Introduction. Numerical methods are usually used to calculate the natural oscillation frequency of building structures. Methods for obtaining analytical solutions are known to estimate the oscillation frequency limits of simple statically determinate structures. If the structure is regular and has a periodic structure, the capabilities of analytical methods are expanded. The induction method adds an additional important parameter to the solution formula — the number of periodic structures of the structure, for example, the number of panels. The approximate Rayleigh method gives an upper estimate of the oscillation frequency, and the Dunkerley method gives a lower estimate. In this paper, a diagram of a cantilever spatial statically determinate truss with a regular structure is proposed and a formula for its first oscillation frequency is derived using three analytical methods.

Materials and methods. The truss consists of six flat trusses with a diagonal lattice connected along their long sides. The cantilever structure is fastened to the vertical base on six supports. To determine the rigidity of the truss, the Maxwell – Mohr formula and the Maple computer mathematics system are used. A formula is derived for the dependence of the first oscillation frequency based on the Dunkerley and Rayleigh methods, which are simplified due to summation. The dependence of the frequency on the number of panels is found by the inductive method of generalizing the results obtained for individual solutions in symbolic form to an arbitrary case.

Results. Analytical solutions are compared with the numerical one obtained for the first frequency from the frequency spectrum analysis. It is shown that the accuracy of the analytical solution depends non-monotonically on the number of panels and this dependence is different for the three methods used.

Conclusions. The modified Rayleigh method for a small number of panels showed the highest accuracy compared to the methods based on the Dunkerley approach. The error of all three methods depends significantly on the dimensions of the structure and the number of panels. The analytical form of the results allows using the found solutions in design optimization problems.

Introduction. Last decades, piles foundations become more popular because of increasing height of buildings. It is necessary to determinate bearing capacity of pile while designing to reach the most efficient way for spending material and technical resources. The safest results can be received from static load tests, that’s why big developer companies in Arkhangelsk-city included this method for all buildings with nine or more floors. Unfortunately, there are a lot of tests that ended when the needed load is reached with small settlement, and the actual value of pile resistance can’t be found.

Materials and methods. In this paper, the analyzed results of static load test for 15 piles are presented. All of them were driven into marine clayey soils in solid or semi-solid state with a porosity coefficient of 0.49–0.61, an internal friction angle of 23–27°, a specific adhesion of 40–75 kPa and a deformation modulus of 25–32 MPa, layers above were close to each other on all construction sites. Processing the results were made by F.K. Chin method.

Results. We reached the ultimate load for every pile, also the proposals to estimate the bearing capacity of piles which didn’t reach the ultimate settlement were made.

Conclusions. Finally, it was determined, that the ultimate load can be evaluated if only loaded it within the range of elastic deformation and after that range you can predict the way of chart with empirical relation for reduce the test time. The relation between ultimate loads and actual loads in the buildings was found for two groups of piles. Also, was made the conclusion about the excessive length of piles.

Introduction. The mechanism of failure of reinforced concrete structures from the action of shear force has been the object of research of Russian and foreign scientists for many decades. This failure mechanism garners significant attention due to its danger — the shear failure is often brittle and sudden. The bearing capacity and the type of failure of reinforced concrete structure within this mechanism depends on a variety of design parameters, which greatly complicates its study. Key parameters influencing load-bearing capacity in shear failure include the strength of concrete, geometric characteristics of the cross-section, span-to-depth ratio, percentage of tensile reinforcement and the transverse reinforcement intensity. Also, to such parameters can be attributed the energetic size effect which concept is disclosed in the paper. The shear design method, presented in building code SP 63.13330.2018 only indirectly accounts percentage of tensile reinforcement. It also does not consider the energetic size effect, which impacts its accuracy. It is urgent to modify the design method by taking into account these design parameters.

Materials and methods. To obtain the coefficients of the refined design method, the regression analysis performed by the least squares method using the Levenberg – Marquardt algorithm was used.

Results. The paper presents a refined method for shear design of reinforced concrete structures which takes into account the influence of the percentage of tensile reinforcement and energetic size effect. A comparison of the refined design method and the original methodology from SP 63.13330.2018 with the results of laboratory tests of 958 specimens is presented. The specimens are divided into groups according to the values of the design parameters.

Conclusions. The refined design method for shear design of reinforced concrete structures is more accurate than the normative method presented in SP 63.13330.2018. The application of the refined calculation method will allow to correctly assess the load-bearing capacity of inclined sections under the action of shear forces, which in some cases will lead to a reduction in the consumption of transverse reinforcement.

Introduction. In bridge and overpass design, the transverse (lateral) load from a vehicle impact on the safety barrier must be accounted for. In the Russian Federation, p. 6.19 of CP 35.13330.2011 specifies a constant value of 165.2 kN for concrete barriers — a value originating from SNiP 2.05.03–84 (1986) and not revised since. A review of U.S. and EU provisions shows that comparable design loads are approximately 3–5 times higher, motivating the present study.

Materials and methods. A vehicle–barrier impact is a dynamically nonlinear contact problem between two deformable bodies. The most effective approach is virtual crash testing. We employed ANSYS LS-DYNA; test parameters (vehicle mass, speed, impact angle) were set per current Russian standards. Model validation used full-scale test data from NAMI. Solution verification included energy balance checks, mesh/time-step convergence, and comparison of impact force metrics with analytical estimates discussed in the paper.

Results. Virtual simulations yielded numerical values of the equivalent transverse dynamic load from vehicle impact on a concrete barrier for retention levels Y1–Y10 in accordance with GOST 33128–2024 and GOST 33129–2024.

Conclusion. The actual impact loads substantially exceed the value prescribed by p. 6.19 of SP 35.13330.2011, leading to insufficient safety margins in current barrier and connection designs on bridges. The findings indicate the need to update the Russian regulatory framework for concrete barriers and for the structures on which they are installed, linking design loads to retention level and impact scenario and allowing the use of verified virtual crash testing results.

Introduction. The analysis of existing studies shows that elevated temperatures significantly alter the physical and mechanical properties of concrete, including high-strength steel fibre reinforced concrete, which reduces the reliability of calculation models for thermally loaded structures. The combined action of thermal and mechanical factors leads to variations in the strength and deformation characteristics of the material. In this context, structures operating under long-term thermal exposure are of particular practical interest. Continuous casting machines (CCM), which are the main metallurgical units for steel casting, require massive foundations operating under prolonged thermal effects, making the study of their mechanical characteristics highly relevant.

Materials and methods. The paper presents the test results of specimens made of high-strength steel fibre concrete with a fibre content of µsfb = 0 and 2.5 %. The influence of the percentage of fibre reinforcement and elevated temperatures on the basic mechanical characteristics of the material is estimated. Based on the data obtained, numerical modelling of the CCM foundation using the finite element method was performed using the diagrammatic calculation method, taking into account physical nonlinearity, real-world operating conditions and temperature conditions. The Lira-CAD 2020 software package was used for modelling, which takes into account the heterogeneity of temperature and shrinkage deformations and the actual deformation diagrams of the material.

Results. The parameters of the stress-strain state and the values of mechanical properties for high-strength steel fibre concrete are obtained, taking into account the duration of heating up to +200 °C. Numerical modelling has shown the influence of the heterogeneity of the temperature distribution over the volume of the structure on the stress-strain state of the studied elements. The use of high-strength steel-fibre concrete as a variable material made it possible to reduce the magnitude of tensile forces and stresses, as well as increase the crack resistance of the structure in question.

Conclusions. The introduction of up to 2.5 % steel fibre into the composition of high-strength concrete significantly increases its mechanical properties at normal temperatures. Experiments have shown that short-term heating reduces the strength and elastic characteristics, and prolonged temperature exposure changes the complex of physical and mechanical properties of the material. The analysis of the stress-strain state of the foundations confirmed the effectiveness of the use of high-strength steel-fibre concrete in conditions of thermal exposure.

Introduction. In the conditions of constant increase of requirements to quality, economy and environmental friendliness of construction materials for road construction it is urgent to obtain warm asphalt concrete mixtures with improved characteristics. When selecting the technology and composition for warm asphalt concrete mixes, an important task is to evaluate the operational properties and calculate the service life of asphalt concrete.

Materials and methods. In the paper the influence of complex additive Viskodor PV-2 in comparison with known imported wax additive Liсоmоnt ВS-100 on physical and operational properties of warm asphalt concrete mixture of A16Vn grade was investigated. BND 70/100 bitumen was used as the initial bitumen, crushed stone and granite rock crushing screenings and limestone mineral powder MP-2 were used in the composition of the mineral part of the asphalt-concrete mixture.
To investigate the physical and operational properties of the asphalt concrete mixture, methods were used in accordance with the current standards.

Results. The results of evaluation of the effect of the investigated wax additives on the compactibility of asphalt concrete mixture at lower molding temperatures than the control hot asphalt concrete mixture are presented. A comparison of load resistance of the control specimen of asphalt concrete without additives and specimens with the investigated additives was carried out. Based on the obtained data, the service life of the tested asphalt concrete specimens was calculated by the criterion of resistance to plastic deformations.

Conclusions. It was established that the investigated additives allow not only to reduce the temperature of preparation and compaction of asphalt-concrete mixture, but also essentially improve qualitative characteristics of asphalt concrete: water resistance coefficient, resistance to loads and plastic deformations. As a consequence, increase the service life of the road surface. It is revealed that the developed complex additive Viskodor PV-2 is not inferior and even significantly exceeds the efficiency of imported additive Liсоmоnt ВS-100.

Introduction. Construction needs new concrete. Self-compacting concretes (SCC) are gaining popularity. The advantage of SCC is high mobility, so the emphasis is on their rheological properties. The technology continues to develop in lightweight self-compacting concretes, that combines high mobility and low density. The study of LWSCC (Light-weight self-compacting concrete) focuses on the effect of the formulation on the properties of the mixture. The purpose of this study is to investigate the effect of the ratio of dry components on the rheological properties of LWSCC on hollow microspheres.

Materials and methods. The object of the study is LWSCC on hollow microspheres. The ratio of dry components varied depending on the target concrete density. The composition includes: Portland cement, ceramic hollow microspheres, silica additive, fractional sand (Sf), quartz powder (Sp), hyperplasticizer and water. The amount of water and the concentration of plasticizer are assumed to be constant: 0.5 and 1.4 %, respectively. The results of studies of the rheological characteristics of LWSCC were obtained. The key rheological parameters are shear stress and viscosity.

Results. Concrete mixtures with a density of 1,400 kg/m3 have a dilatant flow pattern regardless of the Sp/Sf ratio. At densities of 1,500 and 1,600 kg/m3, the flow pattern changes to pseudoplastic at Sp/Sf = 25/75. The possibility of controlling the type of flow of heavy concrete by changing the Sp/Sf is shown. The difference in flow between lightweight and heavy concrete mixtures is reflected in the dependences of shear stress and viscosity on Sp/Sf. An increase in Sp increases the shear stresses and viscosity of LWSCC, for heavy compositions, a downward-to-upward relationship is observed in the range of Sp/Sf = 25/75–75/25 at different shear rates.

Conclusions. The possibility of changing the rheological character of the flow of lightweight and heavy mixtures with changes in the studied factors is shown. A comparative analysis of rheological curves using the Ostwald – Weil equation for heavy and light concrete mixtures has been performed. The role of the dispersion of mineral aggregate and hollow microspheres in controlling the rheological properties of the studied LWSCC is considered.

Introduction. The important way to improve the efficiency of residential building heating systems is to use thermal insulation materials in exterior building envelope. At the design stage, the choice of insulation is based on predicting heat loss through the walls using standard methodologies that do not take into account changes in the thermophysical properties of the materials during operation, such as changes of humidity during the heating season. The purpose of this paper is to develop the methodology for predicting heat loss through exterior building envelope, taking into account changes in the moisture content of the thermal insulation materials during operation.

Materials and methods. The proposed methodology is based on the mathematical model of heat and moisture transfer in the four-layer building envelope, which was developed using the authors’ experimental data on the dependence of thermal conductivity and moisture conductivity coefficients from sorption moisture content for typical thermal insulation materials. The structure under consideration consists of an internal lime plaster layer; a brick (or concrete) wall; thermal insulation material and an external facing layer. The methodology for predicting thermal losses was implemented in the COMSOL Multiphysics 6.2 software package.

Results. Studies of the thermotechnical characteristics and heat losses for the four-layer envelope structure with IZOVOL, TEHNOPAS PROF, PENOPLEX COMFORT thermal insulation materials were carried out on the example of residential buildings of mass construction in Lugansk. The conducted thermal imaging survey of insulated envelopes for operated buildings is consistent with the results of calculations according to the proposed methodology.

Conclusions. The developed predicting methodology ensures the accuracy increase of determining the heat loss of heating systems through exterior building envelopes, taking into account changes of the materials moisture content during operation. The application of this methodology allows assessing the energy efficiency and economic feasibility of using standard insulation materials in building envelopes.

Introduction. In a number of applied engineering problems, questions related to the impact of massive bodies on water and their motion in the water after the impact often arise. Renowned Russian and international scientists, including L.I. Sedov, M.V. Keldysh, G. Wagner, T. Karman, and others, conducted theoretical and practical research in this area of hydrodynamics.
Problems involving determining the dynamic loads arising in liquid-filled containers when various large objects fall into them often arise during the investigation or prediction of emergency situations. This paper examines the problem of an emergency involving the transportation of a container containing radioactive waste over a spent fuel pool, which is found at all nuclear power plants. The container’s attachment breaks, and it falls into the pool. Determining the loads arising in such a scenario is a mandatory task for all nuclear power plants.

Materials and methods. This paper describes in detail the physical processes accompanying the impact of a heavy, flat-bottomed body on a water surface and formulates general principles for the formation and calculation of hydrodynamic loads arising in a fluid. The feasibility of using the concept of “added mass” in the physical interpretation of this phenomenon is analyzed. The limits of its validity in considering various problems of unsteady hydrodynamics are indicated. The results of model experimental studies aimed at studying the impact pressure arising in water when a heavy, flat-bottomed body falls into it are presented. The well-known Godunov method, based on the problem of the decay of an arbitrary discontinuity, was used in the mathematical description of the hydrodynamic phenomena under consideration. This method allows one to determine the dynamic parameters of pressure and velocity of a fluid in the presence of significant discontinuities in the initial and boundary conditions.

Results. Based on data from model experiments and the results of numerical calculations, the authors identified four main phases of a body’s motion as it falls into a liquid. A series of computational experiments was used to formulate a methodology for determining the time dependence of the added mass involved in the impact. It was shown that when a body impacts water contained in a confined pool, there is a time dependence of the added mass, which is determined by the geometric parameters of the pool. As an example, the paper presents several instantaneous impact pressure profiles generated in a pool when a flat body impacts water. Examples of maximum pressure fields generated in a pool when a massive body impacts water are also given.

Conclusions. Model experiments revealed that the shock pressure generated when a flat body impacts water is significantly lower than predicted by the solution to the problem of the decay of an arbitrary discontinuity. The maximum pressure obtained through calculations is 3–4 times greater than that obtained experimentally. The significant reduction in shock load is caused by the presence of an air gap between the flat bottom of the body and the free surface of the water. The presence of an air bubble (air gap) beneath the body leads to an increased time for the formation of a stable hydrodynamic flow around the body and, consequently, a decrease in the intensity of the shock wave.

Introduction. The primary tool for planning labour intensity, duration and cost of construction and repair works are documents of technological regulation. The evidence base of these documents is grounded in statistical processing of a large number of experimental field measurements of these parameters on the construction site, as well as cost calculations considering price fluctuations under market conditions, along with generalization of practical experience from construction organizations.

Materials and methods. In carrying out a set of construction or repair-construction works, an important organizational decision in practice involves substantiation and selection of work sequence, possible overlap in time and space determined by technological requirements. Typically, execution of such works is carried out by a team of workers representing different professions and qualifications, where more complex and critical technological operations are performed by highly skilled workers.

Results. To ensure proper quality of work and efficient use of working hours when performing individual types of repair-construction works, regulatory documents stipulate minimum staffing levels and qualification standards. When organizing work using flow methods to maintain rhythm, the number of personnel may be increased depending on specific volumes of particular tasks and accepted sizes of sections and areas.

Conclusions. For simplifying the procedure of making decisions regarding provision of human resources for a package of capital repair works given specified volumes and durations, a graphic interpretation tool has been developed. This tool helps form rational quantitative and qualitative composition of workers engaged in various activities within integrated teams.

Introduction. The construction sector of the Czech Republic is characterized by high labour intensity, significant wage differentiation, a project-oriented organization of work, and a persistent shortage of qualified labour. These features substantially complicate personnel management and payroll processes, increasing the requirements for employer responsibility in the field of HR management. The aim of this study is to analyze the relationships between structural labour shortages, wage variability, and the institutional complexity of HR processes, as well as to empirically assess their impact on the level of internal corporate responsibility in construction companies.

Materials and methods. The empirical basis of the study includes industry-level macroeconomic data and aggregated operational indicators of HR and payroll processes in construction companies, which made it possible to identify stable management characteristics and ensure the comparability of the analyzed cases. Principal Component Analysis (PCA) and structural modelling based on PLS-SEM were employed to identify latent factors of HR complexity and to analyze causal relationships between the studied variables.

Results. The study demonstrates that increasing wage differentiation and labour shortages act not only as economic pressure factors but also as key determinants of growing complexity in internal corporate responsibility management within HR processes. The digitalization of HR and payroll systems contributes to a reduction in operational errors and enhances the transparency of certain procedures; however, it does not eliminate the institutional complexity of management, nor does it shift responsibility toward technological systems. The findings indicate that the use of digital tools intensifies requirements for the quality of managerial decision-making, process formalization, and coordination in personnel management. Internal corporate responsibility is established as a systemic managerial characteristic that determines the sustainability of HR management under conditions of high workforce uncertainty and project dynamics.

Conclusions. The results contribute to the development of personnel management in the construction sector and substantiate the thesis that the digitalization of HR and payroll systems does not eliminate employer responsibility but rather transforms the requirements for its institutionalization.