was developed and evaluated using the first moment’s reliability method.
The whole process was implemented using the developed MATLAB program.

The real nonlinear diagrams of concrete, reinforcement and steel-fiber concrete under dynamic loading are formulated and analytically described. Theoretical and experimental studies of the operation of compressed and non-centrally compressed elements with different levels of load application eccentricity under static and short-term dynamic loads are carried out. 3 reinforced concrete and 9 steel-fiber concrete elements were manufactured and tested for short-term dynamic load under central and off-center compression. New experimental data characterizing the process of deformation and destruction of steel-reinforced concrete models of columns have been obtained. Also, the schemes of destruction and cracking, the dependence of changes in the dynamic load over time, the movement of concrete, reinforcement and steel-fiber concrete over time are obtained. A method has been developed for calculating the strength and stability of such elements, taking into account the reinforcement of the section with steel fiber concrete. The influence of the use of zone reinforcement with steel fiber of compressed and non-centrally compressed reinforced concrete elements is numerically analyzed. The results of the calculation according to the developed methodology are compared with the results of experimental data. The optimal variant of the application of zone reinforcement made of steel fiber for compressed and non-centrally compressed elements operating under static and short-term dynamic loads is proposed. The analysis of the calculation results based on the developed method for calculating the strength of normal sections of non-centrally compressed reinforced concrete and steel-fiber concrete, based on the deformation model, and their comparison with the data of experimental studies under short-term dynamic loading show that the deviations are on average 10-18 %, which indicates that the developed method has sufficient accuracy to solve practical problems.

Strengthening of soils by jet technology in difficult ground conditions has now become widespread, including in the construction of buried and underground structures. At the same time, a sufficient amount of experimental data has accumulated to predict the properties of the resulting soil cement. The purpose of the work is to determine the optimal consumption of materials for soil-cement structures, taking into account complex engineering and geological conditions.
The study of mineral-based hardening systems in water-saturated soils with inclusions of organic deposits or in conditions of high filtration has a number of features that make it difficult to assign optimal technologies and components of cement-based solutions for the formation of soil cements. To determine the final parameters of soil cement, the parameters of soil cement piles at the facilities during the construction of the subway, laboratory data on mixing mineral components and soils of different types, scientific and technical data were analyzed.

In connection with the prospects for growth in the volume of construction of individual residential buildings, the demand for facing ceramic bricks and large-format porous wall blocks is increasing. With a shortage of high-quality clay raw materials for the production of plastic molded ceramic bricks, it is recommended to switch to the production of semi-dry pressing products. An important task is to increase the strength of ceramic bricks, both carrying a load in the wall and performing a heat-insulating role. It is recommended to introduce an aqueous solution of nanosilica gel into the charge.
The main raw material was non-caking dusty loam of the Verkh-Tulinskoye deposit, containing more than 70% of dusty fractions (5-50 microns). As an additive, we used Lakesil-30 nanosilica gel produced by the Compass Scientific and Technical Center (Kazan). In the article, the authors used both standard research methods and modern methods of X-ray phase analysis to establish the material composition of a ceramic shard.
It has been established that, at optimal prescription and technological parameters, the introduction of Lakesil-30 gel with mixing water into the raw mixture increases the strength limit by 32.8% compared to the non-additive composition, without affecting the average density and water absorption of the ceramic shard. ... The quantitative phase composition of the shard has been studied.
It has been experimentally established that the strength of a ceramic shard is increased due to the use of an additive of Lakesil-30 nanosilica gel in an optimal dosage. To ensure the maximum strength of the ceramic shard, it is necessary that the processes of interaction of the aqueous solution of the additive with the clay component are completed during firing.