Based on the analysis and generalization of research on the deformation behavior of cracked reinforced concrete, the article presents a methodology for calculating crack width using the author’s established reinforced concrete effect—resulting from the influence of reinforcement on the deformation of the crack edges during crack opening. It is shown that when the continuity of the tensile concrete matrix is disrupted and the crack edges deform under the action of an intersecting tensile reinforcement bar, the crack profile and, consequently, its width at the reinforcement level change. The opening of a single or main crack is modeled using a so-called universal double-cantilever element (DCE), which accounts for the described deformation effect and combines the deformation parameters used in traditional reinforced concrete theory and fracture mechanics of reinforced concrete. The compliance of the DCE is related both to crack opening and to the displacements of the entire reinforced concrete structure and its generalized stiffness. It is demonstrated that the deformations of concrete in the reinforcement-adjacent zone change from tension to compression, qualitatively altering the pattern of relative mutual displacements of concrete and reinforcement between cracks.

Structurally organized space is the base for creation of structural design. In a paper, classification of structural erections on geometrical systems, lying in their base, and on purpose of grid shell systems. The history of the appearance of structural erections, the beginning of which was put by the erection of the Eiffel tower in Paris in 1889, is described briefly. Maybe it was earlier, when manufacturing of rolled products began in industrial scale in 1867. It is shown on concrete examples that net shell structures are used at the last years more often than reinforces concrete thin-walled shells. Special attention is given to grid, net, and net-and grid shell structures that were erected at the last 25 years. It is shown that at this time, grid and net shell structures were erected almost in all country except for single regions of the World. Brief information is presented on stress analysis of grid and net shell structures, their geometry, and materials. Now, intensive research of these structures in different directions are carried out. The main directions of research are directed at more accurate definition to the methods of strength analysis, to formation of optimal meshes, and to discovery of grid materials and covering materials.

Experimental and numerical studies of the influence of plastic deformations of reinforcement on the stress-strain state of normal sections of bent reinforced concrete elements have been carried out. The results of investigations have shown that there is a fracture in the strain diagram in the zone of the neutral axis. A bilinear approximation of strain distribution along the section height is proposed. Based on the results of finite element model calculations, the parameter characterizing the ratio of compression and tension strains is estimated. Comparison with the analogous experimental dependence has been carried out, that showed their satisfactory coincidence. To estimate the distribution of deformations along the section height in the elastic and plastic stages of reinforcement operation under one-temporal action of bending moment and longitudinal force, a number of numerical calculations of off-center compressed reinforced concrete elements with the same characteristics were performed. The analysis of the calculation results showed a close character of deformation distribution along the section height in bending and eccentrically compressed elements for the case of large eccentricities.

The article reviews the technological principles of concreting massive concrete structures, using the example of the Lakhta Center Tower the lower slab foundation in Saint Petersburg. Based on the requirement to ensure continuity in the concreting process, recommendations are provided for organizing the technological process that ensures the construction of a massive structure with specified design characteristics. The principles of curing the structure are examined to prevent the occurrence of temperature-shrinkage cracks. The main results of this research can be applied in the design and construction of massive foundation structures for unique buildings and structures.

The article presents the results of experimental studies of shear strength in the plane of horizontal mortar joints of masonry from porous ceramic blocks. The initial shear strength values were investigated (strength of tangential adhesion), as well as the ultimate shear strength values. Experiments with masonry were carried out in accordance with STB EN 1052-3 with simultaneous action of compressive and shear forces. Depending on the compression level, the destruction of masonry occurred due to a shift along the border of the masonry product and the mortar joint and fragmentation of the partitions between the voids of the blocks. It has been established that the limiting values of masonry shear strength, given in the standards for the design of stone structures, significantly exceed the experimental values. The need to correct the provisions of regulatory documents regarding the ultimate values of shear strength of masonry from porous ceramic blocks is indicated.

This study investigates the effect of loading history on the performance of long-term loaded members in compression subjected to dynamic action as a result of accidental situation. In addition, it considers changes in the strength and deformability of concrete. Analytical expressions have been developed to estimate the load-bearing capacity of reinforced concrete members in compression under different loading modes using equivalent bilinear diagrams of concrete deformation. To verify the reliability of the proposed analytical relations, experimental studies of the load-bearing capacity of long- term loaded compressed reinforced concrete members have been carried out under dynamic action which models accidental situation. Comparison of calculation results with experimental data shows that in the region of small eccentricities, close to accidental ones, the ultimate bending moments are smaller than calculated according to the relations presented in SP 63.13330.2018, and at the same time closer to the results of experimental studies.

The most common defect in reinforced concrete structures is corrosion damage of the working reinforcement in the concrete body. The main danger of corrosion damage is caused by several factors: increase of corrosion products in volume and creation of additional tensile stresses in concrete along the length of the rod, which leads to spalling of the protective layer; reduction of the diameter of the working reinforcement; areas of local bare reinforcement due to destruction of the protective layer. In addition to the loss of the total load-bearing capacity of structures due to the reduction of the cross- sectional area of reinforcement and concrete, their dynamic characteristics also change. The change of dynamic characteristics of structures affects the assessment of seismic resistance of buildings when calculated by accelerograms for dominant frequencies of vibrations. The paper presents the analysis of domestic and foreign literature on the assessment of the bond of reinforcement with concrete, the results of tests conducted by the authors of the paper on the assessment of the loss of bond of corrosion-damaged reinforcing bars in the body of concrete and the results of changes in the periods and frequencies of vibrations of damaged columns.

The vision of a sustainable world economy is currently aimed at achieving carbon neutrality and linked to global warming. According to statistics, simply burning one ton of Portland cement clinker causes at least a half a ton of carbon dioxide to be emitted. Therefore, one of the options to solve the problems identified is to revise existing technologies and develop low-carbon, low-carbon binders using industrial waste and unconditioned raw materials. Modification of the system «aluminosilicate raw material - alkaline activator» with sodium tetrabydrate and a fine-dispersed additive of volcanic nature, improves the properties of the cement clay, compacts the structure, reduces the porosity of the stone, which in the end positively affects the activity of the binder. The samples prepared were subjected to electron diffraction studies, as well as X-ray phase analysis of the zone (RFA) on the ARLX'TRA diffractometer. The properties of the binder and cement test have been investigated in accordance with the regulatory documents GOST 310.3-76 Cements. Methods for determining normal density, latch times and uniformity of volume change; GOST 310.4-81 Cements. Methods to determine the strength of bending and compression.. The studies revealed a dependence of influence of chemical modifier on structure and properties of cement stone. When modifying the dehydrated system with tetrabran sodium in dosages of 0.35 - 0.45% of the alkali activator mass, the structure is compacted, the porosity of the stone is reduced, which positively affects the activity of the binding material. The positive concept of filling a binder with a more dispersed volcanic additive in a quantity of 10% containing an aluminosilicate phase has been established. The properties of the cement dough improved, the need for alkali solution decreased by 8-10%, the adhesion times did not increase significantly but increased by 10-40 minutes depending on the active component, water absorption in mass decreased by 5% and strength increased by 10- 12%. Study of microstructure of samples showed that the main mass of heterogeneous systems are volumetric aggregates and lattices, small clusters on their surfaces with pronounced spiciness; features of microstructure indicate mineralization processes.. Therefore, the development of low-carbon construction models will contribute to and open an effective path for climate policy implementation through the rational use of natural resources, the inclusion in the production of industrial wastes and environmental-like technologies.