Introduction. According to SP 63.13330.2018, when calculating the second group of limit states for shortterm loads, the modulus of elasticity of concrete is taken with a reduction factor of 0.85. Historically, this factor accounted for inelastic deformations and short-term creep. However, its validity for modern high-strength (B80–B100 and higher) and modified concretes, as well as for steel-concrete composite structures, has not been experimentally confirmed.

Aim. An experimental and theoretical assessment of the applicability of the 0.85 factor to the initial modulus of elasticity of high-strength modified concretes under short-term actions on pre-loaded structures.

Materials and methods. More than 100 specimens of self-compacting concrete class B90–B100 with a modulus of elasticity of 55 GPa were tested: prisms, cylinders, steel-concrete composite prisms with steel plates, and cores extracted from pre-compressed columns. The following scenarios were implemented: standard tests, increased load holding times, elevated stress levels (up to 80 %), long-term pre-compression (over 3 months) followed by additional loading, and core tests. The modulus of elasticity was determined according to GOST standards and by a developed methodology (between loading stages).

Results. The deformation behavior of the concrete under study was almost linear up to failure, with minimal microcracking and creep. The maximum reduction in the modulus of elasticity across all scenarios did not exceed 10 %, and for reference prisms it was no more than 7 %, which is lower than the standard 15 %. The applicability of the findings to steel-concrete composite structures and the feasibility of estimating the modulus of elasticity from core samples were confirmed.

Conclusions. For high-strength modified concretes, the application of a reduction factor of 0.9 instead of 0.85 under short-term loads is justified, which allows for a reduction in the design horizontal displacements of high-rise buildings by 5–10 %.

Introduction. The mechanism of reinforced concrete structures failure under the action of a transverse force has been the subject of domestic and foreign research for many decades. The key factors influencing the bearing capacity of the structure within the framework of this mechanism of destruction are: the shape and dimensions of the cross-section of the structure, the strength characteristics of concrete and reinforcement, the span-to-depth ratio, the amount of longitudinal reinforcement in the tensile zone, and the amount of transverse reinforcement. Incorrect consideration of these factors negatively affects the accuracy of design methods for inclined sections of reinforced concrete structures under the action of transverse forces.

Aim. Assessment of the accuracy of methods for calculating reinforced concrete structures in inclined sections from the action of transverse forces presented in various regulatory documents.

Materials and methods. To assess the accuracy of the calculation methods, a database was compiled, including the results of 1,183 laboratory tests of reinforced concrete structures, the destruction of which occurred along an inclined section. The accuracy is estimated by comparing the value of the maximum transverse force obtained in laboratory tests and the theoretical value obtained using the calculation method under consideration.

Results. The paper presents the results of comparing the values of the ultimate shear force obtained in the framework of laboratory tests and using the considered calculation methods.

Conclusions. A comparative analysis of the design methods has shown that in certain cases the methodology set out in SP 63.13330.2018 is less accurate than the methods provided in foreign codes. In this regard, the task of improving the shear design method for reinforced concrete structures presented in SP 63.13330.2018 appears to be relevant. Refinement of the calculation methodology will increase its accuracy and expand its scope of application.

Introduction. Changes in the physical and mechanical properties of rubber bearings during service life represent one of the key factors affecting the efficiency and long-term performance of building seismic isolation systems.

Aim. In this context, the development of analytically justified relationships based on experimental aging data, enabling quantitative assessment of shear modulus variation over the design service life of rubber bearings, constitutes an important scientific task.

Materials and Methods. Based on experimental data obtained from accelerated thermal aging tests of rubber bearings and the time–temperature superposition principle according to the Arrhenius model, the shear modulus was determined for each equivalent service life. The experimental results were subsequently subjected to analytical processing, and an approximating function describing the evolution of the relative shear modulus over time was derived. The parameters of the proposed function were identified using nonlinear regression techniques, followed by statistical evaluation of the goodness-of-fit.

Results. It was established that the variation of the shear modulus of rubber bearings during aging represents a nonlinear process that can be described by a monotonic exponential function of asymptotic type. This function reflects the kinetics of elastomer degradation, characterized by an intensive increase in shear modulus at the initial stage of aging, followed by a transition to a regime of gradual change as thermo-oxidative processes become depleted. The analysis shows that, for an equivalent service life of 50 years, the shear modulus increases by more than 28 % compared to its initial value. The obtained analytical approximation demonstrates a high coefficient of determination and low statistical error values, confirming the adequacy of the selected analytical representation of the experimental data.

Conclusions. An approach to constructing analytical approximating functions describing the evolution of the shear modulus of rubber bearings based on a limited set of accelerated aging test data is proposed. The implementation of this approach enables quantitative assessment of shear modulus variation during service life and may be applied in the evaluation of the long-term performance of seismic isolation systems, as well as in technical condition assessment and residual service life prediction of rubber bearings.

Introduction. This paper studies the stability of symmetrical web-tapered I-beams subjected to unequal end moments. Taper angle, which plays a main role in the lateral-torsional buckling behavior of web-tapered beams, is investigated through refinement of differential equations of the original Vlasov technical theory for thin-walled bars. Analytical solutions of refined differential equations are given based on the Bubnov – Galerkin method through the law of change of moment of inertia of the cross section of the beam along its axis. The final bifurcation equation of elastic critical moment contains new terms that includes reduction coefficients of cross-section. Equivalent moment gradient factor for the full range of values is determined and given in closed form with respect to taper angle. Comparative graphs show alignment between analytical and numerical solutions. These results can be used to formulate efficient buckling criteria for prismatic and non-prismatic I-section beams and can be integrated into the current design methods.

Aim. To develop a unified equation for the equivalent moment gradient factor. Refine Vlasov technical theory for web-tapered I-section members.

Materials and methods. Refined Vlasov technical theory and Bubnov – Galerkin method were used in the work.

Results. Based on given refinements, a closed form of elastic lateral-torsional buckling solution of a webtapered beam was obtained. Analytical calculation method is introduced.

Conclusions. The presented theoretical work introduces a unified design method for elastic critical moment and equivalent moment gradient factor determining for lateral-torsional buckling of web-tapered I-section beams. Results show an excellent agreement between numerical and analytical solutions. Equations are given in closed form similar to a constant cross-section but with additional factors and coefficients, that makes it possible to integrate the developed solution into existing calculation methods.

Introduction. Pressure injection of masonry is one of the most effective methods for restoring its integrity in areas with cracks, delamination, repairs, and joints between dissimilar masonry. This injection method is especially valuable for historic buildings.

Aim. To obtain experimental data on the strength and deformations of masonry reinforced by pressure injection of mortar.

Materials and methods. Tests were conducted on specimens reinforced with mortar injection, including those with structural reinforcement, under uniformly distributed loads and localized compression, using historical and modern solid brick in the form of pillars and walls, constructed with mortars of varying strengths. The combined performance of reinforced masonry in repair sections with filler and specimens in which the inner layer (backfill) differed in strength and deformation from the facing layers was studied.

Results. Strengthening coefficients for masonry reinforced by pressure injection were obtained. The research results were used in the development of regulatory documents for masonry structures and recommendations and projects for strengthening masonry structures, including historic buildings.

Conclusions. In cases of multiple cracks in masonry spaced 10–25 cm apart, it is possible to increase the load-bearing capacity of the masonry. The effectiveness of reinforcement increases for masonry constructed with weak mortars. The best results are achieved with epoxy resin injection. The use of cement mortars with hydraulic lime allows for the restoration of the integrity of masonry in historic buildings. A combination of injection reinforcement and indirect reinforcement using drilled holes in the masonry produces significant results.

Introduction. To ensure adequate modern requirements for the mechanical safety of civil buildings and structures (as complex technical systems with enhanced safety requirements), a transition from reliability management of building structures to risk management is necessary.

Aim. For an effective and legally sustainable transition to risk-informed regulation in the construction industry of the Russian Federation, it is necessary to summarize and critically analyze advanced foreign experience.

Materials and methods. Based on the analysis of the data available in the regulatory, scientific and technical literature, a critical analysis of the advantages and identified problems of scientific development and practical implementation of the risk-informed approach in the construction of the Netherlands, Great Britain and Japan was carried out.

Results. The advantages of using risk-informed and parametric approaches together are described, and the problems of their methodological support and regulatory implementation are listed.

Conclusions. Despite observed barriers and difficulties that have manifested themselves in foreign science and practice, the transition from structural reliability management to accident risk management is not only possible, but also capable of producing significant technical and economic effects and increasing the real safety of buildings and people in them. Further work should be aimed at the phased implementation of the proposed approach: the development and testing of industry-specific methods, the formation of criteria for acceptable risk, staff training and the integration of risk-informed procedures into the practice of design, expertise and supervision.

Introduction. A general approach to risk assessment of dangerous climatic phenomena, including hydrometeorological loads and actions on buildings and structures, is considered. The analysis of the main criteria for the development of basic parameters of loads, actions, and environmental influences in order to ensure the required reliability and safety is presented, as well as ways to further improve regulatory documents on their accounting.

Aim. To study dangerous climatic phenomena and develop methods for assessing climate risks for buildings and structures; to improve the principles of rationing in the field of loads and actions based on the formation of common approaches to the methodology of transition to parametric rationing in construction in the Russian Federation; to optimize the design of buildings and structures and increase their economic efficiency.

Materials and methods. Based on the analysis of the data available in the regulatory, scientific and technical literature, a general methodological approach is proposed and ways to solve some important tasks of risk assessment and consequences of dangerous climatic phenomena for buildings and structures in a changing climate conditions are outlined.

Results. An engineering methodology for climate risk assessment for buildings and structures under the influence of major climate threats is proposed, taking into account meteorological and technical monitoring data based on climate hazard indices.

Conclusions. In order to formulate the basic requirements for risk assessment and vulnerability of buildings and structures under dangerous climatic conditions, first of all, it is necessary to classify them, establish critical values of their design parameters, and to determine which structures they primarily affect. The developed methodology will make it possible to take into account the permissible damage to buildings and structures from dangerous climatic phenomena, taking into account the severity of the consequences, and to develop requirements for the protection of load-bearing structures of buildings and structures from dangerous climatic processes and phenomena.

Introduction. The steel structure joints stiffness significantly affects the distribution of internal forces in the frame elements. This point is true for modular buildings too. Intermodular joints affect the stress-strain behavior of the whole building, while the intramodular joints stiffness of affects the stress-strain behavior of each module individually. The object of the research is steel modular buildings made of assembled modules with load-bearing corner columns.

Aim. Studying the stress-strain behavior of steel modular buildings with rigid and semi-rigid intra-modular joints exposed various loads.

Materials and methods. To assess the influence of the joints stiffness to the stress-strain behavior of modular buildings, a series of studies were conducted with various connection parameters using the finite element method. A total of 921 joints models were calculated. To confirm the results obtained by the numerical method, physical tests of full-size specimens of the joints were carried out. The main assumptions for the creating of calculation model have been formulated. Based on the identified assumptions, equations were obtained that explicitly describe the influence of the rotational stiffness of intra-modular joints to the distribution of internal forces in the elements of the module and to the natural vibration frequencies of the building.

Results. Within the framework of numerical studies using the finite element method, a significant influence of the presence of stiffeners and their dimensions on the intra-modular joints stiffness was established. It is shown that nodes without stiffeners are generally semi-rigid. For the design of rigid intra-modular joints, nomograms have been compiled for the assignment of minimum stiffeners sizes. Physical tests of full-size joints specimens confirmed the results obtained in numerical studies. A calculation analysis using the obtained equations showed that failure to take into account the actual joint stiffness o when calculating the rod model of a modular building can lead to significant inaccuracies in determining the internal forces and frequencies of natural vibration.

Conclusion. The conducted researches show a significant influence of intra-modular joints stiffness to the stress-strain behavior of steel modular buildings. It is necessary to take into account the joints stiffness when calculating modular buildings. It is of interest to conduct similar studies for other structural schemes of modular buildings with different structural solutions of joints.

Introduction. The thermophysical properties of soil can be determined in laboratory and field conditions. Field methods are more accurate because they are performed with minimal disturbance to the natural structure and thermal and moisture conditions of the soil. The most common are probe methods based on the introduction of a heat source into the soil and the measurement of the adjacent soil temperature over time using a temperature sensor installed in the probe. One of the most promising areas for developing methods for determining the thermophysical properties of permafrost and thawed soils is the use of the thermostatic probe method (HT-CPT)  – static probing using probes equipped with a heating device and a temperature sensor. This issue requires a comprehensive study, primarily the development of a thermophysical model for the interaction of a cone probe with constant heating power with the soil.

Aim. Development of a thermophysical model for determining the thermal conductivity coefficient of soil using a cone probe with constant heating power.

Materials and methods. The analytical thermophysical model was developed taking into account the fundamental principles of heat transfer theory. The following calculation assumptions were adopted in developing the model: the soil’s thermophysical properties are isotropic and constant; there are no phase transitions in the soil upon heating; the soil’s thermophysical properties do not change; the cone heats uniformly, etc.

Results. An analytical model was developed that allows one to determine the thermal conductivity of soil using a cone probe with constant heating power. The results of numerical and flume experiments confirmed the validity and applicability of the developed analytical model for determining the thermal conductivity of frozen soil during thermostatic probing with an HT-CPT probe.

Conclusions. Based on an analysis of the thermophysical interaction between a cone probe generating a low-power heat flux and thawed and frozen (without thawing) soil, an analytical solution was obtained that allows one to determine the soil’s thermal conductivity from the cone heating thermogram and the probe’s thermal coefficient.

Introduction. The area of permafrost occupies most of Russia’s territory, making it crucial for the country to expand its use for industrial construction. Currently, the Arctic zone of the Russian Federation is a priority region for economic growth and strategic influence, as outlined in the Spatial Development Strategy of the Russian Federation until 2028.

Aim. When designing, constructing, and operating buildings and structures on permafrost soils, the most important task is to ensure the reliability of the soil foundation.

Materials and methods. In this regard, the choice of design, technological, and organizational solutions for industrial construction, primarily the prediction of deformability, measures to ensure the stability of the soil foundation, and the development of rational organizational schemes for their implementation, should be economically feasible, optimal, or close to optimal for a specific engineering structure and the region where it is located.

Results. The possibility of using the technology of jet grouting in the main mode and in the mode of highpressure injection for the construction of artificial bases in thawed permafrost soils is substantiated.

Conclusions. The available experience shows that under certain engineering and geological conditions, jet grouting technology is an effective and reliable method for modifying soils and constructing artificial foundations.

Introduction. When reconstructing buildings shallow foundations, quite often there is a need to strengthen them. One of the ways to increase the bearing capacity of foundations is to change their operating pattern by transferring part of the load from the building being reconstructed to injection piles. The foundation formed in this way in a building is usually called combined and can be separate (free-standing), strip or slab in the form of a continuous monolithic reinforced concrete slab. Existing methods for calculating foundations (combined foundations) of reconstructed buildings strengthened using piles do not allow us to fully take into account the peculiarities of their interaction with the foundation soil.

Aim. Present information on injection piles, the nature of their work in clay soils, methods for calculating the bearing capacity and settlement of piles as part of reinforced foundations of reconstructed buildings.

Materials and methods. The work examines reinforced concrete injection piles made of fine-grained mobile concrete mixture, which are installed in the conditions of reconstruction of buildings.

The results of the studies indicate an increase in the load-bearing capacity of existing foundations due to their conversion into combined foundations with injection piles.

Conclusions. The main conclusion from the research results is the effectiveness of using reinforcement of foundations with injection piles in clay soils for the conditions of reconstruction of buildings.

Introduction. The main cause of foundation deformation in Arctic structures is the significant compressibility of permafrost soils during thawing. These processes are accelerated by anthropogenic impacts and climate change; according to Roshydromet, the rate of warming in the region is reaching 0.5°C per decade. These conditions require the development of methods that not only strengthen structures but also dramatically improve the deformation properties of the soil base itself. Soil stabilization using jet grouting is being considered as a promising solution. The key effect is the virtual elimination of subsidence during thawing. Therefore, stabilization and reinforcement of high-temperature frozen soils appears to be an effective technology for ensuring the long-term stability of foundations in the permafrost zone.

Aim. Development of jet grouting technology in conditions of high-temperature frozen soils (above minus 0.5 °C) to enable simultaneous thawing and reinforcement of the foundation, and an assessment of the degree of change in the deformation properties of frozen soil after thawing and consolidation.

Materials and methods. The methodology consists in analyzing archival survey and design documentation, as well as regulatory and other technical literature on the topic of work, identifying areas for further experimental research, analyzing and summarizing them, as well as developing recommendations for the use of jet cementation technology for permafrost soils used according to principle II.

Results. The results of the analysis of modern scientific, technical, normative and methodological literature are presented. Laboratory studies were performed to determine the physical, thermophysical and deformation properties of the soil in its natural state and fixed, which were later used in modeling the thermal effects from the device of soil cement elements, as well as in computational and analytical research using the example of subsidence calculation. Recommendations have been issued on the use of jet cementation technology for fixing foundations in areas of permafrost soils used according to principle II.

Conclusions. Based on the analysis of the literature, the results of experimental studies and studies on the consolidation of high-temperature permafrost soils, recommendations have been developed for the use of jet cementation technology for the consolidation of foundations within the framework of the distribution of permafrost soils used according to principle II. Proposals have been developed for the application of R&D results in the development and modification of regulatory, technical and methodological documents.

Introduction. Ground subsidence during thawing of permafrost causes deformation of buildings and structures located in the permafrost zone. Previously, it was assumed that frozen soils have a stable bearing capacity, but in the context of modern warming, thawing processes are becoming more frequent, which could become a key engineering challenge in the future. Experts are faced with the task of methods development for buildings adapting to the changing conditions. One of the promising directions is the use of slab foundations on pneumatic membranes capable of compensating for uneven subsidence due to controlled pressure in air circuits. The article discusses the principles of operation of such technology using the example of tray testing, its limitations and potential applications in conditions of degradation of permafrost soils.

Aim. Obtaining experimental data on technology for compensation of uneven subsidence of foundations of buildings and structures by automatically monitoring and maintaining the original position of the building foundation.

Materials and methods. The methodology consisted of analyzing archival, regulatory and other technical literature on deformation compensation methods and determining the directions of experimental research, development of the work program, conducting numerical modeling and tray studies, analyzing and summarizing them, as well as testing the membrane for strength.

Results. In the course of the research, recommendations were formulated to minimize uneven foundation deposits on multi-year frozen soils that contract unevenly with increasing temperature. An approach using elastic support membranes and an automatic control system is proposed to ensure the preservation of the design position of the foundation.

Conclusions. The automatic system is able to operate stably and correctly and effectively ensure timely air supply to the membrane to maintain an almost invariable “zero” position of the foundation slab. Experiments have shown the possibility of using this technology, but its implementation requires an even larger range of experiments.

Introduction. The development of effective intumescent fire-retardant coatings (FRC) for steel building structures requires a deep understanding of their thermal decomposition mechanisms. Modification of classic fire-retardant systems, in particular by adding intercalated graphite to the formulation, is aimed at improving its thermal stability and fire-retardant effectiveness. A key tool for studying these processes is synchronous thermal analysis using thermogravimetry (TG) and differential scanning calorimetry (DSC) methods.

Aim. Study of the mechanism and kinetics of thermal degradation of a thermally expanding fire-retardant coating based on an epoxy dianic resin binder and an amine hardener, with oxidized graphite as the main intumescent filler in inert (argon) and oxidative (oxygen) atmospheres using TG/DSC methods for assessing its fire-retardant potential and identifying the key stages of thermal decomposition.

Materials and methods. Thermal analysis of the coating samples was carried out using a NETZSCH STA 449 F5 synchronous thermal analyzer in argon and oxygen atmospheres at a heating rate of 10 K/min up to 1000 °C. Qualitative characteristics, including thermal effects, were determined, and a comparative analysis of the coating’s behavior under pyrolysis and oxidation conditions was performed after processing the obtained data using Proteus Thermal Analysis software.

Results. Presented are the results of studies of the thermal properties of a thermally expanding fireretardant coating based on an epoxy dianic resin binder and an amine hardener, with oxidized graphite as the main intumescent filler, as well as the oxidized graphite itself. The thermal properties were determined in the temperature range from 24 to 1000°C. It was determined that the thermal decomposition of a thermally expanding fire-retardant coating based on an epoxy dianic resin binder and an amine hardener and oxidized graphite as the main intumescent filler is multistage. The critical temperature of the coating transition to an active state, corresponding to the initiation of intumescence, has been quantitatively determined.

Conclusions. It has been confirmed that the oxidized graphite in the analyzed fire-retardant coating provides a high endothermic effect, which confirms the effectiveness of the fire-retardant coating in fire conditions. The data obtained allow to quantitatively assess the impact of various decompostion stages in the fireretardant effectiveness of the formulation.

Introduction. Moscow’s road network experiences significant traffic loads. To extend the service life of the road surface, stone mastic asphalt concrete is used in the upper layers. With the introduction of the new asphalt concrete design system (American and European) and the abolition of the old system, the issue of determining the optimal asphalt concrete mix composition has become relevant.

Aim. To confirm the hypothesis that new State standards for asphalt concrete allow modeling asphalt concrete mixtures in accordance with real operating conditions.

Materials and methods. A number of hypotheses are considered to explain the obtained results and predict the properties of road asphalt concrete.

Results. This article presents the results of extensive practical work involving the construction of test sections on the Moscow Ring Road (MKAD), where asphalt concrete was designed as the top layer of the pavement in accordance with State Standard 31015-2002, State Standard R 58406.1-2020, and State Standard R 58401.2-2019. Analysis of the monitoring results for the MKAD test sections was conducted over a three-year period.

Conclusions. It was shown that maximum rutting occurs in lanes 1 and 2 regardless of the asphalt concrete mix composition. The results indicate that rut depth is independent of both the experimental mix composition and the aggregate size of the asphalt concrete mix. It was noted that asphalt concrete pavements made from the traditional Moscow mix of SMA-20 on PBB 60 according to State Standard 31015-2002 are comparable in wear resistance to the pavements on seven experimental sections, while being less expensive than asphalt concrete mixes according to the new State Standards R.