Introduction. The paper deals with the development of the theory of the limit state of structures. The method is proposed for determining the limit state of the structure, allowing to describe all possible formulations from a single position, based on a single mathematical model.

Materials and methods. The theory is based on several basic assumptions. The fields of external actions on the structure and the deformation field of the supporting system have different origins and laws of existence. The extreme values of the parameters of the deformable structure are limited by the limiting values of external influences. The extreme values of the deformation field parameters can be found from the eigenvalue problem for the stiffness or flexible matrices of the structure. The result of solving this problem coincides with the solution of the design optimization problem. Solving the eigenvalue problem makes it possible to find the global extremum and take into account solutions at the boundary of the feasible region. The formulation of the problem makes it possible to find the maximum and minimum possible values of the reactive response of the structure to external influences. These values form the domain of admissible values for the internal parameters of the supporting system. The difference between the limiting parameters and the work of external forces gives the value of the residual bearing capacity of the structure.

Results. The problem of calculating a two-bar system is considered. The results are given in the form of an ellipse of limit states, and the values of residual bearing capacity in displacements, forces and deformation energy.

Conclusions. The new formulation of limit states problems is proposed. The calculation method allows finding not only the maximum possible parameters of the structure, but also the residual bearing capacity of the structure in a deterministic form.

Introduction. The current paper examines the stability of cantilevered symmetrical web-tapered I-beams under end point load and uniformly distributed load. Elastic lateral-torsional buckling solutions are given in closed form and based on an energy approach with alternative trial functions for twist rotation. The aim of the paper is to refine and rectify bifurcation solutions of the cantilevered beams and present them in alternative formulations. Results are given in new terms that include lateral-torsional beam parameter ψ0 and load height parameter η. Theoretical work has been done with respect to the current state and philosophy of steel design code CP 16.13330.2017. Unified simple formulae for the lateral-torsional buckling capacities of cantilevered beams can be addressed for solving not only non-prismatic cases but prismatic cases too. Simplicity achieved by minimizing the number of terms in trial functions and subsidized with different and closed ones to real behavior of the beam under transverse loads.

Materials and methods. Refined lateral-torsional buckling solution and an energy method were used in the work.

Results. Based on given refinements, a closed form of elastic lateral-torsional buckling solution of a linear non-prismatic member was obtained. As a result of the theoretical work evaluated, a lateral-torsional buckling formula was introduced.

Conclusions. The current theoretical work shows that the solution of lateral-torsional buckling problem of web-tapered cantilevered I-beam with thin-walled open cross sections can be rectified by introducing alternative trial function for twist rotation and given in closed form with additional coefficients. The solution stays relevant for prismatic cases.

Introduction. A variational formulation of the problem of optimizing the geometric configuration of a layered heterogeneous rod under the condition of constant total cost of materials is considered. The integral criterion of minimum deformation energy is adopted as the optimality criterion when varying the geometric functions profiling the rod layers. Currently, this approach, applied in homogeneous systems, requires development and extension to complex heterogeneous environments, and the development of methods for application in building structures.

Materials and methods. Using the mathematical model of the Timoshenko rod, formulas are given for the main components of stress and rigidity characteristics of zero, first and second orders. An energy functional and a constraint on the total cost of materials were formulated. Euler equations were obtained for varying geometric functions.

Results. The optimization problems of a layered rod by varying the width and thickness of layers for symmetrical and arbitrary structures are solved. The cases of bending, tension, transverse shear and combined bending with tension were investigated. It has been analytically proven that in all the cases considered, surfaces with an equal level of specific deformation energy are formed in the system. It is shown that the isoperimetric variational formulation leads to the minimum cost of the construction’s materials.

Conclusions. A variational formulation with one constraint on the total cost of materials, necessary according to the meaning of the problem, provides a global minimum of the functional of the deformation energy and the cost of materials of the system and reflects, the so-called, reference project. Knowledge of such a project is valuable and useful from a practical point of view. In an optimal system, equipotential surfaces with identical specific deformation energy values are formed. Their shape and location are determined by the emerging efforts and the structure of the system. From the integral energy criterion follow practical criteria for equalizing the specific energy of deformation, as well as the main stress or deformation on the surfaces of areas received by varying of dimensions.

Introduction. The consequences of devastating earthquakes demonstrate that the issue of seismic resistance of reinforced concrete frames after fire is highly relevant. The computational models used to address such problems must account for the nonlinear characteristics of concrete and reinforcement, variability of fire exposure, and design accelerograms. This study aims to identify the most hazardous fire exposure scenarios (from the standpoint of seismic resistance).

Materials and methods. A flat five-story reinforced concrete frame was selected as the research object under various fire exposure scenarios. Fire exposure was applied according to the standard temperature-time curve (ISO 834) with a duration of 120 minutes. Five scenarios were considered. A preliminary thermal analysis was conducted in PC SolidWorks
to determine temperature fields in element cross-sections. Subsequently, nonlinear seismic analysis of the five frames was performed in PC OpenSees. The analysis was carried out in the time domain using the Loma Prieta (1989) accelerogram. Bilinear and trilinear material diagrams were used. Cross-sections were modelled using a fiber model.

Results. A FEM was conducted of the dependence of seismic resistance parameters of reinforced concrete frames on various fire exposure scenarios. The periods of the first mode increased by up to 11.2 % compared to the control frame, roof-level displacements increased by up to 32.2 %, maximum inter-story drifts increased by up to 34.0 %, and maximum bending moments in frame elements increased by up to 26.3 % due to force redistribution. Failure mechanisms changed — plastic hinges formed not only in beams but also in columns; for most frames considered, deformation levels in elements reached critical values.

Conclusions. The most dangerous scenario, which most significantly reduces the seismic resistance of the reinforced concrete frame, is the occurrence of fire on the first floor. The percentage of damaged vertical load-bearing elements is particularly significant here — higher percentages lead to a more substantial reduction in seismic resistance. In some cases, such as localized fire damage on intermediate floors, the frame’s seismic resistance decreases only slightly. During the design stage of buildings in seismic zones, it is recommended to consider the most hazardous fire exposure scenarios. Special emphasis should be placed on enhancing the fire resistance of vertical load-bearing structures in lower floors and reducing the size of fire compartments.

Introduction. The development of technologies for strengthening the soil foundations of buildings and structures of various types is an urgent area in geotechnical construction. Methods that make it possible to create a network of reinforcing elements in a soil mass using various injection solutions are becoming particularly relevant. The aim is to scientifically substantiate and experimentally verify the effectiveness of a method combining the technology of horizontal directional drilling (HDD) and controlled hydraulic fracturing of a soil mass to create a network of injection inclusions in bulk soils.

Materials and methods. The methodology is based on a comprehensive field experiment. The design of a horizontal injector with rubber cuffs and the technology of its installation using HDD were developed and tested. The study included injection of cement mortar with a different water-cement ratio under controlled pressure, geodetic monitoring of the soil surface and subsequent excavation of the near-injection space to determine the morphology and geometry of cement inclusions.

Results. The nature of the formation of injection bodies in loose, unconsolidated soils in comparison with cohesive soils has been established, which is expressed in the formation of spherical volumetric bodies instead of flat lenses. A minor effect of the injection process on the ground surface has been recorded, which confirms its practical applicability.

Conclusions. The mechanisms of the distribution of mortar and the formation of cement inclusions in the soil are analyzed. It is shown that the proposed method makes it possible to purposefully create a network of point-hardened cement inclusions at the base. The technology has proven its fundamental validity and practical importance. The main advantages include the possibility of carrying out work without any interruption of production processes and eviction of tenants. The method is recommended for use in reinforcement under foundations, mainly shallow foundations, of both existing buildings and structures, and in new construction.

Introduction. Prediction of concrete stiffness characteristics within a scientific framework remains a relevant task of modern concrete science. Considering concrete as a three-phase composite material consisting of a cement matrix, aggregates, and the interfacial transition zone between them, analytical homogenization methods are among the most effective approaches for addressing this problem. However, existing computational models for predicting the stiffness characteristics of concrete based on analytical homogenization methods do not fully account for the specific features of its structure, which necessitates their further development.

Materials and methods. The proposed approach for predicting the stiffness characteristics of concrete involves estimating its effective fourth-order stiffness (elasticity) tensor based on analytical homogenization methods from the micromechanics of composites.

Results. The assumptions of the proposed approach are formulated. Solutions are introduced that consider the grains of coarse aggregate as composite particles, both in the form of spheres and as oblate spheroids for flaky grains, and prolate spheroids for elongated grains surrounded by the interfacial transition zone. An iterative method is also proposed, whereby the stiffness characteristics of concrete are determined sequentially, calculating the stiffness characteristics of the composite system “cement matrix – composite particle of the i-th fraction” at each iteration. A numerical method for calculating the effective elasticity modulus of concrete according to the proposed approach is provided.

Conclusions. The proposed approach based on analytical homogenization is designed to evaluate the stiffness characteristics of concrete, taking into account the features of its structure, such as the spheroidal shape of the aggregates, the presence of an interfacial transition zone around them, and the high volumetric concentration of aggregates.

Introduction. The results of a study on the influence of the type and dosage of plasticizing admixtures on the properties of fine-grained concrete operated under the conditions of the Republic of Burundi are presented. The object of the study is fine-grained concrete, while the subject of the study is the quality indicators of the concrete mix and hardened concrete. A distinctive feature of these studies is the use of raw materials sourced from the Republic of Burundi.

Materials and methods. The following raw materials were used: CEM II/V-P 32.5 M cement produced by BUCECO (Republic of Burundi), sand from the Muzazi River in the Republic of Burundi, and plasticizing admixtures from different manufacturers with various chemical compositions.

Results. It was established that the incorporation of the plasticizing admixtures GPM-U and GLENIUM 323 MIX provides a significant water-reducing effect on the cement system. At the same time, an improvement in the quality of the hardened cement paste was observed. The patterns identified for the cement paste were also observed for fine-grained concrete: the incorporation of plasticizing admixtures of any type makes it possible to densify the structure, reduce porosity, and increase the strength of the material. In turn, the increased density of fine-grained concrete ensures lower permeability and, consequently, greater resistance to aggressive environmental exposure. This is particularly important for the operating conditions characteristic of the Republic of Burundi.

Conclusions. As a result of the studies, the following conclusions and recommendations can be made: the optimal dosages of additives (regardless of their type) are within 0.9–1.2 % of the mass of cement (based on the value of the water-reducing effect). At the same time, additives based on polycarboxylate ethers give the greatest effect both on pure cement stone and on fine-grained concrete.

Introduction. The operational durability of asphalt concrete pavements is largely determined by degradation processes occurring in the microstructure of the material under the influence of moisture and alternating temperatures. At the early stages of deterioration, microdefects are formed, which subsequently lead to crack development and a decrease in the performance characteristics of the pavement. Despite numerous studies devoted to the durability of asphalt concrete, the morphological features of the initial stage of operational degradation remain insufficiently studied. The aim of this work is to identify early morphological indicators of damage in the asphalt concrete structure and to quantitatively assess changes in the defect space of the material at the initial stage of operational deterioration.

Materials and methods. The object of the study is stone mastic asphalt SMA-16 specimens. Microscopic imaging of areas with pronounced microdefects was performed for specimens in the initial condition and after water saturation followed by cyclic freezing and thawing. The morphology of the defect space was analyzed using digital microphotographs with automated image processing methods. A set of morphological parameters was used to quantitatively characterize the defect structure, including the fraction of the defective area and parameters describing the shape and extent of defect boundaries.

Results. A total of 40 representative microstructural zones were analyzed. Quantitative estimates of defect evolution after exposure to water and alternating temperature cycles were obtained. It was established that stable features of primary structural degradation appear after five freeze–thaw cycles, manifested by an increase in integral defectiveness and changes in pore-crack morphology. It is shown that at the early stage of degradation, mechanisms of defect network branching and merging of defect regions with their enlargement occur simultaneously.

Conclusions. The obtained results confirm the possibility of diagnosing the early stages of operational damage in asphalt concrete based on morphological analysis of its microstructure. The necessity of combined use of areal and linear morphological parameters for quantitative assessment of the defect space is demonstrated.

Introduction. The impact of indoor noise on human health has been confirmed by systematic reviews and recognized as a risk factor by WHO. Existing comparative studies have predominantly focused on European contexts and have not incorporated criteria from green building certification systems. This paper presents a comparative analysis of regulatory requirements for airborne sound insulation of internal building partitions in 43 countries, along with acoustic criteria of WELL, BREEAM, and LEED.

Materials and methods. A mathematical conversion of national sound insulation indices was performed, reducing them to a unified equivalent in-situ index R′w based on generalized relationships from ISO/FDIS 19488.

Results. At least seven distinct regulatory indices are used globally. For inter-apartment partitions, the median R′w was 52 dB (range: 43–58 dB), with the Russian standard (R′w ≥ 50 dB) falling within the median range. The Russian regulatory framework features a deeper typological classification compared to WELL, BREEAM, and LEED.

Conclusions. At least seven distinct regulatory indices are used globally. For inter-apartment partitions, the median R′w was 52 dB (range: 43–58 dB), with the Russian standard (R′w ≥ 50 dB) falling within the median range. The Russian regulatory framework features a deeper typological classification compared to WELL, BREEAM, and LEED.

Introduction. According to the purpose of the study, soft skills in demand by modern employers in the global construction industry were identified. Real sources of information were used. More than a hundred sites have been studied, more than thirty have been used to collect data. Previously, the characteristics of the global and industry levels in the context of personnel management were not correlated through specific personal qualities. The study found: teamwork is not the only soft skill in demand in modern construction. In this regard, we can conclude that it is important to develop soft skills of personnel in construction organizations.

Materials and methods. The bibliographic method was used, which includes collecting, analyzing, and summarizing data from websites of employers around the world in accordance with selected criteria.

Results. There are seven global trends affecting the world; six industry trends. The individual qualities of employees suggest the presence of seven soft skills, presented in a generalized way. Teamwork, communication skills are most often mentioned by employers. Adaptability is sought after, and qualities that demonstrate a value-based orientation toward people at work are also frequently mentioned.

Conclusions. The multicultural aspect of personnel management, the rapid change in the operating conditions of the industry, the organization do not lose their relevance, but become different under the influence of geopolitical factors. The vector of efforts of representatives of HR departments is also focused on optimizing interaction between representatives of various subcultures and the commitment to the organization.

Introduction. The modern construction industry actively uses end-to-end technologies to assess the productivity of construction workers, reducing the number of defective products. Innovative approaches increase the effectiveness of monitoring workers’ actions on construction sites. The use of modern computer vision technologies, video analytics, and machine learning algorithms can improve the objectivity of assessing productivity on construction sites.

Materials and methods. The developed automated system for analyzing workers’ actions to control labour productivity at construction sites includes a module for recognizing workers’ actions and poses, an action classification unit, and a component for highlighting key points. The MediaPipe platform with the BlazePose model identifies 33 anatomical points on the body to assess the worker’s posture. The computer vision system provides continuous monitoring and accurate recognition of movements. The technology ensures continuous recognition of the worker, even when there is a temporary loss of visual contact, and creates a database with worker characteristics for analytical purposes. The use of an automated system eliminates the need to consider the time factor when analyzing data, which increases the efficiency of the process and allows you to focus on the elements of the scene. By dividing the recording into logical segments, each element of the workflow is examined. LSTM recurrent neural networks optimize the analysis of workers’ actions.

Results. The effectiveness of the automated system was evaluated using a test video of the masonry construction process to determine its accuracy and generalization capabilities. The accuracy of identifying the builder’s actions reached 80.1%. During a total of 46.5 seconds out of the 58-second video, the model correctly recognized the builder’s actions.

Conclusions. The results of the work carried out prove the effectiveness of an advanced system for monitoring labour productivity in construction based on visual recognition technologies. The system provides comprehensive monitoring of work operations, equipment, and external conditions at the facility. The algorithms and information base ensure reliable measurements and the possibility of implementing the methodology in construction production.

Introduction. The preparation of cost estimate documentation for capital construction projects is one of the key processes in investment and construction activities, directly affecting the accuracy of cost determination and the outcomes of state expert review. In the context of the implementation of Building Information Modelling (BIM) technologies, there is a need to develop methodological approaches to the preparation of cost estimate documentation based on digital information models.

Materials and methods. The methodological basis of the study includes the analysis of regulatory legal acts of the Russian Federation, scientific publications of Russian and international authors, as well as the practice of state expert review. The following research methods were applied: analysis, synthesis, classification, formalization, and information modelling. Process modelling was carried out using BPMN notation.

Results. An analysis of typical comments from state expert review bodies was conducted, and their systemic causes related to inconsistencies between design and cost estimate information were identified. A comparison of traditional and BIM-based approaches to cost estimate preparation was performed, demonstrating the advantages of using digital information models. The functional capabilities of domestic BIM-based cost estimation software were analyzed, and limitations preventing full automation were identified. A conceptual model for cost estimate documentation preparation was proposed, including regulatory, information, software, and expert review levels.

Conclusions. The results confirm the need to develop a unified methodological model for preparing cost estimate documentation based on digital information models. The proposed conceptual model ensures the structuring of processes and preservation of structural and semantic data relationships, contributing to improved quality of cost estimate documentation and increased efficiency of state expert review. 

Introduction. The paper is devoted to the development of an organizational and technological model for modular construction of nuclear power plants aimed at reducing the investment and construction cycle while maintaining regulatory requirements for reliability and safety. Under conditions of high capital intensity and long construction periods of power units, the transition to industrialized technology with a high degree of factory readiness requires formalization of process parallelization, module enlargement, and management of transportation and installation risks. The scientific problem lies in developing a reproducible model that ensures quantitative reduction of construction time without compromising structural strength and stability.

Materials and methods. The study employs schedule network modelling, organizational and technological analysis, structural process optimization, and computational verification of temporary structural states in accordance with current construction and industry regulations. A comparison of conventional on-site construction technology and modular erection schemes was performed, taking into account factory fabrication, transportation, and installation stages of large modules. Data from typical Generation III+ power unit projects, as well as regulatory indicators of labor intensity and construction duration, were used.

Results. A formalized model was developed to assess the impact of module enlargement degree and process parallelization level on construction duration. It was established that within a module enlargement coefficient of 0.6–0.75, a 15–30 % reduction of the investment and construction cycle can be achieved while maintaining regulatory requirements for structural strength, stability, and seismic resistance. The structure of transportation and installation risks within the overall project risk system was also determined.

Conclusions. The proposed organizational and technological model provides a quantitatively verified reduction in construction time of power units without compromising safety and reliability. The methodology is reproducible and can be applied to serial construction of power units of various capacities, including small modular reactor projects.