Strength of Materials and Theory of Structures

Influence of mass on the efficiency and dynamics of single-sided and double-sided vibro-impact nonlinear energy sinks

Petro Lizunov, Olha Pogorelova, Tetiana Postnikova, Oleh Gerashchenko — Fri, 29 Nov 2024 00:00:00 +0200

This paper studies the efficiency of the asymmetric single-side and symmetric double-sided vibro-impact nonlinear energy sinks (SSVI NES and DSVI NES), that is, vibro-impact dampers, in mitigating unwanted vibrations of the heavy primary structure (PS) to which these dampers are attached. The dynamic behavior of this vibro-impact system is also investigated. The damper efficiency and system behavior are studied for dampers with four different masses, as optimization is carried out for other damper parameters at a predetermined mass. The effect of the damper mass changing on its efficiency and system dynamic behavior is shown. The dampers with different masses and optimal design exhibit similar high efficiency in mitigating the PS vibrations, but the optimal design of the dampers with lower mass has unusual parameters, namely the huge clearance and small damping coefficient. The SSVI NES hits not only the obstacle hardwired to the PS but also the PS directly. From this point of view, it can be considered as double-sided DSVI NES only asymmetric. The DSVI NES hits the left and right obstacles rigidly connected with PS. The regions of bilateral impacts are narrow and located near the resonant frequency of the exciting force. In the rest of the frequency range, the SSVI NES makes unilateral direct impacts on the PS; the DSVI NES performs shockless motion without any impacts and operates in this frequency range as a linear damper without any nonlinearity.

The numerous numerical tests were able to show the system dynamics with 36 different dampers, namely for four masses, for two damper types for each mass, and for several variants of the optimal damper design. The optimal design is not unique; it can have many variants, since there is a lot of damper parameter sets that provide similar mitigation of the main structure vibrations. Therefore, optimization procedure itself does not and cannot give an unambiguous result, allows for great arbitrariness in its execution and requires great experience and skill from the performer.

Determination of energy parameters of vibrating machines for compaction and formation of concrete products according to different power form of load

Ivan Nazarenko, Andrii Zapryvoda, Andrii Bondarenko, Volodymyr Slyusar — Fri, 29 Nov 2024 00:00:00 +0200

The paper investigates and determines the parameters and energy indicators of vibrating machines with harmonic and vibroshock modes of motion for compaction of concrete mixtures. The equations of motion of the vibration system "working body of the machine - compaction medium" are made on the basis of a hybrid discrete-continuum model, which adequately describes the real process of compaction of the mixture. Calculations were made on the basis of the obtained analytical dependencies to determine the amplitudes of oscillations and the oscillation energy of a two-seater The systems made it possible to assess their changes in different modes of operation. Thus, the first resonance was recorded at a frequency of 5 Hz, and the second at a frequency of 35 Hz. For the action of an external force on the first mass, the resonance mode is determined by the parameters of the second mass, including the energy dissipation coefficient and the ratio between these masses. The conditions for the influence of dissipation in the resonance mode at a frequency close to the partial natural frequency of the mass on which the external force acts have been determined. The energy parameters of the vibrating percussion system have been investigated and determined. The equations of motion of a vibro-percussion installation as a model with discrete-continuous parameters are given and solved.

Amplitude and skeletal characteristics are given, the influence of parameters on their change is determined, and two ways of implementing the resonance mode are revealed: by changing the frequency of the harmonic force, and at the same time, the possibilities of controlling the movement of the installation by changing the frequency and the value of compression of the limiter by a constant force are determined. Formulas for determining the energy parameters of a vibro-percussion installation, which take into account the discrete parameters of the machine and the distributed parameters of the concrete mixture, have been obtained.

One of the approaches to assessing the stability of the soil massif within the grid methods

Ivan Solodei, Vasyl Pavlenko, Oleksandr Kulikov — Fri, 29 Nov 2024 00:00:00 +0200

An important stage for creating the possibility of using landslide and landslide-prone territories in economic activity is the assessment of their stability. To solve this difficult task, a significant number of various methods have been developed, each of which has its own advantages and disadvantages. In this work, a method for assessing the stability of slopes within the framework of grid methods is proposed. This method is implemented in a complex with the finite element method, which allows to estimate the stress-strain state and to determine of the stability coefficient and localize the slip surface using grid methods.

The algorithm for using grid methods for this type of problem is given in detail in the paper. Its essence consists of three key stages, the first using the finite element method to determine the acting stresses in the slope. The second is the creation of a grid based on a finite-element model, which makes it quite easy to switch to a grid graph convenient for analysis. The third is the use of algorithms for analyzing graphs and processing the results. At the same time, one of the most important stages for the efficiency of the algorithms for finding the shortest path is the selection of the weight function of the edges of the graph, an example of the use of acting stresses is given in this work.

Also, the work highlights the results of solving several test problems to evaluate their convergence between the proposed and other widespread methods for assessing the stability of slopes. Calculations were carried out with Plaxis 2D PC and Ukis PC, and LIRA-SAPR PC was used to estimate the stress-strain state for the proposed method. The proposed method showed sufficiently high convergence of results with other methods.

Analysis of the stress state of the bolted connection taking into account the bolt tension

Serhii Pyskunov, Serhii Mitsyuk, Dmytro Mitsyuk, Yuriy Repiakh — Fri, 29 Nov 2024 00:00:00 +0200

One of the most crucial and important points in the design of a structure is the calculation of the connection elements of the nodes, since the reliability of the structureas a whole depends on the accuracy and reliability of the calculation results. Designs chemesare often simplified to reduce labor costs in the calculation of node elements, but this approach sometimes does not allow for a full analysis of the distribution of forces, which can be critical forcerta in types of structures. The main types of joint are welded, riveted and bolted. Bolted joint have many advantages over other types, namely: high manufactur ability, reliability, and speed of installation work. The various approaches to modeling of bolted joint are considered and compired in this paper.

Currently, one of the most effective and least time-consuming means of numerical modeling of the stress-strain state of spatial bodies, including bolted joint, can be considered a semi-analytical finite element method (SFEM).

The bolt body, bolt head and nut were modeled by spatial elements, and the bolt tension was modeled by concentrated and distributed forces and the load from uniform heating, combining displacements in the nodes, and fixing displacements along the contour.

There sults obtained with different approaches to modeling bolt tensionallowustoconcludethatthereis a slight difference in the stress distribution in the spatial formulation of the FEM and SFEM and made it possible to detect discrepancies in the stressed state of the bolted joint for the case of taking bolt tensionin to account.

Development of general principles of fatigue strength assessment steel structures of nuclear power plants units considering special operation conditions

Oleksandr Shugaylo, Serhii Bilyk — Fri, 29 Nov 2024 00:00:00 +0200

The fatigue strength of the steel structures of nuclear power plants determines the possible period of their safe operation in terms of fatigue damage accumulation. These structures are locatedin special operation conditions, including elevated temperatures of environmental conditions, episodic temperature loads with a significant temperature gradient, etc. Reliable assessment of the fatigue strength of steel structures is of particular relevance because most units at Ukrainian nuclear power plants have already exhausted their design life and are at the stage of long-term operation. At the same time, in terms of fatigue strength assessment, state building codes are focused on traditional steel structures subjected to standard loads and impacts and do not take into account these special operating conditions. Nuclear and radiation safety regulations do not contain technical requirements for calculating the fatigue strength of steel structures and establish only general regulatory requirements. The article develops and formulates general principles of fatigue strength assessment of steel structures of nuclear power plants, taking into account the special operation conditions, as well as the degree of their responsibility for ensuring nuclear and radiation safety.

Energy-Based Assessment of the Ultimate Limit State of a Physically Nonlinear Structure

Anatolii Perelmuter, Mykhailo Perelmuter — Fri, 29 Nov 2024 00:00:00 +0200

The paper addresses issues of nonlinear analysis of load-bearing structural members. It highlights the main distinction from the traditional approach, which involves a two-step procedure where static and dynamic analyses are separated from the local reliability check of design sections. In contrast, the nonlinear analysis employs a single-step analysis and a global assessment of the structural behavior while simultaneously checking the performance of all sections.

It is proposed to use the work done by external forces as a measure for determining the ultimate load. An incremental procedure is analyzed, through which the equilibrium state curve is constructed and this work is calculated. The paper highlights the issue of numerical instability in the computational process as it approaches the failure load. As a way to address this problem, it is suggested to consider a state of the structure as ultimate when it significantly loses its ability to resist the increasing load (loss of resistance).

The paper proposes a method for finding design combinations of independent load cases, based on the energy approach, which offers sufficient applicability. It is noted that in the case of nonlinear (global) analysis, the selection of a design load combination should be based not on a local criterion but on a global one, which defines the composition of loads and actions constituting the design combination. The energy of deformation is suggested as such a criterion. The algorithm for searching for dangerous load combinations relies on a plausible hypothesis that the energy-based composition of load combinations leading the system to its ultimate state, due to the global nature of energy assessments, will be the same as in the case of linear analysis. This algorithm enables to solve the problem without resorting to an exhaustive evaluation of all possible load combinations.

Stochastic stability of parametric oscillations of elastic shells

Olga Lukianchenko, Dmytro Poshyvach, Iryna Kara — Fri, 29 Nov 2024 00:00:00 +0200

There is a powerful mathematical apparatus which appeared up on the basis of the theory of Brownian motion of Markov processes and processes of diffusional type nowadays. It allows deciding intricate dynamic problems taking into account fluctuation processes. A classic result in this area is the article of O.O. Andronov, L.S. Pontryagin and O.A. Vitt, in which firstly the methods of the theory of Markov processes were applied to research of problems of statistical dynamics of the nonlinear systems. Later, the strict mathematical theory of stochastic differential equations of Ito was presented in an article of I.I. Gikhman and A.V. Skorokhodov. An important step in application of this theory to research of dynamic problems of the elastic systems was become researches of R.L. Stratonovich. These researches were based on combination of Krilov-Bogolyubov method of averaging with the method of theory of Markov processes. The strict ground of this approach was done by R.Z. Khasminski. A significant contribution to the development of the theory of stochastic systems and the introduction of probabilistic methods for the calculation of structures was made by V.V. Bolotin and his followers. V.V. Bolotin performed significant work on the application of probabilistic methods to the calculation of structures. Also important are studies of stochastic parametric oscillations of various systems by Dimentberg, V.I. Klyatskin and others. From the beginning of 80-th of the last century the scientists of Structural and Theoretical mechanics department of the Kyiv National University of Construction and Architecture were engaged in development of the numeral research of stochastic stability of elastic systems. Results of numerical researches of stability of parametric oscillations of the cylindrical and shallow shells under different stochastic influences were presented at this article. Parametric oscillations models of the shells were formed on the basis of the asymptotic or functional approaches and Monte-Carlo method using the calculation procedures of finite element analysis software. Stochastic stability of elastic shells was formulated as stability in probability, on average and with respect to the moment functions of different order. The critical values of stochastic load intensity and the regions of stochastic stability of shells were obtained by Runge-Kutta method of the fourth order and the continuation by parameter method.

Modal analysis of a thin coupled composite shell

Olga Krivenko, Petro Lizunov, Anton Polianskyi, Oleksandr Kalashnikov — Fri, 29 Nov 2024 00:00:00 +0200

The results of the study of natural vibrations of a coupled shell of revolution are presented. The shell is a spherically biconical structure that has sharp bends in the mid-surface at the junction of different shapes. The material is a unidirectional fibrous carbon/epoxy composite. The shell structure, by its geometric shape and material parameterss, is an approximate model of the fairing of the launch vehicle. The modal analysis of a thin elastic shell is based on the use of a finite element model of a inhomogeneous shell and the application of a universal 3D finite element. The governing finite-element equations are constructed using a moment scheme of finite elements. The universal finite element is based on a standard isoparametric 3D finite element with polylinear shape functions for coordinates and displacements. It is characterized by the presence of additional variable parameters. Two nonclassical hypotheses are used to describe the features of the stress-strain state of a thin inhomogeneous shell. The static hypothesis of the constant of compressive stresses throughout the thickness of the shell layer is used. The kinematic hypothesis of deformed straight line is used, which is not necessarily normal to the mid-surface of the shell. The hypothesis allows us to join three-dimensional finite elements, keeping compatibility of the coordinates and displacements, and naturally modeling sharp bends. This phenomenon is inherent, for example, to folded and coupled (combined) shells. The performed modal analysis of the spherical biconical structure demonstrates the effectiveness of the method. Based on the universality of the approach, the method can be applied in studying the behavior of structures whose shell elements are made of different materials.

The investigation of progressive collapse of steel structures considering physical nonlinearity

Maksym Vabishchevich, Nataliia Nestor, Ihor Fesun, Mykhailo Burkivskyi — Fri, 29 Nov 2024 00:00:00 +0200

The article comprehensively analyzes the problems of research into the phenomenon of progressive collapse, defines the current stage of research, identifies key issues during the simulation of sudden removal of structures, gives the results of the study of sudden collapse of steel structures without taking into account and taking into account physical nonlinearity.

A number of factors have been identified for the revival of interest in the topic of progressive collapse research, which began at the beginning of the new millennium and continues to this day. This includes the occurrence of world-famous cases of progressive collapse, a huge number of destroyed buildings and structures as a result of the full-scale invasion of the Russian Federation into Ukraine, a significant number of buildings and structures that, according to obvious signs, should have been completely destroyed due to the destruction of certain key load-bearing structures, but remained partially damaged, a low-income state regulatory framework regarding stability in the event of progressive collapse of buildings and structures, the emergence of technological possibilities for performing spatial calculations, etc.

An approximate list of factors has been defined, the consideration of which at the stage of numerical modeling of the emergency situation of a progressive collapse can increase the stability and reserve of the load-bearing capacity of structures. The current regulatory requirements for taking into account the physical nonlinearity of steel structures are analyzed. In addition, the parameters of physical nonlinearity modeling were evaluated, namely the selection of the "stress-strain" diagram, the selection of the deformation limit, etc.

Quasi-static and dynamic methods of modeling sudden collapse are compared, and the implementation algorithm of both methods is briefly analyzed. The scenarios according to which the simulation of the sudden collapse process took place are described.

Multi-criteria parametric optimization of the strength and weight of a shell of a minimum surface on a square contour under thermal and power loading, taking into account geometric nonlinearity

Grigory Ivanchenko, Oleksandr Koshevyi — Fri, 29 Nov 2024 00:00:00 +0200

In applied and structural mechanics, many examples of optimal design with different objective functions are considered, but there is a need to take research in this area to a new level. The object under study with two or three simultaneous types of optimization is an actual applied problem in the field of construction and applied mechanics.

One of the main tasks of designing minimal surfaces is to find the optimal shell shapes for given overall dimensions and shape in plan, taking into account parametric optimization - it is necessary to implement a modern optimization algorithm in the calculation of this structure. Its solution should be brought to ready-made formulas, graphs, tables, calculation examples and practical.

The system of solving equations of the finite element method is formed using the Lagrange's variational principle, according to which the total potential energy P of a finite element model of a body is in a state of stability and equilibrium has a minimum value.

Within the framework of the study, a methodology for obtaining the ratio of the finite element method with regard to geometric nonlinearity is presented that does not depend on the shape and properties of the finite elements, so it can be implemented for a plate finite element of a shell of minimal surface.

To study the multicriteria parametric optimization of the minimum surface shell with regard to geometric nonlinearity, a special additional optimizer module created by the authors is used, which is linked to the Femap with Nastran calculation complex [12]. The computational model is built by the finite element method, which makes it possible to perform a qualitative study of optimization taking into account the objective functions: Mises stress and structural weight.

This methodology proves to be effective in the study of multi-criteria parametric optimization with consideration of geometric nonlinearity. Such an approach to the calculation of building structures makes it possible to use structural materials efficiently, and modern calculation complexes based on the finite element method (FEM) can be used in further development at the level of building codes of Ukraine.

Dynamics of layered conical shells under non-stationary loading

Viktor Gaidaichuk, Kostiantyn Kotenko, Alirza Mamedov — Fri, 29 Nov 2024 00:00:00 +0200

The peculiarities of the oscillatory process of the bearing layers of three-layer conical shells depending on changes in the geometric and physical and mechanical characteristics of the material of their bearing layers at different properties of the polymeric filler material of the structure are investigated. Theсases of dynamic behavior of three-layer conical shells are considered and a comparative analysis of the parameters of the stress-strain state characteristics at different ratios of elasticity of the bearing layers of the structure and the polymer aggregate material is given.Taking into account the difference in the material parameters of the bearing layers and the distance between the reinforcing ribs of the structure exceeding the value of their cross section, the model of the shear theory of shells and rods by S. P. Timoshenko was used in the study.Finite-element modeling and numerical calculations of normal deflections and normal stresses of the bearing layers of the structure, which determine its stress-strain state, were performed.The influence of the elasticity of the polymer aggregate on the dynamic behavior of three-layer conical shells under non-stationary loading was evaluated.The article shows that by changing the material of the conical shell package, the thickness of the bearing layers and the elasticity of the aggregate, it is possible to select a structure design with the predicted dynamic behavior under non-stationary loading.The obtained results of the study of dynamic processes in the considered three-layer structures under different geometrical and mechanical parameters can be of significant interest for design developments.

Numerical analysis of the stress state of non-thin corrugated cylindrical shells made of continuous-inhomogeneous materials

Liliia Rozhok, Artur Onishchenko, Lesia Kruk, Zoryna Naidonova — Fri, 29 Nov 2024 00:00:00 +0200

Cylindrical shells of circular and non-circular cross-section are used as structural elements in many branches of economy. To increase the reliability of operation of such elements, continuous non-homogeneous materials are used.

This research investigates non-thin cylindrical shells with corrugated as cross sections made of the continuously inhomogeneous materials. The shells are subjected to internal pressure under conditions of simple support on the ends.The subject of the study is the stressed state of the shells and, as a consequence, the establishment of dependencies between its characteristics and the geometric parameters of the reference surface, the thickness of the shells, and the law of change of the modulus of elasticity of the material.

The aim of the work is numerical analysis of the stress state of shells of such class depending on the amplitude of the corrugation, the thickness of the shells and the law of variation of elastic properties of their material. The solution of the problem is based on reduction of the original three-dimensional boundary value problem for the system of partial differential equations with variable coefficients to a one-dimensional boundary value problem for a system of ordinary differential equations with constant coefficients of higher order. At the same time, the analytical method of separating variables in two coordinate directions is used, together with approximation of functions by discrete Fourier series. The one-dimensional boundary value problem is solved by the stable numerical method of discrete orthogonalization.

An analysis of the stress state of the considered shells was carried out depending on the amplitude of the corrugation, the thickness of the shells and the law of change of the elastic characteristics of the material. It is shown that with a slight deviation of the shape of the cross-section from the circular one, for a certain thickness of the shells, the presence of corrugations can be neglected when choosing the calculation model.In addition, the presence of corrugations causes a redistribution of the values of displacements and stresses in the characteristic sections of the shells, which must be taken into account when calculating the strength and reliability of the structures under consideration.

Method of estimating the number M of occurrence of transonic flutter of aerodynamic control surfaces of supersonic aircraft and aerospace systems

Oleksandr Safronov, Bogdan Semon, Oleksandr Nedilko, Anna Horina — Fri, 29 Nov 2024 00:00:00 +0200

Evaluation of the characteristics of aerodynamic surfaces in transonic air flow by theoretical methods remains an actual scientific and applied problem that must be solved to ensure the safety of flights of supersonic aircraft and aerospace systems at transonic flight speeds.

Difficulties in solving the problem are due to the need to take into account the effect of air compressibility on the change in the characteristics of the aerodynamic profiles of supersonic aircraft in the transonic range of flight speeds. In some works, the influence of air compressibility on the change in the characteristics of aerodynamic profiles is estimated using various corrections.Additional difficulties in evaluating the characteristics of the aerodynamic surfaces of supersonic aircraft at transonic flight speeds arise in the formation of compression jumps on the surface of the aerodynamic profile, the effect of which cannot be determined by these corrections.The article proposes a method for estimating the M number, in which the occurrence of transonic flutter of the aerodynamic control surfaces of supersonic aircraft and aerospace systems is possible.The method is based on the analysis of the characteristics of the interaction of the oscillations of the sealing jumps with the oscillations of the aerodynamic control surfaces and on the basis of the analysis of the patterns of expansion of the local supersonic air flow on the surface of the aerodynamic profile.The possibility of using this method for preliminary estimation of the number M of transonic flutter of aerodynamic control surfaces is substantiated by comparing the results obtained using the proposed method with the results obtained in a laboratory experiment during blowing of a wing model with a control surface.The obtained results can be used to carry out a preliminary approximate assessment of the M number, in which transonic flutter of the aerodynamic control surfaces of supersonic aircraft and aerospace systems is possible, and in the preparation of recommendations to the flight crew regarding the features of controlling supersonic aircraft in the transonic range of M flight numbers.

Modeling of elastic properties of the reinforced layer of composite elements of structures of complex shape

Serhii Pyskunov, Tymur Bakhtavarshoev — Fri, 29 Nov 2024 00:00:00 +0200

One of the distinctive properties of composite materials is their anisotropy, which allows, in particular, to use their strength properties as efficiently as possible. Elements of structures that are made of composite materials, for structural reasons and to ensure strength, can have a geometric shape, which is characterized by a change in characteristic geometric dimensions along a certain coordinate. This can lead to an increase in the distance between the fibers, and, as a result, to a change in the reinforcement density along one of the coordinates. This is characteristic, for example, when increasing the length of the parallel of the conical shell in height when reinforcing the shell along the meridian, or increasing the length of the circle of the spherical belt when it is reinforced along the radius. The case of rectangular panels (plates or slabs) of variable thickness can be highlighted separately. In order to take into account the influence of these circumstances on the physical and mechanical characteristics of the layer, the variable reinforcement parameter characterizing the volume fraction of the fiber material is introduced from the characteristic coordinate. It is assumed that the fiber and matrix materials are in perfect contact at the separation boundary, local changes in the stress state are not taken into account there. The material of the fibers perceives compressive and tensile stresses, the fibers are arranged regularly. To formalize the description, the shape of the fibers is assumed to be rectangular. On the basis of these provisions, the relations for describing the elastic properties of a layer of a unidirectional fibrous composite material with a variable reinforcement ratio in one of the characteristic directions of the layer are obtained - the components of the stiffness matrix of the orthotropic composite, on the basis of which the effective characteristics of the composite material can be determined in the future (moduli of elasticity and Poisson's ratios in the directions along and across the fibers).

Mathematical model of the stress-strain state of multilayered structures with different elastic properties

Fri, 29 Nov 2024 00:00:00 +0200

The article examines the features of stress-strain state of structures made of two and multilayer elements. The relevance of use of multi-layer load-bearing structures in rapidly constructed protective structures in Ukraine under conditions of possible shock-explosive and fire damage is justified.The method of interpolating trigonometric Lagrange polynomials in mixed plane problems of theelasticity theory is described. In the problems of elasticity theoryfor the regionunder conditions of planar setting, two of the four boundary conditions are known. It is proposed permissive system of integral equations relative to an unknown pair of boundary conditions on each side of the area under consideration, based on the solution of theorem on reciprocity of work and reciprocity of displacements for a plane under the influence of a unit force.Solutions for each of the sides of region are built by developing the Multopa-Kalandia collocation method. The boundary conditions are the result of solving the system of integral equations. Features on the contour, namely points of application of unit forces, boundary breaks, etc., are taken into account by additional functions that are introduced into the kernels of integral expressions in the form of coefficients of the required boundary conditions.To represent the cumbersome functions of movements and stresses of multilayer structures in a compact form, the apparatus of the theory of functions of a complex variable is used, which leads to compact expressions that are convenient for programming. To obtain more accurate solutions and reduce the duration of computer programs, all ordinary and singular integrals given in the work are calculated analytically, that is, the system of integral equations to be solved is reduced to a system of linear algebraic equations with unknown density functions at the interpolation points.The proposed mathematical model provides the universality inherent in general numerical methods and allows to study the general stress-strain state of multilayer structures and local effects in zones of junction of layers with different elastic properties.

The influence of random loading on the strength of concrete and reinforced concrete structures

Tetiana Chyrva, Vira Koliakova, Viacheslav Martynov, Volodymyr Chyrva — Fri, 29 Nov 2024 00:00:00 +0200

It is known that practically all structures during operation are subjected to small but repetitive loads, the magnitude of which in some cases may exceed operational levels and have a random nature. Such influences include wind pulsations, accidents, seismic, technological, temperature-humidity loads. Existing methods for calculating structures do not take into account the peculiarities of concrete behavior under real conditions subject to random loading. However, such loading leads to an increase in residual deformations, an increase in the number of cracks, disruption of the bond between concrete and reinforcement, and can lead to the exhaustion of bearing capacity and premature failure.

Among various structural elements of buildings and structures, columns are most often subjected to technological and emergency influences, which determined the purpose of this research.

The determination of the scope of experimental research was carried out taking into account active experimentation. When developing the plan of a full factorial experiment, the following variable quantities were set: number of cycles n; load level η; relative eccentricity value . The research results showed that repeated loading for the investigated specimens led to an increase in bearing capacity compared to a one-time load by 18-30% depending on the magnitude of the eccentricity and the load level. To describe such loading, methods of random variables and processes were used. In this work, this approach is implemented based on the Monte Carlo method. The technology of applying this method is as follows: by reproducing a set of pseudo-random numbers, a selective realization of random loading is modeled according to a given distribution law as a function of the number of cycles. After testing concrete prisms according to a specified program, the realization of the parameters of the stress-strain state of concrete was obtained.

By conducting statistical processing of the obtained realizations, probabilistic characteristics of the investigated parameters were calculated. Statistical processing of test results allowed obtaining approximating equations for building dependencies on each load cycle. To confirm the possibility of using the test results of prisms in studying the stress-strain state of off-center compressed elements, their bearing capacity was determined in the work.

Determining the bearing capacity by this methodology was agreed with the values of the bearing capacity obtained using regression equations based on a full factorial experiment.

This approach to the study of concrete can be used to determine the strength and reliability of building structures operating under various types of external influences (loads) using the apparatus of the theory of random variables and processes.

Dynamic analysis of the simultaneous starting of the boom and load lifting mechanisms hoisting for the jib and the cargo of the jib crane with a hydraulic drive

Fri, 29 Nov 2024 00:00:00 +0200

Combining the work of individual mechanisms is carried out to improve the productivity of jib cranes. In particular, the task of joint starting of hoisting mechanisms of jib and cargo is considered in this article. Dynamic loads on crane structural elements, drives, and cargo on a flexible suspension increase with such movement of mechanisms. Increased loads lead to a decrease in the reliability of the crane and an increase in energy costs. When researching the dynamics of the joint starting of hoisting mechanisms of jib and cargo, the jibs system is represented by a mechanical system with four degrees of freedom, which takes into account the main movement of the mechanisms and the oscillatory movement of links with elastic and dissipative properties, as well as the cargo on a flexible suspension in the plane of departure change. A mathematical model of the joint movement of hoisting mechanisms of the jib and cargo was built for such a dynamic model of the boom system of the crane. The obtained model is a system of nonlinear differential equations of the second order, the solution of which was carried out by a numerical method in the form of a computer program. The dynamic of the joint starting of the hoisting mechanisms of the jib and cargo in the jib crane with specific numerical parameters were calculated and studied based on the developed program. The performed calculation made it possible to conduct a dynamic analysis of the joint starting of the hoisting mechanisms. High-frequency oscillations of links with elastic and dissipative properties in the drive of the hoisting mechanism were found as a result of the analysis. Also, low-frequency vibrations of the load on the flexible suspension were found. In the process of starting the mechanisms, high-frequency oscillations are attenuated during the transition process, and low-frequency oscillations of the load are sufficiently long and are attenuated during a significant period.

It is recommended to optimize the starting and braking modes to improve the dynamic properties of the hoisting mechanisms of the jib and cargo during their joint movement.

Investigation of the influence of geometric and physico-mechanical parameters of bearing layers and polymer filler on the oscillation process of a layered cylindrical shell at non-stationary load

Viktor Gaidaichuk, Kostiantyn Kotenko, Mykola Klymenko — Fri, 29 Nov 2024 00:00:00 +0200

Dynamic transient processes are studied and the results of the assessment of the influence of geometrical, physicaland mechanical parameters of bearing layers and polymer aggregate on the behavior of a three-layer cylindrical shell structure under non-stationary impulse loading are given. The used model of the theory of shells and rods by S.P. Tymoshenko, taking into account independent static and kinematic hypotheses for each layer of the structure. Numerical calculations of normal deflections and normal stresses of the load-bearing layers of the structure, which determine its stress-strain state (STS), have been performed. The finite-element model was created using a three-dimensional volumetric finite element of the Solid type, which, according to quality criteria: narrowing and curvature, internal angles and other indicators, met the requirements for providing a calculation mesh at the finite-element level.Variants of the structure with discrete-symmetric rib-reinforced aggregate of different elasticity are considered. A comparative analysis of the deflections and stresses of the load-bearing layers of the structure with the parameters of the light aggregate is given: Е_1;2/Е_t=500 and Е_1;2/Е_t=50.The general trend of all the considered cases of the study of the dynamics of the three-layer cylindrical shell structure was found to be a significant response to the change in the modulus of elasticity of the light aggregate, the value of which significantly affects the nature of its oscillationsThe article shows that the parameters of the geometry of the bearing layers of the structure, the physical and mechanical properties of their material, and the elasticity of the aggregate significantly affect the dynamics of oscillatory processes of cylindrical shell structures under non-stationary loading.

Аnalysis of methods for calculating the penetrating effect of the main types of missiles and fragmentation damage to the structures of protective constructions

Fri, 29 Nov 2024 00:00:00 +0200

Relevance. The full-scale invasion of Ukraine by Russia raised a number of questions, including those related to the construction of defensive and fortification structures. It turned out that this direction in our country was practically undeveloped. There is a lack of regulatory framework for accounting for many specific factors, such as blast waves, penetration of projectiles and fragments. It is worth noting separately that means of attack are constantly evolving and improving, while the scientific approach to countering them has almost stagnated worldwide. This article is dedicated to reviewing existing methodologies that can be applied in calculating elements of construction for fragment penetration. Choosing the right methodology for calculations will help develop a methodical approach to designing fortifications and structures for the engineering protection of critical infrastructure objects, which is currently a very important and relevant task. This approach could eventually be included in specialized regulatory documents for calculating and designing defensive and fortification structures, significantly improving their quality and reliability considering modern wartime threats.. The aim of this work is to review of existing methods of engineering and analytical calculations of penetration of protective barriers by the main elements of damage from enemy attack means. The importance of choosing the right calculation methodology for different types of threats and materials of protective obstacles is a very important task for the proper design of fortifications and protective structures. Results. The paper considers the existing world methods of penetrating effects of various kinds of destructive elements (missile warheads, shells, bullets, fragments). The question of the need to develop a clear engineering methodology for calculating the penetrating effect of all possible destructive elements in obstacles of various materials is raised. The algorithms for calculating fragmentation damage from various types of ammunition, as well as for calculating the protective properties of fortifications and engineering defenses are presented.

Some features of nonlinear calculation in the building design system

Anatolii Perelmuter — Fri, 29 Nov 2024 00:00:00 +0200

Abstract. The work is devoted to the analysis of discrepancies between linear and non-linear calculation of building structures that deform under the influence of load. It is recalled that there are two fundamentally different procedures inherent in the design calculation, namely:

(i) static or dynamic analysis of the behavior of the mechanical system, the result of which are the parameters of the stress-strain state of the system and (ii) assessment of the possible resistance of the system elements and the structure in general.

It is shown that when using linear analysis, these procedures set the content of independent calculation stages, while when using nonlinear analysis, they are combined and mutually influence each other.

Attention is drawn to features inherent only to the non-linear version of the analysis, for example, such as:

- the impossibility of using rod finite elements without crushing the length of the rod into elementary sections;

- the occurrence of tension-compression stress during bending, as a result of asymmetric development of plastic deformations along the cross-section height;

- the possibility of realizing extreme responses of the system at intermediate (not extreme) values of load intensity.

The problem of determining the limit state of the system, which corresponds to the global assessment of the carrying capacity, is considered. Taking into account the computational difficulties of numerical analysis when the system approaches the state of the mechanism, it is proposed to accept the state in which the resistance of the system decreases by several orders of magnitude compared to the beginning of the load. Attention is also drawn to cases where the limit state is determined by the level of deformation of the system.

A description of the main features of the global safety format is given, and a description of the latest known proposals for global reliability assessment and information on the implementation of these proposals in the new edition of the European Design Standards is provided.

Features of the work of reinforced concrete arches with adjustment of effort under repeated loads

Fri, 29 Nov 2024 00:00:00 +0200

In two-hinged arches, by adjusting the tightening force, it is possible to reduce the maximum values of bending moments in cross-sections under certain loads and dimensions of the structure. Solid two-hinged arches can be manufactured both at factories of reinforced concrete structures and directly at construction sites, depending on the size of the structure, the possibility of transportation, their number and other factors. Such arches are used in constructions covering industrial and public buildings, bridge structures, spatial coverings of buildings (shell diaphragms). In the process of operation, arches as a part of coverings in industrial and civil buildings and structures can be subjected to repeated loads, sometimes overloading and damage, which significantly affect the stress-deformed state of the cross-sections of the arch and tension. In two-hinged arches, there can be a redistribution of forces between the upper belt of the arch and the tightening, which affects their strength and stiffness.

The work of two-hinged reinforced concrete arches was experimentally investigated, which makes it possible to investigate the features of the stress-strain state of the belt sections and the nature of the redistribution of arch forces between the upper belt and the tension, the development of deflections and cracks under one-time and repeated short-term static loads.

As a result of the formation and development of cracks, the growth of plastic deformations in concrete, the stress-strain state changes and there is a redistribution of internal forces in the cross-sections of the arch, the rigidity of the reinforced concrete belt of the arch decreases and it works as an elastic element. The methodology for calculating the internal forces of two-hinged reinforced concrete arches is presented, taking into account the redistribution of forces during repeated loads. The proposed method will make it possible to more reliably design reinforced concrete arched structures, namely to reduce the moment of cracking of the stretched concrete zone, the deflection of the structure without reducing the bearing capacity of arched structures.

Current state of development of permanent pontoon bridges and prospects for their construction in Ukraine

Serhii Buhaievskyi, Tetiana Nenastina, Volodymyr Buhaievskyi, Yuliia Buhaievska — Fri, 29 Nov 2024 00:00:00 +0200

The history of the development of the most famous pontoon bridges, from ancient times to modern structures, is considered. The technical requirements for permanent pontoon bridges are systematized in accordance with the world experience in their design, construction, and operation. The most rational area of their application is outlined. The classification of permanent pontoon bridges according to the continuous and separate pontoon construction is presented. The variants of layout schemes depending on the peculiarities of their design, as well as variants of pontoon shape with a description of the peculiarities of their application are systematized. For reference, the table systematizes the main technical characteristics of modern permanent pontoon bridges located around the world. Modern projects of permanent pontoon bridges are considered in detail on the example of the coastal route E39, which is planned to be built in Norway using various bridge schemes, including cable-stayed and suspension bridges, as well as a floating tunnel. Conclusions are drawn regarding the further development of pontoon bridge structures in the future and the prospects for their construction in Ukraine.

Hyperbolic models in the analysis of heat and moisture exchange in inhomogeneous porous materials

Fri, 29 Nov 2024 00:00:00 +0200

The paper uses hyperbolic models for the analysis of heat and moisture exchange in inhomogeneous porous materials in which short heat pulses propagate. The heat transfer in sharply inhomogeneous media at room temperature is not described by Fourier and Cattaneo laws, but is modeled by Guyer-Krumhansl-type equations. The O.V. Lykov system of equations of interrelated heat and mass transfer taking into account the finiteness of heat and mass (moisture) transfer rates is solved using a one-dimensional formulation. However, the heat propagation velocity is of the order of the sound speed, so due to the short relaxation time, the solutions of the hyperbolic equation of thermal conductivity largely coincide with the solutions of the classical parabolic equation, although there are some significant differences. They depend on processes occurring on the surface (in thin layers) of porous bodies. The moisture diffusion rate in capillary-porous materials is approximately 10⁶…10⁷ and more times lower than the heat propagation rate, so, accordingly, the relaxation time of diffusion processes is much longer and should be considered in mass transfer equations. Exact analytical solutions of the one-dimensional Guyer-Krumhansl equation are obtained using the operator method. This equation is also used to study heat pulses of different shapes in the medium with respect to phonon/ballistic methods of heat transfer. The obtained results are used to model the heat and moisture propagation in thin films of capillary-porous bodies with account taken of molecular effects in systems of reduced dimension. The very short heat pulses propagation simulating isolated heat waves is modeled with reference to Knudsen number, as well as the solutions for the periodic initial function. The exact solutions of the above problems in the model of thin films of capillary-porous bodies are obtained.

Some approaches to modeling blast wave impact on structures in LIRA-FEM

Mariia Barabash, Oleksii Bashynskyi — Fri, 29 Nov 2024 00:00:00 +0200

The article is devoted to the methodology of modeling the calculation of structures for the action of dynamic loads caused by the impact of a blast wave and considers in detail the process of applying these dynamic loads to building structures in the LIRA-FEM software. This article describes the main stages of the calculations, starting from the calculation of the main parameters of the blast wave to the collection and application of dynamic loads to structural elements to perform the calculation by the direct dynamic method.

One of the key aspects of the article is to determine the main parameters of the blast wave that affect the magnitude and nature of the effects of the explosion loads. These parameters include pressure peak, blast wave duration, blast wave impulse, and wave front shape. The article discusses the typical values of these parameters depending on the explosion conditions, such as the type of explosive and the distance to the explosion epicenter.

The preference is given to modeling the effect of explosive loads on a structure as a dynamic impact. Such an impact can lead to significant deformations of structures and reveal additional features of the structure.

The article also describes the sequence of analysis of structures for explosive loads, which includes several stages. The first step is to determine the type of explosive device and its parameters, as well as the distance from the epicenter of the explosion to the structure. Next, the static load (pressure) from the blast wave is calculated and applied to the structural elements. The next step is to set the dynamic parameters of the blast wave, which are determined using special methods or regulatory documents. At the final stage, calculations are performed using the Time Dynamics module of the LIRA-FEM software package, which allows taking into account dynamic effects and assessing the behavior of the structure during the blast wave action.

Free vibrations of layered anisotropic thick-walled cylindrical shells

Volodymyr Trach, Andrii Podvornyi, Nataliia Zhukova, Oleksandr Bondarskyi — Fri, 29 Nov 2024 00:00:00 +0200

The article presents an approach to the calculation of free oscillations of thick-walled elastic layered anisotropic cylindrical shells. Anisotropy is due to the use of material whose elastic characteristics are in one plane parallel to the middle surface of the shell. This type of anisotropy arises due to the non-coincidence of the main directions of elasticity of the orthotropic fibrous composite with the axes of the cylindrical coordinate system.

Calculations describing the free oscillations of thick-walled cylindrical anisotropic shells are implemented by deriving a system of six differential equations of motion in partial derivatives of the spatial linear theory of elasticity. For this purpose, the authors modified the Hu-Washizu variational principle accordingly, which allows writing not only the equations of motion, but also the boundary conditions corresponding to them. When using the Bubnov-Galyorkin analytical method, an infinite one-dimensional system of differential equations of the normal Cauchy form is obtained, which allows finding the frequencies of free oscillations of thick-walled layered anisotropic cylindrical shells. The unknowns in the system of equations of motion describing the parameters of the stress-strain state of the shells are selected in the radial direction. To implement a one-dimensional solving system of differential equations of cylindrical shells, the numerical method of discrete orthogonalization was used, which was adapted accordingly by the authors. On this basis, an algorithm was written and a software complex was created for personal computers, which allows solving problems related to setting parameters of free oscillations of thick-walled layered anisotropic composite cylindrical shells.

The solutions of problems on the influence on the frequencies of free oscillations of an anisotropic thick-walled cylindrical shell are presented, taking into account: the angle of rotation of the main directions of elasticity of an orthotropic fibrous composite; increasing the number of cross-stacked layers; changes in the geometric parameters of the structure; four types of boundary conditions.

Numerical research of the coefficients of the dynamic work of steel framing covers reduced to a beam structure under the action of a concentrated impulsive load

Artem Bilyk, Maksym Ternovyi — Fri, 29 Nov 2024 00:00:00 +0200

The study of the operation of the steel truss of the covering of buildings during the action of a concentrated impulsive load. A generalized methodological approach to assessing the dynamic properties of steel roof trusses under the action of a concentrated impulsive load is given. The work of the steel structure is considered as the work of a single-span hinged Euler-Bernoulli beam taking into account the coefficient of shear deformation of the section. Analytical solutions of deflections and bending moments are traditionally presented in the form of the sum of series of trigometric functions by the forms of oscillations. The evaluation of the dynamic performance of the beam-type elastic structure was performed through numerical studies of the values of the structure's dynamism coefficients for deflections and the dynamism coefficient for the bending moment. It has been confirmed that the work of beam structures during the action of an impulsive concentrated load is divided into two phases, the first phase of the construction is described by analytical dependences during the action of the impulse. The second phase of the structure's operation is described by analytical dependences for the time when the action of the he study of the operation of the steel truss of the covering of buildings during the action of a concentrated impulsive load. A generalized methodological approach to assessing the dynamic properties of steel roof trusses under the action of a concentrated impulsive load is given. The work of the steel structure is considered as the work of a single-span hinged Euler-Bernoulli beam taking into account the coefficient of shear deformation of the section. Analytical solutions of deflections and bending moments are traditionally presented in the form of the sum of series of trigometric functions by the forms of oscillations. The evaluation of the dynamic performance of the beam-type elastic structure was performed through numerical studies of the values of the structure's dynamism coefficients for deflections and the dynamism coefficient for the bending moment. It has been confirmed that the work of beam structures during the action of an impulsive concentrated load is divided into two phases, the first phase of the construction is deimpulsive load occurred, but the structure continues to move, and the spans and the calculated bending moment acquire maximum values. Numerical studies of the accuracy of the values of the dynamism coefficients for deflections and bending moments of the steel structure of the coating by the number of members of the series were carried out. The accuracy of the solution is shown. Thus, for initial calculations, it is enough to keep members of the series from the first to the seventh. The analysis of numerical studies showed that reducing the pulse action time can significantly reduce the value of the dynamism coefficient in terms of deflection and bending moment. Increasing the duration of the impulse to half the period of natural oscillations brings the dynamic coefficient (dynamic coefficient of the impulse) closer to the value of the impact load. For initial studies, at certain values of the duration of the impulse, formulas were obtained for determining the coefficients of dynamism according to the first form of oscillations.

Steel tower structures fatigue analysis taking into account the influence of wind vortex shedding

Valerii Nuzhnyj — Fri, 29 Nov 2024 00:00:00 +0200

In this work, the aspects of solid cross-section steel tower structures fatigue analysis, taking into account vortex shedding, are considered. In scientific and regulatory literature on the design of building structures, as well as in design practice, it is customary to take into account the influence of frontal wind on buildings and structures as a whole, as well as their structural elements. At the same time, tower structures are characterized by a special phenomenon - vortex shedding, when under the action of a frontal wind due to the successive breakdown of vortices, the structure oscillates in a plane perpendicular to the wind. Oscillations from vortex shedding occur according to their own oscillation frequencies at wind speeds higher than critical values, which, as will be shown, can be in the range of already moderate winds and higher. There is a question of assessing the number of oscillation cycles and the stress-deformation state of construction structures and their details for the entire period of operation in order to determine their durability. Analytical studies of the effect of vortex wind shedding were conducted in four tower structures with a continuous cross-section from 12 m to 48 m in height, which showed that most often in structures with vortex excitation, oscillations at the first natural frequency of oscillations are manifested, and the effect of vortex shedding increases significantly with an increase in the height of the structure. The time of winds with a speed higher than the critical speed was determined in one randomly selected year for the city of Kyiv from the weather archive published on the Internet resource, which showed that the number of oscillating cycles per year for the structures under study exceeds 1 million. This indicates the need to limit stresses in systems to the limit of endurance. Also considered is the aspect of the influence of the shape of the cross-section of structures on the stress-strain state, taking into account vortex shedding.

Development and computer testing of equipment for cutting soils with spatially oriented knives of a bulldozer blade

Yurii Maksymiuk, Volodymyr Rashkivskyi, Mykola Prystailo, Bohdan Fedyshyn — Fri, 29 Nov 2024 00:00:00 +0200

The paper uses approaches to the creation and computer testing of a model of an experimental installation for cutting soil with spatially oriented working bodies of earthmoving machines used on construction sites. Today, there is a need for the efficient performance of construction work related to the operation of construction machinery with blade equipment. This, in turn, poses the task of determining the productivity of mechanized earthworks in various working environments. The main method of mechanical soil development is cutting. The main geometric conditions are the position of the cutting wedge edge relative to the cutting direction and the surface of the massif, the contour of the cutting edge, the contour and number of working surfaces of the cutting wedge, the number of so-called side cutting surfaces and the so-called blocked cutting surfaces. The peculiarity of the digging process is that its power and energy indicators depend on the kinematic conditions and geometric parameters - thickness, width and cut area, as well as on the angles of orientation of the working body in space. The creation of such a computer model of the experimental setup is due to the need for continuous improvement of existing equipment and the creation of new equipment to meet existing needs. The model of the experimental setup was created in accordance with the working hypothesis, where the movement of the spatially oriented knife occurs perpendicular to the movement of the blade equipment, at different ratios of the speed of the blade and the movement of the knife, which creates a simple interaction with the working environment, and the deviation of the application of the full cutting force by an angle α. According to the working hypothesis, depending on the plan of movement of the spatially oriented knife, its geometric interaction with the working environment changes and the cutting force changes accordingly. The necessity to create more productive and efficient earthmoving equipment requires the use of modern design solutions. Using the calculations of soil cutting by spatially oriented earthmoving tools in the form of a dihedral blade of dump equipment, a computer study of stress equivalents, linear displacement, yield strength factor, tensile strength factor, and loss of stability factor was carried out. The results are summarized in the form of tabular data and graphical display.

Numerical simulation of the spatial model of a damaged shopping and entertainment complex with parking for assessing the strength and rigidity of structures and creating a reconstruction project based on survey results

Fri, 29 Nov 2024 00:00:00 +0200

The main ideas and possibilities of the created numerical modeling technique of a complex spatial model of research and analysis of the stress-strain state, strength and stiffness of a shopping and entertainment complex with a parking lot at the address: Kyiv, st. Zdolbunivska 17, damaged as a result of the armed aggression of the Russian Federation, based on the results of an engineering survey by visual and experimental methods.With the help of our own software, using the modified method of straight lines, and the calculation software complex LIRA, from the action of the complex load, an assessment of the strength and rigidity of the load-bearing structures was carried out and the possibilities of their restoration and further operation were analyzed.A comprehensive model of the restoration of a damaged building was created, based on VIM technologies, which is used to further make optimal project decisions and significantly accelerates project work.The created numerical research method of the complex spatial model of the damaged building of the shopping and entertainment complex with parking allows, on the basis of conclusions about the strength characteristics of the structures and the building as a whole, to significantly expand the possibilities of making optimal project decisions and creating promising developments based on them.

Volumetric-planning decision of buildings of spiritual educational complexes

Olha Zhovkva — Fri, 29 Nov 2024 00:00:00 +0200

In the modern world, the issue of finding mechanisms for interaction between different religions, increasing the level of tolerance and tolerance towards representatives of other cultures is becoming increasingly relevant and necessary. Strengthening intercultural and interreligious ties will help avoid many conflicts. In this regard, the issue of forming modern spiritual educational complexes with a comfortable multicultural environment for the preparation of tolerant, highly educated public and religious figures is extremely relevant. The purpose of this study is to develop rational volume-planning solutions and recommendations for the design of modern spiritual and educational complexes for representatives of various religions of the world. Also relevant is the search for expressive, modern architectural solutions for these complexes, the architecture of which, at the same time, would not contradict certain canons. Theoretical and empirical methods were used to conduct the research (the method of comparative analysis, field survey of functioning domestic and foreign spiritual educational institutions, grapho-analytical method, which was used to develop several optimal modern volume-planning models, etc.). As a result of the study, scientific principles and recommendations were formulated for the design of a modern spiritual and educational complex for representatives of different religions to obtain different levels of education: from primary to higher education. A functional-planning and volume-spatial analysis of the modern spiritual complex was carried out and the necessary optimal composition of premises was proposed to ensure comprehensive education, as well as intellectual and spiritual development. The use of developed and proposed scientific principles for the design of modern spiritual complexes will contribute to the formation of a harmonious multicultural environment, as well as increasing religious tolerance in society, achieving cultural and religious unity, reducing the level of aggression and intolerance.

Behavior to shear force of a reinforced bar in the concrete

Yurii Klimov, Dmytro Smorkalov, Andrii Kozak — Fri, 29 Nov 2024 00:00:00 +0200

In the existing design practice, there are quite a lot of cases when it is necessary to take into account the behavior of the reinforcing bar located in the concrete to the shear force. Such behavior is interpreted as a dowel action in the reinforcement. The dowel action occurs and requires consideration when calculating the shear force at the intersection of longitudinal reinforcement with a critical inclined crack, calculations of joints of prefabricated and monolithic structures of columns with beams, joints of slabs, roadway pavements, structural connections for precast concrete buildings, column anchors and other cases. Numerous experimental and theoretical studies have been devoted to the study of the dowel action in the reinforcement. However, the existing methods of calculation, primarily practical, still remain far from perfect. This work presents the results of theoretical research of the dowel action in longitudinal reinforcement, based on the systematization and analysis of experimental researches and practical design methods developed on their basis. A reinforcing bar located in the concrete was considered as a beam on an elastic base, for which the effective bending length, Foundation modulus is determined, then the forces in the bar are determined and the cases of reaching the ultimate limit state, both in the bar itself and in the surrounding concrete (crushing of concrete under the bar). At the same time, corresponding design dependencies were obtained and comparison with experimental data was performed, which revealed a fairly high accuracy of the developed calculation method.

Modelling the thermal resistance of layered structures for blocking infrared radiation

Fri, 29 Nov 2024 00:00:00 +0200

Ensuring high thermal resistance of building, cladding, finishing and other materials helps to solve the problems of energy efficiency of buildings and energy saving in general. Typically, building and cladding structures have several layers. This makes it difficult to predict their heat transfer. To solve these problems, it is proposed to model the thermal resistance of layered structures. The mathematical functions that should be used in modelling are determined. In particular, the mechanisms of heat transfer due to thermal conductivity and radiant heat transfer are separated. The assumptions and simplifications in the calculations that are acceptable in terms of errors are determined. The use of glass fibres for blocking infrared radiation is theoretically substantiated. The thermal resistance of a layered structure with an arbitrary number of layers and different thermal properties of each layer was modelled. The modelling was carried out using COMSOL tools. Changes in the thermal state of the layered structure in space and time were obtained. The modelling results were verified. Samples of materials based on glass fibre were manufactured and tested using a standard thermal imager. It was found that such a three-layer glass fibre material actually completely blocks infrared radiation at an initial temperature of up to 40 °С. Comparison of the results with the efficiency of a standard thermal insulation product shows that the predominant mechanism for blocking infrared radiation in a glass fibre-based product is the scattering of infrared radiation. This opens up the possibility of using glass fibre fabrics both to increase the thermal resistance of building and finishing materials and to produce infrared camouflage.

Research of the interconnections of the "structure - technology - mechanized equipment" system in the construction of frame buildings

Fri, 29 Nov 2024 00:00:00 +0200

The article was developed and implemented for calculation models of the frame building and the lifting module bu using computing complex Autodesk Inventor. The dimensions and number of models elements allow to correctly investigate the technical structure. The basic scheme of connections in determining the structural scheme of the building, the method of its construction, and technical means of implementation is considered. Actuality of this work is the need for qualitative analysis of interrelated solutions in construction when using new construction technologies and modernization of mechanized support for their implementation.

Modern approaches to the formation of the structure of the building frame are analyzed. The main propouse is based on using of lifting assembly modules to reduce the specific share of the use of heavy crane equipment at the construction site.

Approaches to the formation of a system for monitoring the construction process, in particular the installation of the covering, were also considered.

Based on the results of the research, technical solutions are proposed to support the process of installing the building covering, which take into account the structural features of the building and are formed taking into account the functional features of the construction technological process.

Determination of parameters of dry building mixtures based on gypsum and polymer additives for finishing works

Fri, 29 Nov 2024 00:00:00 +0200

The properties study of raw materials and dry building mixtures based on gypsum was carried out in accordance with the current regulatory documents of Ukraine. In the course of laboratory studies, the rheological and physico-mechanical properties of construction gypsum from two quarries were determined. The fundamental difference between these two types of materials was determined and the expediency of using each of them was justified both from the point of view of quality and availability of each of the materials. A number of studies of multi-component building compositions have been carried out, both in terms of rheological and physical-mechanical properties of the finished coating without the use of additives-modifiers (composite system "binder ‑ aggregate"). The interaction of two binder types with two types of inert fillers of natural origin (chalk, limestone) separately or their combination was considered. Modifier additives were considered as components that have an impact on the required properties of the finished material. Additives-modifiers are considered depending on the spectrum of their action, conclusions are drawn regarding the expediency of their use, the conditions under which they are necessary components of the composite system are determined. The most rational dosage of components that influence on the properties of the working mixture and the finished coating is provided. Laboratory studies of the product’s properties of the most well-known manufacturers of gypsum-based dry construction mixtures, which are used by Ukrainian consumers (produced in Ukraine and Turkey), were conducted. The research results are presented and a comparative analysis of the obtained results is made. Information is given on the quality of raw materials used by these manufacturers. The main parameters of the technology for performing internal furnishing works with the use of building mixtures based on gypsum and polymer additives according to all technological operations during manual and machine application of gypsum coating are determined. The fundamental points related to the smoothness of strength gain of the finished building composition have been determined. Recommendations for the use of regulators of the process of gaining the strength of materials based on building gypsum are presented.

Methodology for taking into account the process of soil compaction when assessing the interaction of structures with the soil base using the finite element method

Oleksandr Lytvyn — Fri, 29 Nov 2024 00:00:00 +0200

During the interaction of structures with the soil base, the process of soil compaction under the foundations predominates, when irreversible deformations associated with a decrease in the volume of pores in the soil begin to develop. Usually, zones of plastic deformations associated with shear deformations will also arise, but they will be local, not large in size and do not significantly affect the redistribution of stresses in the “Base-Foundation-Building” system. Based on this, the article proposes a methodology for assessing the interaction of structures with the soil base under conditions close to compression pressing, which is based on the use of a mathematical model that describes the process of soil compaction and compression test data. The presented approach allows using data from oedometer soil tests conducted at small pressure ranges (0.1-0.3 MPa) to assess the interaction of foundations with the base of most modern structures such as high-rise buildings, industrial facilities and others, under which the pressure in the base only starts from 0.3-0.4 MPa.

To implement the method, the semi-logarithmic law of soil compaction of K. Tertsagi was chosen, which allows extending the compression curve obtained in laboratory conditions at small pressure values to the required pressure ranges with larger values and determining the deformation modulus in this wider pressure range. The method is implemented in the Simulia Abaqus environment using the user subroutine UMAT (user subroutine). It is shown that the results of numerical modeling are consistent with the data from laboratory tests. In addition, it was found that taking into account the process of soil compaction and the dependence of the deformation modulus on pressure allows you to practically eliminate the influence of boundary conditions on the stress-strain state of the "Base-Foundation-Superstructures" system, which is especially important when assessing the mutual influence of closely located structures with significantly different limits of the compressible layer. The advantage of the proposed approach is also that in addition to compression test data, other data on soil deformability obtained on more modern laboratory devices, such as a stabilometer, can also be used.

Redistribution of forces in foundation structures of a building made of precast reinforced concrete depending on the type of panel connection

Oleh Kryvenko — Fri, 29 Nov 2024 00:00:00 +0200

Reinforced concrete monolithic frames are widely used in the construction of high-rise buildings. One of the main advantages of such a frame is the possibility for architects to freely plan spaces (walls, pilasters, columns), while for design engineers, it ensures an even redistribution of forces in the load-bearing elements, which leads to more uniform settlement of foundations. At the same time, the construction of monolithic buildings is a rather time-consuming process, so to accelerate construction timelines, the load-bearing structure is often made of precast reinforced concrete. However, considering that in precast concrete, structural elements are connected through mortar and embedded parts, it is more challenging to achieve an even distribution of forces under the vertical load-bearing elements of the frame compared to a monolithic frame, where the entire building acts as a single rigid disc. Uneven settlement is also influenced by the fact that there are self-supporting panels and panels that support floor slabs (from one or both sides).

The stiffness of load-bearing structures (and consequently the building as a whole) in a panel building primarily depends on the connection of panels with each other. Depending on how the panels (as well as floor slabs) are connected, different displacements will occur, which in turn create additional forces in the foundation structures, ultimately causing uneven redistribution of forces in the pile field.

Based on the above, we can conclude that studying the effect of panel jointing on the redistribution of forces in the foundation structures of high-rise panel buildings is a relevant task.

The purpose of this work is to investigate the influence of panel jointing in a high-rise residential building on the stress-strain state of foundation structures based on numerical modeling of the "base-foundation-superstructure" system.

Justification of the technological possibility of connecting rolled polyethylene film with adhesive seams during the construction of anti-flood dams with diaphragms

Oleksii Petrochenko — Fri, 29 Nov 2024 00:00:00 +0200

Polyethylene is the most common material of films used in hydraulic construction. In the process of construction of hydro technical structures, rolled polyethylene film, manufactured in factory conditions, is connected into continuous anti-filtration structures: screens, diaphragms, curtains. A reliable method of joining the edges of polyethylene film is welding. But in some cases, for example, during the construction of anti-flood dams with anti-filtration diaphragms using a high-performance trenchless method of laying rolled polyethylene film in the soil, there is a need to use a more convenient method of joining the edges of the film, namely gluing. However, it is known that polyethylene, being a non-polar polymer, does not have sufficient adhesion to adhesives. In the article, the possibility of using the operation of gluing polyethylene film in certain processes of hydraulic construction is substantiated by successively conducting theoretical, experimental and field studies. According to the results of theoretical studies of the stress-strain state of adhesive seams of thin films made of materials obeying Hooke's law, it was established that the use of adhesives with a small modulus of elasticity provides a more uniform distribution of tangential stresses across the seam, compared to the use of adhesives with a large modulus of elasticity, which helps to increase the tensile strength of the adhesive seam of the films. This theoretically obtained result was first accepted as a hypothesis, and then confirmed by experimental studies. Samples of polyethylene film, connected with the help of glues with different modulus of elasticity, were tested for stretching on the MP-05-1 machine. It was established that with the use of rubber-based adhesives, the destruction of the adhesive seams of the films occurred at the moment when the tensile stress in the samples of polyethylene films in all cases exceeded the yield point of polyethylene. According to the results of field studies of the process of trenchless laying of rolled polyethylene film during the construction of earthen anti-flood dams with anti-filtration diaphragms, the possibility of joining the edges of the polyethylene film using glue based on nairite rubber was established.