Polyurethane foams (PUFs) constitute a major class of polymeric materials, widely appreciated for their excellent mechanical strength, chemical resistance, and physical versatility. They are used in a wide variety of applications, such as insulation, cushioning, coatings, and structural parts. Traditionally, PUFs are prepared through polyaddition reactions involving polyols, diisocyanates, and water, where the in-situ generated CO₂ in the reaction mixture serves as the blowing agent. However, there are significant concerns with the use of isocyanates as they are toxic, classified respiratory sensitizers, and contribute to environmental pollution. These issues have directed both researchers and industry experts to search for safer and more sustainable alternative feedstocks.
The polyaddition reaction between cyclic carbonates (CCs) and polyfunctional amines has been one promising alternative. The reaction leads to the formation of non-isocyanate polyurethanes (NIPUs), specifically polyhydroxyurethane foams (PHUFs). Foaming is achieved by using external chemical blowing agents or through self-blowing reactions, where gases are generated directly in the system. The generated   foam cells – the structures that give foams their unique properties – depends largely on the gas-forming reactions.
This review focuses on the different blowing agents used in NIPUF synthesis, such as poly(methylhydrogensiloxane) (PHMS) and liquid fluorohydrocarbons. It also looks at recent advances in self-blowing techniques, which eliminate the need for external agents and make the process more sustainable. Special emphasis is placed on NIPUFs derived from renewable feedstocks, as these align with global trend towards green chemistry and circular materials. The review provides an overview of both externally blown and self-blown biobased NIPUFs, detailing their synthesis, performance, and potential industrial applications.

Keywords: biobased polyurethane, blowing agent, non-isocyanate polyurethane, polymeric foams, polyurethane foams, self-blowing

The relevance of the study is due to the fact that: firstly, the proposed topic is in line with the Government-approved "Strategy for the development of the construction industry and Housing and Communal Services of the Russian Federation for the period up to 2030 with a forecast up to 2035" dated October 31, 2022, which assumes an increase in the share of industrial housing construction, including panel construction; secondlySecondly, the existing methods for calculating the joints of panel buildings have come down to us almost unchanged from the level of development of construction science and engineering in the 1980s. of the last century, which leads to increased material costs and rising real estate prices, therefore, the current trend in the development of the construction industry requires the improvement of these techniques. Modern approaches to nonlinear modeling and calculation of reinforced concrete will allow, in relation to panel joints, to reveal the reserves of their bearing capacity and obtain a more rational design, which will reduce the cost of constructing the buildings in question as a whole. PURPOSE. To carry out a comparative analysis of existing methods for calculating panel joints in two groups of limit states, to identify their advantages and disadvantages. Identify ways to improve them. METHODS used in the course of the research: theoretical methods – chronological, formalization, classification, analysis, synthesis, generalization, comparison. RESULTS. The analysis of existing methods of foreign and domestic design standards, as well as various author's methods, showed that: 1) foreign and domestic standards are based on the limit state method; 2) the nonlinear deformation model is not used in the calculation of joints of reinforced concrete panels; 3) to obtain a more accurate VAT of reinforced concrete panel joints, it is necessary to process a large amount of data using computer technology. CONCLUSION. The analysis shows that the use of computer software systems is the most promising method for calculating building structures, allowing fast and accurate calculations, reducing the cost of construction.

Keywords: large-panel construction, reinforced concrete, panel joint, joint calculation, joint classification, platform joint, deformation model, limiting forces, computer modeling, finite element

The paper analyzes the influence of damage to the protective layer of concrete of the zone of maximum bending moments of single-span beams on the load-bearing capacity of the structure and the possibility of restoring the initial load-bearing capacity. The study is based on laboratory research and numerical experiment, as well as on the analysis of earlier tests and accumulated experience in the restoration of structures. As a result, conclusions are drawn about the effect of concrete protective layer failure on the load-bearing capacity of bending structures, and recommendations are given for further research into the calculation and design of these systems.

Keywords: damage of concrete protective layer, corrosion of reinforcement, restoration, reinforcement

This article explores the architectural and engineering significance of surfaces of the second order, with a particular focus on the one-sheet hyperboloid of revolution. The study begins with a historical overview of architectural forms, highlighting the evolution from primitive shelters to complex spatial structures. Mathematical foundations are introduced through quadratic equations, illustrating the formation of second-order surfaces such as the elliptic paraboloid and hyperboloid. Special attention is given to the structural properties of the one-sheet hyperboloid, a doubly ruled surface that enables construction using straight beams, despite its curved geometry. Its advantages—strength, wind resistance, and material efficiency—are discussed, along with typical assembly methods such as segment welding and overlapping connections. The article further examines the iconic Shukhov Tower in Moscow, a pioneering example of hyperboloid design. It outlines the construction methodology, including the telescopic assembly process and challenges such as structural fatigue and support failure. The analysis demonstrates how Vladimir Shukhov’s innovations contributed to global architectural and engineering practices. Finally, the article emphasizes the hyperboloid’s relevance in modern construction and research, illustrating its blend of geometric rationality, aesthetic expressiveness, and structural efficiency. This synthesis of art and science continues to inspire both professionals and the public, highlighting the enduring value of advanced geometric principles in architecture.

Keywords: hyperboloid, quadratic surface, hyperboloid of revolution, engineering structure, architectural form, Shukhov Tower, steel structure, spatial lattice, structural technology, lattice shell

The article examines architectural approaches to the design of temporary museums and exhibition pavilions. Particular attention is paid to the concept of modularity as a tool for spatial adaptation and rapid installation, as well as mobility as a strategy for expanding cultural presence beyond stationary institutions. Historical and contemporary examples are analyzed, including so-called pop-up museums, container galleries, and disassemblable exhibition modules. The role of innovative materials, digital design, and transport logistics in the formation of a flexible architectural environment is emphasized.
The article reveals the potential of temporary exhibition structures as a tool for social inclusion, urban renewal and cultural decentralization. Special attention is paid to Russian and international experience. The modular museum is presented as a type of architecture sensitive to time, place and cultural context.

Keywords: museum, exhibition complex, architecture, modularity, mobility, flexibility, adaptability, design, construction

The article presents the results of an experimental study of the effect of loading speed on the deformation and strength characteristics of concrete of class B45 under central compression. 15 prisms measuring 100×100×400 mm, divided into three series according to the loading speed, were tested. Regression dependences are constructed, correlation coefficients (up to 0.9975) and determination coefficients (up to 0.9950) are determined, confirming the high degree of consistency of the models with experimental data. It is established that an increase in the loading rate contributes to an increase in strength and a decrease in the magnitude of the marginal relative deformation of concrete. The obtained dependences can be used as an experimental basis for constructing a nonlinear deformation method for calculating bent and non-centrally compressed reinforced concrete structures made of concrete of the class under consideration (B45), subject to static and high-speed impacts.

Keywords: experiment, concrete samples, high-speed loading, central compression, statistical processing of results, least squares method, regression curve

When constructing reinforced concrete floors on profiled steel sheeting, it is possible to significantly reduce the construction time and provide simple and convenient support units. The article discusses the standard methods for calculating composite reinforced concrete floor slabs with profiled sheeting according to SP 266.1325800.2016. A series of calculations were performed using ultimate forces and a nonlinear deformation model (NDM), and a comparison was made with experimental data. The data obtained indicate a significant overestimation of the bearing capacity for a number of samples calculated using the NDM method. This indicates the need to change the approach to NDM calculations and the need to make adjustments to the σ-ε calculation diagram for profiled steel sheeting, reflecting the actual operating conditions of the element.

Keywords: steel profiled sheeting, floor, deformation model, stress-strain diagram, static load

The influence of the geometric hypothesis on the field of crack directions in the calculation of structures based on inclined sections is considered. The angle of inclination of the crack to the vertical is determined from the condition of the minimum external load necessary for its formation and determined in turn from the equation of the energy balance. The influence of coefficient A of the bilinear cross-section hypothesis on the angle of crack inclination is estimated for cases of uniformly distributed load and concentrated force. Based on the calculation results, it is concluded that the influence of the geometric hypothesis is insignificant in the case of a uniformly distributed load, and in the case of a concentrated force, its influence is most significant in the middle part of the slice span when the ratio of the slice span to the section height is greater than 2. Based on the results of numerical calculations of models of hinged beams, the dependence of coefficient A on the relative coordinate of the crack origin for different intensity of transverse reinforcement is obtained.

Keywords: inclined sections, geometric hypothesis, field of crack directions, energy balance equation

The arrangement of protective structures of civil defense is currently vitally important, especially for populated areas located near the combat zone. A pressing issue in the design of shelters is the correct determination of the volumes of air exchanges required to ensure the stay of those sheltered during the standard periods. An analysis of changes in climate and microclimate parameters over the past years and methods for calculating air exchange in protective structures was conducted. A classic model of the process of changing the temperature and humidity of the air with a variable coefficient of inclination of the beam of such a process was built. The redundancy of air exchanges calculated according to the data and methods of the latest regulatory document is shown, leading to an increase in capital costs for the arrangement of a shelter.

Keywords: air exchange, civil defense shelters, climate parameters, indoor microclimate, graph-mathematical model of air exchange

The article is dedicated to analyzing the changes in museum design in the context of the rapid integration of digital technologies. It examines the ways of integrating multimedia systems, virtual and augmented reality into the architectural structure of museum spaces. Based on the analysis of domestic and foreign examples, new approaches to exhibition formation are identified, built on principles of flexibility, interactivity, and immersiveness. The emphasis is placed on the changes in typological models of museums: from traditionally hierarchical to adaptive, transformable formats. Special attention is given to the evolving role of the architect, acting as a mediator between digital scenarios and spatial expression. As a result, the museum of the future is envisioned as a complex spatial-technological ecosystem, in which architecture becomes an active participant in communication with visitors through digital content and technological interfaces.  

Keywords: typology, digitalization, museum, immersiveness, architecture, multimedia, museum of the future, design, digital exhibition, exhibition space

Evaluation of the strength characteristics of concrete is an important criterion for the quality of building structures when examining the engineering and technical condition of buildings with a monolithic reinforced concrete frame. The main controlled indicator when assessing strength is the class of concrete by compressive strength, determined in accordance with GOST 18105-2018 by statistical processing of test results by destructive or non-destructive methods. The article assesses the methods used to control the strength of concrete in buildings under construction or in operation, provides the main requirements for the tests carried out, gives examples of the necessary equipment, and presents the most rational algorithm for assessing strength. The research materials will be useful for specialists in the field of construction and researchers dealing with issues of the quality of building materials.

Keywords: non-destructive testing, concrete compressive strength, concrete testing, concrete class, calibration dependence, monolithic structures

The article presents and analyzes the algorithm for calculating bending reinforced concrete structures by normal section based on a nonlinear deformation model recommended in the standards for the design of reinforced concrete structures SP 63.13330.2018. Calculation of reinforced concrete structures based on a nonlinear deformation model is a priority, since it expands the set of controlled parameters, which leads to a more accurate description of the operation of building structures. The features of performing the calculation using this algorithm, as well as other approaches to calculating bending reinforced concrete structures by a normal section based on deformation and other models, are considered. The sequence of calculations using computer technologies is shown using the example of calculations in the engineering nonlinearity1 system of the LIRA-SAPR software package. The results of calculating a rod element of the calculation scheme are given: changes of the bending moment, stiffness, and deformation modulus for finite elements along the rod length. In this case, the calculation in the engineering nonlinearity1 system is performed with subsequent adjustment of the stiffness characteristics of the finite elements, carried out during the iterative calculation, with clarification of the stress-strain state, deflection of the element and its reinforcement. Additional capabilities of performing calculations using the engineering nonlinearity2 system are described: expanded the possibilities of assigning various laws of material deformation, describing the loading of the calculation scheme, reinforcement of structures, and the possibility of using a step processor.

Keywords: bending reinforced concrete structures, nonlinear deformation model, calculation scheme, calculation algorithm, PC LIRA-SAPR, engineering nonlinearity, system

The kinematic characteristics of rod systems are given in the order of kinematic analysis of the mechanism diagram, made taking into account the sizes and mutual arrangement of links and hinges; by analogy with the structural analysis of kinematic characteristics, they also include the degree of kinematic anomaly and the degree of kinematic irrationality. The first characteristic relates to the mutual arrangement of the axes of the links in the circuit chain and uses the dimensions of the links, the second relates to the mutual arrangement of the axes of the kinematic pairs (joints). It is shown that the mobility of kinematic chains depends on dimensional conditions - general and particular, and kinematic connections are imposed by dimensions. Based on the contour approach, a knowledge base has been formed for a highly formalized analysis of kinematic chains, allowing the identification of kinematic anomalies - both excess mobility due to a special position and kinematic redundant connections. It is shown that for flat kinematic chains the degree of irrationality of kinematics can be expressed through structural parameters.

Keywords: kinematics, characteristics, rod systems, analysis, diagrams, links, hinges, axes, anomaly, irrationality, connections, dimensional conditions

The article describes the features of using a two-layer membrane with the use of injection control fittings in the installation of underground waterproofing. The circumstances preventing the mass application of this technology have been identified, the main part of which is related to the increase in the cost of work at the initial stage. However, the use of the technology is justified because it allows you to localize the location and period of leakage, has increased maintainability and durability.

Keywords: waterproofing, modern waterproofing technologies, double-layer membrane, injection control fittings

The article discusses issues related to assessing the quality and safety of road traffic. An analysis of the accident rate on the roads of the southern part of the Far East has been performed. The main causes of traffic accidents are considered. An analysis of the quality of road marking has been performed and an assessment of its durability has been given, depending on the operating conditions. Recommendations for improving the durability of road markings are given.

Keywords: highway, pavement, horizontal markings, traffic safety

This paper provides an analysis of the main problems encountered during the installation of bitumen-polymer roofing materials. Special attention is paid to typical defects and errors related to insufficient qualifications, as well as problems related to violations of installation technology.

Keywords: bitumen-polymer roofing, installation of a surfaced roof, waterproofing defect, quality management, recommendations for improvement

Within the framework of this article, experimental studies of concrete reinforced with polypropylene fiber of two geometric dimensions of 6 mm and 12 mm are presented. Studies were carried out on samples of cubes 10 × 10 × 10 cm and samples of prisms 10 × 10 × 40 cm. In total, more than 100 samples were tested. The objectives of the experimental study: testing fiber concrete samples for compression, analyzing the results obtained, identifying changes in strength and deformation characteristics as a result of fiber reinforcement. Tests of the samples showed an increase in strength of up to 20%, as well as the effect of the percentage of fiber reinforcement on strength properties. The limit percentage of fiber reinforcement was determined, when exceeding which a decrease in strength properties occurs

Keywords: polyarmoured fibre concrete, fibre concrete, low-modulus fibre, polypropylene, strength properties

The article is devoted to the design of local treatment facilities in the city of Borovsk, Kaluga Region. Treatment facilities play an important role in the modern world. They are necessary for processing wastewater so that it becomes safe for the environment and can be discharged into water bodies or drainage networks. Since the discharge of untreated water can cause irreparable harm to the ecosystem, it is important to provide treatment facilities in the sewerage system of the settlement. The article considers the tasks and importance of treatment systems, their role in the life of modern cities, and also presents in detail the step-by-step organization of work on the device of local treatment systems and their subsequent commissioning

Keywords: wastewater treatment plants, ecosystem, water disposal, wastewater, modular structures

The paper presents an analysis of experimental data reflecting the influence of the loading rate on the strength and deformation characteristics of concrete of class B25 under conditions of central compression. 12 prismatic samples with dimensions of 100×100×400 mm, distributed in three series with different load application rates, were prepared and tested for the study. Statistical data processing, including analysis of variances and the construction of regression models, allowed not only to predict the behavior of concrete under various loading conditions, but also to confirm the theoretical prerequisites associated with the dynamic hardening of the material. The high values of the correlation coefficients (up to 0.9943) and determination (up to 0.9922), as well as the Fisher criterion, which significantly exceeds the tabular thresholds, characterize the high reliability of the results obtained, indicating an increase in concrete strength with an increase in loading speed and a simultaneous decrease in its deformability. The derived dependences can serve as an experimental basis for the development of a nonlinear deformation method for calculating bent and non-centrally compressed reinforced concrete structures made of concrete of this class (B25), subject to short-term impacts, including classical static loads, as well as dynamic loads of medium duration, characteristic of the operating conditions of structures under the influence of factors such as the movement of overhead cranes along crane beams or the passage of fire trucks along the overpass. The results obtained contribute to a more accurate consideration of dynamic effects in the design and calculation of reinforced concrete structures operated in such conditions.

Keywords: experiment, concrete samples, central compression, loading rate, strength, marginal relative deformations, dynamic hardening, correlation and regression analysis

The article presents an analytical solution for a specific case of a system with unilateral constraints: a beam freely resting on a tensionless Winkler foundation, loaded with identical vertical forces F at both ends. It is shown that beam separation from the foundation occurs when the reduced beam length αl exceeds π (αl > π); the size of the detachment region does not depend on the magnitude of the applied force. An increase in foundation stiffness (for a constant beam length) leads to an expansion of the detachment zone. The bending moment at the midpoint of the beam with detachment is maximal at the «detachment moment» and equals 0.4F⁄α. The deflection at the midpoint also depends on the foundation stiffness and is proportional to the applied force. As the foundation stiffness increases, the bending moment and deflection decrease, approaching zero for an infinitely stiff foundation. The article provides a calculation algorithm for the described beam and an example demonstrating changes in the stress-strain state parameters of the beam with increasing foundation stiffness. The obtained results, in the author's opinion, are interesting in themselves and can also contribute to the set of verification problems for structurally nonlinear systems.

Keywords: system with unilateral constraints, tensionless Winkler foundation, beam, contact region, detachment region, Krylov functions

The article examines the key climatic and operational factors that determine the duration of safe operation of ice winter shelters in the northern regions of Russia. Based on the analysis of the temperature regime, precipitation and dynamic loads from transport, patterns of changes in the strength and deformation of the ice cover have been identified. Practical recommendations on monitoring, ice reinforcement and load management have been developed to extend the service life of crossings and minimize risks.

Keywords: regime, dynamic loads, snow cover, hydrological factors, crossing safety, ice monitoring

Adhesive joints of reinforcing rods and wood are the weakest point in reinforced wooden structures, since they have low shear resistance of the reinforcing rod and contribute to the development of plastic deformations of wooden elements. To achieve elastic operation and increase adhesion to the rods, a reinforced adhesive compound with the inclusion of quartz sand is used. This article examines the operation of a reinforced adhesive joint with various types of core fittings – steel periodic profile, smooth steel and fiberglass. The work of the adhesive joint in solid and glued wood was also recognized as an important factor for the operation of the reinforced adhesive composition. Experimental studies are confirmed by graphs and tables of numerical results, which allows us to establish the reliability of the results obtained and conclude that it is necessary to improve certain methods of manufacturing reinforced wooden structures.

Keywords: rebar, reinforcing bar, reinforced wooden structure, pulling out, wooden structure, wood, glue, adhesive joint, strength, epoxy resin

Fiberglass core reinforcement could find its application in wooden structures due to a number of specific practical advantages not inherent in steel rods or other types of reinforcement. However, due to the weak adhesive properties of the surface of fiberglass rods, their full-fledged joint work with wood as a single body is not observed. The study suggests some ways to increase the strength of the adhesive joint of fiberglass reinforcement and wood, such as applying quartz sand to the surface of the rods, grinding the surface of the rods, as well as adding sand-resin casting molds to the adhesive composition. Tests of each of these methods were carried out and the results obtained were compared with the initial model of the adhesive joint, as well as with the calculated model of the adhesive joint in order to determine the most effective method.

Keywords: adhesion, reinforcing rod, pulling out, wood, adhesive joint, adhesive composition, bearing capacity, strength, fiberglass rod, epoxy glue

The paper investigates the formation and propagation of flexural cracks in beams made of ultra-high performance steel fiber reinforced concrete (UHPFRC). A comprehensive series of laboratory tests was carried out on seventeen beams of rectangular and T-shaped cross-sections, varying in longitudinal reinforcement ratios, fiber volume contents, and fiber types (straight and wave-shaped). The results demonstrate that the inclusion of steel fibers significantly enhances the crack resistance of the beams, promotes a more uniform crack distribution, and improves their load-bearing capacity. In under-reinforced UHPFRC beams, failure typically occurs due to fiber pull-out localized within one or more dominant cracks. Prior to the onset of deformation localization in the tensile zone – which coincides with the yielding of the longitudinal reinforcement – the crack widths in fiber-reinforced specimens remain below 0.25 mm. This behavior ensures that even under service-level loads (65–70% of ultimate), the crack openings stay within the allowable design limits (0.3–0.4 mm). The experimental findings contribute to a better understanding of the cracking mechanisms in UHPFRC beams and provide a valuable foundation for refining numerical models and optimizing design approaches for flexural members made of advanced high-performance cementitious composites.

Keywords: ultra-high performance concrete, beams, bending moment, steel fibers, flexural cracks

The article presents the results of laboratory testing of a precast lintel made of D600 aerated concrete blocks fastened together using assembly adhesive for laying aerated concrete blocks and three reinforcing bars, two bars in the lower zone with a diameter of 20 mm A400 and one bar in the upper zone with a diameter of 16 mm A400. When testing the beam lintel, 3 loading schemes were assembled, each of which was a beam hinged on concrete supports. The obtained data were analyzed. Based on the test results, destructive loads, the nature of destruction were determined and the resulting deformations were assessed. The nature of destruction is similar to that of reinforced concrete beam structures with insufficient transverse reinforcement; destruction in all tested prototypes occurs in the support zone along inclined sections. The bearing capacity of aerated concrete lintels made of piece material is sufficient for use in construction practice.

Keywords: testing, bearing capacity, reliability, deformability, gas blocks, lintels, destruction