Strength of Materials and Theory of Structures

Comparative analysis of the stress state of a bolted joint based on an analytical approach using SFEM and experimental results

2025-05-05T15:24:00+03:00

The main types of connections are welded, riveted, and bolted. Bolted connections have many advantages over other types of connections, namely: high manufacturability, reliability, and speed of installation work, so we will further consider various approaches to modeling bolted connections.

One of the most crucial and important points in the design of a structure is the calculation of the connection elements of the components, since the reliability of the structure as a whole depends on the accuracy and reliability of the calculation results.

For a wide range of tasks, the finite element method (FEM) is often used in calculations; this numerical method has proven to be one of the most common and versatile. When calculating elements of assemblies such as bolts, rivets, etc., simplified design schemes are usually used, but this approach does not allow for a complete analysis of the distribution of forces. For a complete analysis, it is necessary to create detailed spatial models, which in turn leads to the need to solve systems of high-order equations. To increase the efficiency of the FEM, it is necessary to combine it with the method of distribution of unknowns, as a result, the resulting approach is called the semi-analytical finite element method (SFEM).

The bolt, bolt head, and nut were modeled by spatial elements, and the bolt tension was modeled by a load from uniform heating.

The obtained results of the stress-strain state using the finite element method and the semi-analytical finite element method allow us to conclude that there is a slight difference in the stress distribution in the spatial formulation of the FEM and SFEM with experimental data and allowed us to identify a rational approach to modeling bolt tension.

Tuning of vibro-impact nonlinear energy sinks under changing structural parameters. Part 1

2025-05-05T16:25:41+03:00

This paper studies the efficiency of vibro-impact nonlinear energy sink, that is, vibro-impact damper, in mitigating the primary structure vibrations, i.e., in reducing its total mechanical energy. The primary structure is a linear oscillator that forms a strongly nonlinear vibro-impact system when a vibro-impact damper is coupled to it. When the damper is tuned to a certain value of a structural parameter, in particular, the primary structure damping, its sufficiently high efficiency is maintained in some this parameter range and deteriorates in a wider range. Then tuning the damper design to the appropriate value of the primary structure damping allows to significantly improve its efficiency. Optimization procedures are carried out by the tools of standard software Matlab. However, the optimized parameters of the low-mass damper acquire unusual “strange” values, namely, very large clearance and small damping coefficient. In addition, the areas of bilateral damper impacts both directly on the primary structure and on the obstacle are narrow; the areas of unilateral direct damper impacts on the primary structure are wider. These phenomena, observed in our previous works for one particular value of the primary structure damping, persist for its different values. It is also shown how a VI NES attachment can replace the additional PS damping. The system dynamics with the single-sided vibro-impact nonlinear energy sink coupled to the primary structure is always complex; the amplitude-modulated responses are often occur. The characteristics of such a regime are shown, namely, the time history of displacements with upper envelope, left and right contact forces, the phase portraits with Poincaré maps, and Fourier spectra. Modeling the impact using the nonlinear Hertz’s contact force in accordance with his quasi-static theory allows us to calculate the impact contact forces, take into account and optimize the characteristics of the colliding surfaces.

Qualitative figures and tables accompany a large volume of numerical experiments.

Influence shape imperfections on stochastic stability of elastic shell parametric vibrations

2025-05-05T16:48:08+03:00

Mathematical modeling of stochastic parametric oscillations of an elastic cylindrical tank shell with real and modelled shape imperfections under the action of a random axial load was performed. Finite element models of the imperfect shell were generated in the NASTRAN software. A functional approach was applied to the formation of a reduced model of parametric shell oscillations in the form of a system of differential equations of the first Markov approximation with respect to moment functions of the second order, taking into account specific values of the constant components of the parametric load. The stochastic component of the parametric load was given in the form of a delta-correlated random load. The members of the stiffness matrix of the reduced mathematical model are the squares of the frequencies of the natural oscillations of the perfect shell, obtained by the Lanczos method. The members of the reduced matrix of the geometric stiffness of the shell without and with shape imperfections were obtained using a two-stage calculation. At the first stage, the nonlinear statics problem under the action of the constant component of the parametric load was solved by the Newton-Raphson method. At the second stage, a modal analysis was performed using the Lanczos method taking into account the pre-stressed state of the shell. The influence of the stochastic component of the parametric load on the dynamic behavior of the shell was investigated using the fourth-order Runge-Kutta method. Response realizations and phase trajectories of the shell with real and simulated imperfections at a given frequency of the hidden periodicity of the stochastic load, damping coefficient, and correlation parameter were obtained. The stochastic stability of parametric oscillations of an imperfect shell was investigated using generalized Hill determinants. The stochastic stability problem was reduced to determining the characteristic indices of a linear autonomous system. The influence of real and simulated imperfections of the shell shape on the stability of parametric oscillations at different values of the constant and stochastic components of the axial load was estimated.

Investigation of nonlinear deformation, buckling and natural vibrations of elastic shells under thermomechanical loads using a universal three-dimensional finite element

2025-05-06T15:38:38+03:00

The article presents the fundamentals and features of the method for solving static problems of nonlinear deformation, buckling, post-buckling behavior and natural vibrations of a wide class of thin elastic inhomogeneous shells of various shapes and structures under the action of thermomechanical loads. The method is developed from the unified positions of the three-dimensional geometrically nonlinear theory of thermoelasticity based on the finite element method. A universal 3D finite element is used. The distinctive feature of the finite element is the presence of its additional variable parameters. This approach allowed for the use of a single universal finite element in all sections when modeling shells with different inhomogeneities. On this basis, a unified model has been developed that takes into account the geometric features of the structural elements and the multilayer structure of a material of the thin shells (constant or piecewise variable thickness, ribs, cover plates, channels, holes, sharp bends in the middle surface, layers, etc.). The algorithm for solving the shell buckling problem finds the branching points and allows obtaining adjacent deformation modes in their neighborhood. A method for the integrated solution of problems of stability and natural vibrations of shells under the action of thermomechanical loads has been developed. Based on this approach, the loss of stability is determined by static and dynamic criteria. The efficiency of the method is demonstrated by a numerical example. The method is used to identify the branching point of the solution on the load-deflection curve for panels of different curvatures.

Experimental hydropneum tests of pipelines made of monolithic and composite pipes in polygon (natural) conditions

2025-05-05T17:34:45+03:00

The expediency of reducing the parallellaid the reads in one direction, the need to increase the economic indicators of gas transportation caused a rapid increase in the diameter of the used pipes and the value of the working pressure; the current diameter of the used pipes is 1420 mm at a pressure of about 7.5-8.0 MPa, as shown by the results of experimental studies, including field tests, close to the optimal. All this contributed to the fact that in recent years much attention has been paid to the development of new pipe designs, in particular the use of multilayer pipes in the manufacture of pipelines using current automated production technology. Multilayer pipes satisfactorily resist the spread of brittle and ductile fractures. The fractures topped in both tested sections along the length of one pipe. At the same time, the brittle nature of the fracture at the entrance to the multilayer pipe immediately changed to ductile. Due to the fact that the transverse stiffness of multilayer pipes is much lower than the stiffness of the same pipes with a monolithic wall, the force driving viscous fracture along the gas pipeline in the section of multilayer pipes is correspondingly lower than in the section of pipes with a monolithic wall. The reduction in the force of driving destruction occurs due to a sharp decrease in the area of the pipe sides, which perceive the gas pressure and load the metal at the crack tip. Therefore, a typical scheme for stopping fracture in a gas pipeline made of multilayer pipes is the transition of a longitudinally propagating crack in to an annular one with the stopping of fracture along the boundary of multilayer and monolithic pipes. During the experiments, the operability of the pipes was also checked in the case of depressurization of the outer layer of a multilayer pipe loaded with internal gas pressure, which simulated mechanical damage to the pipe. It was found that in a four-layer pipe, a complete rupture of the outer layer does not violate its operability even with a rupture length of 700-900 mm, which is 3 times greater than the critical crack length for similar pipes with a monolithic wall. Thus, while ensuring the tightness of the inner layer, multilayer pipes provides at is factory operability of gas pipelines and situations requiring a sudden stop of the gas pipeline in the event of a through crack will be practically excluded. It should be recommended that the total number of layers in multilayer pipes beat least three. A significant increase in the number of layers in a multilayer pipe and the associated reduction in layer thickness is not recommended due to a decrease in transverse stiffness, which complicates the process of pipeline construction due to the possibility of loss of stability or breakage of pipes during installation and laying work.

Calculation of the t-shaped shank of the steam turbine rotor blade

2025-05-06T16:02:51+03:00

The broad possibilities of the developed approach [8, 9, 11, 12] are illustrated by the solution of a new practically important task related to specific design developments.

The most important load-bearing elements of the rotors of steam turbines are the blade shanks. This paper presents the calculation of the T-shaped shank, which is affected by the forces caused by the rotation of the rotor. They consist of the surface load blade distributed over the area of the root section of the blade and mass forces distributed over the volume of the shank. but along some of its central parts. This leads to an uneven distribution of contact forces along the axis along the shank. The results of the calculation allow us to draw the following conclusions that in the case of a uniform load, the determination of stresses can be carried out within the framework of a flat setting, since this leads to a relatively small (five, eight percent) error compared to the spatial setting. Taking into account the uneven nature of the load distribution along the length of the shelf allows you to significantly clarify the level of maximum stresses in comparison with a flat problem. Thus, the value of the intensity of tangential stresses increased by more than thirty percent and exceeded the yield strength of the material. The results of the calculation of the shank beyond the elastic properties of the material are presented in this work and reflect the development of the zone of plastic deformations in the plane Z^3'=0. By studying the influence of the geometric parameters of the shank, it was found that a decrease in the level of plastic deformations can be achieved by simultaneously increasingthe radiusthe gap and the width of the shelf.

Research of the design of a T-shaped node of cold-rolled profiles, the connection of which is made by a plate using a bolt connection

2025-05-06T16:43:10+03:00

Warehouse complexes and premises used to accommodate storage equipment, move lifting equipment and personnel require the creation of modern load-bearing structures of mezzanines and platforms. Such structures must simultaneously meet the requirements of low metal consumption, sufficient strength, stability and withstand a large number of cycles of application and removal of loads. The nodes that connect the beams of such structures are designed as hinged. They allow the rotation of the beams and do not transmit bending moments from one element to the wall of another. The work proposes the design of a connection node(joint) that consists of a corner of a special design that is rigidly fixed to the walls of the profiles using a bolted connection. The peculiarity of the node is that it is conditionally hinged and ensures the absence of transmission of bending moments between the elements of the node. This is achieved due to the design of the corner, which has the necessary and sufficient flexibility (rotational plasticity)to compensate for the rotation of the ends of the connected beams due to its operation within the limits of plastic deformations at the plasticity limit of the material. On the other hand, the strength of this corner should be such that the transfer of loads between the structural elements occurs without its destruction. Numerical modeling of the design of the conditional hinged node was performed and the values of stresses in the elements included in the node were obtained. It has been confirmed that under working loads in all elements of the joint, except for the corner, the stresses do not exceed the plastic strain limit of the materials from which they are made, equivalent plastic deformations do not exceed the limit values (5%). The corner structure operates within the limits of plastic deformations and plays the role of a conventional hinge assembly. In certain zones of the corner structure, under working loads, stresses arise that exceed the limits of plastic strain limit of the material from which it is made. The destruction of the assembly does not occur. Such studies allow us to obtain detailed information about the magnitude of the stresses in all elements of the structures and to predict their behavior in real operating conditions, which ultimately provides the opportunity to develop modern structures with low metal consumption that are capable of operating throughout the entire service life without premature failure.

Review of mathematical models and methods to research the explosive loads propagation in continuous environments

2025-05-06T17:24:17+03:00

Design calculations in building and structure engineering are inextricably linked to the analysis of strength, stability, and the stress-strain state (SSS) of structural elements. Today, the importance of assessing structures under special loads and impacts has significantly increased. However, such analyses are often complicated due to the underdevelopment of the mathematical framework and insufficient understanding of the nature and propagation characteristics of such loads. As a result, the creation of adequate computational models becomes nearly impossible. A distinct category among special load analyses is dynamic assessment under seismic, impulsive, and impact loads, including explosive effects.

The current state of the problem of constructing blast loads waves propagation mathematical models and approaches to study the dynamic response of structures and buildings under their influence is considered. The classification of different intensity dynamic processes in relation to the deformation rate is given and recommendations for choosing the most effective methods for integrating the computational equations of motion in the time coordinate are given. A review of works on the study of dynamic waves in anisotropic and isotropic environments and soil masses is conducted.

The aim of this series of studies is to develop new effective models, methods, and algorithms for analyzing the propagation of shock stress waves in continuous media using the finite element method (FEM). Based on this, the goal is to create numerical tools capable of providing rapid assessments of the impact of extreme transient loads of impulsive or explosive nature on aboveground and underground civil and engineering structures.

Dynamics of a three-layer hemispherical shell under non-stationary loading

2025-05-07T12:09:35+03:00

Dynamic processes are decisive in calculating the behavior of layered structures. Currently, the problem of studying non-stationary dynamic processes of layered shell structures to assess their performance under dynamic loads is quite relevant.On the example of a three-layer hemispherical shell of a symmetric and asymmetric structure with a discrete-inhomogeneous filler, non-stationary dynamic processes were investigated. In the studies, the shear theory of shells and rods of S.P. Tymoshenko was applied using independent static and kinematic hypotheses for each layer and the finite element method was used to calculate the characteristics of the stress-strain state (SSS) and structural vibrations.To derive the oscillation equations of an asymmetric three-layer structure inhomogeneous in thickness, the Hamilton-Ostrogradsky variational principle of stationarity was used.A finite element model of the structure was created for numerical analysis of the dynamics of a layered hemispherical shell with a discrete rib-reinforced filler under the action of dynamic loading.The influence of the physical, mechanical and geometric parameters of the load-bearing layers on the SSS of a three-layer shell under dynamic loading was revealed. Numerical results of solving specific problems are presented.The general trend of the dynamics of all considered variants of the three-layer hemispherical shell structures was a significant response to a change in the elastic modulus of the polymer filler, the magnitude of which significantly affected the nature of the oscillation.The obtained calculation results indicate: an increase in the elastic modulus of the polymer filler by an order of magnitude significantly reduces the effect of the reinforcement action in the structure.The conducted studies show that by selecting the material of the layered package of the hemispherical structure, the thickness of its bearing layers, and the elasticity of the filler, it is possible to create a hemispherical shell structure with predicted dynamic behavior under unsteady

Damage kinetics of anisotropic materials in construction

2025-05-07T12:48:08+03:00

Anisotropic materials are widely used in modern construction and are subjected to various types of elastoplastic loads. Assessing their service life remains a relevant and pressing challenge. The study of damage kinetics in anisotropic materials holds both theoretical and practical significance, particularly in the field of residual strength assessment ‑ one of the leading research directions. The technical and economic efficiency of damage accumulation modeling under external force factors depends on the accuracy of predicting the material's damage evolution while maintaining strength and rigidity during operation.

This paper investigates the kinetics of damage accumulation in anisotropic materials under loading conditions, taking into account changes in the volume and shape of a unit-size representative element (RE), as well as the material’s physical and mechanical properties. Generalized Hooke’s laws, aligned with the symmetry axes of orthotropic materials, are analyzed, including cases where stress planes coincide or do not coincide with these symmetry axes. Theoretical and experimental studies of damage kinetics are carried out using polyvinyl chloride (PVC) samples employed in window and door profiles for residential buildings.

Over time, the operation of structures made of anisotropic materials leads to structural changes that initiate, propagate, and accumulate micro-damages of various origins and forms. These are driven by physical and chemical fluctuations within the material, such as the rupture of intermolecular bonds and breakdowns at the matrix-filler interface, resulting in the formation of macroscopic damage and ultimately leading to crack formation and structural failure. The emergence of such micro-damages degrades the material's physical and mechanical properties—namely, elastic moduli and Poisson’s ratios—ultimately altering the test volume of the RE in planes that are not aligned with the material’s symmetry axes and modifying its shape by introducing additional angular distortions.

The research shows that, in anisotropic materials, normal stresses in arbitrary directions lead not only to longitudinal but also angular damage. Shear stresses can cause both angular and longitudinal damage. Hence, the absence of angular change between two mutually perpendicular planes does not imply the absence of damage, as deformation still occurs on these planes. In general, the direction of damage-induced volume change in anisotropic materials does not align with the direction of principal stresses. The axes of the damage ellipsoid coincide with those of the stress ellipsoid only when the principal stresses act along the axes of elastic symmetry. In all other orientations, the damage and stress ellipsoids are not coaxial.

Comparison of experimentally obtained and theoretically determined in the Dlubal RFEM 5 software physical and mechanical properties of massive, glued laminated and cross-laminated timber beams

2025-05-07T13:13:42+03:00

The article presents the results of research and verification of experimentally obtained physical and mechanical characteristics of beams made of massive, glued laminated (glulam) and cross-laminated timber (CLT). The purpose of the study is to compare the real and theoretical deflections of the beams, determined with the Dlubal RFEM 5 finite element analysis software. Previously, experimental studies were conducted to determine the modified deformation modulus (deformation modulus with consideration of influence of shear modulus) for each type of timber beams.

The modeling was performed in three stages: using 1D member finite elements, 3D Solid finite elements and a 3D Solid model of the CLT beam considering the orientation of the lamellae fibers in each layer. For each type of timber beam, characteristics were determined for the corresponding material models: isotropic linear-elastic material model for 1D finite elements and orthotropic linear-elastic 3D material model for 3D finite elements. Theoretically calculated deflections were compared with experimentally obtained values, which made it possible to evaluate the accuracy of each model.

The results showed high accuracy of modeling for massive and glulam timber beams with an error of up to 2%. For CLT beams, an underestimation of the theoretical deflections for models from 1D and 3D finite elements and an overestimation of theoretical deflections for models from 3D finite elements, taking into account the orientation of the fibers of the lamellae, was noted.

The research confirms the expediency of using both simplified and detailed models in the analysis of deformations of timber structures. To increase the accuracy of the calculations, it is recommended to further refine the characteristics of the studied materials, in particular, the dependence between the deformation modulus and the shear modulus, as well as considering complex loading conditions, types of supports, and long-term effects in future studies. It is also advisable to carry out additional experiments to clarify the parameters of strength and stiffness characteristic of various configurations of cross-glued beams.

Dynamic analysis of the joint movement of derricking mechanism and lifting mechanism of a load during a steady-state turn of a jib crane

2025-05-07T16:46:46+03:00

Increasing the productivity of jib cranes is an urgent problem of improving their operation. Combining the work of separate mechanisms is one of the ways to increase the productivity of jib cranes. The aim of the study is to build a mathematical model and conduct a dynamic analysis of the crane jib system with simultaneous operation of the derricking mechanism and lifting mechanism of the load during a steady-state crane rotation. Methods for constructing discrete dynamic models of a jib crane by using Lagrange equations of the second kind, numerical methods for solving the obtained differential equations, which are presented in the form of a computer program at a steady-state crane rotation, and methods for dynamic analysis of crane mechanisms are used in the conducted research. The task of researching the dynamics of the simultaneous movement of the mechanisms for turning the boom, extending its section and lifting the load during a steady-state crane turn is solved in the presented work. The method of dynamic analysis was developed to study dynamic processes in the hydro-mechanical system of a jib crane during the simultaneous operation of crane mechanisms. The crane boom system is represented by a dynamic model with six degrees of freedom, which takes into account the main movement of the mechanisms and the oscillations of the links and the load on a flexible suspension. The kinematic, dynamic, and energy characteristics of individual links of the crane jib system with simultaneous operation of several mechanisms are determined on the basis of the constructed mathematical model. The high-frequency oscillations of the drive links of the load lifting mechanism and the low-frequency oscillations of the load on a flexible suspension are investigated. It was found that high-frequency vibrations of the links damped within the start-up process, while low-frequency vibrations of the load practically did not damp and continued throughout the entire movement cycle.

Drive modes that ensure smooth movement of the actuators, which leads to reduced loads and increased reliability of the crane are recommended to minimise oscillatory processes of simultaneous movement of the jib system mechanisms.

Analysis of dynamic behavior of a multi-storey frame building in the railway traffic area

2025-05-07T17:23:24+03:00

The impact of loading from rolling stock on a 25-storey monolithic-frame office building section with a 9-storey parking garage, located near the movement of railway trains in an urban area, was investigated. A two-stage numerical approach was applied to mathematically model the dynamic behavior of multi-storey buildings under loading from rolling stock. At the first stage, a finite element model of the ballast prism and soil was developed in the form of a flat elastic-plastic half-space with a length of 200 m and a depth of 60 m, created using the NASTRAN software package. The loading from the rolling stock was presented as a vertical periodic excitation, concentrated at the center of mass of the system, comprising the bogie frame, wheelsets of a freight train wagon, and the ballast prism. The impact of rolling stock load on the base was studied in a nonlinear static formulation using the Newton-Raphson method. Modal analysis of the base and ballast prism was performed using the Lanczos method. The dynamic behavior of the base was analyzed using the fourth-order Runge-Kutta method. Horizontal and vertical ground accelerations were obtained at various distances and depths of the base model relative to the railway track axis. At the second stage, a 3D model of the building was developed in the SCAD software package. Modal analysis of the structure was conducted using the subspace iteration method. The stress-strain state of the building under the influence of calculated loads and kinematic ground excitation, applied along the height of the building foundation as acceleration vectors, was investigated using the spectral method. The conditions for reliability and structural safety of the building were verified under load combinations, including the influence of base ground vibrations caused by rolling stock.

The influence of green structures of blue infrastructure on the load of building structures

2025-05-07T17:47:30+03:00

The paper considers the place of green structures in the blue infrastructure of cities. A scheme of integrated rainwater management using green structures is built. The combination of different green structures allows to creation of a unified and effective rainwater management system. The impact of green building structures on their supporting structures plays an important role. The loads from green roofs have two components: the load from structural elements and plants, including wind loads, and the load from precipitation-retained rainwater and snow. The first group of loads is constant, except for periodic wind loads, but its peak values vary little during rain and snow. It is impractical to consider snow load management. It can be reduced by snow removal. However, this will lead to a high risk of improper performance of snow removal duties with overloading of the supporting structures. Therefore, for safety reasons, the calculation is based on the maximum load. The load from rainwater depends on the runoff coefficient, which can be changed. Therefore, the paper underestimates the snow load for different snowy regions and average recurrence periods. The critical water retention of rainwater with the same load as the snow cover was determined. In the worst-case scenario of the first snow region and an average recurrence period of 10 years, we have a critical water retention of 56.2 dm³/m², which is significantly higher than the intensity of precipitation. This means that the load of retained rainwater will be less than that of snow. Therefore, it’s necessary to ensure maximum water retention by the amount of precipitation. This cannot affect the bearing capacity of structures, which will be determined by the snow load. The possibility of utilising melt water for household needs is shown. The tasks for future research have been set.

Nonlinear optimal control of the construction trajectory of a deep well

2025-05-08T12:11:08+03:00

The use of optimal design and control theory methods can provide significant advantages in developing optimal trajectories for drilling oil and gas wells. Today, the oil and gas industry faces problems associated with the production and redistribution of oil and gas resources. Modern drilling is often carried out at great depths, where the limiting values of speeds, hydrostatic pressures and temperatures, as well as the strength and wear parameters of drill string materials are observed, under the influence of frictional phenomena, intense vibrations and instability of the entire system. The geometric shape of the well trajectory, which depends on the structure of the oil and gas field and adjacent geological rocks and their mechanical properties, has a significant impact on drilling efficiency, well productivity, as well as on the risks of abnormal and emergency situations.

The trajectory of the well, as well as the labor costs, length and cost of its penetration, largely depend on the location of the drilling rig relative to the oil and gas reservoir. Therefore, the coordinates of this rig on the surface of the earth or sea, i.e. its positioning, can act as one of the control parameters in the trajectory optimization problem.

Based on the methods of differential geometry, nonlinear programming, and computational mathematics, the problem of optimal control of deep well trajectory tracing is posed. Nonlinear differential equations of the well centerline are formulated, and its curvature is chosen as the control function. Various forms of objective functions are considered that allow smoothing trajectories, as well as minimizing the cost of drilling operations under various constraints caused by the geological heterogeneity of rocks in the drilling zone and the location of oil and gas layers. The optimization problem is solved by the method of orthogonal projection of the antigradient of the objective functional onto linearized constraints.

Rational topology of steel i-beams with various gradients of changing wall height and shelf width at specified sections along the length of the beam

2025-05-08T12:38:08+03:00

A methodological approach has been developed for determining the rational topology of steel I-beams with variable stiffness under uniformly distributed loading along the beam length. It has been shown that for such beams, with varying web height and flange width, the maximum stress does not occur in the section where the maximum bending moment acts. The problem of finding the optimal cross-sectional height is solved using the Lagrange multipliers method in conjunction with the Kuhn–Tucker conditions. For steel I-beams with variable web height and flange width, the sufficient condition for structural optimality is confirmed: the area of the web is equal to the total area of the two flanges. However, under linear reduction of web height and flange width in the direction of decreasing bending moments, new critical cross-sections arise along the beam length in which the normal stresses in the flanges exceed those in the section with the maximum bending moment. This indicates that beams with variable stiffness may have multiple governing sections. An improved physical–mathematical model of the stress–strain state of I-beams in bending is proposed. A steel I-beam with the proposed new topology has the ability to adapt to its stress–strain state by introducing reverse variation of flange width: in selected sections, the beam height decreases or remains constant, while the flange width and accordingly the flange cross-sectional area increases relative to the section where the maximum bending moment acts. This improved design approach allows for achieving stress levels in all current cross-sections that do not exceed the yield strength of steel along the entire length of the I-beam. The numerical studies conducted demonstrate the possibility of finding new rational design solutions for variable cross-section steel I-beams. The existence of an admissible set of rational solutions based on the obtained results has also been confirmed. Thus, the problem of determining the rational topology of steel I-beams with linearly varying flange width and web height represents a design task with appropriately formulated and adequate design condition.

Cylindrical shells in a wind flow: regression analysis of the wind pressure distribution coefficient

2025-05-08T13:04:38+03:00

The article considers the behavior of thin-walled vertical cylindrical steel shell structures (capacities range from 300 to 5000 m³) in a gas flow. Under wind load, the main danger for such structures is global or local buckling. In technical applications, in order to simplify buckling analysis, we usually perform a transition from a complex distribution of a wind pressure q_2w to an equivalent uniform pressure q_2we=q_2w·k_w. According to the design standard for storage tanks, it is assumed that the wind pressure distribution coefficient k_w equals to 0.5 for all tanks, regardless of geometric parameters of the shells. However, this generalization is not accurate since the value of the coefficient depends on the parameters of cylindrical shells subjected to a gas flow with specific characteristics. The value adopted in normative documents does not provide the required level of reliability. However, under certain conditions, k_w can be calculated as the ratio of the critical value of the external uniform pressure p_cr2 to the critical value of the frontal wind pressure q_cr2w. In this article, the critical frontal quasi-static wind load q_cr2w (which causes shell buckling) is determined through numerical simulation of a wind flow in OpenFOAM using the k-ω Shear Stress Transport model. The critical uniform pressure p_cr2 and, thus, buckling of the shell are determined by verifying the singularity of the tangent stiffness matrix of the corresponding shell structure. The k_w coefficient is calculated using obtained values of the critical pressures, as described above. Using machine learning methods in the R statistical package, we have built a regression model, which allows us to calculate the k_w coefficient using the geometric parameters of the shell. The adjusted Akaike Information Criterion (AICc) and the leave-one-out cross-validation method have been used to verify the adequacy of the model, along with the estimation of the mean squared error (MSE) and mean absolute error (MAE). The final regression model for the k_w coefficient quite accurately corresponds to the data obtained through numerical simulation.

Analysis of calculation methods for explosion shock wave parameters in the design of protective structures

2025-05-08T13:48:47+03:00

Relevance. The full-scale invasion of the Russian into Ukraine revealed a fairly large number of issues, including those related to the construction of defensive and fortification structures. As it turned out, this direction in our country has not actually developed. There is no regulatory framework for taking into account many specific factors, such as the blast shock wave, penetration by ammunition and fragments (fragments). It should be noted separately that the means of attack are constantly developing and improving, and this requires constant improvement in countering them. This article is devoted to a review of existing methods that can be used to determine the parameters of the blast shock wave, which should be used when calculating building structures and structures. Choosing the right method for the calculation will allow you to work out a methodical approach to the design of fortifications, structures for engineering protection of critical infrastructure, and civil defense structures, and this is a very important and relevant task. This approach can later be included in specialized regulatory documents for the calculation and design of defensive and fortification structures, which would significantly improve their quality and reliability, taking into account modern wartime threats. The aim of the work is to review existing methods of engineering and analytical calculations of parameters of explosive shock waves and building structures and structures for damage by enemy attack means. The importance of choosing the correct calculation method for different types of threats is a very important task for the correct design of fortification and protective structures. Results. The paper considers existing global methods for determining the parameters of explosive shock waves for calculating building structures and structures for damage by enemy attack means. The issue of the need to develop a clear engineering method for calculating building structures and structures for the action of an explosive shock wave is raised. Algorithms for determining the parameters of explosive shock waves and further calculating building structures of fortifications and engineering protective structures for damage by enemy attack means are presented.

The influence of defects on the dynamic characteristics of three-layer cylindrical shell structures

2025-05-08T15:12:31+03:00

With repeated use of shell structures, specific problems arise in theoretical studies of the influence of the appearance of various structural cracks on the dynamic characteristics of three-layer cylindrical elements with inhomogeneous filler under different boundary conditions. Studies of the influence of such cracks on the dynamic characteristics of shell elements with inhomogeneous filler are quite important and relevant.The theoretical study of the natural frequency spectrum of a three-layer cylindrical shell with a discretely symmetric light, ribbed filler in the presence of annular cracks has been conducted. The finite element method solves the current problem of determining the natural frequencies of a three-layer element of special equipment under different boundary conditions.When studying such cylindrical shells, two types of defects were considered - through-through circular cracks in the reinforcing ribs of structures and three cases of their location. Frequency spectra are given for different types of boundary conditions. For typical cases of rigid clamping without foam plastic and hinged fastening with foam plastic, the shapes of the corresponding natural frequencies are additionally given for visualization.The analysis of the obtained numerical results made it possible to determine the nature of the influence of cracks of different lengths on the frequency spectra of three-layer cylindrical shells with a inhomogeneous filler.Frequency analysis of a three-layer cylindrical element for the presence of defects showed that the presence of a crack in the edge of the structure is a significant factor affecting the natural frequency of such an element and essentially leads to structural changes in this element.The obtained theoretical results indicate that small cracks have a small influence on the natural frequency of the structure. When relatively large cracks occur, a significant change in the frequency spectrum of an almost new three-layer structure is observed.

Justification of the indicator of the security of military vehicles in combat conditions

2025-05-08T16:02:49+03:00

In connection with hostilities, the question of the development of the reliability of military vehicles (MV) remains relevant. Equipping parts and units of the Armed Forces of Ukraine with modern military vehicles ensures a high level of combat capability of the troops. At the same time, one of the components of the combat capability of military vehicles is their protection against the effects of enemy weapons.In the conditions of hostilities, increasing the security of vehicles ensures the success of military operations. The protection of the MV should be considered as an objectively necessary combat property of weapons and military equipment, which characterizes its ability to maintain its integrity and continue to perform the tasks set before them in the conditions of the overwhelming influence of the enemy.

The probability of carrying out timely planned transportation of MV in conditions of overwhelming enemy influence can be estimated mathematically, which will allow, based on the totality of the obtained indicators, to assess the level of combat capability of a unit or a military unit both before the start of hostilities and during their conduct.

A forecast of the state of combat capability of the troops during hostilities is impossible without an objective assessment of the security of the MV, as well as its changes during the battle. Therefore, it can be argued that the indicator of the security of the MV can be determined and integrated through the indicator of the probability of carrying out the transportation of the MV under conditions of overwhelming influence of the enemy.

The scientific basis of research on the assessment of the level of security of the MV is: the theory of the effectiveness of the use of weapons and military equipment, the operation of military vehicles, the basics of the theory of MV reliability, the theory of probabilities and mathematical statistics. The concept of MV security is not defined by state standards, as a result of which various interpretations of this property arise.

Therefore, the purpose of the article is to obtain a dependency for determining the level of security of military vehicle equipment when units perform combat tasks as assigned and to determine the influence of individual factors on it.

Method for determining the foundation stiffness coefficient based on its physical and mechanical characteristics and the theory of a linear-elastic half-space

2025-05-08T16:47:41+03:00

The reliability and durability of building structures largely depend on the proper consideration of their interaction with the soil foundation. Determining foundation deformations is a key stage in design, as it defines the structural behavior under load. Both analytical methods and numerical approaches are used for calculations, among which the finite element method (FEM) is the most widely applied.

Numerical modeling based on FEM allows for the simulation of the soil foundation as a finite bounded domain, using various mathematical soil models and appropriate boundary conditions. An alternative approach is to model a flexible foundation as a slab on an elastic Winkler foundation, where a critical step is determining the stiffness coefficients (coefficient of foundation subgrade reaction): C₁ (subgrade reaction coefficient) and C₂ (shear coefficient). However, regulatory documents do not provide clear recommendations for their determination.

The authors propose a method for calculating the bed coefficient C₁, which eliminates the need for settlement calculations and relies solely on the average soil deformation modulus, the compressed layer depth parameter, and special coefficients that account for the decrease in stress intensity with depth according to the theory of a linear-elastic half-space. These coefficients are provided in an easy-to-use tabular format and can also be applied for analytical assessment of settlement magnitudes using the derived formulas.

Stressed state of a two-layer coating of a container with increased internal pressure

2025-05-08T17:08:49+03:00

Storage of individual bulk materials in containers requires their isolation from external influences, for example, moisture ingress. Waterproofing is provided by maintaining increased pressure in the container. In order to slow down the possible pressure drop, the upper part of the container is made of an elastic two-layer material. One layer provides waterproofing. The second layer provides sufficient strength of the two-layer coating. Its stressed state of the material significantly affects the service life and safety of flexible coatings. Establishing and taking into account the influence of operating conditions, mechanical properties of material layers on the stressed-deformed state of the coating is a relevant scientific and technical problem. Its solution allows to increase the reliability and safety of using pressure vessels. In the article, the layers are considered as isotropic with reduced mechanical characteristics. Using the stress functions (Erie functions) of the classical linear theory of elasticity, a mathematical model of the plane deformed state of the two-layer coating is constructed. The model takes into account the boundary conditions for the external surfaces of a two-layer coating: a uniformly distributed normal load given by Fourier expansion acts on the surface of the first layer. A normal stress acts on the external surface of the second layer. The model also takes into account the conditions for the joint deformation of the layers: equality of the forces of mutual pressure of the layers, tangential stresses arising on the surfaces of interaction of the layers and their displacements. Based on the solution of the mathematical model, an algorithm for determining the stress-strain state of a two-layer coating is formulated. It takes into account the assumption of stress functions, respectively, of the components of the stress-strain state of the material of the coating layers in the form of sums. The dependence of the coating deformations on the mechanical properties of the material of the layers has been established. Thus, an increase from the minimum to practically maximum value of the Poisson's ratio of the layer material that provides waterproofing reduces the coating deflection by almost an order of magnitude.

Research on the influence of the simulation method of the soil base of a slab foundation on the stress-strain state of building structures

2025-05-08T17:46:14+03:00

The paper is devoted to the study of the influence of the simulation method of the soil base of a monolithic reinforced concrete slab foundation on the stress-strain state of underground and above-ground structures. A comparison is made of: 1) bending moments in the foundation slab; 2) foundation subsidence; 3) stress in monolithic reinforced concrete basement walls; 4) bending moments in the floor slab above the basement; 5) stress in wall panels of a typical (4th) floor; 6) horizontal displacements of parapet wall panels; 7) time spent on calculating the model. It has been established that the use of a simplified approach to numerical simulation, namely the use of a model with soil base rigidity coefficients makes it possible to obtain information on the stress-strain state of foundations and above-ground structures several times faster (approximately three times) than when using volumetric finite elements for the soil simulation. It has been studied that the use of a model with stiffness coefficients leads to overestimated displacement values, namely: foundation subsidence by 3.4 times, and horizontal displacements of above-ground structures by 2 times compared to the use of models with a volumetric soil massif.

It has been revealed that the bending moments in the foundation slab when using a simplified approach to numerical modeling will differ within 10% from the approach using volumetric FE as a basis.

It has been studied that horizontal stresses in monolithic reinforced concrete basement walls differ both quantitatively and significantly depending on the base modeling method. Vertical stresses in the basement walls when using foundation stiffness coefficients will be 10% greater than in models using the imperial approach.

It has been found that the bending moments in the floor slab above the basement are almost independent of the base modeling method. It was found that horizontal stresses in wall panels of a typical (fourth) floor will be 25% lower when using a model with foundation stiffness coefficients. Vertical stresses correlate well with each other, regardless of the soil basesimulating method, the difference is about 2%.

Selection of the rational height of the steel roof trusses taking into account the effect of the impulse load

2025-05-08T18:10:27+03:00

The objective function of the aggregate steel consumption for the steel truss of the roof with a cross-lattice is described, taking into account the dynamic coefficient and the time of action of the concentrated impulse in the middle of the span of the structure. The objective function of the steel consumption describes the nonlinear patterns of the influence of the impulse load on the aggregate steel consumption for the steel trusses. The numerical research effects of the pulse action time on the selection of the rational height of the steel trusses with a cross-lattice with a span of 15.0 m and 18.0 m are carried out. It is established that when the dynamic coefficient for the bending moment is less than 1.0, a tendency to reduce the rational height of the steel truss of the covering is revealed relative to the constructive solution in the absence of an impulse load or a short time of its action. When the pulse load action time is increased to a value relative to the natural oscillation period τ1 /Тtr,1 > 0.2, the dynamic coefficient increases quite rapidly, which leads to an increase in the rational height of the steel truss structure of the roof with a cross-lattice. It is confirmed that a decrease in the pulse action time can result in a decrease in the values of the dynamic coefficient for deflection and bending moment, and the values of these quantities can be less than unity. It is also confirmed that an increase in the pulse action time to half the natural oscillation period (τ1 /Тtr,1 = 0.5) gives an approximation of the dynamic coefficient of the impulse for deflections to the value of the impact load kdin,η,2→2.0. The described patterns are related to two other patterns of influence on steel consumption. An increase in the overall bending stiffness of the structure leads to an increase in the dynamic coefficient, and accordingly to an increase in steel consumption for the structure, on the other hand, an increase in the height of the structure reduces steel consumption due to a decrease in steel consumption for the roof truss belts. Thus, taking into account two opposing trends leads to finding a rational height of the steel roof truss. The dynamic coefficient is also affected by the duration of the impulse and the ratio of the quasi-static load from the impulse to the self-weight of the protective enclosing structures.

Determination of the resistance of underground structures to the impact-explosive effect of adjusted aircraft bombs

2025-05-09T12:09:21+03:00

The purpose of the article is to publish the procedure for determining the resistance of underground structures to the shock-explosive action of adjusted aircraft bombs.The course of the Russian-Ukrainian war shows that currently one of the most dangerous means of defeating our troops in defensive positions are adjusted aerial bombs. Under such conditions, an effective way to protect personnel and material and technical means from enemy strikes is to shelter them in underground structures that must be resistant to the shock-explosive action of these weapons.The article presents the procedure for determining the resistance of underground structures to the shock-explosive action of adjusted aviation bombs, in particular FAB-500 M62 with a universal planning and adjustment module, using calculations of the required value of the protective of the soil layer of underground structures, which consists of determining the depth of penetration of a corrected aircraft bomb into the soil and calculating the radius of the sphere of destruction of the soil layer of the structure.The scientific novelty of the proposed calculations lies in the comprehensive consideration of indicators, the numerical values of which characterize: the final velocity of the aircraft bomb at the moment of impact; the depth of its penetration, taking into account the inclined position in the protective soil layer of an underground structure; radius of the sphere of destruction of the protective soil the thickness of this structure, taking into account the bomb penetration coefficient; tactical and technical characteristics of the FAB-500 M62.The practical significance of the results obtained lies in the obtained formalized description of the sequence of calculations for determining the resistance of underground structures to the shock-explosive action of adjusted aviation bombs and the ability of commanders (chiefs),military command bodies to more correctly determine the stability of the specified structures and promptly make appropriate decisions regarding effective shelter and protection of personnel and material and technical means from enemy strikes.

Analysis of natural oscillations of the offshore fixed platform

2025-05-09T15:55:09+03:00

Offshore fixed platforms are the main hydrotechnical structures for the development of marine oil and gas deposits. They are designed for drilling wells, the oil and gas extraction and preparation, the pumping water into a layer, the wells repair, the preparation of raw materials for the transportation.Structures for development of marine deposits are the most numerical group of offshore structures. At the same time, such structures are one of the most difficult and largely problematic. To avoid the threat of the resonance that is accompanied by the sharp increase in the oscillation amplitude it’s very important to know values of periods and frequencies of natural oscillations of the structure. In this article the impact of the flexibility of the pile foundation on values of dynamic parameters of the offshore fixed platform with the depth of immersion 11 m were analyzed.The analysis of natural oscillations of the platform on piles was performed using its two discrete finite-elements models: the flexibility model,wherethe interaction of soil basis and piles was implemented by using of finite elements that simulated the elastic connection between joints,and the rigid model,where piles were rejected and the platform was considered to be rigidly attached to the absolutely immovable rigid body.For every model first twelve basic form of natural oscillations were analyzed. In first two models of natural oscillations of the platform took part basically only the flexible connection mast, in the third form of natural oscillations took part basically only the flambeau consoletherefore values of frequencies and periods of oscillations didn’t depend on the flexibility of the supporting foundation of the platform. In all other forms of natural oscillations of the platform taking into account the flexibility of the supporting foundation changed values of dynamic parameters of 1,25-1,5 times that indicates the need to take into account this factor when analyzing of stress-strain state of members of the oil production structure.

Features of reinforced concrete corrosion processes in aggressive environments and methods of corrosion protection of building structures

2025-05-12T12:51:36+03:00

The article deals with the production of concrete with high corrosion resistance in the most common environments and in sulfate, chloride, acid, etc. It is shown that the corrosion resistance of concrete is determined by two main indicators - a slight permeability to an aggressive environment and positive reactivity with the components of an aggressive environment. Quantitative values of these indicators are given. The use of concrete with high corrosion resistance makes it possible to create concrete and reinforced concrete structures with high durability in aggressive environments with out the use of additional (secondary) protection against corrosion. Respectively, on average it is 1300, 1850 and 2700 mg/dm³. In addition, these values may vary depending on the diffusion coefficient of chlorine ions. It is shown that with a change in the pH of the environment (from 3.5 to 1.0), which is in contact with the concretere inforcement, the rate of concrete corrosion changes from 0.3 to 20 mm/year, respectively. The essence of corrosion processesin a sulfate environment lies in the structure of concrete, gypsum and hydrosulfoaluminates with an increased volume of solid phases, which causes the appearance of internal stresses exceeding the strength of concrete, which inevitably leads to the destruction of concrete. Sulfate corrosion is observed under the action of various sulfate solutions or when using aggregates that contain gypsumim purities (sulfide-containing aggregate in concrete). Classic measures to prevent sulfate corrosion are the use of sulfate-resistantce ments that contain a small amount of aluminates and tricalcium salt, the use of mineralad mixtures that bind the calcium hydroxide of the cement stone into low-base calcium silicates. Reducing the permeability of concreteto SO₄²-ions coming from an aggressive environment is an effective means of protection against sulfate corrosion. This is achieved by introducing admixture complexes into the composition of concrete, including water-reducing and mineral iones. An example can be the use of concrete modifiers of the MB series. Such similar complexes make it possible to obtain highly sulfate-resistant concreteon or dinary medium-aluminate portlandcements, which eliminates the need to use deficient sulfate-resistant portlandcement, which ensures high corrosion resistance of concrete. Increasing the water proofing grade of concreteto W8 and above prevents corrosion damage to concrete. However, this applies to highly diluted solutions of acids. Notice able corrosion was observe din ordinary concretes of W4 water proofing grades at pH 6.5 and below, in particularly low-permeability concretes of W10 - W12 grades at pH 3.5 and below. Inrecent decades, two destructive processes have attracted the attention of researchers – the late formation of ettringite and taumansite. Late formation of ettringite (in hardened concrete) in the absence of exposure to an aggressive sulfate environment was observed in cement concrete with an unbalanced content of aluminates and sulfates in the cement. In the case when the concrete hardens at an elevated temperature, the monosulfate form of hydrosulfoaluminate is mainly formed. At the next moment, the monosulfate form can be transformed into the trisulfate form with the addition of an additional amount of water and an increase in volume.

Multicriteria parametric optimization of the strength and weight of a shell of a minimum surface on a circular contour consisting of two inclined ellipses, taking into account geometric nonlinearity under thermal and power loading

2025-05-12T13:33:44+03:00

In the modern design of building spatial structures of the thin shell type, a new method of multicriteria parametric optimization under thermal and power loading with consideration of geometric nonlinearity has been developed. This approach to the design of the structure can be coordinated with the method of calculation for two groups of limit states. The first group of limit states includes strength and stability. The second group of limit states includes deflections and, for reinforced concrete structures, crack resistance.

External loads are taken into account in accordance with state building codes, which allow for safety factors to be taken into account with regulated safety factors for a combination of static thermal loads applied to finite elements. The calculation is performed using the finite element method in the Femap with Nastran calculation package. The optimization study is performed by connecting additional modules of our own software, which specify a pair of target Mises stress functions and the weight of the structure. The design variables are represented by the shell thickness of the minimum surface. The constraints are in the form of Mises stresses of 240 MPa, corresponding to the corresponding steel grade.

This research paper considers the object of study - a shell of minimal surface on a circular contour consisting of two inclined ellipses. This type of spatial thin shells makes it possible to use several types of optimal design simultaneously. The first type of optimal design is the optimization of the shape of the minimum surface hull, which is performed using application programs. The second type of optimal design is parametric optimization, which makes it possible to use the optimal thickness of the minimum surface shell. This approach to the design of spatial thin shells makes it possible to use minimum weight while maximizing the strength characteristics of the structure.

Numerical studies were carried out taking into account geometric nonlinearity. By taking into account the geometric nonlinearity, it was possible to take into account the actual stresses and displacements, which gave an additional optimization effect of 3% compared to the linear formulation. This approach to structural design makes it possible to use the optimization technique to calculate and design thin steel shells with minimal surfaces on real objects. This methodology has been verified by other authors.

Stress state of a laminated beam under normal load

2025-05-12T14:17:29+03:00

An analytical method for determining the bending stresses of a beam of a layered structure with an arbitrary number of layers, including the last layer of semi-infinite thickness, is proposed. The method consists in taking the indicators of the stress-strain state of the layers using the Eri stress functions of the linear theory of elasticity. They are taken in the form of sums of products of exponential and trigonometric functions and such products multiplied by the coordinate of the axis normal to the beam. Based on the boundary conditions, conditions of compatibility and continuity of deformation of the connected layers, a system of linear algebraic equations is formulated. The solutions of the systems are found to the values of the coefficients of the stress functions. The known coefficients of the Eri functions allow determining the stress-strain state of the layers of the beam. The cases of supporting the beam by parts of its surface and its holding by the ends are considered. The following is established. Compressive deformations are small relative to deflection deformations provided that the length of the beam significantly exceeds its thickness. The calculated deflection of the lower surface of the beam is close to parabolic in nature. The dimensions of the supporting surfaces exceeding 1% of its length significantly affect its deflection - they reduce it. The analytically determined average deflection of the beam is 0.7% less than the deflection calculated by the methods of material resistance. Beam deflections also depend on the properties of the material of the beam layers, so the increase in Poisson's ratio from a minimum, equal to zero, to a practically maximum, taken equal to 0,45, leads to a decrease in the deflections of the surfaces of the layers. The decrease does not exceed 10%. The proposed method is based on the provisions of the linear theory of elasticity. The transformations are carried out without simplifications. The results obtained do not contradict the results obtained by the methods of material resistance, within the limits of the linear formulation have a sufficiently high level of reliability. They can be used to calculate the stress-strain state of beams of a layered structure of rectangular cross-section, including beams on an elastic base.

Development of the optimal composition of gypsum self-leveling floors and comparative analysis with commercial mixtures

2025-05-12T16:25:33+03:00

The article is devoted to the development of optimal composition of gypsum self-leveling floors by adding basalt fiber. Thestudyexaminestheeffect of there in forcing component on the main quality parameters including compressive strength, flexuralstrength, wear resistance and porosity. Laboratory tests were conducted for three experimental mixtures with different proportions of gypsum binder, water and basalt fiber. Scanning electron microscope microscopic analysis showed that the addition of basalt fiber increased the adhesion between fiber and gypsum, reduced porosity and improved mechanical properties.

For comparison, the developed composition was analyzed along with three commercial mixtures presented on the Ukrainian market: “Budmeister D-319”, “Polymin TP-5” and “BaumitNivelloQuattro”. Commercial samples were evaluated for compressive and flexural strength, microstructural integrity and wear resistance.

The study confirmed that the addition of basalt fiber to gypsum self-leveling floors significantly improves their mechanical performance, microstructural density and durability. Further studies are recommended to evaluate the long-term performance of the coatings, their thermal conductivity, cost effectiveness and environmental impact.

Use of hydrophobized soils in oil and gas pipeline construction

2025-05-12T17:10:41+03:00

For the first time, systematic experimental and field tests on the effect of hydrophobized soil on the corrosion activity of underground pipelines were carried out in the work. Field, laboratory, and in situ tests conducted over 5, 10, and 15 years on covering insulated pipelines with hydrophobized soils howed that in samples of film coatings that were stored in hydrophobized soils, there lativeelongation was on average 20% higher, and the breaking strength was 15% higher, adhesion - by 10% compared to samples stored in ordinary mineral soils. The transient resistance of insulating coatings of pipe samples covered with hydrophobic oils changed significantly less than that of pipe samples covered with mineralized soil. Due to the improved physical and mechanical properties of hydrophobized soils, in particular, low values of permeability, filtration, water saturation, corrosion activity, swelling, high values of water resistance and adhesion, the transition resistance "pipe-soil" of insulated pipe samples decreasess lightly. It was established that the greatest effect in reducing the corrosion activity of soils (10 times) is observed at temperatures above 10-12^oC, when the binder dosage is increased to 10%, and the refore on themostdangerousintermsofcorrosioninthe “hot” sections of the pipelines, for example NS and KS, to increase the reliability of operation, it is necessary to back fill pipelines with hydrophobic soils. As a result of the above experimental studies, a significant decrease in the corrosion activity of hydrophobized soils was established with an increase in the dosage of binders. The experiments, which were carried out according to three methods and according to the loss of mass of steel samples, specific electrical resistance and pole density of the cutting current, show edidentical results – the corrosion activity decreases from high to very low. According to the classification of regulatory documents. Field tests was α= 0.10 1/year, and for ordinary soils, according to regulatory documents, it is 0.125 1/year. Thus, the service life of the insulation increases by approximately 35-50% when the pipeline is sprinkled with hydrophobic soils.

Application of the low-rank adaptation method on the example of fine-tuning a latent diffusion model

2025-05-12T17:43:17+03:00

This article explores the Low-Rank Adaptation (LoRA) method, a fast fine-tuning technique for large-parameter neural networks, and its potential application in various fields, with a focus on architecture, construction, and structural mechanics. The study applies LoRA to fine-tune a Latent Diffusion Model (LDM) for generating images of buildings in various architectural styles, serving as an illustrative example of LoRA’s effectiveness for adapting large models to specialized tasks.

Large-scale neural networks, such as Latent Diffusion Models (LDMs) and Large Language Models (LLMs), have shown significant potential in various fields, but their training from scratch is computationally expensive and time-consuming. Fine-tuning offers a more efficient approach by adapting pre-trained models to specific tasks and data. LoRA further enhances efficiency by adding a small number of parameters to the model instead of adjusting all weights. LoRA uses low-rank matrix representations to reduce the number of trainable parameters during fine-tuning. By introducing smaller matrices for each layer and training them on new data, LoRA significantly speeds up the fine-tuning process and reduces computational costs.

The study demonstrates the application of LoRA for fine-tuning the LDM Stable Diffusion 1.5 to generate images of buildings in various architectural styles using the OneTrainer tool. The results show that fine-tuning Stable Diffusion 1.5 using LoRA effectively generates high-quality images of buildings in specified architectural styles, highlighting LoRA’s potential for adapting large models to specialized tasks. The use of a validation dataset is emphasized for preventing overfitting and determining the optimal stopping point for training, ensuring the model's generalizability.

This research contributes to the broader exploration of LoRA’s applicability for fine-tuning large neural networks in various domains. While the study focuses on LDMs for architectural applications, the underlying principles and demonstrated effectiveness of LoRA extend to other types of large models, such as LLMs, for addressing specialized tasks in different fields.

Theoretical foundations for design of reinforced concrete under plane stress states

2025-05-13T16:27:04+03:00

The plane stress state occurs in beam walls in the zone of action of shear forces, column consoles, shear walls, slabs, shells and many other reinforced concrete structures. When calculating the strength of such structures, various, sometimes different from each other, theoretical approaches and design methods are used, based, in a number of cases, on empirical dependencies. At the same time, there are real prerequisites for the creation of methods for design the strength of reinforced concrete elements under a plane stress state based on a unified approach based on the theory of concrete plasticity and taking into account the presence, position, intensity, stress state and strength characteristics of the reinforcement.

This paper presents the theoretical foundations for design the strength of reinforced concrete elements based on the theory of concrete plasticity and consideration of reinforcement as an internal connection that ultimate transverse deformations of concrete under compression, causing the occurrence of reactive compressive stresses. Calculation dependencies have been obtained for determining the ultimate stresses in a reinforced concrete element under axial compression, plane stress state compression-compression, compression-tension when stresses are transferred directly to concrete or through stretched reinforcement, which take into account the strength characteristics of concrete, content, position and strength characteristics of reinforcement. The graphs are given that allow to estimate the influence of the listed factors on the value of ultimate compressive stresses in concrete. The developed theoretical approach is extended to the design of the strength of compressed elements with welded mesh reinforcement and the possibility of its use for the design of similar elements with confinement reinforcement, as well as pipe-concrete elements, is shown.

The Newest Method for Optimizing Clusters of Special-Purpose Structures through BIM Modeling

2025-05-13T17:08:18+03:00

A method of cluster geometric modeling is proposed and the results of this method application were considered to optimize resources when solving defense issues. An example of the necessary solution to the problem of reforming the placement of special-purpose facilities and structures in the light of the new concept of Ukrainian defense has been chosen, and on this basis an algorithm for quantitative and qualitative solution of the problem has been developed using modern neural networks.The article proposes a general method of cluster geometric modeling in resource optimization, which will be an urgent need to solve the problems facing Ukraine. For the effective formation and functioning of the Armed Forces of Ukraine and their development, it is necessary to maintain their material and technical support at a high level, which must meet modern requirements and world standards. The current relevance of the problem indicates an urgent need to study the problems of norming and standardization and the creation of territorial planning and urban planning solutions for property defense complexes under the conditions of the transition to a new concept of defense construction in Ukraine, close to world standards.

The purpose of the study is to create a toolkit to optimize the solution of problems that will arise in the process of developing the concept of complex modeling of the characteristics of special-purpose structures and related issues of territorial planning and urban development solutions.According to the authors, currently, complex, mainly anthropological, expert methods are mostly used when planning resources. Creating mathematical models requires a lot of time, which is unacceptable under current conditions, but if an already developed algorithm is used, which will be operated by a modern neural network, this drawback can be eliminated.The topic of decision optimization is currently a poorly structured multi-criteria problem. In addition, the existing correlations between influencing factors require the development of a complex apparatus for making urgent decisions.

Parametric optimization of a cylindrical shell under static loads

2025-05-15T17:40:45+03:00

Optimization in modern structural design plays a crucial role, particularly for thin-walled cylindrical shells, which are widely used in mechanical engineering and construction. Optimization enables the development of efficient design solutions that minimize structural weight while maintaining strength and stiffness. The main objective of this study is to perform parametric optimization of a cylindrical shell used for liquid storage, aiming to minimize its weight while considering operational loads such as liquid pressure, self-weight, and wind load. The finite element method (FEM) was employed to simulate the structural behavior under these external forces. The results of the study demonstrate that parametric optimization enables the identification of balanced design solutions that meet strength requirements while minimizing weight. This makes optimization not only a theoretical tool but also a practical necessity for enhancing the competitiveness of engineering designs.