Strength of Materials and Theory of Structures

Optimization of a vibro-impact damper design using MATLAB tools

Petro Lizunov, Olha Pogorelova, Tetiana Postnikova — Wed, 17 Apr 2024 00:00:00 +0300

The paper studies the dynamics of a vibro-impact system consisting of a main (primary) structure and a vibro-impact damper coupled to it. A vibro-impact damper is a vibro-impact nonlinear energy sink (VI NES). The optimal damper design should provide the best vibration mitigation for the primary structure. The optimization procedures for finding the optimal NES design are carried out using standard MATLAB tools. We used different MATLAB programs, namely surf program, which graphically shows the ranges of parameter pairs to be optimized; fminsearch and fminconprograms, which search for local minima of the objective function. It is shown that the optimization procedure itself is ambiguous and contains a sufficient amount of arbitrariness. Its result is also ambiguous. It is due to the presence of the many possible sets of damper parameters that can provide maximum mitigation of the main structure vibrations. We do not use the genetic algorithm gabecause it selects random intermediate results and yields randomly selected parameter sets from the optimal parameters manifold. Setting the objective function and its parameters plays a crucial role in the optimization process. We have chosen the maximum total energy of the primary structure as the objective function. Each resulting variant of the damper parameter set should be carefully tested and analyzed. We compared the five obtained optimal designs for dampers with two different masses. When analyzing them, we observed different motion modes, namely periodic modes of different periodicity with different number of impacts per cycle, with different ratio of bodies motion periods: 1:1 resonance with resonance capture and 2:1 resonance; amulti-periodic mode with many impacts per cycle, which turned out to be an amplitude-modulated mode – Amplitude Modulated Signal . The final decision on the optimal damper design may be made taking into account various engineering considerations regarding its mass and other parameters. It should be based on the options obtained as a result of the optimization procedure.

Application graph theory to evaluate the stability of landslide slopes

Ivan Solodei, Vasyl Pavlenko — Wed, 17 Apr 2024 00:00:00 +0300

Evaluation of the stability of slopes is a complex and important engineering task, the solution of which requires the analysis of a significant number of factors. Many different methods of slope stability calculation have been developed to solve this type of problem. However, two groups of methods - limit equilibrium methods and the finite element method (FEM) - have become the most widely used. However, these methods have certain disadvantages. Limit equilibrium methods are limited by the assumptions used during the calculation, including the hypothesis of a solid compartment, which does not allow analyzing the stress-strain state. The FEM of the elements does not make it possible to unambiguously localize the sliding surface of the slope, and the determination of the stability coefficient using the method of reducing the strength of the soil requires a large number of complex iterative calculations. The methods and approaches of graph theory can be used precisely to combat the shortcomings of FEM.

The paper examines the basics of graph theory. The main methods of specifying graphs, as well as certain types of graphs with an indication of their key features, are presented. The concept of isomorphism of graphs and some features of their graphical representation are revealed.

The article presents the basic idea of using graph theory to calculate the stability of slopes. The main questions that must be solved when applying graph theory to the given type of problem are outlined. Two methods of converting a mesh of finite elements into a graph are considered in detail. The advantages and disadvantages of the proposed methods are analyzed. The transformation of the calculation scheme of an imaginary slope with a given geometry, which was simulated in the LIRA-SAPR software complex, into graphs using the above methods is demonstrated. An overview of the approaches that can be used to create a graph weight function is given.

Ways of developing assessments of the technical condition of buildings and structures

Anatolii Perelmuter — Wed, 17 Apr 2024 00:00:00 +0300

The main differences between the norms for assessing the technical condition of buildings and structures and the norms for their design are analyzed, which are due to different levels of awareness and the degree of uncertainty of the parameters of the structure. It is indicated that the current standards of structural design are not sufficient for assessing the reliability of existing structures, for designing their repair or modernization. Existing design standards do not provide for procedures for assessing the current state of existing structures and the resistance of materials. In addition, they do not deal with the uncertainty of the situation, which is fundamentally different from the design conditions when it comes to the existing structure. During the design of a new structure, the uncertainty of the parameters is taken according to the data averaged for the entire country. But the implemented design is not the average across the country, but is a specific unique structure with characteristics that are refined and, therefore, uncertainties are reduced. It is proposed to take into account the level of knowledge about the technical condition assessment object by using special uncertainty coefficients.

The possibility of applying reduced values of target levels of reliability, the values of which are substantiated by calculations based on the quality of life index, is emphasized. The recommendations of the international standard ISO 13822, regarding the possibility of reducing the target reliability index, were compared with calculations based on the quality of life index LQI, based on Ukrainian statistics.

It is considered appropriate to use new risk-oriented approaches in order to improve the decision-making system for planning the life cycle of construction structures and assessing the residual resource. A list of tasks that need to be solved for this is provided.

Strength analysis and force distribution in a tensile metal joint

Sergii Pyskunov, Serhii Mytsiuk, Dmytro Mytsiuk, Yuriy Repiakh — Wed, 17 Apr 2024 00:00:00 +0300

One of the methods of connecting several elements of mechanical structures to form an assembly is bolting. Unlike other types of connections, such as welding or riveting, this type of connection has the advantage of being disassembled, which is why bolted connections are quite common. At the same time, like other types of connections, it is an important structural element that requires additional attention in calculations. The most common calculation of a bolted connection is using analytical formulas.

Every day, the requirements for accuracy, speed and versatility of approaches to the calculation of building structures are increasing. In addition, special attention should be paid to the calculation of nodes where structures abut each other, since depending on the operating conditions of the node, different distribution of the NDP is possible, which in turn affects the geometr2ic characteristics and operation of structures.

In this regard, we compared the results of the distribution of stresses and forces in the bolt using the finite element method with the use of universal quadrilateral shell FEs, universal spatial eight-node isoparametric FEs, and the semi-analytical finite element method.

The obtained results of solving the test case using universal quadrilateral shell FEs and universal spatial eight-node isoparametric FEs allow us to conclude that there is a slight difference in the stress distribution in the spatial formulation of the FEM and SFEM. In addition, based on the FEM and NEM calculations and, accordingly, the calculation according to the DBN, it can be concluded that when calculating according to the DBN standards, an analytical calculation can be used to determine the safety margin of a bolt for simple tasks.

Definition of the stress-strain state of a glued laminated timber beam reinforced with composite strips using experimental method

Mykola Komar, Denys Mykhailovskyi — Wed, 17 Apr 2024 00:00:00 +0300

The trend in the development of the construction industry worldwide requires increasing attention to ecological aspects, which means that materials with minimal negative impact on the environment are becoming increasingly popular. At the same time, these materials must possess high strength and durability against various external influences and loads. From this perspective, constructions made of wood and its derivatives are gaining the most popularity. Such constructions, made from renewable natural resources, exhibit relatively high strength at relatively low density, thus belonging to such materials. Although wood has its drawbacks, such as susceptibility to drying, rotting, and anisotropy of properties, these drawbacks can be completely mitigated in glued laminated timber structures. Glued laminated timber beams, which are the primary structural element of many buildings and structures, are the most widespread. Therefore, the issue of significantly increasing their rigidity and strength through reinforcement with composite materials is particularly relevant.

This article proposes a methodology for determining the stress-strain state of a glued laminated timber beam reinforced with composite strips. The results include deformation parameters of the experimental model, actual elastic modules during bending, maximum longitudinal stresses at the center of the span, along the load application axis, and along the support axis. Additionally, maximum transverse and shear stresses along the load application axis and along the support axis are determined. The actual maximum load-bearing capacity of the experimental model reinforced with composite strips is established.

The current state of the problem of numerical investigation of metal structure refusal based on dynamic monitoring

Maksym Vabishchevych, Oleh Dedov, Dmytro Savchuk — Wed, 17 Apr 2024 00:00:00 +0300

The article considers the critical role of long-term dynamic monitoring of building structures in ensuring their safety and stability. The importance of studying the structural behavior of truss structures after local failures is emphasized, which is key to the development of effective monitoring methods. The value of vertical deflections and modal frequencies as indicators of the general behavior of structures is pointed out, as well as the high costs associated with traditional monitoring methods requiring a large number of sensors. It is also emphasized that modern engineering practice does not have universal monitoring methods that would take into account all the features of construction structures, especially spatial structures with a complex design and a variety of elements. Authors calls for the development of new approaches and technologies to improve risk monitoring and management, which can prevent catastrophic consequences, as was the case with Viadotto Polchevera and other structural collapses. Attention is also drawn to current research that uses dynamic monitoring to inform the design of civil structures, including updating finite element models based on measured in-service performance. It is highlighted that long-term monitoring can provide valuable information about structural behavior, which allows for a better assessment of the condition of the structure and the prediction of potential defects. It is emphasized that a local failure can lead to the progressive destruction of the entire structure, which makes monitoring extremely important to prevent such incidents. The article concludes with conclusions about the need to establish management and maintenance procedures to maximize the life cycle of structures and obtain optimal return on investment.

Natural frequencies and modes of parametric vibrations of reservoir shell with shape imperfections

Petro Lizunov, Olga Lukianchenko, Oksana Paliy, Olena Kostina — Wed, 17 Apr 2024 00:00:00 +0300

Development of software on the basis of the finite element method led to intensive creation of the numeral methods for the decision of static and dynamic problems of the thin shells. The finite element model of the thin shell has an infinite number of freedom degrees and natural frequencies, so solving the dynamics problem of the shell is difficult. If behavior of natural vibrations of the shell was researched, it is possible to talk about shell internal properties which take a great place at the forced vibrations including parametric one. It is important to take into account influence of the constant component of parametric load on natural frequencies and modes of the shell. Nowadays forming of an effective model of parametric vibrations of the shell with shape imperfections and choice of the most dangerous imperfections model remain relevant. Influence of real and modelled imperfections on natural frequencies and modes of reservoir shell parametric vibrations excited by axial load and on shell stability loss was investigated in this article. The finite element models of the shell was formed by software NASTRAN. The modelled shape imperfections as a lower buckling form of perfect shell under static pressure were presented. The real imperfections as the deviations of the shell wall from the vertical were obtained by theodolite surveying. The natural frequencies and modes of the imperfect shell taking into account the its previous stress state from action of the constant component of the parametric load were received by the Lanczos method. Investigations showed that the real imperfections of shell a little influenced on natural frequencies and modes of parametric vibrations. These decreased the critical loads on the first natural frequency on 0,58 % and increased on the second natural frequency shells on 0,79 %, but qualitatively changed the form of stability loss on these frequencies. Modelled imperfections had a greater but not considerable influence on natural frequencies and modes of the shell. But the modelled imperfections of the shell under constant component of parametric load considerably increased the critical load on the first and second natural frequency accordingly on 12,3 % and 5,26 % and changed the shell forms of stability loss. So the modelled imperfections of the shell in the form of the regular circular half-waves increased shell carrying capacity, but not decreased. This positive effect takes place at constructing of cylinder shells from the corrugated rolled sheets.

Analysis of the stress-strain state of the rotary device fastening part by the semi-analytical finite element method

Wed, 17 Apr 2024 00:00:00 +0300

The possibilities of the numerical apparatus developed on the basis of the semi-analytical finite element method are shown on the example of solving a specific problem. In the areas of maximum values, the parameters of the stress-strain state of the re-device fastening part were compared. It is worth noting the relatively complex configuration of the cross-section of the object, which led to a thorough study of the principles of constructing a grid area. The surface of interaction between the axis and the hull was modeled by a fairly thin layer of elements in relation to their thickness, which absorb only normal stresses. Analysis of the stress-strain state of the rotary device fastening part should be carried out from the standpoint of a spatial problem. Moreover, according to the results of the elastic calculation, the transition section between the body and the base plate turned out to be more loaded compared to the zone of contact interaction between the body and the axle. The data of the calculation performed in the elastic-plastic formulation made it possible to clarify the idea of the operating conditions of individual sections of the object and to draw a conclusion about the uniformity of the hull.

The carried out studies confidently demonstrated the wide possibilities of the developed approach in solving new, practically important problems of elastic deformation of prismatic bodies of complex shape in the spatial formulation of new ones. To substantiate the reliability of the results of the calculation of the elements under consideration, a sequential increase in the number of FE in the cross-section and the number of retained terms of the decomposition along the length of the body, as well as an increase in the accuracy of solving systems of equations, are given. In addition, an assessment of the satisfaction of natural boundary conditions on the surface of the body and the conditions of equilibrium in the integral sense is given according to the characteristic sections within the region, which showed their fairly good performance. New data on the regularities of behavior of critical structures in the process of loading, due to the consideration of their physical and geometric parameters, have been obtained.

Influence of perforation on static characteristics of the enclosing corrugated panel under the wind action

Olga Lukianchenko, Serhii Tsybulnyk, Andrii Kozak, Oleh Gerashchenko, Iryna Kara — Wed, 17 Apr 2024 00:00:00 +0300

The application of the enclosing panels with perforation in construction practice for protective structures is economic advantageous due to reduction of financial costs for their production, transportation and installation. But influence of perforation on static and dynamic characteristics of the enclosing panels was not enough investigated. With the purpose of wind protection of the buildings and structures at the Ukrainian Antarctic station „Akademik Vernadsky” static stress and stability analyses of the protective structure were executed in according with the first and second groups of limit states of State building regulations of Ukraine. The protective structure as the enclosing corrugated steel panel and supporting columns was appeared. In the article the results of numeral research of the stress strain state and stability of the corrugated panel are presented. The panel width and height were accepted permanent, and a panel thickness was explored and accepted according to requirements for its stiffness, strength and stability. The four corrugations in the form of trapezoids are located along the panel height. Perforation of the panel in the form of round holes with a radius of 12.5 mm was presented. Two finite element models of the corrugated panel using the software NASTRAN were built. The corrugated panel without perforation model as a collection of rectangular shell finite elements with six degrees of freedom at the node was modeled. This model contained 35161 finite elements and 32540 nodes. The finite element model of the enclosing corrugated panel with perforation contained 383043 triangular shell finite elements with six degrees of freedom at the node and 211609 nodes. Boundary conditions were imposed on the modal nodes along the height on both sides of the corrugated panel in the form of fixing, taking into account its rigid attachment to the columns. Wind action on the enclosing panel was presented as uniform distributed static load, the limit calculation values of which were got according to State building regulations of Ukraine and statistical data of wind at the Ukrainian Antarctic station. The main attention was given to research of influence of perforation on the corrugated panel equivalent stresses and displacements, critical values of wind load and form of loss of corrugated panel stability. Computational procedures of static stress and stability analyses of software NASTRAN were applied.

The problem of the structure and the soil plastic environment interaction in the conditions of dynamic evolutionary processes

Ivan Solodei, Oleksandr Ruvin, Vira Koliakova, Oleksandr Kulikov — Wed, 17 Apr 2024 00:00:00 +0300

Dynamic influences are one of the important factors affecting project decisions during the construction of buildings and structures. In the case of dynamic analysis, the range of possible variations in structural response is very difficult to determine. The complexity is determined not only by the parameters of the load itself (intensity, the law of change over time), but also by the characteristics of the research object (their values and change over time), which is an interconnected system of the structure and the soil base. Dynamic factors of influence can include periodic vibration or shock loads, the effects of explosions that cause a sharp change in pressure on the structure of the building, seismic fluctuations, etc. In many cases, the load is the result of stress waves propagating in the soil base. These factors can act on the natural environment long-term, relatively short-term, short-term and instantaneous. Therefore, the development of refined approaches for assessing the stress-strain state of structures during the interaction of the structure and the soil environment under the conditions of dynamic evolutionary processes remains an actual task today.

In order to effectively find a solution to the dynamics problems, it is necessary to possess the entire set of analysis tools, to clearly present the rules and limits of their application. The ability to correctly assess the engineering and geological conditions of the construction site, the properties of the soils, the joint work of these soils with the foundations and structures of the building has always been and remains the basis of reliable and effective engineering design.

The given statement of the problem is a theoretical basis to build the numerical approaches to the study of the vibrational processes of heterogeneous spatial bodies during their contact interaction with an elastic-plastic medium. The paper considers the modeling aspects of the structure and the soil elastic-plastic environment interaction under the conditions of dynamic evolutionary processes. The basic geometric and physical equations of the elasticity theory for heterogeneous circular and prismatic spatial bodies are given. In the range of solving the dynamics problem, the peculiarities of the mathematical model implementation, regarding the representation of the variation of kinetic energy as part of the equations of dynamic equilibrium of linear and nonlinear mechanical systems, are considered.

Universal three-dimensional finite element for analyzing of elastic inhomogeneous shells under thermomechanical loads

Oleksandr Kalashnikov, Olga Krivenko, Petro Lizunov — Wed, 17 Apr 2024 00:00:00 +0300

The work is devoted to the development of a new modification of the finite element intended for the calculation of inhomogeneous composite shells of thin and medium thickness. The element is constructed on the basis of a universal three-dimensional isoparametric 8-node multilayer finite element of a continuous medium. The layers of the modified finite element are made of composite materials reinforced with continuous unidirectional fibers. Within the framework of a finite element model of a multilayer shell of stepwise variable thickness, a technique for modeling the properties of a unidirectional fibrous composite material has been developed, based on a method for structuring material inhomogeneities iby thickness and by plan. The shell can consist of an arbitrary number of layers of varying thickness bonded into a single piece. Each layer can have its own type of material: traditional or composite. Effective physical and mechanical characteristics of the layer material are determined using known micromechanical methods for predicting the thermoelastic constants of a fiber composite through the known physical characteristics of the matrix and fiber. The fibrous material of the layer is presented as homogeneous transversely isotropic with planes of isotropy normal to the direction of reinforcement. Additional variable parameters of the "basic" universal finite element are supplemented with new attributes that determine the thermoelastic properties of the composite components. The new parameters are related to the choice of the type of fibrous composite material in the layer of the finite element, to the setting of structural micromechanical parameters of its components, and to the setting of the reinforcement orientation angle. This allows the calculations to use both traditional and fiber-composite materials in layers of inhomogeneous shells. Numerical examples demonstrate the effectiveness of the developed approach.

Contribution of system elements to its static indeterminacy

Anatolii Perelmuter — Wed, 17 Apr 2024 00:00:00 +0300

The article contains an overview of the main ideas regarding the new direction of construction mechanics, which considers the issue of survivability and is intensively developing. From the point of view of redundancy, as the ability of the system to provide alternative ways of transferring the load, which is one of the main possible strategies for designing reliability and survivability, the static-kinematic analysis of rod systems is also considered.

The fundamental measure of the level of redundancy of rod systems is the degree of static uncertainty. But this numerical sign does not contain information about the role of each element of the system in forming the degree of static uncertainty. This role is performed by a specially constructed distributed static indeterminacy matrix (DSI-matrix), which contains comprehensive information about the contribution of system elements to its static and kinematic properties.

Using the fundamental provisions of linear algebra, the properties of the matrix of coefficients of the system of linear equilibrium equations as an operator over the vector spaces of forces and displacements are analyzed. The mechanical content of the four fundamental subspaces associated with this matrix is indicated. This analysis determines the mathematical properties of the RSN matrix and its mechanical interpretation.

Methods of forming the DSI-matrix are considered both for the case of a geometrically constant system and for the analysis of geometrically variable systems, when it is necessary to resort to singular decomposition of the matrix of equilibrium equations. All theoretical explanations are accompanied by illustrative examples, although the issue of numerical implementation of the considered methods of analysis is not considered. It is obvious that they deserve independent consideration.

Information is provided on the possibility of using the DSI -matrix to assess the reliability and survivability of the structural complex and its use to analyze the sensitivity of the system to the inaccuracy of manufacturing elements.

Deformation of layered soil

Ivan Belmas, Alik Trikilo, Olena Bilous, Hanna Tantsura, Oleksandr Fesan — Wed, 17 Apr 2024 00:00:00 +0300

One of the consequences of the aggression of the russian federation in Ukraine is a change in the properties of the surface layers of some regions of the soil. Construction of structures in such areas must be carried out considering the above. In order to create prerequisites for taking into account the artificially created layering of the soil, an algorithm for analytical determination of the stress-strain state of a two-layered soil was developed in a linear setting within the limits of plane deformation. Layers are considered as linear elastic bodies of limited dimensions in the plan. The algorithm is based on the Ery stress function with arbitrary coefficients, on the dependence of the indicators of the stress-strain state of the soil layers on it and on the mechanical indicators of the material of the layers, the thickness of the artificially formed surface layer. The algorithm provides for the formulation of the load conditions by the normally distributed force of part of the soil surface, the conditions of the interaction of the layers, and the unlimited thickness of the main soil layer.The listed conditions and features of the layers constitute a system of linear algebraic equations. The solution of the system of levels provides an opportunity to determine the coefficients of the stress function and, accordingly, to determine the indicators of the stress-strain state of the two-layer soil support. The generalization of the results, carried out by planning the experiment for the selected limits of possible realizations of the mechanical properties of the soil layers, allows for determining the deflections of the surfaces of the layers depending on individual factors.The following is established. The characteristics of the dependences of the deflections of the layer surfaces on other parameters are similar. Maximum deflections decrease with increasing surface layer thickness. Deflections of the interaction surface of the soil layers are linearly dependent on the Poisson ratio of the main soil layer and decrease as the ratio increases. The results obtained within the limits of the linear formulation can be considered sufficiently reliable because they are obtained analytically and generalized by the methods of the linear theory of elasticity and the method of planning the experiment.

Determination of stress intensity coefficients using PC LIRA CAD

Oleksii Shkryl, Yurii Maksymiuk, Volodymyr Dolgoshey, Vladyslav Buchko — Wed, 17 Apr 2024 00:00:00 +0300

Today, the issue of involving fracture mechanics approaches to the calculation of structures with cracks is becoming more and more relevant. For the most part, the implementation of such approaches is carried out using software complexes in which the finite element method is implemented. Among them, such software complexes as Abaqus, Ansys, Nastran stand out, where the implementation of fracture mechanics approaches is constantly being improved. However, the cost of licenses for the use of such complexes, especially in the conditions of Ukraine, does not allow most researchers to fully use such programs. Therefore, it is relevant to study the possibility of applying fracture mechanics approaches in software complexes, the use of which is free. In construction, a significant number of structures are isotropic bodies. Operation of most of them is accompanied by elastic deformations. If there are cracks in them, the load-bearing capacity is assessed using stress intensity factors (SIF). This article examines the possibility of determining the TIN based on the results of the specified stress-strain state obtained with the help of the free software package "PC LIRA-SAPR 2016 R5 (non-commercial)".

The calculation of SIF is performed by a direct method based on the determined distribution of displacements and stresses around the crack tip. The crack is modeled by setting appropriate boundary conditions.

Implementation of the direct method is performed in 2 ways. According to the 1st method, the SIF calculation is performed in the apical area according to the values of stresses and displacements. According to the 2nd method, the SIF is calculated by moving the node closest to the top of the crack. Approbation of the approaches was carried out on the test problem of tension of a plate with a central crack. A study of the influence of the dimensionality of the discrete model and the types of finite elements both outside the apex region and in the apex region itself was conducted. The obtained results showed the possibility of obtaining reliable SIF values in this software complex in two ways, subject to compliance with certain rules for building a discrete model.

Analysis of thermo-mechanical incompatibility of fullerenes with polymer matrices of composites

Nataliia Shlyun — Wed, 17 Apr 2024 00:00:00 +0300

Unique strength and rigidity properties of carbon nanotubes and fullerenes do them very perspective reinforcing admixtures into composites produced on the basis of polymeric and metallic matrices. It is established that even relatively small their dopes into composites can essentially enlarge physico-mechanical characteristics of polymers. At the same time, comparatively low value of the linear thermal expansion coefficient of carbon nanomolecules results in the possibility of the emergence of the internal mechanism of the additional intrastructural stresses origination in the polymer conditioned due to thermomechanical incompatibility of the composite fractions. To examine this possibility, the theoretical modelling of the thermomechanical deforming of the considered heterogeneous structures under thermal change action was carried out. In doing so, the fullerenes were simulated as a thin elastic shell with adduced (effective) thickness, elasticity modulus, Poissonn’s coefficient and linear thermal expansion coefficient, the polymer matrix was supposed to be a homogeneous elastic medium with the prescribed parameters of thermoelasticity. The system of constitutive ordinary differential equations was deduced, which described the thermoelastic stress-strainedstate of the elastic fragment chosen for consideration. These equations solutions were deduced in the closed form for the case when the system temperature changed in. Fenolformaldegid, epoxy rezin, polycarbonate, polyamide, polystirol, polyester, and polypropylene, possessing increased values of the linear thermal expansion coefficients, were chosen as the matrix materials. With these initial data, the values of the fullerene radial displacements were calculated for two magnitudes of the sphere radius. It is demonstrated that owing to the high value of the fullerene effective elasticity modulus, the thermal deflections of its wall poorly depend on the properties of the encompassing matrix and practically are equal to its free thermal displacements. The thermal stresses of the polymer matrices have the largest values in the zones of the interface surfaces and they decrease proportionally to cube of the radial coordinate, so, the damages provoked by them have localized character.

Investigation of the influence of the elastic medium on the dynamic behavior of a three-layer elliptical cylinder under non-stationary loading

Viktor Gaidaichuk, Kostiantyn Kotenko, Mykola Klymenko — Wed, 17 Apr 2024 00:00:00 +0300

Dynamic transient processes are studied and the results of evaluating the influence of an elastic medium on the behavior of a three-layer cylindrical shell structure of elliptical cross-section 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 (SSS), have been performed. Variants of the structure without a polymer aggregate and with a discrete-symmetric rib-reinforced aggregate are considered. A comparative analysis of the deflections and stresses of the load-bearing layers of the structure in the absence of light aggregate and in its presence is given.Numerical results regarding the dynamics of the three-layer structure were obtained using the finite element method.

Numerical modelling of temperature effects on the overpass to create a spatial computer model of reconstruction

Wed, 17 Apr 2024 00:00:00 +0300

Numerical modelling of temperature effects on the reinforced concrete overpass No. 11a of PJSC "Azovstal Ironand Steel Works" in Mariupol was carried out to assess the technical condition of building structures, identify possible defects affecting the strength and bearing capacity of the structure, load capacity and residual life, along with engineering surveys using instrumental methods, to develop a project for the overpass overhaul. A comprehensive methodology for studying the stress-strain state, strength and stiffness of structures was created and a calculations of tware package based on the semi-analytical modified straight line method was developed, which works along side the LIRA and SCAD calculations of tware packages and provides accurate and objective results. Based on the results of the study, the concept of the overpass reconstruction was adopted on the basis of the created spatial computer models and a project for the overpass overhaul was developed.

Belt conveyor starting mode optimization

Viacheslav Loveikin, Yurii Romasevich, Ruslan Kulpin, Kostiantyn Pochka — Wed, 17 Apr 2024 00:00:00 +0300

The work is aimed at increasing the efficiency of belt conveyors by choosing the drive mechanism movement mode.

During the operation of belt conveyors, significant energy and dynamic loads occur in the elements of the drive mechanism and traction body. The available loads significantly affect the energy losses and the reliability of the drive mechanism and the traction body. Energy and dynamic loads during transient processes (starting, braking, changing speed or performance and emergency stop) are especially dangerous. At this moment, high-frequency oscillations of both the traction body and the drive elements arise. With such fluctuations in the traction body (belt) of the conveyor, significant breaking forces arise, which create additional unwanted stresses in it and, as a result, contribute to premature destruction. In addition, the stator and rotor windings of the electric motor are heated, which accelerates their wear and failure.

In order to reduce dynamic loads, it is proposed to optimize the movement mode of the drive mechanism. For this purpose, the conveyor is presented in the form of a three-mass dynamic model, based on which a mathematical model was created. From the conducted dynamic analysis of the belt conveyor, it was established that during the start-up process, significant power and energy overloads occur in the elements of the drive and the traction body, which depend on the driving force of the drive. In addition, high-frequency oscillations of the tape are observed. Since the undesirable properties of the belt conveyor largely depend on the magnitude of the driving force of the drive, it should form the basis of the optimization criterion. In addition, the driving force of the drive must be reflected in the optimization criterion during the entire movement process, that is, the optimization criterion must be presented in an integral form. To eliminate the possible compensation of negative and positive values of the driving force on the conveyor, the latter should be represented in the integral criterion in quadratic form. Therefore, the rms value of the driving force of the drive during the start-up time was chosen as the criterion for optimizing the motion mode of the belt conveyor.

Optimization of the conveyor movement mode was carried out by minimizing the integral dynamic criterion. As a result of the optimization, the start-up mode of the belt conveyor was determined, which minimizes the effect of dynamic loads. This start-up mode makes it possible to increase the reliability of the conveyor and reduce the energy consumption of the drive.

Numerical-analytical approach to solving problems of non-stationary thermal conductivity of a non-thin annular plate

Wed, 17 Apr 2024 00:00:00 +0300

This paper considers the first stage of calculating the initial boundary value problem of non-stationary thermal conductivity of cylindrical bodies using a modified method of lines, namely dimension reduction of the original differential equations, initial and boundary conditions. The original equations of thermal conductivity are defined in a cylindrical coordinate system in a spatial setting. An object is a cylindrical body with commensurate dimensions. This area of research is relevant, because when calculating the load bearing elements of structures to thermal effects, the first step is to determine the distribution of temperature fields. Boundary conditions are considered as conditions of convective heat transfer, which by means of boundary transition are transformed into boundary conditions of the first and second types.

Dimension reduction with respect to spatial coordinate is performed by the Bubnov-Galorkin-Petrov projection method using local basis functions. These functions are called "cover" functions, which are related to the lines drawn on the domain of the task. Normalized trigonometric series are used to reduce the dimensionality of the equations with respect to circular coordinate. All transformations are performed in index form. In addition to differential equations, the projection method reduces the dimensionality of the initial and boundary conditions. In this paper, the most optimal form of writing reduced equations is determined, which provides the ease of reducing the dimensionality of the original differential equations. Initial and boundary conditions take into account the impact of the environment. All this makes it possible to set a reduced initial boundary value problem for further calculation by numerical finite difference methods.

Thermally stressed state of asphalt concrete layer on a metal base

Viktor Gaidaichuk, Liudmyla Shevchuk — Wed, 17 Apr 2024 00:00:00 +0300

The results of a finite element study of the thermally stressed and deformed states of a fragment of a two-layer bridge structure, consisting of a bearing metal orthotropic slab with a layer of asphalt concrete applied on it, are presented. It is believed that the materials of the layers are characterized by different thermomechanical parameters, which determine the inhomogeneity of the stress and strain fields. An analogue of these phenomena can be the effect of transformation in electric thermal relays of thermal action on a bimetallic plate with different coefficients of thermal linear expansion into its mechanical displacements, which are used to actuate the switch and switches.

Using the method of computer modeling, it was found that these factors lead to the concentration of stresses and strains and changes in the stress-strain state in all elements of the bridge structure end are not taken into account in the modern practice of designing and operating bridges, as well as are one of the reasons for the premature destruction of asphalt concrete pavements. To eliminate these shortcomings, on the basis of finite element algorithms, a theoretical analysis of the thermally stressed state of a metal bridge slab with an asphalt concrete pavement at various ratios of their thicknesses is carried out. It is shown that an increase in the thickness of the upper layer can lead to an increase in shear and normal tensile stresses initiated in it. Therefore, when designing bridge structures, these features should be additionally taken into account.

Study of the thermal effect of fire on fragments of reinforced concrete columns based on the results of experimental tests

Oleksandr Nuianzin, Andrii Kozak, Vadym Yanishevskyi, Vasyl Kryshtal — Wed, 17 Apr 2024 00:00:00 +0300

The paper analyzes the thermal effect of fire on fragments of reinforced concrete columns based on their heating according to the standard fire temperature regime in a small-sized installation for the study of the thermal effect of fire on building structures. Based on the proposed method, a technique was created that makes it possible to estimate the fire resistance limit of a full-size structure by calculation. The course and results of the conducted fire test are described, and the adequacy and reproducibility of the experimental data are verified. The temperature distribution over the entire area of the fire furnace, the studied fragments was analyzed and the obtained results were processed. The possibility of creating a standard fire temperature regime in the fire furnace chamber has been verified. According to the results of this work, it was established that the heating of the structure at all levels was uniform in the planes of placement of thermocouples, the maximum temperature on the surface was 709 °C, it was observed at the last minute of the experiment and continued to increase linearly, the maximum temperature reached in the center of the rock column was 105 °C, it was observed at the last minute of the experiment and continued to grow linearly; The adequacy of the experimental data was confirmed: the relative deviation did not exceed 4%, and the calculated adequacy criteria (Fisher, Student and Cochrane) were below the critical value.

Multi-criteria parametric optimization of the displacement and weight of a shell of minimal surface on a circular contour consisting of two inclined ellipses under thermal and power loading with consideration of geometric nonlinearity

Hryhorii Ivanchenko, Oleksandr Koshevyi, Gherman Zatyliuk — Wed, 17 Apr 2024 00:00:00 +0300

Thin shells are well suited to optimal design problems, and the finite element method and gradient descent method make it possible to solve inverse problems in structural and applied mechanics. The calculation process takes into account geometric nonlinearity.

In modern numerical studies, a formulation taking into account geometric nonlinearity in the finite element method is used, namely, a stepwise loading procedure. It becomes necessary to take into account the relations between displacement vectors and their derivatives and strain increments. These relations help to determine the stiffness matrix of the finite element at each loading step, which leads to a qualitative study of real displacements in the structure.

The geometrically nonlinear calculation of a shell of minimum surface on a circular contour consisting of two inclined ellipses in a multi-criteria parametric optimization is performed by the finite element method. The finite element method is a universal variational method that is focused on solving the most complex problems of elasticity theory and applied and structural mechanics using separate calculation complexes.

Stiffness matrix - for the whole body is formed on the basis of the finite element stiffness matrix. 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 in a state of stability and equilibrium has a minimum value.

As part of the sensitivity analysis, gradients of the design variables of the structure, displacements in the form of partial derivatives of these characteristics along the design variables, and shell thickness are calculated. The sensitivity information serves as the basis for building an optimal design algorithm using the gradient descent method of the objective function.

Standard multi-criteria parametric optimization allows for an average of 10% steel savings, with geometric nonlinearity increasing to 20%. At this study site, 24.4% of sheet steel was saved, which is a significant relative saving.

This methodology of the authors shows high results for innovative design and production of steel thin shells in Ukraine and around the world, and also makes it possible to apply several types of optimization to one research object.

Analysis of the influence of external factors on the deformation of high-rise buildings in the process of their construction and operation

Wed, 17 Apr 2024 00:00:00 +0300

During the construction and operation of high-rise buildings, their vertical axis changes its position in space. The greater the height of the structure, the greater the amplitude of oscillations. This causes problems of geodetic construction support and the need to monitor deformations during the operation of high-rise structures. In real conditions, part of the structures will be in the shade and their temperature will be lower than the structures that will be under the influence of solar radiation, the temperature of which will be much higher. Thus, the building will deform as a result of uneven thermal expansion, that is, it will bend. From DBN B.1.3-2:2010 "Geodesic works in construction". Also, during the geodetic provision of the construction and operation of high-rise buildings, changes in the temperature regime of building structures should be taken into account in connection with significant absolute values of changes in the geometric dimensions of the building as a result of thermal expansion, which significantly exceed the accuracy regulated by the regulatory document. The article examines and analyzes the influence of external forces on changes in the geometry of high-rise structures and focuses attention on solving the scientific problem of geodetic support for the construction and operation of modern high-rise structures under dynamic loads.

Aluminum dome structures' stability study

Vitalii Tonkacheiev, Serhii Bilyk, Hennadii Tonkacheiev — Wed, 17 Apr 2024 00:00:00 +0300

The large spans dome structures made of aluminum alloys work is considered. The dome elements material choice is due to the lower weight compared to steel elements, the material corrosion resistance and the lower thermal expansion coefficient. An existing scientific research analysis related to the structures made of aluminum or aluminum alloys stability loss problem was carried out. A two-rod three-hinged model — the von Mises truss (MT) — was used as the research model. The normal stresses on relative deformations dependences graphs for a low-pitched truss with rod inclination angles of 80 and 85 degrees from the vertical for aluminum alloy 5083 with different tubular profiles thicknesses were obtained. The research was carried out in accordance with the provisions described in DSTU-NB EN 1999. An analytical expressions system was derived for determining the aluminum alloy elasticity modulus on strain diagrams. Analytical dependences describing the aluminum MT trusses' operation for all alloys with known mechanical and deformation properties have been obtained. The relative concentrated force in the truss's ridge node on the relative vertical deformations dependences graphs are plotted, taking into account the geometric and physical nonlinear material operation. The conducted research practical significance is that the obtained dependencies allow modeling the MT trusses with aluminum-based rods operation, taking into account various truss geometries. When modeling trusses, an inclined load and the presence of elastic supports in the ridge node were taken into account. Dependencies make it possible to predict the aluminum ribbed-ring domes stability loss, which are modeled by MT trusses.

Complex hydraulic studies of welded pipes with different visco-plastic characteristics

Wed, 17 Apr 2024 00:00:00 +0300

For the first time, complex hydraulic studies of pipes welded according to three different schemes were carried out, which made it possible to combine pipes of different viscosities, which affects the performance of welding joints. It was found that in the experimental temperature range, the zone of thermal influence of the second welding variant has the greatest resistance to the initiation of fractures under shock loading, and the lowest - the first variant. The static strength and ductility of the welded pipe joints of the second and third pipe welding options are approximately equivalent, and the resistance to the initiation of the thermally affected zone in all options is almost the same and not lower than that of the base metal. The results of the performed experimental studies indicate a weak correlation in the area of small values of impact viscosity with the characteristics of resistance to fracture propagation of welding joints in the conditions of full-scale pipe tests. The characteristics obtained from tests of full-thickness DWTT specimens are closer than the Charpy specimens to the actual performance characteristics of the weld joints in the pipe. In particular, it was established that the values of A_z (-15⁰C)=0.75 kJ and A_r (-15⁰C)=0.45 kJ provide satisfactory resistance to the initiation and propagation of fractures in welding joints (at the base metal level). These characteristics correspond to KSU_-60 = 0.5 MJ/m², which is close to the impact toughness requirements for the base metal (0.55 MJ/m²). The use of optimal structural materials, that is, materials with high resistance to hydrogen destruction of both the base metal and zones of welding joints subjected to a thermo-deformation cycle of welding. A significant effect can be achieved by technological measures that will reduce residual welding stresses, as well as significantly reduce stress concentrators due to structural improvement of the shape of the welding unit. Application of such heat treatment regimes that restore the stability of metal with a coarse-grained and defective structure. Use improved pipe steels and welding materials, such as 06G2BAand 08 KhMCHA steels, which are characterized by increased resistance to hydrogen embrittlement and high crack resistance in aggressive environments, for the construction of pipelines of responsible purpose.

Environmentally safe installation for determining the fire resistance of coatings and fire resistance tests of small fragments building structures

Wed, 17 Apr 2024 00:00:00 +0300

Actuality. Taking into account fire statistics, the task of preventing the occurrence and spread of fires is urgent. It is obvious that the fire resistance of building structures, which must be taken into account at the design stage, is of the greatest importance and influence on the development and spread of fires in buildings and structures. Conducting fire experiments makes it possible to obtain the most complete information about the behavior of building structures under fire effects, however, the scale of field tests, labor-intensiveness, energy consumption and damage to the environment prompts the search and development of alternative methods that would ensure the environmental friendliness of the tests, compliance with the conditions of the experiment ( standard fire temperature regime), and at the same time would make it possible to estimate the limit of fire resistance of a building structure in reduced dimensions or to experimentally determine the fire-resistant ability (efficiency) of fire-resistant coatings. Purpose. The main goal of the article is rationale use of an installation for determining the fire-resistant capacity (efficiency) of fire-resistant coatings and fire resistance tests of small-sized fragments of building structures, taking into account the reduction of the harmful load on the environment. Main results. Research has been carried out and the design features of the installation have been substantiated, the principle of which is to heat the inner space of the chamber with the help of electric heating elements, which, unlike liquid fuel (diesel fuel, fuel oil, gas), do not harm the environment. A control unit-module of variable voltage regulation designed to regulate the heating temperature of the radiation panel in the test chamber has been developed. The design of the created test setup makes it possible to increase or decrease the temperature on the heating surface of the test sample, not only with the help of the heating temperature regulator, but also in manual mode, by moving the test sample closer or further away from the radiation panel along the guides. Conclusions. According to the results of experimental tests, it was established that the chamber of the installation warms up uniformly and according to the standardized temperature-time dependence Ts = 345lg (8t+1)+20). At the same time, the temperature regulation process using BP-10 with triac output ensures stable operation of electric heating elements up to temperatures of 1000 °C. A feature of the created installation is the possibility of additional lowering or raising of the temperature on the heating surface of the experimental sample, in case of its deviation during the experiment, by means of approaching or moving away from the sample to the heating panel. The conducted studies confirm the necessary reproducibility of experimental results.

High-precision modelling of deformation of sandwich structures under bilateral symmetric and oblique-symmetric loading

Oleksii Gurtovyi, Serhii Pyskunov — Wed, 17 Apr 2024 00:00:00 +0300

The analysis and assessment of the stress-strain state (STS) of multilayer plates with orthotropic layers under the action of stationary transverse and tangential loads is an urgent task. It includes calculations on the strength and deformability of various homogeneous and multi-layered plates with layers of constant thickness but arbitrary structure according to the thickness of the plate. Combining materials with isotropic and transversely isotropic physical characteristics into a multilayer package allows you to create multifunctional structures. The SSS of such structures, due to their structural heterogeneity and relatively low transverse stiffness of the individual layers, is significantly associated with the influence of transverse shear deformations and transverse compression deformations. Therefore, the problem of refined modeling of SSS plates, which would take into account these types of deformations, is urgent. Based on the decomposition of the SSS plate into flexural and unflexural components, it is proposed to optimize the design scheme of deformation of a rectangular multilayer plate. This significantly simplifies its modeling. For unflexural and exclusively flexural SSS, a two-dimensional, high-degree iterative approximation, but three-dimensional models of deformation of multilayer rectangular plate on a rigid foundation with isotropic, transverse-isotropic and orthotropic layers are constructed in an elastic formulation. That models takes full account deformation of transverse shear and transverse compression at transverse and the tangential loading of a plate. The model is continuous, that is, the number of equations and the order of differentiation of the calculation system of equations does not depend on the number of layers in the slab. This order of differentiation and the number of calculation equations can depend only on the order of iterative approximation of the model. A way of precise satisfaction of all defining correlations of the layers of material under keeping the conditions of their contact is found, while in the known continual models the dependence between the cross normal stress and cross deformation is only integral.The results of the analytical solution of the problem of deformation of a rectangular plate under boundary conditions of the Navier type under the action of transverse and tangential loads are given. By solving the test problems of the deformation of two-layer plates with transversally isotropic layers and three-layer plates with orthotropic layers and comparing the solutions with the exact three-dimensional solutions of these problems obtained by known methods, an assessment of the accuracy of the proposed refined models is given. The limits of admissible parameters of elastic characteristics of transversely isotropic and orthotropic plates for application of the offered models are established.

Research of technological processing of semi-finished products in the manufacture of profile products from composite materials

Viktoriia Ihnatieva — Wed, 17 Apr 2024 00:00:00 +0300

This article examines the process of technological processing of semi-finished product in the manufacture of rod profile products from fibrous composite materials, in particular - round. The purpose is to determine the theoretical value of the parameter which ensures the necessary impregnation of the winding layer during the final moulding of profile products.

It is mentioned that in order to ensure a defined structure and degree of filling during the production of rod profile products from spirally reinforced semi-finished products, they are compacted. Compaction can take place in one of two methods: by pressing in a spinneret, crimping with winding. The second method is used in the production of round cross-section rods. In this case, the spirally reinforced structural elements, which initially have a circular cross-sectional shape, deform and acquire an elliptical shape. At the same time, the degree of reinforcement filling of the central part of the structural element changes.

The volume of binder removed during deformation per unit time is presented as a function of the ellipse parameter.The displacement of the binder at steady-state mode of moulding is considered.Law of change of pressure gradient along the length of formed element before molding front is defined. The volume of binder removed during bundle formation per unit time is determined. Required molding pressure necessary to ensure a given degree of filling has been determined.

It is shown that it is possible to calculate the parameters of a deformed element that will ensure that the binder fills the space between the elements. An equation for determining the value of the parameter of the degree of crimping of an element, depending on the diameter of the used semi-finished product and the thickness of the winding layer is obtained. Data on critical values of a parameter of a degree of crimping of element, depending on diameter of a half-finished product and thickness of a layer of a winding is resulted. A method of determining the parameter of the degree of crimping of the element, which ensures the necessary impregnation of the winding layer during the forming of the profiled products, is proposed.

Changein the stress-strain state of elements of the «base – foundations – load-bearing structures» system dueto a possible progressive collapse

Oleksandr Havryliuk, Dmytro Nechyporenko, Veronika Zhuk, Viktor Nosenko — Wed, 17 Apr 2024 00:00:00 +0300

The calculation of a building for stability against progressive collapse using the LIRA SAPR-2019 software is considered. Two calculation approaches are compared: using a quasi-static formulation and direct integration of dynamic influences overtime. The first approach to calculating the local failure of an element used the force application principle defined for this element under normal operating conditions, but with the opposite sign (dynamism coefficient K_d=2, “pulldown” loading). These cond calculation approachis characterized by the dependence of the system response on the loading rate and the rate of removalof structures. To take into account damping, Rayleigh coefficients were determined by natural frequencies for two dominant modes of natural vibrations (No. 7, 10) based on the modal analysis of the system.The local failure time of the element was assigned as 0.1T (oscillation period) for natural vibration mode No.7, as the closest to the expected response of the system to the removal of the pylon. According to the calculation results, in the quasi-static formulation, a qualitative changein forces was recorded, where in stead of compression, tension appeared in the chain of pylons, which are located above the remote one, and in the dynamic formulation, a decrease of 70...90% in the magnitude of longitudinal forces in the pylons was recorded, that is, work was recorded on the principle of a hanging scheme. An increase in the load on the piles under the vertical load-bearing structures around the removed element is predicted under the scenario of a local failure of the structure; depending on the calculation method, the expected increase in the load on adjacent piles is 15...25%. Based on the results of the study, in order to increase the survivability and ensure the protection of building structures from progressive collapse, a decision was made to increase the reinforcement area by 30...35% for pylons in the entrance area to a dual-use structure, as well as in the radius of influence of a remote element, in order to absorb increasing forces by these elements when redistributing loads when removing an adjacent building element and assessing the load-bearing capacity of the remaining elements. It has been established that in this case, progressive collapse does not occur for this building.

Мethodical approach to the calculation of field fortification structure for the action of penetrating radiation

Vitalii Kosenko, Oleksandr Voloshchenko — Wed, 17 Apr 2024 00:00:00 +0300

The purpose of the article is to publicize a methodical approach to the calculation of field fortification structures for the action of penetrating radiation.

The experience of the Russian-Ukrainian war testifies to the aggravation of potential nuclear threats from the Russian Federation, in the case of which, in the event of their implementation, ensuring the survivability of our troops due to the radiation factor during hostilities will be significantly complicated. This development of events requires the Defense Forces of Ukraine to be constantly ready for action in the event of the enemy's use of nuclear weapons, and to strengthen the capabilities of the troops to protect against the impact factors of a nuclear explosion.The most effective way to protect troops in the conditions of the use of nuclear weapons is their shelter in field fortifications, the construction and covering of which will prevent or maximally reduce the impact of the impact factors of a nuclear explosion, in particular, penetrating radiation.The essence of the proposed methodological approach consists in the consistent determination of the dose of gamma radiation and neutrons inside the field fortification structure, taking into account a number of indicators, which will allow us to draw a conclusion about the compliance of the coating and construction of this fortification structure with the existing requirements for the protection of troops.The scientific novelty of the given methodical approach to the calculation of field fortification structures for the action of penetrating radiation consists in the comprehensive consideration of indicators that quantitatively characterize the main characteristics of a nuclear explosion, the conditions of the environment and the properties of various covering materials and the construction of field fortification structures.

Experimental studies of the influence of hydrogen and sulfur on sulfide-corrosion destruction under tension of pipelines

Wed, 17 Apr 2024 00:00:00 +0300

For the first time, comprehensive experimental studies of the influence of hydrogen and sulfur on sulphide stress corrosion cracking (SCR) of pipe steels in a corrosive-aggressive environment of NACE were carried out. In the research, experimental steels of the 06G2BA and 08KHMCHA brands, which are widely used in the construction of pipelines for various purposes, were used an analytical system (analyzer of non-stationary processes – ANP) was developed and tested in laboratory conditions, into which the installation for tests on corrosion-mechanical cracking under stress was integrated. For the first time, comprehensive experimental studies of pipe steel samples of grades 06G2BA and 08KHMCHA under the influence of sulfur and hydrogen were carried out, which made it possible to develop an understanding of the mechanisms of SCDS (sulphide-corrosion destruction under stress) and HID (hydrogen-initiated destruction). For the first time, experimental studies of the corrosion kinetics of 06G2BA and 08KHMCHA steels were carried out depending on the duration of the tests in the NACE model environment, while three periods of the formation of corrosion products were determined. It was found that sulfur and hydrogen, which are dissolved in test pipe steels, have a strong influence on the growth rate of corrosion cracks of SCDS, which made it possible to determine the optimal content of sulfur and hydrogen in steel 06G2BA. It is shown on the basis of the results of experimental studies that to ensure high crack resistance of pipe steels under conditions of static and cyclic loads both in air and in conditions of corrosive-aggressive environments, the sulfur content should not exceed 0.015-0.020%, and the dissolved hydrogen content should not exceed 2-3 ppm . The obtained results make it possible to improve pipe steels in the process of their smelting at metallurgical enterprises thanks to the use of economical modification with niobium, chromium, cerium and other impurities, which contribute to the fragmentation of the structure and reduce the content of non-metallic inclusions and harmful impurities.

Methodological basis of BIM-analysis of damage and assessment of impacts, consequences, resources for restoration of buildings and structures

Dmytro Prusov, Dmytro Makatora, Ruslan Kubanov — Wed, 17 Apr 2024 00:00:00 +0300

The methodological basis of the BIM-analysis of damage and assessment of impacts, consequences, resources for the restoration of buildings and structures is the basis of the methodological foundation that provides a holistic approach to the planning and development of the territory, including multifactorial aspects. There is a need to study the components of damage assessment of buildings (structures) and to develop a systematic method of their diagnosis on a damaged object in order to achieve efficiency in making a decision on reconstruction or the impracticality of restoration depending on the generalized coefficient of destruction. The task of the research consists in the development of a step-by-step assessment algorithm - a method of systematic assessment of damage to buildings and structures based on the application of the generalized Harrington function as a tool for determining the level of technology development, using a system of indicators, the normative values and weight of which are established by certified civil engineers under the condition of substantiation, regarding feasibility reconstruction or impracticality of restoration. The developed methodology for assessing damage to buildings and structures consists of a number of interconnected sequential stages aimed at obtaining a quantitative and qualitative assessment, choosing a comprehensive strategy for assessing buildings and structures.

To achieve the specified goal, it is proposed to develop a methodological basis for the BIM analysis of damage and assessment of the effects, consequences, resources for the restoration of buildings and structures, which can be the basis for performing construction and technical examinations, which is the determination of the technical condition of the object of examination and the causes of its damage and destruction , in four stages: planning, diagnosis, implementation, control. The given technique will help to make this process more organized and efficient, and its implementation in information modeling can provide a technical opportunity to move from the traditional process of information management to the creation of expert models to optimize key project indicators based on reliable, consistent data, contributing to the creation of the necessary conditions for further transition to the principles of managing the assessment of impacts, consequences, resources for restoration, and the subsequent life cycle of construction objects.

Stress state analysis of a cylindrical tank with water of an under water sports palace

Wed, 17 Apr 2024 00:00:00 +0300

The paper analyzes the stress state of a cylindrical tank, which is one of the main structural elements of a sports facility - an underwater sports palace. In the calculation of the cylindrical shell of the tank of constant thickness, the moment theory was used. The reservoir is, in fact, a swimming pool for conducting training sessions on underwater swimming in fins, diving, diving, is considered fixed in its base and filled with liquid (water of a special composition, homogeneous in depth, with a given specific gravity). It is known that integration of the calculation equations of the moment theory (of circular cylindrical shells), namely: a) differential equations of equilibrium; b) equations of deformations; c) equations of forces attributed to the unit length of the coordinate line (tangential forces, bending moments), is a complex mathematical problem associated with solving a system of partial differential equations with variable coefficients. Only the calculation of the curve of a cylindrical shell ultimately leads to a system of differential equations with constant coefficients. Under the assumption of significant depth of the tank compared to the thickness of its walls and the value of the radius of the cylinder base (which allows us to consider it as infinitely long), displacements and forces (tangential and transverse), bending moments are analytically found. The locations of the cylinder surface points, in which the indicated forces and moments acquire maximum values, have been determined; sketches of their diagrams, determining the character of change of these physical quantities (parameters) along the height of the tank, have been given.

The results obtained in the work can be further used to clarify and improve engineering methods of calculation of structural elements of sports facilities of this type, both at the stages of their design and in the modes of real operation in order to prevent situations associated with the loss of their strength and stability.

Research of stochastic stability of constructions parametric vibrations by the Monte-Carlo method

Dmytro Poshyvach, Olga Lukianchenko — Wed, 17 Apr 2024 00:00:00 +0300

The stochastic parametric vibrations of the elastic systems behave to the statistical dynamics section of the nonlinear systems. Under stochastic parametric influence the vibrations of the elastic systems, which is a random process more frequent are not stabilized, but their amplitudes are fading or unlimited are growing. Therefore important is stability of stochastic vibrations, which can be examined as stability by probability, on average or by the moment functions of different orders. The mathematical models which describe the stochastic parametric vibrations of the elastic systems are building by analytical or numeral approaches. Researches of stochastic stability of parametric vibrations are executing by probabilistic methods. Stability of parametric vibrations of modern constructions under the action of operating random loads are not enough investigated.

In the article the numeral method of research of dynamic stability of the elastic systems under stochastic parametric influence was presented. The mathematical model of stochastic parametric vibrations of construction in the form of a reduсed finite element model was formed. Matrixes of the reduced model were obtained using calculated procedures of finite element analysis software NASTRAN. The dynamic loading as stationary ergodic random process with the spectral density was presented in the form of a finite amount of harmonic functions. Stochastic stability of the constructions was investigated using the Monte Carlo method and the Runge Kutta method of direct numeral integration of the equations of reduсed model. Stochastic stability as stability by probability of appearance of tendency to fading or unlimited growth of amplitude of parametric vibrations was examined during the time interval in space of the random parameters of loading. Dynamic stability of a I-beam with corrugated wall under narrow-band parametric influence was investigated using the numeral method.