The article presents the results of experimental studies of the complex resistance of reinforced concrete structures with a square cross-section, made of B25 heavy-concrete, which includes graphs of deflection and rotation angles, as well as the dependence of concrete deformations obtained from the indications of strain gauges. The main deformations of elongation (and shortening) of concrete were determined using data, obtained from the proposed scheme for installing strain gauges. Rebar for experimental samples was selected in such a way that it achieved yield stress in the stage before destruction. The obtained experimental data is required for evaluation of proposed methods for calculation of structures with a rectangle cross section structures in the considered stress-strain state, for example, to check the values of the general load of crack appearing, its value relative to the distruction load; distance between cracks at different levels of crack formation, width of cracks opening at the level of the main reinforcement axis and at the distance of two diameters from the reinforcement axis, coordinates of spatial cracks formation, schemes of crack formation, crack development and crack opening. It was found, that in the tested structures the width of crack opening at the level of the main reinforcement axis is two to three times less than at a distance of two diameters from the main longitudal (or transverse) reinforcement axis. The parameters and crack patterns established during the experiments allow us to clarify the accepted working hypotheses for constructing a calculation model of the resistance in reinforced concrete structures of rectangular cross-section under torsion with bending.

A significant part of the territory of Russian Federation refers to seismically dangerous areas. In the current code in design of reinforced concrete buildings for seismic loads the development of plastic strains is supposed. They are taken into account while determining loads by introduction of reducing factor K1, but their influence on the strength of elements is neglected. Plastic strains of reinforcement lead to appearance of residual cracks in compressed zone of concrete and due to this the reduction of bearing capacity of bending elements takes place on following loading cycles. The approximate method of determination of the depth of open cracks and of the residual height of sections when changing the sign of internal forces after reaching the maximum deflection has been proposed. The depth of residual crack is determined from the condition of equilibrium of longitudinal forces with regard to stress-strain state of a section at three stages of loading: at a moment of achievement of maximum plastic strains, at the unloading stage and at a moment of the beginning of crack formation after changing the sign of internal forces. The comparison of results obtained by the approximate method and results of calculation of finite elements model of a beam has been carried out.

The static load test of a bored hanging pile does not provide sufficient data on the resistance of clay soils of the pile base. Based on the results of a standard test, it is impossible to judge the causes of linearity and nonlinearity of base deformations, changes in the settlement rate, types of resistance and distribution of forces, and the effect of a loaded pile on adjacent piles and underground structures. Based on the analysis of test materials and observations of structures under construction and in operation, laboratory modeling and calculations, a foundation resistance scheme and methods for determining its parameters are proposed. The diagram includes resistance forces along the lateral surface, under the lower end of the pile and at the periphery of the base. Part of the external load is transferred by the soil to the periphery of the base by shear and separation cracks formed in soils, which are fragilely destroyed during deformations under the action of elastic forces at the contact of the soil with the lateral surface and under the lower end of the pile. The reaction of the soil at the periphery of the base contains both elastic and plastic components of vertical and horizontal orientations. The implementation of the scheme is possible when testing the pile by the method of a constant rate of loading (CRL) with continuous measurement of soil deformations at the contact with the lateral surface, at a distance from it using depth marks, soil pressure under the lower end of the pile and registering their readings synchronously registering pile settlement.

High-strength steel fiber concrete, made on the basis of fine-grained high-strength concrete, is a quite promising building material, in particular, for the construction of high-rise buildings and structures of increased massiveness. The introduction of steel fiber into the concrete matrix can significantly reduce the influence of such shortcomings of fine-grained concrete as increased fragility and explosive nature of fracture, and also positively affects the tensile properties of concrete. However, the widespread use of high-strength steel fiber concrete is currently limited, among other things, by the lack of an experimentally relied normative framework for this material. The proposed article aims to bridge this gap. Modern engineering trends are aimed at introducing into practice diagram methods of calculation based on real diagrams of material deformation under load. This article describes the technique of constructing isochron diagrams for fine-grained high-strength concrete and steel fiber concrete with disperse reinforcement in the amount of 1.5% by weight, made from Russian-made components. Isochron diagrams allow you to calculate the deformation of the material depending on the level of load at any time, including during prolonged loading. There have been made changes to the existing methodology, allowing to take into account the nonlinearity of both current and ultimate creep characteristics depending on the level of loading. The proposed theoretical dependences give good convergence with the experimental data.

As it was found previously, the concrete fracture surface formed from tensile force is described by fractal geometry methods. It is shown thatthe fractal dimension value is related to the tensile stress gradient , to the aggregate size and, as shown earlier, does not depend on the strength of concrete. Moreover, the fractal dimension depends on the size of the sample only until its size reaches a value to which linear fracture mechanics is applicable. The stress intensity factor is related to the fractal dimension, and both characteristics are related to the aggregate size. A connection for the critical stress intensity factor () characterizing the crack resistance of the material in nonlinear fracture mechanics with the crack size l and the specimenis proposed. The stress intensity factor for a fractal crack () can be used to calculate structures using nonlinear fracture mechanics.

At emergency situations caused by the sudden removal of one of the load-bearing elements from the building frame, a stress-strain state is more disadvantageous in comparison with their stress-strain state at the stage of normal operation. In cases where the eccentrically compressed elements have an "elegant" section, or have acquired environmental (corrosion) or mechanical (chips) damages during operation, as a possible scenario for the exhaustion of their bearing capacity is buckling. The paper proposes an approach to the construction of deformation criteria for assessing the special limiting state of eccentrically compressed bar elements of reinforced concrete frames. The approach is based on the use of a combination of nonlinear deformation analysis and nonlinear form stability analysis. It is shown that the limiting values of deformations for the considered reinforced concrete element can be determined by the criteria of strength or stability, depending on the ratio of the sizes and structure of sections of the bar elements, as well as the ratio of the forces acting in them.

The paper considers the system "beam - elastic foundation", in which a beam with free edges was at first on a solid elastic foundation, but when a defect suddenly forms in the foundation under the right side of the beam, part of foundation was removed from design model. As a result of calculations performed by the method of initial parameters, the displacements and internal forces for the static problem are determined. The dynamic problem of determining the forces and displacements was solved, taking into account the three vibration loads F (t) = F sin γt applied at arbitrary points d when the conditions for supporting the right side of the beam on an elastic foundation were changed, the values of the dynamics coefficients were determined. Conditions are formulated that must be taken into account when analyzing the dynamic behavior of a structure under the influence of vibration loads in the case of a change in the conditions of bearing on an elastic foundation.

It has been substantiated that plasma treatment of raw components is expedient to enhance the physical and mechanical properties of building mortars based on cementitious binder. The developed method of plasma modification of raw components is notable for high efficiency and usability. It has been considered how repair compositions based on cementitious binder have influence on the mechanical strength of the reconditioned and armored floor slabs simulating flat floor slabs of communication conduits. It is shown that the repair compositions based on cementitious binder restore the bearing capacity of the floor slabs by 72.1-96.5%, and when tested for breakdown the reconditioned slabs fail within the repair composition. It has been found that after external reinforcement of the reconditioned armored floor slabs with CarbonWrap Tape 230/150 their bearing capacity increases by 1.7-3.8 times. The effectiveness of epoxy composite materials for strengthening of the building constructions of various functional purpose is proved with the results of experimental studies and checking calculations of the armored floor slabs.

The paper attempted to produce geopolymer construction materials with improved biological resistance based on glass waste to create an alternative to cement. With the use of modern physical methods, processes of structure-forming of cementing substances based on sodium-potassium silicate glasses have been studied. It has been found that when the glass-absorbent binder-based composite materials are solidified, the complex alkaline composition is formed. Stability of developed materials under conditions of exposure to biologically active media was investigated. Potential mechanical devices of materials operated in rooms with different microclimates, provided by the production process, have been identified.

The quality of the indoor environment depends on the comfort and safety of people living inside. Scientists are working to overcome the negative impact of the environment on the population in the cities. Nevertheless, the existing residential areas of the country often do not meet today’s environmental hygienic requirements. When choosing building constructive solutions and microclimate support systems for buildings, it is necessary to take into account the factors leading to the entry of harmful substances that pose a real threat to the health and life of people. Intensive use in residential construction of new polymer materials and other impacts on the internal environment of buildings can lead to a decrease in the quality of the internal environment of the buildings. It is crucial to take into consideration these factors when choosing building solutions and creating comfort with engineering systems providing the microclimate of buildings.

The aim of the study was to determine the relationship between the structure and properties of a gypsum composite based on semi-aquatic gypsum with a filler in the form of hollow glass microspheres with characteristics of water demand and the degree of filling of the mixture with microspheres. We used a glass filler with the sizes of hollow microspheres of 0.1 - 50 microns with a vacuum inside. To solve this problem, a two-factor planned experiment was chosen, where the ultimate compressive strength and the average density of the gypsum composite were selected as the output factors. The data obtained confirm the effectiveness of using hollow microspheres for producing light materials based on calcium sulfate hemihydrate. Domestic samples of glass microspheres were used. It is shown that they have a plasticizing effect in the composition of raw mixtures based on gypsum binder and contribute to a decrease in their average density.

Ceramic brick based on interlayer clay and lime flour is obtained without using natural traditional materials. The process of drying ceramic bricks should be carried out according to the optimal mode, which means a combination of its possibly short duration, minimum expenses of energy and quality semi-finished product ─ lack of buckling, Cracks and hidden stresses, which contribute to the formation of cracks in the burning When making ceramic brick only from interlayer clay, Used as clay binder, without the use of repellents, there is a sharp drop in the limit shear stress in the temperature range of 20-80 °C, obviously due to the appearance of cracks and deformation curves. The use of lime flour in ceramic masses in the production of ceramic brick slows down the drop of the limit shear stress in the temperature range 20-80 °C. Researches showed that for improvement of drying properties of ceramic weight the "limy flour interslate clay water" system is more uniform, in relation to the "interslate clay water" system. Analysis of the shear stress limit under hot molding conditions has shown that the function of plastic strength versus molding humidity Pm = f (W, t) is of particular importance in this case than the function of plastic strength versus temperature Pm = f (t).

The object of study is a cement composite material with powdered utilized optical discs. The objective is to establish the dependences of the main strength characteristics - compressive strength, bending strength, and density - on the amount of waste added into the mixture and the water-cement ratio. The compositions of the mixtures for the production of the cement composite material samples consisted of the following components: cement, sand, powdered waste in the form of utilized optical discs and water. Based on the results of testing the samples, mathematical models have been developed which describe the dependences of the physical and mechanical properties of the cement composite material samples on the fraction of waste and water-cement ratio. It was found that with an increase in the amount of powdered waste added into the mixture, it reduces the compressive strength, bending strength, and density of the samples under study, however, the optimization of the water-cement ratio makes it possible to obtain equal strength compositions with a different fraction of waste. Component compositions of cement composite material mixtures with the addition of powdered utilized optical discs in the amount of 10 to 25 % of the total filler mass, which can provide construction products with a compressive strength class B20, are presented.

Generalization and analysis of scientific hypotheses and theories of domestic and foreign researchers in the field of the frost action mechanism on concrete has been performed. A critical author's assessment of them from the point of view of the basics of physical chemistry of silicates and solid state physics is presented. The initial prerequisites for the frost resistance of heavy concrete and equal-strength structural light concrete in connection with their structure are formulated, including of this article author's targeted experimental studies on the relationship of the frost resistance of these concretes with their pore structure. Thermodynamic models of freezing-thawing of water, including its adsorption layers in capillaries of cement materials porous structures are used. The data of studies of the critical degree of water saturation of concrete are considered and a reasonable assessment of it is given as an integral characteristic that determines the possibility of formation of micro- and then macro-defects in the concrete structure during its cyclic freezing and thawing. Based on the results of analytical and experimental studies, using the basic principles of physics of the solid state, as well as the physical and physical-chemistry of silicates, has been developed the physical-chemical basis for the resistance of structural lightweight concrete in comparison with equally strong normal weight concrete to the effects of low (up to minus 70 °C) subzero temperatures. The results of this work are considered by the authors as a modern scientific basis for the development of the main provisions of the technology for manufacturing structural lightweight and normal weight concretes with high durability (frost resistance and water resistance), intended for reinforced concrete structures of engineering constructions, operated in severe climatic conditions, including in the conditions of the Arctic coast.