Strength of Materials and Theory of Structures

Possibilities and limits of applying the method of assessing the stability of soil massifs using FEM and graph theory

Ivan Solodei — 2025-10-30

The selection of a method for solving complex engineering problems is an integral part of any calculation process, on which the accuracy and reliability of the obtained results largely depend. At the same time, all methods and approaches, even the most universal, have certain limits of their rational application. In this case, it is important to determine the limits and possibilities of using certain methods. This paper briefly considers the limits of using a combined approach based on the finite element method and graph theory, as well as options for its use as a separate toolkit or in combination with other methods to eliminate their shortcomings or to perform alternative calculations. In addition, the possibility of combining the approach based on graph theory with other numerical methods is considered.

The paper also presents the results of practical use of this combined approach in assessing the stability of a non-uniform landslide-prone slope, the calculation and analysis of the stress-strain state of which were carried out using the semi-analytical finite element method in the spatial formulation of the problem, and the stability assessment was carried out using graph theory approaches for the specified calculation sections. In the course of solving this problem, five different settings were considered in stages, from the slope in its natural state to the built-up slope, taking into account a possible option for engineering protection of this area. Accordingly, for one of the calculation sections, the obtained values of the stability coefficients and the shapes of potential sliding surfaces are given in accordance with some of them, shear pressure diagrams were determined and constructed, which can be used as initial data for the placement and calculations of engineering protection structures.

Tuning of vibro-impact nonlinear energy sinks under changing structural parameters. Part 2. Comparison with tuned mass dampers

Petro Lizunov — 2025-10-30

This paper studies the dynamics and efficiency in mitigating the primary structure (PS) vibrations with using the single-sided vibro-impact nonlinear energy sink (SSVI NES) and tuned mass damper (TMD). It is considered the PS coupled with vibro-impact and linear dampers with mass ratio of 2% and 6% under periodic excitation with change in structural parameters such as the PS damping, its stiffness, and exciting force intencity. The paper focuses on the ability of these dampers to maintain their tuning. The numerous numerical experiments, which results are reflected in expressive graphs and tables, convincingly show that both the SSVI NES and the TMD retain their tuning and demonstrate high efficiency in mitigating the PS vibrations across fairly wide ranges of these parameters. The TMD retains tuning no worse than SSVI NES, and in some cases even better. At the same time, SSVI NES, which always exhibits complex dynamics, provides narrow zones of bilateral damper impacts on the PS directly and on the obstacle located near the resonance. Thelighter SSVI NESsexhibit a specialbehavior. Their high efficiency is ensured by non-standard unusual values of large clearance and small dampingcoefficient. Furthermore, selecting the optimal SSVI NES design difficult because there are many sets of optimal parameters that provide their similar performance.

The energy approach is used to estimate the mitigation of PS vibrations, that is, the reduction of maximum mechanical energy of the PS is considered as criterion of mitigation. The energy of dampers, which is taken away from the PS energy, is shown. The zones of nonlinearity for SSVI NES include the zones of bilateral and unilateral damper impacts on the PS and obstacle; these zones also are shown. The characterisitics of irregular motion of SSVI NES are also shown.

Simulation of shock wave action from an explosive device on a protective shell

Olga Lukianchenko — 2025-10-30

The numerical approach to investigate the protective shell behavior under shock wave from an explosive device was presented. Comparison of shock wave characteristics from different explosive devices that were obtained experimentally and by Sadovsky’s analytic formulas was made. The hemispheric geometrical model of shock wave and two finite element models of the cylindrical steel protective shell with the surface areas that had certain values of overpressure and positive impulse were created using NASTRAN software. As an example, the positive phase of shock wave from an explosive device with a TNT equivalent of explosive mass 250 kg was considered. Overpressure was given as the evenly distributed load which depended on the distance from explosion epicenter to the shell surface areas. Shell behavior from the static action of overpressure was investigated in the nonlinear formulation by the Newton-Raphson method and compared with the results of the linear static and buckling analysis. The critical load coefficients and static characteristic of shell were obtained. The first step of the dynamic investigation was modal analysis of shell using the Lanczos method. The positive impulse was presented in the shape of a triangle with a certain time of action. The largest period of shell natural oscillations was taken account. Influence of positive impulse of shock wave on the dynamic behavior of the two shell models was investigated by the fourth-order Runge-Kutta method. The shell state at the different time of positive impulse was presented. The results of static and dynamic analysis allowed to assess the impact of shock wave action from the explosive device on the stressed deformed state of the protective shell.

Glued laminated timber beam reinforced with composite strips

Denys Mykhailovskyi — 2025-10-30

Abstract. Modern trends in the development of the construction industry demand increased attention to environmental aspects. This leads to the growing popularity of materials that are environmentally friendly and have minimal negative impact on the environment. At the same time, such materials must possess high strength and resistance to external influences and loads. In this context, timber structures are gaining widespread use. They are made from renewable natural resources and are characterized by relatively high strength and low weight, which qualifies them as sustainable building materials. Despite certain disadvantages of wood, such as shrinkage, decay, and anisotropic physical and mechanical properties, these drawbacks can be almost completely eliminated in glued laminated timber structures. In particular, glued laminated timber beams are key elements in many structures and are widely used in construction. Therefore, the issue of increasing their stiffness and strength through reinforcement with composite materials is especially relevant.

This paper proposes a reinforcement technology, a methodology for determining the stress–strain state, and a calculation method for glued laminated timber beams reinforced with composite strips. The results of deformation parameters of the experimental model are presented, including actual flexural modules of elasticity, maximum longitudinal stresses at mid-span, at the load application axis, and at the support axis. The actual maximum load-bearing capacity of the experimental model reinforced with composite strips is determined and compared with numerical studies conducted in a modern software package.

Features of modeling bolted joints of thin-walled steel elements in dynamic monitoring tasks

Maksym Vabishchevych — 2025-10-30

The article considers the issue of modeling joints in thin-walled steel structures, which are actively used in construction, mechanical engineering and other branches of engineering. These structures are characterized by high efficiency and economy, however, their mechanical characteristics and features of the interaction of individual elements require detailed analysis to ensure reliability and durability. Bolted joints are one of the key methods of fixing elements of such structures, as they provide strength, ease of installation and the possibility of replacing components. The research focuses on the development and improvement of numerical models that describe the operation of bolted joints in real operating conditions. The use of numerical methods allows predicting the behavior of joints, assessing their strength and determining factors that affect the accuracy of calculations. Special attention is paid to the analysis of geometric parameters and material characteristics of the connected elements, as well as their impact on the effectiveness of structural solutions. A special place in the study is occupied by the issue of model verification, because the reliability of numerical methods must be confirmed by comparison with experimental data. The article considers the possibilities of using various computational complexes to assess the correctness of models, as well as analyze their compliance with real tests. An important aspect is the consideration of dynamic monitoring of the condition of joints, which allows ensuring the safety of structural operation and preventing potential emergency situations. The results of the study confirm the effectiveness of the applied models and methods, and also open up prospects for further improvement of approaches to design and optimization of structures. The results obtained can be used in practical engineering solutions, which will contribute to increasing the reliability of joints in difficult operating conditions.

Research of nonstationary vibrations of an elastic space with two circular cylindrical holes

Hryhorii Ivanchenko — 2025-10-30

The paper presents a comprehensive study of nonstationary vibrations of an elastic medium with two circular cylindrical holes subjected to time-dependent boundary loading. The formulation of the problem is carried out under zero initial conditions, with the transition into the frequency domain implemented by Fourier series expansion. This approach allows reducing the system of dynamic equilibrium equations to a sequence of boundary value problems for different values of the frequency of harmonic vibrations. To solve the problem, the potential method is applied, which transforms the formulation into a system of boundary integral equations in the frequency domain. A fundamental solution is introduced in closed analytical form, incorporating Hankel functions of the first kind of orders zero, one, and two, and its generalized derivatives are employed in the integral kernels. Since these kernels become singular when the observation and integration points coincide, direct numerical evaluation is impossible. This obstacle is overcome by applying the Maclaurin series expansion of the kernels, in which the leading term coincides with the static potential kernel, while higher-order terms remain finite. As a result, the algebraization of the system of boundary integral equations becomes feasible. The efficiency of the proposed approach is verified by solving a benchmark problem on steady-state vibrations of a medium with a circular cylindrical hole under harmonic radial loading. The results demonstrate that the use of piecewise-quadratic approximation of the unknowns ensures high computational accuracy over a wide frequency range. Numerical experiments confirm the validity and stability of the method in predicting radial displacements and tangential stresses at different characteristic points of the boundary, thus establishing its applicability for analyzing dynamic behavior of perforated elastic structures. Furthermore, the analysis highlights the importance of applying advanced mathematical techniques to address complex problems of structural dynamics where traditional numerical methods face limitations. The proposed methodology demonstrates robustness not only in capturing local stress concentrations but also in preserving accuracy under high-frequency regimes, making it suitable for engineering applications requiring precision. The developed framework can be further extended to problems with multiple interacting cavities, anisotropic materials, or three-dimensional geometries, which are often encountered in aerospace, mechanical, and civil engineering. Hence, this work provides not only theoretical advancement but also a practical computational tool that can be integrated into modern simulation environments to support the design and safety assessment of complex structural systems.

Stress-strength state of the wooden frame structure of energy-efficient buildings of the NZEB standard

Ivan Nazarenko — 2025-10-30

The work investigates the stress-strain state of wooden frame elements of buildings with close to zero energy consumption. It is substantiated that wooden frame structures are widely considered as an effective alternative to traditional ones (concrete, steel) from the point of view of ecology and energy efficiency. An analysis of architectural, planning and structural solutions of a low-rise residential energy-efficient building Start TM “Business House” of the NZEB standard for industrial production from typical structural elements was carried out. Using the model of the spatial calculation scheme of the building and the “LIRA” software complex, the stress-strain state of the adopted structural solutions of the building was investigated. An analysis of the level of use of the load-bearing properties of the frame elements (stairs of the first and second floors) and the floor truss (lower belt, braces) at maximum forces from calculated load combinations was carried out. A verification calculation of the frame elements: the first and second floor racks, the floor truss elements for the strength of the sections along the normal to the axis of the load, for chipping, stability, as well as for fulfilling the requirements for ultimate flexibility. The calculation data indicate the rational use of the selected cross-section of the first floor racks and floor truss elements. It is proven that the wooden frame provides both the energy efficiency requirements of the NZEB standard and a high level of operational reliability.

Strength of webs of I-shaped reinforced concrete elements under shear forces

Yulii Klimov — 2025-10-30

All existing methods for calculating the strength of reinforced concrete elements are based on experimentally established possible types of element failure under certain forces caused by external forces. Thus, under the action of bending moments or the combined action of moments and longitudinal forces, failure occurs as a result of the crushing of the concrete in the compressed zone when the stresses in the longitudinal reinforcement reach or do not reach the limit values for tension (yield strength) and compression. under the action of torsional moments – along a critical spiral crack, when a compressive force is applied over a small area – from the crushing of concrete under the area. The resistance of reinforced concrete elements to shear forces differs significantly from other forces of action, as it is characterized by different types of failure – concrete fragmentation above a critical inclined crack, concrete shear above a critical inclined crack, crushing of concrete in an inclined strip between inclined cracks or a support and a load, loss of adhesion of longitudinal reinforcement to concrete in the tension zone beyond a critical inclined crack, and failure along inclined cracks during punching, which is explained by the influence of the loading pattern, the geometry and design features of the element. Accordingly, to assess strength in the event of possible types of failure, the appropriate calculation tool is used, which is not always implemented within a single calculation model for elements. Therefore, in practice, different calculation methods are used for each of the possible types of failure.

This paper presents a method for calculating the strength of I-beam reinforced concrete webs when they fail along a strip between inclined cracks, based on the principles of reinforced concrete plasticity theory, considering the concrete of the web under conditions of plane stress compression-tension when tensile stresses are transferred to the concrete from shear reinforcement. Within the framework of the developed method, the criterion for failure is taken to be the attainment of the main compressive stresses in the concrete strip of the web at the corresponding stress state. The general case of the ultimate equilibrium of a beam within the strip between inclined cracks with arbitrary content and location of transverse reinforcement is considered. Calculated dependencies are obtained for calculating the limit values of stresses in the strip and shear force at wall failure.

Buckling analysis of elastic thin shells with stepwise variable thickness under static thermomechanical effects

Olga Krivenko — 2025-10-30

The results of a comprehensive analysis of elastic shell behavior under static thermomechanical loads are presented. The study focuses on geometrically nonlinear deformation, buckling, and natural vibrations of shells. Special attention is given to the identification of bifurcation points in the pre-buckling domain of shell deformation.The proposed comprehensive method is implemented as a two-stage algorithm. At each step of the thermomechanical loading, it combines the solution of the geometrically nonlinear static problem for the shell with a modal analysis at the same step. This approach allows the determination of critical states according to both the static criterion (maximum point of the load–deflection curve) and the dynamic criterion (load at which the lowest natural frequency of the shell becomes zero). The method is based on the geometrically nonlinear theory of thermoelasticity, the moment scheme of finite elements, and a universal three-dimensional finite element. We apply the methodology of introducing small non-symmetric perturbations into the initial geometry of the midsurface of the shell to determine bifurcation points iin the pre-buckling domain. This approach enables tracing new solution branches corresponding to adjacent forms of buckling. The presented numerical examples confirm the accuracy, universality, and effectiveness of the proposed method.

Finite element modeling of the static behavior of an elastic-plastic soil base under the action of rolling stock

Olga Lukianchenko — 2025-10-30

A numerical method for studying the static behavior of the soil base in a geometrically and physically nonlinear formulation from the action of rolling stock is proposed. A mathematical model of the boundary value problem of the statics of the ballast prism and the soil base is constructed using the computational procedures of the finite element analysis program NASTRAN. Single-layer and multilayer base models in the form of a flat half-space are considered. The static action of the rolling stock is presented in the form of a concentrated force applied to the ballast prism from the weight of empty and loaded freight train cars. To describe the elastic-plastic behavior of a single-layer soil base, the Mohr-Coulomb model is used, and for a multilayer one, the Drucker-Prager model. To assess the elastic-plastic behavior of the soil base, a comparison of the results of linear and nonlinear static calculations of two models from two loads is performed. The Newton-Raphson method is used to study the static characteristics of the models in a nonlinear formulation. The influence of taking into account the elastic-plastic models of single-layer and multi-layer soil bases on their stress-strain state was assessed. Due to the physical nonlinearity of the soil in the elements of the single-layer base model under the action of the weight of an empty and loaded car, an increase in the Mises deformation was observed by 15.9% and 16.7%, respectively, while the plastic deformation was 20% and 31.4% of the total deformation, the Mises stress decreased by 53.94% and 54.02%. The results of the study of the multilayer base under the action of the weight of an empty and loaded car showed that due to the physical nonlinearity of the soils, the Mises deformation of the elements increased by 5.8% and 7.4%, respectively, while the plastic deformation was 54.1% and 54.33% of the total deformation, the Mises stress decreased by 43.45% and 43.34%. The proposed methodology allowed us to form a computational model of the ballast prism and base and to investigate the nonlinear deformation of soils taking into account their elastic-plastic properties under the static action of rolling stock.

Non-stationary bending vibrations of helicopter rotor blade under distributed aerodynamic load. Part 1. Blade`s eigenbending vibrations

Petro Lukianov — 2025-10-30

The stability of helicopter behaviour during flight depends on many factors. One of them is directly related to the non-stationary elastic bending vibrations of the rotor blades. Air pressure on the blade surface causes bending deformations in this element. Since the movement of the helicopter rotor is periodic, the non-stationary load on the blade varies according to a harmonic law. As a result, we have a variable pressure and a change in lift. All of the above leads to a change in aerodynamic parameters, which causes helicopter motion instability. In this paper, the study of the blade's bending vibrations is based on its modelling as a thin rectangular plate.

The available experimental data from photographs recorded the movement of the helicopter blade in the form of oscillations similar to those of a cantilevered plate. It is known that helicopter blades are made quite rigid due to the existing stiffeners - nerves.

Therefore, in this work, the Kirchof-Love hypothesis and the Lagrange-Sophie Germain equation are used to simulate the non-stationary bending vibrations of a helicopter blade as a thin plate.

A review of existing works has shown that many studies have been dedicated to the study of bending vibrations of a rectangular plate described by the Lagrange-Sophie Germain equation. However, there is no exact solution to the problem of free vibrations of a plate in the case of its cantilever mounting. There are only approximate solutions using the Ritz method.

In this paper, an attempt was made to solve analytically the problem of free oscillations of small amplitude of a thin plate under classical boundary conditions of cantilevered plate fixation by two different methods. As it turned out, the analytical solution obtained by the Levy method is not unique. The system of equations for determining the coefficients of the general solution has a rank less than the number of unknowns. This indicates the dependence of the eigenvalues of the problem, i.e. the coupling of oscillations, which was previously found by Levy under other boundary conditions. Since the goal of this paper is to find a single solution, Part 2 of this paper presents an example of refined boundary conditions that allowed us to find a single solution to the problem.

Conditions for implementing tutorial technology in teaching construction mechanics

Kostiantyn Pochka — 2025-10-30

The conditions for implementing tutoring technology in teaching construction mechanics have been established, covering pedagogical, organisational, material, technical and psychological aspects of the educational process. Pedagogical conditions include training teachers as tutors, developing methodological strategies for individual and group support of students, and creating teaching and methodological support that promotes the development of competencies of future professionals. Organisational conditions include optimising the structure of the educational process, determining the mode of interaction between the teacher as a tutor and students, planning training modules, and coordinating work between departments and laboratories. Material and technical conditions provide access to modern teaching aids, digital platforms, laboratory equipment and electronic resources, enabling personalised learning and active practical activities. Psychological conditions consist of creating an atmosphere of trust, motivation, support for independence and responsibility among students, which shapes their readiness for professional development and self-improvement. The structural components of the tutorial technology for teaching construction mechanics are revealed, among which the target, content, technological, activity and result blocks are distinguished. The target component determines the directions of training and program learning outcomes, while the content component shapes the content of the educational process in accordance with standards and competency requirements. The technological component includes methods, techniques and tools of tutoring support, the activity component involves specific activities of students and tutors, and the result component evaluates the effectiveness of learning and the achievement of educational goals. The key determinants of the effectiveness of tutoring support for students are substantiated, among which the level of pedagogical competence of the tutor, the degree of individualisation of learning, the motivational potential of students and the integration of digital learning technologies are highlighted. The main approaches to personalising learning are identified, which involve building an individual educational trajectory, adapting learning material to the needs and abilities of students, systematic assessment of results, and correction of the educational process.

Study of the stress–strain state of the «Soil – Foundation -Structure» system with consideration of genetic nonlinearity

Ivan Solodei — 2025-10-30

The study examines the features of modeling the stress–strain state of the “soil–foundation–structure” system with consideration of genetic nonlinearity, which reflects the sequential changes of the calculation scheme during the construction of a building. It is shown that traditional linear calculations do not fully represent the actual processes of interaction between structures and the soil foundation. Three calculation models were considered for the analysis: a traditional scheme with “instantaneous” load application; a scheme with genetic nonlinearity but fixed vertical dimensions of the foundation model; and a scheme with genetic nonlinearity combined with refinement of the deformation properties of the foundation by adjusting the compressible layer thickness at each stage of construction.

The results demonstrated that Model 2 leads to overestimated settlement values at the initial stages, resulting in a conservative outcome. The most realistic results were obtained with Model 3, which accounts for changes in the compressible layer thickness at each construction stage. This approach makes it possible to reduce not only the absolute settlement values but also the relative deformations of the foundation slab, thereby decreasing stress levels in the underground structural elements of the building and revealing certain reserves in their performance.

Study of the behavior of a mesh shell roof structure upon deactivation of individual elements

Olena Kostina — 2025-10-30

The stress–strain state of a dome-shaped grid shell roof model under the failure of individual elements has been investigated. A spatial model of the shell was created in the LIRA software package and loaded with a uniformly distributed load applied to the nodes. The model contains 37 nodes and 90 elements. The steel tubular bars were modeled using beam finite elements with a circular cross-section of 10 mm in diameter and a wall thickness of 1 mm. All shell nodes were assumed to be rigid by default, and the support nodes of the lower ring were fixed. A numerical approach in the static formulation was applied. The problem was solved in three stages. First, a finite element model of the intact shell was created and its stress–strain state was analyzed. Then, one element was removed, and its effect was simulated by applying to its end nodes forces equal in magnitude and opposite in direction to those obtained in the first stage. The system with the removed element was recalculated, and the behavior of the neighboring elements and the overall load-bearing capacity of the structure were analyzed. At the final stage, another element adjacent to the first was removed, taking into account the state of the structure after the failure of the first element. The stress–strain state of the shell was analyzed again. To determine the effect of excluding individual elements from the structure on the stress–strain state, the nodal displacements and forces in the elements located near the removed ones along the load-transfer path were examined. Significant changes in the stress–strain state of a large number of elements were detected. In some members, internal forces increased by 116% and 308%. Moreover, in certain elements the nature of the stress–strain state changed: before the removal, the bars were in compression, whereas after the removal they experienced tension. Such changes indicate the potential danger of progressive collapse.

The stability of rotating rods during the excitation of higher-order bending oscillations under the axial vibro-impact load

Petro Lizunov — 2025-10-30

The paper presents the investigation results of vibro-drilling machine’ drill-rod dynamic behavior under the action of axial vibro-impact load, in order to identify the frequency ranges of higher-order vibration excitation and make the analysis of the impact of such excitation on stability. The material destruction during the vibro-rotary drilling occurs via the complex effect of the vibration impulses and rotational motion. This fact significantly facilitates the drilling process of wells in hard rocks. In this case, the oscillations can occur with change of half-waves number which the mode of oscillations is changed. In this way, the task of the dynamic behavior of studying system in order to identify the frequencies of vibro-impact action at which the bending oscillations occurs with growth of half-wave number becomes interesting. To find such frequency ranges of axial impact load action on oscillating rod during rotation, the theoretical study was done by developed software, in which the technique of computer simulation of the oscillating motion of considerable length rotating rods under the action of axial periodic loads is implemented. Using this software the diagrams that show the ranges of impact frequencies in which the oscillations occurs with growth of half-wave number of rod elastic line were drawn for different parameters of the considered system. These diagrams were drawn against the background of dynamic stability fields depending on the ratio of rotation speed and impact frequency. The presented results show that for rods with different lengths there are ranges of frequencies of vibro-impact load at which the transverse oscillations occurs with growth of half-wave number. It is noted that with increasing of rotational speed for certain length rods the range of impact frequencies where the half-waves number is increased, expands. In this region, the oscillation amplitude is increases, too, with intensive growth in regions of unstable oscillations. The conclusion about the possibility of running the equipment in certain frequency ranges is made.

Analysis of the Stress–Strain State of a Flanged Connection Based on an Analytical Approach Using the Finite Element Method and Comparison with Experimental Data

Serhii Mitsyuk — 2025-10-30

This study presents a comprehensive analysis of the stress–strain state of a flanged bolted pipe connection under bending moment using the finite element method (FEM) in a spatial formulation. The investigation was conducted using three-dimensional eight-node isoparametric and quadrilateral shell finite elements in specialized software packages, as well as using the component-based finite element method. This approach allows detailed reproduction of the spatial behavior of the structure and enables the evaluation of local stresses and deformations occurring in critical areas of the connection.

Particular attention was given to the connection nodes, especially bolted joints, which determine the overall stiffness and load-bearing capacity of the system. The modeling accounted for bolt pre-tension, compression and tension zones in the flanged connection, as well as the potential eccentricity of the applied load, which can arise from both initial and acquired defects in the structure. Such a comprehensive approach enables prediction of the connection behavior under operational loads and assessment of the overall structural reliability.

The numerical modeling results were compared with experimental data and calculations performed using different software packages. The comparison showed high consistency in stress distribution and local deformations when using three-dimensional eight-node isoparametric elements, whereas the use of quadrilateral shell elements and the component-based finite element method exhibited greater deviations from experimental observations. The analysis demonstrated that the accuracy of predicting the stress–strain state largely depends on the chosen element geometry and the adequacy of modeling contact interactions between elements.

The results confirm the effectiveness of three-dimensional eight-node isoparametric finite elements for accurately predicting the stress–strain state of flanged bolted connections. The study also emphasizes the importance of considering the pipe-to-flange attachment zones during design and operation, as well as the potential of FEM-based methods for optimizing structural parameters and improving overall reliability.

Application of surrogate models based on neural networks for fast optimization of reinforced concrete frame structures

Serhii Getun — 2025-10-30

This paper presents the development, implementation, and validation of a comprehensive software pipeline for creating and applying a high-fidelity neural network-based surrogate model, designed to solve the multi-parameter optimization problem of building structures. The design optimization of cast-in-situ reinforced concrete frames is a fundamentally complex computational challenge. Its difficulty arises from the high cost of Finite Element (FE) analysis, which is the primary tool for verifying compliance with regulatory requirements, rendering traditional multi-variant searches for optimal solutions via direct enumeration impractical within realistic design timelines.

The proposed methodology involved the creation of a detailed parametric FE model of a spatial cell of a reinforced concrete frame in the Ansys environment, the automated generation of a representative dataset with 12000 unique design parameter combinations, and their subsequent engineering post-processing. A key stage of the post-processing, which ensured the physical correctness of the training data, was the calculation of the required reinforcement area for each element. This calculation was performed using a specially developed iterative algorithm that fully implements the nonlinear deformation model in accordance with the current Ukrainian State Standard DSTU B V.2.6-156:2010 (harmonized with Eurocode 2: EN 1992-1-1).

Based on this enriched dataset, a Multi-Layer Perceptron (MLP) model was trained and validated. The results of the final testing on a hold-out set demonstrated that the trained surrogate model achieved high predictive capability with a coefficient of determination R² = 0.9946. When applied to a practical optimization problem with a minimum cost criterion, the model was able to analyze 10 million candidate designs in approximately one minute – a task that would require an estimated 8 years of continuous computation using direct FE analysis. The final verification of the top 10 optimal solutions, performed by their full analysis in Ansys, showed a high convergence between predicted and actual values, with the prediction error for the objective function (cost) not exceeding 2.1%.

Thus, this work demonstrates that the proposed approach, which combines modern engineering computational models and machine learning methods, enables the creation of reliable predictive tools that accelerate the process of finding optimal structural solutions by orders of magnitude, opening new possibilities for efficient and economically justified design.

The Influence of Explosive Loads on the Strength of Shallow Underground Bomb Shelters

Oleksandr Lytvyn — 2025-10-30

This study investigates the impact of explosive loads on the strength of shallow underground bomb shelters under the detonation of a kamikaze drone warhead with a 90 kg TNT equivalent. A numerical modeling methodology is proposed, employing the finite element method in the ABAQUS software with a coupled Eulerian-Lagrangian approach. The JWL equation of state is used to describe the behavior of explosives, the Concrete Damaged Plasticity model accounts for damage and degradation in concrete, and the Johnson-Cook model simulates the nonlinear elastic-plastic properties and failure of steel. The stress-strain state of the shelter’s structures and soil base is analyzed, alongside pressure changes in the soil and the dimensions of the resulting crater. The numerical results are validated by comparison with empirical relationships derived from field tests, including those by Gould and Cooper. It is found that the shelter’s entrance groups facilitate blast wave penetration, leading to localized damage and failure of load-bearing structures, particularly near entrances. A modified shelter design is proposed, with entrance groups separated from the main structure and a damping soil backfill, significantly reducing the blast wave’s impact and preserving structural integrity. To enhance resilience, it is recommended to position entrance groups at a maximum distance from the shelter, incorporating a system of two to three airlock chambers with hermetic armored doors, aligning with Swiss standards. Future research will involve full-scale tests to calibrate model parameters and refine finite element removal algorithms for more accurate simulation of physical processes.

Analysis of stress-strain state of hydrotechnical structure in operation modes

Roman Ostapenko — 2025-10-30

In complex conditions of open sea and in areas with increased seismic activity, hydrotechnical structures must ensure stable and reliable operation throughout their entire operation. The stress-strain analysis is very important component of the design, the reconstruction and the operation of hydrotechnical structures, as it determines the reliability and the durability of their bearing elements, timely detection of critical areas can extend the operation of the object, and optimize repair costs. This is why the problem of analyzing the stress-strain state of bearing elements of hydrotechnical structures is of particular relevance in the modern engineering practice. The purpose of this analysis is to determine the maximum values of internal forces and displacements that arise in elements and joints of the hydrotechnical structure, taking into account real operating conditions. The object of this research is the hydrotechnical structure that represents the offshore stationary oil-production platform on piles, installed at the depth of 11 meters.The analysis was performed for two variants of the discrete idealized model of the platform: with the grillage foundation rigidly attached to a perfectly rigid support surface and with consideration of the elastic soil base and pile foundation. The analysis showed: the largest internal forces in both models occur in elements of upper sections of piles, spatial column trusses, and connections of columns with the superstructure;the localization of the largest displacements in both models occurs in nodes of the flambeau console and the communication mast, among nodes of main bearing structures – in nodes of the superstructure; in elements of the «rigid» model, the decrease in bending and torsional moments, shear forces, and the variable nature of the longitudinal force are observed compared to the corresponding elements of the «flexible» model;taking into account the foundation flexibility affects the stress-strain state of the structure significantly.

Research of the deformation patterns of existing structures near excavations using the finite element method

Liudmyla Bondareva — 2025-10-30

The article discusses a number of common issues related to modelling the system «base - pit enclosure - existing building» using the finite element method (FEM) and investigates the impact of the pit dimensions on the deformation of the existing building. The first part of the article is focused on the aspects related to the determinations of the finite element model (FEM), its discretisation, as well as the contact interaction of structures with the soil massif and their impact on the accuracy of calculations.

The investigation of the effect on the stress-strain state of the foundation and structures of the existing building revealed the sensitivity of the Mohr–Coulombmodel to the vertical dimensions of the model, with an error of up to 47% in additional displacements when its dimensions in depth change by 2.5 times. Using of a model with hardening soil, which allows for the change in stiffness with depth, showed a reduction in error of up to 4%, but determining the input parameters for these models is a non-trivial task and requires not only compression and triaxial tests, but also the competence of a geotechnical engineer. It is emphasized that the introduction of contact elements is mandatory in the modelling of deep structures, and the weakening of the contact between the structure and clay soil with a strength coefficient to R_inter=0.6, according to the results of calculations, showed an increase in displacements by a quarter and a quantitative change in bending moments in the retaining wall.

In solving the experimental tasks, it was found that additional settlements of theexisting building foundation depend on the local stiffness of the pit enclosure, and the non-uniformity of deformations develops along the wall near the pit, which must be taken into account during monitoring. The investigation has shown that the location of the pit at a distance greater than its depth in dispersed soils significantly reduces the settlement of the building due to the exclusion of additional pressure within the collapse prism. Additional stresses of up to 250 kPa under the footings of the foundations of an existing building, in the conditions of excavation of a 6 m deep pit, cause the soil to work mainly within the limits of elastic deformations, but when this value is exceeded, a nonlinear increase in additional settlements is observed due to the development of plastic deformations.

Analytical solution of the boundary value problem for Euler-Bernoullie beam using Green functions

Nataliia Bondarenko — 2025-10-30

Analysis of the dynamic behavior of beams is a fundamental task in the construction, transport and mechanical engineering industries, as it plays a key role in ensuring the safety, reliability and durability of engineering structures. The paper investigates the dynamic response of a simply supported Euler-Bernoulli beam, which is simultaneously subjected to a concentrated force and a moment load. Unlike most previous studies, where these factors were considered separately, their combined effect is taken into account here. To solve the problem, the Green's function method was used, which provides an analytical solution in closed form. This approach has a number of significant advantages: it allows you to avoid additional determination of eigenvalues and eigenfunctions, which are required in the series decomposition method, and is also a universal tool for analyzing various types of loads. Since the Green's function describes the response of a beam to a localized disturbance, any external load, represented as an integral of Dirac delta functions, can be taken into account through an integral convolution transformation. In particular, the concentrated force is modeled by the Dirac delta function, and the action of the concentrated moment is described by its first derivative. As a result, an analytical solution of the Euler-Bernoulli boundary value problem in a closed form is obtained, which allows not only to determine the response of the beam, but also to study the behavior of the beam under different load parameters. The constructed graphs illustrate the influence of different values of loads on the shape and nature of the structure. The obtained analytical solution can serve as a reference model for testing numerical methods, be used in structural optimization problems, and also become a basis for further research of more complex systems with different fastening schemes and combined loads.

The influence of structural defects on the dynamic characteristics of layered conical shell structures

Kostiantyn Kotenko — 2025-10-30

The problem of dynamic deformation of a three-layer conical shell with rigidly clamped ends under the action of an internal distributed load was considered. The theoretical study of transient dynamic processes of three-layer conical shell structures with discrete-symmetrical rib-reinforced aggregate in the presence of annular discontinuities in the reinforcing ribs of such structures has been carried out. Finite element modeling has been performed and numerical calculations of normal strains and von Mises stresses of the load-bearing layers of the structure, determining its stress-strain state, have been carried out.According to the Hamilton-Ostrogradsky variational principle, the equation of motion of a three-layer conical shell with discrete-inhomogeneous aggregate has been obtained. The stress-strain state of three-layer structures under axisymmetric internal impulse loading has been investigated. The results of the magnitude of the first natural frequency of the considered structures are presented.The numerical results obtained by the finite element method made it possible to determine the significance of the influence of defects in the form of circular discontinuities on the characteristics of the stress-strain state of three-layer conical shells in the presence and absence of interlayer filler.Calculations of the values of normal strains and von Mises stresses of the inner layer of the three-layer conical structure with rigid clamping of its edges in the presence of a break in the fifth reinforcing rib showed a change in the middle surface between the fourth and fifth ribs. And in the presence of an interlayer filler, the values of these characteristics turned out to be practically the same.The calculated value of the first natural frequency of the considered three-layer structures in the presence of a defect in the form of a break in the fifth reinforcing rib almost does not change.

Theoretical and experimental principles of designing sound insulation of buildings and structure

Nataliia Burdeina — 2025-10-30

The principles of designing sound insulation of buildings and structures using materials of different physical characteristics are developed. The possibilities of simplifying sound insulation calculations for small values of the phase velocities of bending waves in the surface material are shown. It is shown that such a condition corresponds to small values of sound frequencies compared to the critical frequency of the surface. The limits of the acceptable error of calculations are determined, taking into account mainly resonant and inertial sound absorption. These limits roughly correspond to the sound frequencies f < 0,5f_c, 0,5f_c< f < 1,2f_c and f > 1,2f_c, f_c being the critical surface frequency of these mass and dimensional parameters. The mathematical functions for calculating the sound insulation of surfaces made of soft materials are obtained. The values of the response functions of surfaces of different sizes are determined. It is shown that for frequencies above 300–400 Hz, the response function approaches unity and can be ignored. This conclusion is confirmed by experimental data, which have an acceptable agreement with the calculations. This greatly simplifies the practical design of soundproof structures. The principles of designing a two-layer structure to improve sound insulation are determined. It was found that sound insulation increases with an increase in the gap between the surfaces. However, at distances greater than 7-8·10^-2 m, there is no increase in sound insulation, so an increase in the overall dimensions of soundproof structures is impractical.

Parametric optimization of the stability and weight of a minimal surface shell taking into account geometric nonlinearity under thermomechanical loading

Hryhorii Ivanchenko — 2025-10-30

Optimal design plays an important role in the approach to and formation of building structures. This stage of structural calculation has been little studied and is virtually unused by practicing engineers in the field of mechanical resistance and stability.

The active development of optimal design began in the mid-20th century with the development of computers. The first works were performed on proprietary software in the Fortran language. Over more than half a century, computers have been modernized into PCs, and software complexes such as Femap and Ansys have been created, which include sections on optimal design. For the optimal design of fairly unique structures, it is not enough to have a basic functional set in these calculation complexes, so for interesting target functions such as stability and weight, it is necessary to add this part to the optimization functionality.

The object of study is thin-walled shells of minimal surfaces. The essence of these spatial structures lies in the uniqueness of their surface, which has been optimized using the parameter continuation method based on the defined contour and height of the future shell of the minimal surface. After integration, the optimal shape for the future structure is derived, which has a minimum area and minimum internal forces, which are compensated by the geometric shape of the thin-walled shell of the minimal surface.

Optimal design in construction and applied mechanics is divided into four types. The first type is shape optimization. The second type is parametric optimization. The third type is topological optimization. The fourth type is optimization of physical and mechanical characteristics.

To study multi-criteria parametric optimization of a minimum surface shell, taking into account geometric nonlinearity, a special additional optimizer module created by the authors is used, which is linked to the Femap with Nastran calculation complex [12].

This scientific article reveals the essence of four types of optimal design and an approach to the optimal design scheme. A numerical study of multi-criteria parametric optimization of the stability and weight of a minimal surface shell with a square plan consisting of two straight lines and two semicircles was performed. The thickness of the shell after optimization calculation ranges from 40 to 1 mm under thermo-mechanical loading. A graph of the target functions of weight and stability loss coefficient λ has been constructed. The weight on the target function graph decreased from 31 tons to 25.5 tons, which is 17.75% in percentage terms, while the stability loss coefficient decreased from 2.12 to 1.08, which means the maximum use of structural material in this optimization calculation.

Сritical analysis of analytical and numerical models of bond between reinforcement and concrete

Ihor Yakovenko — 2025-10-30

This paper presents a comprehensive critical analysis of existing approaches to modeling the bond between reinforcement and concrete, which is a fundamental factor in ensuring the reliability and durability of reinforced concrete structures. The relevance of this research is amplified in the context of the current challenges posed by the full-scale war in Ukraine, which demands accurate prediction of the behavior of protective structures under dynamic, impact, and blast loadings.

The key research areas have been systematized and analyzed: experimental methods, analytical models, and numerical simulations. The limitations of classical experimental methods, such as pull-out tests and beam-end tests, are reviewed, and the advantages of modern monitoring technologies are highlighted. These include distributed fiber optic sensing (DFOS) for quasi-continuous measurement of reinforcement strains and digital image correlation (DIC) for analyzing crack kinematics, both of which provide detailed data on local bond behavior.

A critical review of analytical bond-slip models is conducted, ranging from semi-empirical relationships like the BPE model to more theoretically grounded approaches based on the thick-walled cylinder theory and the fictitious crack model. It is demonstrated that due to their dependence on specific experimental conditions and significant data scatter, these models often lack universal applicability.

Particular attention is given to the classification and analysis of numerical models based on their level of detail. Macroscopic models, from simplified (SDOF, perfect bond model) to advanced approaches (layered section model with equivalent stiffness, models based on systems of differential equations), are evaluated in terms of computational efficiency and accuracy in accounting for the slip effect. Mesoscopic approaches that model reinforcement and concrete as separate bodies are discussed in detail, including models with spring and cohesive zone elements (CZM), frictional-cohesive zone models (FCZM), contact algorithms (1D Slide Line), and lattice models. The advantages and disadvantages of each method, from physical justification to computational complexity, are highlighted. Furthermore, the prospects of applying machine learning methods (e.g., NARX, SSA-ELM) for the rapid and accurate prediction of failure modes and bond-slip relationships are considered.

The paper concludes that accounting for the bond-slip effect is critically important for the adequate modeling of the behavior of reinforced concrete structures, especially after the reinforcement reaches its yield point. The choice of a model should be based on a balance between the required accuracy and available resources. Finally, promising directions for future research are formulated, aimed at creating universal and computationally efficient numerical models.

Research, assessment and increase in the strength of steels and economic efficiency of the use of innovative materials in construction

Valerii Makarenko — 2025-10-30

Systematic and comprehensive studies of micromodified steels (seven grades) alloyed with vanadium, chromium, cerium, nickel, molybdenum, niobium were carried out, from which reinforcing bars with a diameter of 22 mm were manufactured on a rolling mill. After that, the bars were subjected to heat treatment to obtain various structures, in particular, ferrite-pearlitic, pearlitic, structures of incomplete austenite transformation (bainite transformation) - structures of sorbite and trostite, as well as martensite. After that, samples were prepared from the reinforcing bars for testing fatigue strength (fatigue), static mechanical properties {strength limit σВ , MPa , yield strength σТ , MPa , relative elongation – δ (%), transverse narrowing – ψ (%)}, as well as criteria of modern fracture mechanics {К1С, MPa˖m1/2, δC, mm, RMC , MPa}. In addition, corrosion rate indicators were also determined in corrosion-aggressive environments containing chloride ions, СО2, sulfuric acid anions, as well as in bacterial model environments with bacteria of the SVB, GTB and ZB types.

Based on the use of innovative steels, technical re-equipment of energy transport engineering and the hydraulic engineering industry is possible. The resource of such structures for various purposes increases from 50 to 100% compared to standard ones. Therefore, it is necessary to continue work on improving the technologies for obtaining such high-quality materials on a metal basis in order to improve the complex of their properties. The strategy for such a breakthrough of powder metallurgy in the economy should be based on the development of development priorities and the consistent implementation of short-term target programs at the national and regional levels, as well as the development of a long-term comprehensive program at the national level and bringing the work to practical implementation. Therefore, it is also necessary to significantly expand the funding of this area.

Study of the performance parameters of sprayed concrete works in the restoration and strengthening of infrastructure facilities

Vitaliia Harkusha — 2025-10-30

The substantiation of the parameters of sprayed concrete works during the restoration, repair and strengthening of infrastructure facilities of various purposes is presented. A study of the properties of raw materials and dry building mixtures based on cement, mineral fillers and additives was carried out in accordance with the current regulatory documents of Ukraine. A number of studies of multi-component building compositions from the point of view of their rheological and physical and mechanical properties of the finished coating have been conducted. The ratio of raw components and curing accelerator additives was determined. Two types of curing accelerator additives are recommended for use. Recommendations are given for the amount of each of the recommended types of curing accelerators relative to the mass of cement. The possibility of using the fly ash as a component of dry mortars for shotcrete works has been investigated. The most rational amount of fly ash was determined, and changes in the bulk mass and density of the material in the wet state were determined for all options. Based on the obtained ratio, the possibility of introducing weak mine rocks and coal beneficiation waste into the sprayed concrete mixture as large aggregate was investigated. The most rational dosage of components that have an impact on the properties of the working mixture and the finished construction coating is presented. The main indicators of the strength of sprayed concrete mixtures using mine rocks and coal beneficiation waste have been determined. Recommendations for the rational use of the given range of raw materials and information on possible differences in their quality are given. The feasibility of rational processing of multi-tonnage waste from the mining and energy industries as a diverse and cheap raw material base for construction has been proven. The main parameters of the technology for the execution of sprayed concrete works using construction mixtures based on cement, mineral fillers and additives and their possible combination with similar polymer materials have been determined.

The specifics of implementing an integrated approach while teaching the course “Structural Mechanics” at higher education institutions

Iryna Ilchenko — 2025-10-30

The article is dedicated to the specific aspects of teaching the integrated course «Structural Mechanics» in technical educational institutions. The importance of identifying modern methods, tools, auxiliary instruments, and contemporary educational technologies is emphasized, as their implementation in the educational process can ensure the achievement of the expected learning outcomes. Particular attention is given to the structure of learning materials aimed at improving the quality of organization and implementation of practical classes in the subjects. The course «Structural Mechanics» holds a key position within the cycle of general technical training, as it integrates several engineering subjects (theoretical mechanics, strength of materials, computer technologies etc.) and occupies the largest share of academic time within its cycle, encompasses foundational knowledge of theory of buildings and structures, relies on fundamental subjects, and provides a basis for studying specialized subjects. The quality of teaching this course and its special status within the system of general technical education are crucial for the professional training of future specialists. Therefore, the article highlights the features of teaching this course, which is characterized by practical orientation, integration of theory and practice, and the use of various tools, modern technologies, interactive simulations, specialized software products, digital resources, and more. Given the specific nature of the course, a key condition for the successful acquisition of core knowledge by students is the identification and use of modern auxiliary tools that facilitate the rational assimilation of practical material. The prospects of applying digital technologies and computer-aided design systems are also essential in preparing students for real-world engineering tasks. The study outlines the advantages and priorities of implementing integrated learning in higher education institutions. Additionally, an overview of international experience is provided. The authors’ experience in delivering lectures, conducting practical and laboratory classes in Structural Mechanics enabled them to conduct their own analysis of certain teaching features of the discipline and to present an overview of learning tools used by the Department of Strength of Materials and Mechanical Engineering at the National Transport University (NTU).

Impact of stress–strain state evaluation method in raft foundation analysis

Ostap Kashoida — 2025-10-30

Accurate determination of contact stresses in the soil base is essential for the reliable design of raft foundations. Traditional analytical methods, such as the corner points method, offer simplicity but are based on simplified assumptions, which may lead to errors under complex engineering conditions. Numerical finite element modeling provides a more realistic representation of soil behavior but requires considerable resources. Comparing these approaches is relevant for defining their applicability limits and improving calculation accuracy.

The article presents a comparison of stresses in a soil base under a rectangular raft foundation obtained by the analytical corner points method and finite element numerical modeling for elastic–linear and elastic–plastic soil model with the Mohr–Coulomb failure criterion. The aim of the study is to refine the influence coefficients used in the corner points method, to identify quantitative and qualitative differences between the approaches, and to outline the boundaries of their correct application. The comparison revealed significant discrepancies not only in the values of contact stresses but also in the shape of their distribution surface. Preliminary discrepancy coefficients for the studied case have been determined.

The results confirm that even for relatively simple geometry and loading conditions, discrepancies between the methods can have a substantial impact on the assessment of bearing capacity and the uniformity of soil foundation performance. The proposed approach lays the groundwork for further comprehensive studies of the influence of geometric parameters of the foundation, type and magnitude of loading, and the physical–mechanical properties of the soil on the consistency of results obtained from analytical and numerical calculation methods.

Spatial and temporal evolution of one-dimensional nonlinear deformation waves in cylindrical shells

Yurii Chovniuk — 2025-10-30

In this paper, the physical-mechanical and mathematical models designed to analyze nonlinear wave formations in cylindrical elastic shells are substantiated. Using the perturbation reduction method, the spatial and temporal evolution of nonlinear longitudinal and longitudinal-shift waves in elastic cylindrical shells in the framework of Kirchhoff-Liave theory is investigated. It is established that in elastic cylindrical shells (in one-dimensional formulation of the problem) there exist one-dimensional solitons and nonlinear periodic waves (of the cnoidal type), which are partial solutions of the Korteweg-de Vries equation (KdV). All the main parameters of these types of waveforms are analytically found. Taking into account dissipative effects, the evolutionary Korteweg-de Vries-Bürgers equation (KDB), which is close to the integrated ones, was obtained for the longitudinal deformation component. Partial solutions of this equation in the form of kinks and waveforms, which are described by the elliptic Weierstrass function, have been found analytically (using the reduced expansion method). The analysis performed allows us to describe the spatial and temporal evolution of a weakly two-dimensional beam of nonlinear longitudinal and longitudinal-shift waves in an elastic cylindrical shell as follows. There is a fast (linear) time scale during which there exists a wave running without profile change with constant velocity.

Further, there is a slower time scale, during which the change of wave parameters due to nonlinearity, dispersion, and diffraction divergence leads to the splitting of the initial pulse into one-dimensional (or weakly two-dimensional) solitons or the formation of cnoidal (periodic) waves. The interaction of longitudinal deformation waves unstable to transverse perturbations with longitudinal-shift waves (solitons/cnoidal waves) leads to their overturning and, possibly, to their destruction. This circumstance essentially distinguishes the spatial and temporal evolution of solitons in deformed solids from hydrodynamic solitons, which collapse gradually due to natural dissipation.

An effective method of strengthening reinforced concrete structures with low shear resistance and its CAD implementation during building reconstruction

Dmytro Prusov — 2025-10-30

The proposed technology involves directly increasing the amount of shear reinforcement results in a proportional increase of the shear resistance, and the solutions available presently in the industry are typically minimally invasive and will reduce disruption to other members. Conversely for the concrete shear resistance, the use of other solutions typically results in an under-proportional increase, apart from concrete overlay, which is accompanied by its own trade-offs.

In recent years, the development and sufficient maturity of post-installed anchoring technology have led its use in applications beyond steel-to-concrete fastenings and concrete-to-concrete connections. One use in strengthening is in concrete overlay where both bonded and mechanical fasteners function to reinforce the interface between the existing and new concrete.

Another use of the bonded anchor system in strengthening is in a recently developed Hilti strengthening solution “HIT-Shear” which directly increases the resistance to shear loading of reinforcement concrete members, akin to cast-in stirrups.

Hilti’s cloud-based design software Profis Engineeringincludes a new dedicated module for assessing and strengthening concrete members deficient in shear that assists structural engineers when evaluating the resistance of existing members and strengthening them, thereby ensuring a safer and more efficient workflow, with subsequent implementation in the CAD system module.

Optimization of soil cutting process by ripper tip with dynamic cutting edge

Mykola Prystailo — 2025-10-30

The mechanical processes of interaction between the ripper tip with the dynamic cutting edge on the pneumatic accumulator and the soil massif are investigated in the paper. Rheological models of the soil are considered, describing its elastic and viscoelastic properties, as well as the regularities of deformation under the action of the working element. The movement speed of the ripper tip, the dynamics of changes in cutting force, and the formation nature of the compressed zone for different soil categories are investigated based on the combination of analytical methods and experimental tests. The results obtained allowed us to establish the influence regularities of the ripper tip parameters on power loads, energy consumption and stability of the technological process. It is shown that the ripper tip use with the dynamic cutting edge on the pneumatic accumulator contributes to the decrease in peak and average loads, the decrease in friction forces and vibration oscillations. This leads to an increase in energy efficiency, the decrease in dynamic shocks and the increase in the resource of the working element. It’s found that the maximum effect is achieved during the development of light and medium-density soils, where the greatest reduction in cutting force and the highest process stability are observed. The energy effect is less pronounced for strong soils, but the positive effect on load stabilization is preserved. The practical significance of the results obtained lies in the possibility of improving the designs of ripper tips, substantiating rational modes of their operation. It also aims at increasing the efficiency of technological processes during preparatory works in transport and industrial construction, mining and the agricultural sector.

Dynamic analysis of the simultaneous movement of the jib lifting and crane turning mechanisms

Viacheslav Loveikin — 2025-10-30

The efficiency of jib cranes largely depends on increasing their productivity when performing loading, unloading, and installation operations. The simultaneous operation of individual mechanisms increases the productivity of jib cranes. The purpose of this study is to construct a mathematical model and perform a dynamic analysis of the crane jib system during the simultaneous operation of the jib lifting and crane turning mechanisms. The presented research is based on methods for constructing discrete dynamic models of a jib crane using second-order Lagrange equations, numerical methods for solving nonlinear ordinary differential equations, which are presented in the form of a computer program, and methods for dynamic analysis of the simultaneous motion of crane mechanisms. The problem of the dynamics of simultaneous motion of the jib lifting and crane turning mechanisms is solved in this article. The crane jib system is represented by a dynamic model with four degrees of freedom, which considers the main motion of the jib lifting and crane turning mechanisms and the oscillation of the cargo on a flexible suspension. As a result of the dynamic analysis, the kinematic, dynamic, and energy characteristics of individual links of the crane jib system are determined during the simultaneous operation of the jib lifting and crane turning mechanisms. The main movement of the drive mechanisms for lifting the jib and crane turning, as well as the low-frequency spatial oscillations of the cargo on a flexible suspension, were investigated. It has been established that the dynamic motion of the mechanisms depends on the character of the change in the driving forces of the drives. Low-frequency oscillations of the cargo on a flexible suspension practically do not dampen and continue throughout the entire movement cycle.

To improve the dynamics of simultaneous motion of mechanisms and minimise oscillatory processes of the jib system links, it is recommended to select modes of smooth change of driving forces of drives in transition processes (starting, braking), which ensure the desired movement of executive mechanisms and lead to a reduction in loads.

Stress-strain state of a damaged railway overpass and its strengthening with carbon fiber reinforced plastic materials

Tetiana Chyrva — 2025-10-30

The research addresses the problem of strengthening damaged reinforced concrete structures of transportation facilities using modern composite materials based on carbon fiber (CFRP). Using the railway overpass of the Zaporizhzhia Ferroalloy Plant as an example, a detailed investigation of the stress-strain state of structural elements before and after damage occurrence was conducted using the finite element method in the ANSYS software environment. It was revealed that failure in the form of rupture of two lower rows of longitudinal reinforcement causes an increase in beam deflection by 32.9%, tensile stresses in concrete by 33.3%, and stresses in reinforcement by 32.7%.

A strengthening methodology was developed through bonding unidirectional carbon fiber reinforced plastic with a thickness of 1 mm, elastic modulus of 121,000 MPa, and tensile strength of 2,231 MPa to the bottom flange of the beam. The obtained results of numerical modeling of the strengthened structure demonstrate high efficiency of the proposed approach: the deflection of the strengthened beam exceeds the parameters for the undamaged structure by only 13.0%, while stresses in the reinforcement increase by only 4.2%. Maximum stresses in the carbon fiber reinforced plastic do not reach 5% of its ultimate strength, indicating significant load-carrying capacity reserves of the strengthening system and justifying the use of composite materials for restoring the serviceability of damaged reinforced concrete elements.

The conducted review of international experience in the use of FRP composites in the construction industry revealed advantages of strengthened structures compared to traditional restoration methods: efficient work execution, minimal dead load, high strength characteristics, resistance to corrosion and aggressive environments, preservation of element dimensions, and rapid restoration of operational characteristics. The research substantiates the feasibility of applying carbon fiber composite materials for reconstruction and strengthening of transportation infrastructure facilities in Ukraine under conditions of limited financial resources and the need to reduce construction work duration.

The Effect of the Continuous-Discrete Soil Base Model on the Stress-Strain State of the Large-Sized Pile-Raft Foundation of a High-Rise Building

Oleksandr Samorodov — 2025-10-30

The paper firstly reviews existing approaches to simulating soil bases for large-sized pile-raft foundations of multistory buildings and structures using up-to-date calculation software packages such as SOFiSTiK, ABAQUS, Plaxis, SCAD, LIRA and others when calculating the base-foundation-building system, and points out their shortcomings.Additionally, the paper considers the methodology for improving the soil base model for pile-raft foundations asa method for simulating the soil base of pile foundations, which is patentpending in Ukraine. The main part of the paper is concerned with investigating the effect of the improved linearly deformed (elastic) combined (continuous-discrete) “Layer-Winkler” subsoil model to calculate a large-sized pile-raft foundation of a high-rise building.The combined “Layer-Winkler” model combines the parameters and properties of the two most well-known and widely used models in design calculation such as the model of the continuous layer of finite distribution capability (the “Layer” model) and the discrete model of no distribution capability with vertical braces of finite stiffness under the raft foundation structure (known as the “Winkler” model). The obtained numerical results, their analysis and comparison indicate that the use of the combined “Layer-Winkler” model reduces the reaction forces in the corner and peripheral piles of the foundation compared to the “Layer” model, while the reaction forces in the middle piles appear to be greater than those resulting from the use of the “Winkler” model of no distribution capability.As a result, when using the combined “Layer-Winkler” model, the raft foundation structure takes up the smallest total bending moment in accordance with the proposed method for assessing the stress state of the foundation.Therefore, unlike the conventional “Layer” model, the use of the combined “Layer-Winkler” model in the calculation of large-sized pile-raft foundations may be of practical importance in the rational design of this type of foundation, as reinforcement can be significantly reduced with an appropriate field-based experimental justification.At the current stage of theoretical and experimental research, the improved combined “Layer-Winkler” model(with the corresponding simulation method) is recommended to be used as an alternative soil base model in the calculation of large-sized pile-raft foundations for buildings and structures, which allows for its implementation in the domestic calculation software packages such as SCAD and LIRA.

Experimental study of foam concrete as a fire protection material and a material capable of absorbing γ-radiation

Roman Veselivskyi — 2025-10-30

Actuality. An analysis of accidents at nuclear power plants and power plants has shown that these incidents are accompanied by high temperatures and high-intensity radiation. In an emergency situation, the technological equipment of the protective shell must ensure the localisation of all radioactive materials released during the accident within its volume, protect the environment from ionising radiation, and counteract high temperature effects. Today, there are various forms and design solutions for protective shells, each of which has its own advantages and disadvantages. Therefore, when choosing protective shell designs, it is necessary to take into account the conditions of construction, operation, and possible emergency impacts. Modern construction encourages the use of new materials such as foam concrete (aerated concrete), which will reduce material consumption and construction costs, as well as improve thermal and ionising protection. Purpose. The main objective of the article is to study the fire protection effectiveness of foam concrete and its γ-absorbing capacity. Main results. Two methods were developed for the research: to determine the fire-retardant properties of foam concrete and to determine the effectiveness of foam concrete in absorbing γ-radiation. It has been established that the fire resistance of foam concrete for steel structures ranges from 130 to 150 minutes for slab thicknesses from 20 mm to 60 mm, accordingly. Studies of the absorption of γ-radiation by foam concrete have shown that foam concrete with a bulk weight of 1200 kg/m³ has a γ-radiation attenuation coefficient similar to that of fine-grained concrete with graphite (with a bulk weight of 1800 kg/m³), which indicates its significant effectiveness (1,5 times). Conclusions. A series of experimental studies has shown that foam concrete is an effective fire-retardant material and can be used for fire protection of steel building structures. It was found that with a foam concrete thickness of 20-60 mm, the fire resistance limit of a steel structure in terms of load-bearing capacity is 130-150 minutes, and in terms of thermal insulation capacity – 80-150 minutes. The effectiveness of using foam concrete to protect technological equipment and its ability to absorb γ-radiation has been substantiated.

Experience of Field Tests of Window Units of Various Composition for Shock Wave Resistance

Mykhailo Orlenko — 2025-10-30

This paper reviews the experience of a series of practical tests of samples of translucent structures for resistance to shock wave. The tests were conducted in 2023-2024 at a testing range near Kyiv in the territory of an abandoned industrial building. The samples had the same size, but differed in the material and brand of profiles (PVC and aluminum), the presence of additional reinforcement, the type and thickness of glass sheets, and the brand of fittings. Most consisted of one blind section and one sash, separated by a central rack, except for the last tests, where samples of other configurations were tested. According to the test results, some samples were assigned shock wave resistance classes EXR1 or EXR2, which is confirmed by the test protocols.

The tests were accompanied by photos of samples before and after the test and measurements of conditions using pressure free-field (side-on) sensor and reflected target sensor near the specimen.

The statistics of the test results show that the use of laminated glass is a necessary prerequisite for ensuring the resistance class and preventing the occurrence of secondary impact elements. At the same time, the use of protective films and tempered glass does not provide the expected advantages.

Windows with PVC profiles with a thickness of 82 mm are able to provide the resistance class EXR1, but at higher loads they lead to the destruction of the profiles and the penetration of fragments into the room. To ensure the EXR2 class, it is necessary to use aluminum profiles or PVC with reinforcement. In this case, a sample of a window with two sashes was destroyed under similar conditions. Thus, the result also depends not only on the composition, but also on the configuration of the window - the ratio of blind sections and sashes in it. The study of this factor using digital modeling methods and full-scale tests is planned in the authors' subsequent works.

The study is important as a direction for reducing harm to the life and health of the population of countries have suffered damage due to military actions.

The application of the modified method of sections for calculations of curved flat rods

Valerii Sokov — 2025-10-30

In the paper there is presented the application of the modified method of sections (MMS) for calculation of flat curved rods approximated by the sequence of straight rods under the plain deforming in frames of the linear Bernoulli-Euler’s theory. It allows to simplify calculations of curved rods without using of the apparatus of the differential geometry. The orthogonal cross section is symmetrical relatively the plane of deformation to avoid warping. In the work there are presented the relations for transformation of defined internal force and kinematical parameters when there’s transition of the boundary of joining of two angle joint straight rods on plane. These relations are used for calculations by MMS of aggregate sequence of straight rods which approximate a curved rod. For checkups there was made the calculation of the quadrant circular arc using relations of the differential geometry and the calculation for the broken-line rod consisting of the aggregate sequence of five identical straight rods which approximate the quadrant circular arc for the same loadings. The kinematical parameters obtained in the particular point for the both calculations distinguish between themselves not more than for 1.5% which allows accurately to reveal the static redundancy using MMS. The areas of curvilinear diagrams of all internal forces equal to appropriate areas of diagrams obtained by MMS for the broken rod which proofs the conservation of the energy balance using MMS. The appropriate values of internal bending moments obtained on curvilinear diagrams and obtained by MMS for the broken rod are identical which enables to pass accurately the strength estimation or design using bending moments. The diagrams of axial and shear forces obtained by MMS for the broken rod are stepped where values of internal forces at each step approximately equal the mean values obtained from appropriate segments of the curvilinear diagram.

Genesis of the development of hypotheses, theories and experimental research on the strength and destruction of building materials and structures

Mykola Tereshchuk — 2025-10-30

For the first time, a historical overview of the development of hypotheses and theories on the nature and mechanisms of destruction of brittle and plastic materials has been conducted. The contribution of Ukrainian experimental scientists and theorists, in particular B. E. Paton, G. S. Pysarenko, V. V. Panasyuk, and others, to the development of modern mechanics of deformed bodies is shown. The main causes of destruction of machine parts and elements of building structures are physical and chemical factors. In order to identify mechanical factors, the existing force fields of the structure are studied, the maximum stresses near the concentrators and the center of destruction are established, its macro- and microanalysis is performed, residual stresses and deformations are determined, and defects such as cracks, brittle zones, dislocations, etc. are found. To define chemical factors, the surface in the failure zone is analyzed, the nature of the chemical reaction at the end of the corrosion crack is determined, the causes of local changes in the material structure are diagnosed, etc. To eliminate or reduce the risk of failure, it is necessary to modify the design as required, replace the material, eliminate external causes, and perform additional technological operations, such as applying protective coatings. There are various theories of destruction. The presence of structural inclusions such as grains, microcracks, and dislocations in virtually all materials leads to their strength becoming significantly lower than theoretical. At the same time, the greater the defectiveness of the structural material (the deviation of its structure from the ideal), the lower the strength under other identical conditions. If destruction occurs under the action of repeated or cyclic loading, it is called fatigue destruction. This phenomenon was discovered by W. Rankine and A. Weller over 100 years ago. Today, fatigue mechanics is the basis for the design and calculation of most dynamically stressed structures and machines. This is due to increased operational reliability, reduced weight, and improved economic performance of structures. Thanks to the work of scientists from Ukraine and Western European countries, a variety of testing machines have been created in recent years, which have been put into practice in various countries (Germany, France, Belgium, Great Britain, etc.), based on the work of M. M. Davydenko, I. A. Odin, S. V. Serenesen, G. S. Pysarenko, E. O. Paton, V. I. Trufyakov, Ya. B. Friedman, O. M. Guz, V. I. Panasyuk, S. V. Malashenko, and others, appropriate modern testing machines, measuring instruments, and devices have been created, and relevant research has been conducted. This allowed the fundamental knowledge obtained about the mechanical properties of materials to take one of the leading places in world science. Domestic scientists studied the strength and creep characteristics of many materials depending on different deformation rates and temperatures, and established the presence of residual stresses and other factors. It should also be noted that in recent years, new methods of experimental research have come into practice, such as electro-tensometric, polarization-optical, membrane analogy, lacquer coatings, ultrasonic, X-ray, laser, and others. Further technical progress is impossible without the creation of new methods of experimental research of the mechanical properties of materials.