Introduction. Concrete and masonry structures constitute the majority of old buildings in use.

The aim of this research is to propose a methodology for assessing the seismic resistance of the cross-sections of elements ofconcrete and masonry structures. This research developes the previous research results in this area, which began in the USSR in the early 1980s.

Materials and methods. The methodology of assessing the maximum accelerations and design seismic resistance classes for concrete elements of building structures is considered. For concrete elements the seismic resistance class is assessed by the position of the resultant force in the section (limitation of concrete tension) and by compressive stresses in concrete. The minimum seismic resistance class is assessed under the assumption of elastic work of the section. At the first stage, three values of the calculated peak accelerations are assessed, ensuring the following: the elastic work of the section, the limit state with the limit state coefficient К₁ = 0.5 and the limit state with the limit state coefficient К₁ = 0.25 respectively.

Results. Basing on the resulting accelerations, one can assess the intensity of the design earthquakes using the Russian Standard scale of earthquake intensity.

Conclusions. Basing on the research results, the authors assessed the intensity and repetitiveness of earthquakes resulting in various limit states of concrete and masonry structure sections, including the occurrence of section tension, the appearance of various cracks, complete section unloading, the appearance of spalls in the compressed zone of concrete, etc. These data are of interest to both facility owners and insurance companies.

Introduction. The durability and retention of fire-retardant properties of thin-film intumescent coatings are largely determined by the resistance of their chemical composition to atmospheric influences, primarily moisture. Direct in-situ observations of degradation processes require extensive time, making the use of instrumental analytical methods, such as infrared spectroscopy, essential for rapid diagnostics and identification of degradation mechanisms. This article discusses the application of Fourier-transform IR spectroscopy for comparative analysis of the chemical state of fire-retardant coatings after operation in various climatic conditions.

Aim. To conduct a comparative identification of functional groups and assess the degree of chemical degradation of an epoxy-acrylate-based fire-retardant coating after prolonged (2 years) exposure to atmospheric moisture during operation in an open industrial atmosphere in a cold climate (open circuit) compared to protected operating conditions (closed circuit).

Materials and methods. This study analyzed fire-retardant coating samples collected from operational sites. Infrared absorption spectra were recorded on a Fourier spectrometer in the range of 4000–400 cm^-1 using KBr pellets in accordance with State Standard R 57941-2017. Qualitative interpretation of the spectra was based on an analysis of the characteristic absorption bands of the functional groups of the polymer matrix, organophosphorus flame retardant, and mineral filler.

Results. IR spectroscopy revealed significant differences in the chemical state of the samples. The open-loop sample showed the almost complete disappearance of bands in the range of 1240–980 cm^-1, characteristic of the stretching vibrations of the P=O and P–O–P bonds of the polyphosphate flame retardant, indicating its profound hydrolytic degradation and leaching. Concurrently, a significant strengthening of the broad band of bound OH groups (3600–3200 cm^-1) and a weakening of the epoxy matrix signatures were observed. In the closed-loop sample, the key bands of the flame retardant and polymer are preserved, but the presence of the OH band indicates the initial stages of hydrolysis.

Conclusions. It was established that the dominant degradation mechanism of the fire-retardant coating is hydrolytic degradation, the intensity of which directly depends on the level of moisture load. The results confirm the high sensitivity of the organophosphorus flame retardant and the polymer matrix of the epoxy-acrylate-based fire-retardant coating to long-term exposure to moisture.

Introduction. The article is debatable in nature. The authors present the results of their research, offering them for discussion and evaluation to a wide range of the engineering community: drafters of standards, developers and users of computer programs, employees of design, expert and research organizations, teachers and university students.

Aim. To compare the results obtained when calculating the normal cross-sections of reinforced concrete structures using two methods: the nonlinear deformation model (NDM) and the ultimate efforts method (UEM). To analyze the implementation of NDM in various computer programs for calculations of reinforced concrete structures: OM SNiP Reinforced Concrete, Ing+, Arbat, LIRA-CAD, Lira 10, STARK ES.

Materials and methods. When comparing the results obtained by NDM and UEM, bendable and non-centrally compressed elements were studied. In the case of offcenter compression, the case of a positive and negative values deformation diagram in NDM calculations is considered. Calculations were performed according to the OM SNiP Reinforced Concrete program. When analyzing the implementation of NDM in various computer programs, the algorithms provided for in SP 63.13330.2018 and used by program developers were compared, and the results obtained from the programs were analyzed.

Results. Cases of significant discrepancies between the results obtained by NDM and UEM have been identified. It turned out that NDM requires significant unjustified overspending of the reinforcement installed to ensure the strength compared to UEM. The reasons for the discrepancies are indicated. The annual economic damage caused by overspending of fittings, which occurs due to incorrect calculations, is over 100 billion rubles. Accidents are also possible. Questions have been formulated for discussion in order to remedy the situation.

Conclusions. The general state of calculations of reinforced concrete structures should be recognized as requiring adjustments. Discussion of the issues raised should help solve this problem. It is advisable to develop a document with a set of reference examples that allows to obtaining the same results for different programs with the same source data. 

Introduction. The concentrated action of loads is one of the main causes of brittle failure in reinforced concrete structures. The punching calculation of reinforced concrete slabs in domestic and international codes is based on the geometric characteristics of a contour located around the load application area. In the case of a concentrated force, the only geometric characteristic considered is the perimeter. Punching calculation provisions also require accounting of concentrated moments, which consequently necessitates the calculation of the corresponding geometric characteristics. The methodology for their calculation is described in general terms in regulatory documents. Ready-made formulas are not available for complex contours. This creates the need to develop a universal method for calculating the geometric characteristics of arbitrary contours.

Aim. To develop a universal method for calculating the geometric characteristics of arbitrary punching contour composed of straight-line segments and arcs. Materials and methods. The method proposed in the article is based on general approaches from the course of strength of materials. The main distinction is that the geometric characteristics are calculated for a contour. This leads to differences in the units of measurement of the corresponding quantities for bar cross-sections and for a contour.

Results. The geometric characteristics of elementary figures, such as a straight-line segment and an arc, are derived. These expressions are then used to determine the corresponding characteristics for the entire contour. The obtained formulas eliminate inconsistencies in units of measurement. An example calculation of a contour composed of straight-line segments and arcs is provided based on the derived formulas.

Conclusions. A universal coordinate-based method for calculating the geometric characteristics, including the rotational moment of inertia, of an arbitrary punching contour composed of straight-line segments and arcs is proposed. The approach can be implemented using commonly available software tools, spreadsheets, etc.

Introduction. In current practice of reinforced concrete structures erection, traditional measurement control using manual tools followed by drafting schemes in CAD systems remains the most labor-intensive stage of technical supervision. The discreteness of such measurements and the lack of a direct link to the project digital environment complicate the rapid verification of completed work. The introduction of Building Information Modeling (BIM) technologies opens up opportunities for creating fundamentally new quality control mechanisms based on continuous reality scanning.

Aim. Substantiation of technological efficiency and development of a methodology for automated comparison of field measurement data (point clouds) with project BIM models to increase the speed of executive documentation formation.

Materials and methods. The study is based on the use of terrestrial laser scanning (TLS) as a tool for capturing the actual geometry of monolithic columns (a project in Kaliningrad). Data processing was carried out in the Revit environment. To compare “As-Built vs As-Designed” states, the method of aligning the point cloud and the information model using shared base coordinates was used. Mathematical estimation of the accuracy of the obtained point array relative to control measurements was carried out using the distance root mean squared (DRMS) indicator.

Results. The fundamental possibility of full automation of the process of identifying reinforced concrete structures geometric deviations in the BIM environment is proved. It has been established that automated comparison of the actual point cloud with project elements allows for the formation of executive schemes significantly faster than with the traditional approach. A comparative analysis showed a multiple reduction in labor costs for cameral data processing. It is noted that the direct transfer of deviation data to calculation complexes (LIRA-CAD allows for rapid verification calculations of the bearing capacity of elements whose parameters have exceeded the standard tolerances, which is technically unfeasible within traditional drafting in AutoCAD.

Conclusions. The use of BIM technologies in conjunction with laser scanning allows moving from selective manual inspection to systematic automated monitoring of reinforced concrete structures quality. This approach ensures acceptance transparency and updating of the building’s digital twin, minimizing time losses at the technical supervision stage.

Introduction. This paper presents the results of a study of the particle size distribution and specific surface area of natural and manmade materials used as components of repair and restoration mortars for architectural and historical monuments in southern Russia.

The aim of the study was to investigate the particle size distribution of eight types of locally sourced mineral materials (dolomite, limestone, marl, shale, gypsum, anhydrite, bentonite, crushed burnt brick) to further elucidate the influence of particle size distribution on the reactivity, hydration, and microstructure of binder systems.

Materials and methods. Based on sedimentation analysis of aqueous suspensions of these minerals using Stokes’ law, particle size ranges were determined and specific surface areas were calculated.

Results. It was found that anhydrite and dolomite are characterized by the highest dispersion (average size  14–15 µm), ensuring high reactivity and a dense microstructure, while gypsum and bentonite have larger particles (17–25 µm), affecting the water demand of the mixtures. Gypsum has the highest specific surface area (153.1 m²/kg), while bentonite has the lowest (86.7 m²/kg). Conclusions. The obtained data, based on the theoretical basis of materials science (provides an understanding of the relationship between the structure, composition, production technology and operational properties of materials) and colloidal chemistry (the behavior of dispersed systems, including processes at the phase boundary – adhesion, capillary phenomena), make it possible to substantiate recommendations for the targeted selection of components of repair and restoration compositions to ensure the required balance between strength, adhesion, water absorption and compatibility with the original materials of monuments and form a scientific and practical basis for the creation of authentic, economical and environmentally friendly compositions based on local mineral raw materials.

Introduction. The article presents the results of a study on vibrocompressed concrete slabs produced using various technological additives. Modern methods for evaluating their structural and performance characteristics are reviewed.

The aim of the work is the approbation of a method for rapid prediction of the frost resistance of concrete products. The implementation of such a method will significantly reduce the time required for assessing product durability compared to traditional prolonged cyclic tests.

Materials and methods. The objects of the study were samples of vibrocompressed paving slabs manufactured under plant conditions. The nominal characteristics of the samples correspond to concrete strength class B30, frost resistance grade F200, and service group B in accordance with State Standard 17608-2017. Complexes of technological additives were used to modify the properties of the concrete mixture: plasticizing, water-reducing, and air-entraining. The following tests were conducted: determination of frost resistance in accordance with Appendix E of State Standard 17608-2017; Microstructural analysis using the method of State Standard R 70753-2023.

Results. Microstructural analysis revealed significant changes in the structure of the hardened concrete that directly affect its frost resistance. Based on the data obtained, a hypothesis was put forward that the key factor for durability is the presence and quantitative ratio of pores of two fractions: large pores with a diameter from 1 to 4 mm; small pores with a diameter from 0 to 0.3 mm.

Conclusions. The conducted research confirms the relevance and scientific novelty of the topic. The obtained results allow for the following conclusions: а correlation was identified between the parameters of the pore structure formed during vibrocompression and the frost resistance of the concrete; the proposed comprehensive approach, combining standard frost resistance tests and quantitative microstructural analysis, is a promising basis for developing an express method for predicting durability. For the successful implementation of the methodology, it is necessary to develop a detailed program for further research aimed at establishing quantitative assessment criteria and validating the method for various concrete compositions.

Introduction. The development of self-healing cementitious composites for cracks represents a promising approach to increasing the durability of reinforced concrete structures and reducing repair costs. Accelerated restoration of water resistance after defects in concrete is important for hydraulic engineering and infrastructure projects.

Aim. The aim of the study was to evaluate the self-healing ability of cementitious materials with a waterproofing additive and to develop and test an effective method for permeability monitoring through artificial defects of controlled size.

Materials and methods. Experiments were conducted in laboratory and field conditions in Portugal and Russia. Permeability was assessed using both rapid methods (visually, by the appearance of bubbles) and specialized equipment (BB-2, installation according to EN 123908, UVF-6). The study compared compositions with and without a waterproofing additive, monitoring defects of 0.3–0.5 mm in width.

Results. The developed method ensures highly accurate self-healing assessment. It has been established that the additive accelerates the restoration of water resistance; the effect is particularly pronounced for cracks of 0.3 and 0.4 mm and with acid treatment of the surface. Under field conditions, a significant reduction in the length of filter cracks and the formation of crystalline deposits confirming chemical self-healing are observed.

Conclusions. The method is practical for assessing the self-healing properties of cementitious materials. The waterproofing additive facilitates complete restoration of water resistance even with defects up to 0.5 mm, while maintaining the vapor permeability of the structure. The obtained results can be used to standardize the assessment and improve the maintainability of reinforced concrete structures.