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An approach to estimating the long-term strength of concrete in building structures in the calculation of reinforced concrete structures of buildings and structures of various types is proposed. The process of increasing the initial modulus of concrete deformations in time as a consequence of a certain physicochemical reaction of strength gain is considered. The function of the age of concrete is presented, taking into account the change in the modes of temperature effects during the period of hardening. It is shown that the entropy criterion of strength is more flexible compared to the criterion of the energy barrier of destruction. The application of the entropy strength criterion allows us to take into account the effect of temperature on the long-term strength of concrete.

The specific properties of deformation and failure of a reinforced concrete frame are investigated under sequential realization of arch and catenary action of beams after removal of the middle row column. Numerical modeling with the use of solid- and beam-type finite element models is performed for the purposes of the study. It was found that at the failure of the column of the second row the beam of the frame above the point of column removal transform to catenary structure, as evidenced by the relative deflection 1/29.8 (179 mm). The compressed concrete at the outer face of the corner column then collapsed, followed by the complete collapse of the frame. It is shown that the results of calculation performed with the use of the frame model based on solid finite elements were visually close to the results of numerical modeling with the use of bar finite element models before the onset of catenary action of the beams. For more correct modeling of reinforced concrete frame structures when catenary action of beams is realized in them. It is advisable to use specific modeling methods, such as accounting for additional rotations of sections at crack formation.

The article formulates proposals for improving the calculation methodology for punching. The methods in the current regulatory documents for assessing the tensile strength are based mainly on empirical dependencies obtained on the basis of numerous experimental studies. It should be noted that they give reliable results if certain design requirements are met (typical column sections). Along the interface line of the plate with a rectangular (square) column, supporting bending moments act in two orthogonal directions. The magnitude of these moments for the most common spans is large and, in an elastic setting, exceeds the span by two times. Taking into account the redistribution of forces and the most likely formation of cracks in the stretched zone, it can be argued that in the operational stage, the support sections of the plates have compressed and stretched zones. With such a stress-strain state, in the calculation scheme, when evaluating the tensile strength, the stretched part of the side surface of the “reduced” pyramid, bounded by the neutral axis along all faces, should be excluded. As a result, expressions are presented to determine the parameters of the reduced punching pyramid and the value of forces in concrete and reinforcement at the maximum bearing capacity stage.

The main directions of development of the theory of structural safety of buildings and structures have been formulated. A hierarchical approach to the assessment of structural safety of objects under corrosion damage from structural materials to structural system is proposed. Peculiarities of corrosion damageability of concrete of reinforced concrete structures are determined, mechanisms of force and corrosion effects and their influence on progressive destruction of structural systems of exploited buildings are analyzed.

The methodology of calculation of reinforced concrete frames of buildings for a special design situation caused by initial local failures, taking into account the violation of the continuity of the concrete matrix during crack formation, is proposed. The verification of the proposed methodology is carried out by comparing it with the results of experimental data for a U-shaped reinforced concrete frame with prestressing. The bending moments in the frame, determined by the proposed calculation method, are in practically complete agreement with the values found experimentally. As a result of cracking, there was a redistribution of bending moments in the beam of the frame: the moments in the structural nodes decreased by 148 % and increased in the span by 37.5 % compared to the results obtained using the traditional finite element method approach. On the basis of the results of the calculation of the reinforced concrete 3-storey frame by the proposed method, the increase of longitudinal tensile forces in the beam support sections above the zone of local failure at failure of the middle row column is revealed in comparison with the traditional approach to modeling. The revealed effect may lead to an increase in the influence of longitudinal bending for the outermost row column to which the beam is adjacent.

The article is devoted to the fatigue of bending reinforced concrete beams under reinforcement corrosion. The influence of lugs and rebar notches periodic profile in concrete under repetitive loads, which act as stress concentrators, leading to the appearance of fatigue cracks and to the reduction of fatigue strength, is considered.

Currently, scientists search for new materials for temporary implants that can dissolve in the body, which leads to the fact that there is no need for repeated surgery. In the last decade, scientific interest has focused on zinc-based materials because, unlike other metals, it has suitable corrosion rates and good biocompatibility. The paper describes an experiment for the study of the influence of deformation on the microstructure, strength and corrosion properties of an alloy of the Zn–Fe–Mg system. The authors carried out energy dispersive analysis and calculation of the volume fraction of the second phase of the Zn–Fe–Mg zinc alloy. The corrosion properties of the Zn–Fe–Mg zinc alloy with different microstructures (before and after high-pressure torsion) were studied using the gravimetric method under conditions simulating conditions inside a living organism (temperature, corrosive environment composition). During the tests, the corrosion mechanism was determined, its rate and mass loss of the samples were calculated. The relief of the corrosion surface was studied using scanning electron microscopy. It has been found that the destruction of the material in a corrosive environment occurs through a matrix containing the active Mg metal. The results of calculations of the corrosion rate for the original sample and samples subjected to high-pressure torsion differed due to a more even distribution of second phase particles during severe plastic deformation. In this work, by alloying zinc with iron and magnesium, as well as using high-pressure torsion, it was possible to increase the microhardness of the samples to 239.6±8 HV, which is a high indicator for zinc alloys.

In recent years, the range of silicon-containing steels subjected to hot galvanizing has been expanding. Alloying of steel with 0.5–1 % of silicon leads to the formation of a zinc coating of great thickness with a matte or multi-colored surface. This is associated with the changes in phase reactions between iron and zinc in the Fe–Zn–Si system. The development of ways to neutralize the negative influence of silicon on the formation of zinc coating is an urgent task. The purpose of the work is to study the influence of preliminary plasma cutting and plasma surface hardening of 09G2S (S355J2) steel on the thickness and structure of zinc coating formed on treated surfaces. It was found that after plasma cutting, the structure of the surface layer of steel is martensite, and after plasma surface hardening, it is martensite and ferrite. Analysis of the change in microhardness from the steel surface to the middle showed that the hardened layer depth is 400 μm. A zinc coating consisting of a δ-phase and a ζ-phase is formed on the surface of the steel without pretreatment. On the surface of the steel after plasma treatment, a zinc coating is formed characteristic of low-silicon steels and consisting of the δ-phase, ζ-phase, and η-phase. It was found that the thickness of the zinc coating on the surface after plasma cutting is two times less than on the untreated surface, and the reduction in the coating thickness occurs due to a decrease in the ζ-phase thickness. A hypothesis was suggested that the martensite formation on the steel surface leads to the disappearance of the ordered FeSi phase and changes the phase equilibrium in the Fe–Zn–Si system. Consequently, preliminary plasma treatment of the steel surface allows controlling the structure and thickness of the resulting zinc coating and is therefore recommended for introduction into the hot galvanizing process of silicon-containing steels.

High-chromium martensitic steels are a promising material for the production of elements of boilers and steam pipelines, as well as blades and rotors of steam turbines for new coal-burning thermal generating units. The use of such materials will give an opportunity for the transition to ultra-supercritical steam parameters (temperature of 600–620 °C and pressure of 25–30 MPa), which will allow increasing the efficiency of generating units to 45 %. Modifications of the chemical composition of high-chromium steels have led to significant improvements of high-temperature properties such as 100,000 h creep strength and 1 % creep limit, while resistance to softening due to low-cycle fatigue remains understudied in this field. This work covers the study of low-cycle fatigue at room temperature with different amplitudes of deformation of martensitic high-chromium 10%Cr–3%Co–2%W–0.5%Mo–0.2%Cu–0.2%Re–0.003%N–0.01%B steel. The steel was pre-subjected to normalizing at 1050 °С followed by tempering at 770 °С. After heat treatment, the steel structure was a tempered martensitic lath structure stabilised by the particles of secondary phases of M23C6 carbides, NbX carbonitrides, and M6C carbides. The average width of martensite laths was 380 nm, and the dislocation density was 1.4×1014 m−2. At low-cycle fatigue, with an increase in the strain amplitude from 0.2 to 1 %, the number of cycles before failure significantly decreases, and the value of plastic deformation in the middle of the number of loading cycles significantly increases. Maximum softening (18 %) is observed at a strain amplitude of 1 % in the middle of the number of loading cycles. In general, the steel structure after low-cycle fatigue tests does not undergo significant changes: the width of the laths increases by 18 % at a strain amplitude of more than 0.3 %, while the dislocation density remains at a rather high level (about 1014 m−2) at all strain amplitudes.

One of the important parameters influencing the formation of a weld during friction stir welding is the tool geometry, which affects the processes of heat generation and stirring of metals in their connection zone. These processes influence the formation of a high quality and strength welded joint without continuity defects. In this regard, it is relevant to analyze the influence of tool geometry on the welding mode parameters, at which the welded joint is formed without continuity defects, as well as on the welded joint strength under static tension. The work considers the influence of the cylindrical and conical shapes of the tool pin, as well as the conical shape of the pin with a thread on its outer surface and a spiral groove on the end surface of the tool shoulder on the welding mode parameters, at which the welded joint is formed without continuity defects. The study shows that changing the shape of the pin working surface from cylindrical to a conical one had no effect on the range of welding mode parameters, at which the welded joint is formed without continuity defects. It has been found that the presence of a thread on the pin outer surface and a groove on the end surface of a tool shoulder allows producing welded joints without continuity defects in a wider range of welding mode parameters compared to a simpler tool geometry. The macrostructure of the resulting welded joints was considered. It has been found that the studied tool geometry has almost no influence on the maximum strength values of welded joints produced by friction stir welding and reaches 95 % of the strength of the base metal.

Currently, step quenching of steels in the temperature range of martensitic transformation, including quenching – partitioning, has found wide application in the automotive industry. Step quenching technology is successfully used to increase a set of properties, which most often include temporary tensile strength and relative elongation. The authors carried out a dilatometric study of the supercooled austenite transformations occurring in the 20Cr2Mn2SiNiMo steel, when implementing various options of step quenching with holding in the martensitic region. It was found that after single-stage quenching, single-stage quenching followed by tempering, and two-stage quenching, primary martensite, isothermal bainite, and secondary martensite are formed in various quantitative ratios. Using X-ray diffraction phase analysis, the amount of residual austenite was determined during step quenching. It has been shown that two-stage quenching makes it possible to stabilise up to 14 % of residual austenite, in the structure of the studied steel, at room temperature. Research has revealed that 20Cr2Mn2SiNiMo steel is characterised by a decrease in the crystal lattice parameter of the residual austenite, with an increase in its content in the steel structure. Uniaxial tensile and impact bending tests were carried out, and the values of the mechanical properties were determined. It has been found that during two-stage quenching, higher strength and elongation values, with lower values of relative contraction and impact strength are achieved compared to oil quenching and low-temperature tempering. The study showed that, with regard to the structural reliability of machine-building parts, step quenching is not the optimal heat treatment mode for the steel under study. The best combination of strength, ductility and impact hardness is achieved after quenching and low-temperature tempering.

Nickel coatings consisting of oriented structures have unique catalytic properties. However, the temperature range for the use of such coatings is not determined, and a comprehensive study of their thermal properties in aggressive environments is required. This work studied the influence of the characteristics of the habit of nickel crystals on their reactivity with increasing temperature (thermoreactivity). The authors studied nickel coatings produced by electrodeposition with the addition of inhibitory additives, in the form of alkali metal chlorides to the electrolyte. Differential thermal analysis was used to study the reactivity of coatings in temperature fields. Oxygen was used as an aggressive medium. The phase composition of the samples after heating was determined, using a powder X-ray diffractometer. The introduced additives in the form of alkali metal chlorides allowed forming coatings consisting of crystals of a cone-shaped habit. It was found that the introduction of additives, in the form of alkali metal salts into the electrolyte, makes it possible to change the habit of nickel crystals, and increase the surface area of the coating by approximately 10–15 %. The study showed that electrodeposited nickel coatings, consisting of crystals in the form of micro- and nanocones, have (compared to the control coating) a reduced thermoreactivity. Experimental data allowed concluding that a decrease in the intensity of oxidation on the coatings under study, may be associated with the presence of a preferential development of certain crystallographic faces of the crystals, which causes a change in the nature of the nickel-oxygen interaction, and as a consequence, a change in the oxidation intensity.

The modern electrical engineering industry requires cheap and easily reproducible aluminum alloys with advanced mechanical strength and electrical conductivity. This work studies the influence of small (up to 0.3 wt. %) copper additions on the microstructure and physical and mechanical properties, as well as phase transformations in the Al–Fe system alloys with an iron content of 0.5 and 1.7 wt. %, produced by continuous casting into electromagnetic crystallizer. Alloys of the above chemical compositions were produced, and subsequently annealed at 450 °C for 2 h. In all states, the microstructure (via SEM), yield strength, ultimate tensile strength, elongation to failure, and electrical conductivity were studied. It has been shown that copper additions lead to an increase in the strength of both alloys and a slight decrease in their ductility compared to similar materials without copper. An increase in strength and a decrease in ductility due to the copper addition is associated with the formation of more dispersed intermetallic particles in copper-containing Al–Fe system alloys. Additional spheroidizing annealing leads to a decrease in the length of the interphase boundary between the aluminum matrix and iron aluminide particles due to a change in their morphology, which leads to an increase in electrical conductivity. In general, copper-containing alloys showed higher mechanical strength with lower electrical conductivity, as well as higher thermal stability.

The study of the acoustic properties of maraging steels operated under various energy force and temperature actions is a critical task, since it is the method of acoustic structuroscopy that provides the most reliable connection with the structure, stress-strain state and mechanical properties of steels. The paper is devoted to research of the acoustic properties of the 15-5 PH maraging steel samples under various types of heat treatment under the conditions of mechanical tensile and cyclic loads. Samples of the 15-5 PH maraging steel were studied in three structural states: solid solution annealing and subsequent aging at 470 and 565 °C; during tensile tests; during cyclic tension-compression loading. The research used a unique scientific installation “Information-measuring complex for investigation of acoustic properties of materials and products”. It implements the acoustic mirror-shadow multiple reflections method using electromagnetic-acoustic and piezoelectric transducers based on polyvinylidene fluoride film to excite and receive waves and allows determining the velocity of wave propagation with an error of no more than 2 m/s. The acoustic (wave velocity, elastic moduli, electromagnetic-acoustical (EMA) transformation coefficients, acoustic anisotropy coefficients, acoustoelastic coupling coefficients) and electromagnetic (coercive force and electrical conductivity) characteristics of the samples were examined. The samples were studied in the initial state (before loading); stepwise in the process of tensile loads and subsequent unloading; after tensile tests; during cyclic tension-compression loading. It was revealed that the following acoustic parameters of 15-5 PH steel samples are the greatest structural sensitivity to mechanical tensile load and cyclic loading: transverse wave velocity, Poisson’s ratio, double EMA-transformation coefficient, and acoustic anisotropy coefficient.

This study evaluates the use of gingelly oil as an eco-friendly cutting fluid for the turning operation. Experiments were conducted to determine the effect of nose radius, and rake angle on tool wear, surface formation, and cutting force. In addition, different lubrication techniques, such as cutting fluids and bio-oils, were investigated to determine their potential for minimising friction, heat generation, and tool wear during machining. In comparison to dry cutting, and conventional petroleum-based lubricants, the results demonstrate that gingelly oil consistently produces smoother surface finishes, and reduces cutting forces. The relationships between cutting parameters, and surface finish were analysed using statistical modelling, with R-square and p-values used to quantify correlations and predictor significance. The findings highlight the viability of gingelly oil as a cutting fluid and the significance of optimising process parameters for increased machining efficiency.

Friction stir welding is an advanced method of joining various metals and alloys in the aircraft and mechanical engineering industries. This type of welding is used to join materials that are difficult to weld or not weldable by conventional methods. The high-strength D16 aluminum alloy is difficult to weld by fusion, which is associated with the formation of a dendritic structure in the fusion zone leading to a decrease in the mechanical strength of the joint. In the work, the microstructure and microhardness of a welded seam of the D16 aluminum alloy produced by friction stir welding was studied. Using scanning electron microscopy and optical metallography, the authors identified the presence of three zones: the weld core, the thermomechanical impact zone, and the heat effected zone. In the central part of the welded joint (in the core), a laminated onion ring structure was discovered. A change in the chemical composition of the aluminum solid solution was identified in different areas of the weld zones, as well as the presence of a concentration gradient within each zone. In the upper part of the welded seam, the solid solution is silicon-enriched and depleted in copper. Due to the solid solution depletion in alloying elements, the aluminum content in the solid solution in the zone of the welded joint is higher compared to the initial state. The microhardness values in different areas of the welded joint correlate with changes in the chemical composition. In the welded joint zone, a significant decrease in microhardness was found compared to the initial state, and a change in microhardness associated with the chemical composition gradient within each zone was also observed.

В роботі проведено аналіз зносу різців та виявлено, що більшість з них придатна для використання, так як форма твердосплавного наконечника не дуже змінилась та може використовуватися для подрібнення асфальто-бетонної суміші. Була розроблена та запропонована методика відновлення хвостової частини корпусу різців. Маршрут відновлення наступний: 1. Очищення різця. 2. Нагрівання пропаново-кисневим полум’ям хвостової частини різця. 3. Пластичне деформування корпусу різця у штампі. 4. Охолодження на повітрі. 5. Контрольне вимірювання зміни розмірів. Рекомендована температура термообробки під пластичну деформацію залежить від концентрації вуглецю і легуючих елементів сталі та знаходиться в діапазоні температур від 800 до 1280°С, час нагріву 1,33 хв. Попередньо перед деформацією, корпус різця нагрівали за допомогою пропаново-кисневого полум’я. Осадку проводили в закритому штампі за допомогою спеціального пуансона. В матриці розміщували головку різця, на яку встановлювалась направляюча з пуансоном. Відпрацьована технологія відновлення хвостової частини різця роздаванням. За запропонованою технологією відбувається роздавлюваня хвостової частини корпусу різця від 0,04 мм до 0,73 мм на сторону. Таким чином відновлюються різці дорожніх фрез майже до розмірів нової деталі, що дає змогу повторного використання.

The rapid development of educational technologies requires the active involvement of new means and effective teaching methods. One of the innovative tools of learning in the field of robotics is the use of robot simulators in the educational process, which open up many opportunities for better assimilation of knowledge and development of practical skills among students. Robot simulators are software complexes that allow you to visualize and simulate the behavior of real robots. With these tools, students can: • program robots in a virtual environment, test code and debug without the risk of damaging real equipment; • to study robotics and the principles of robot operation, exploring different types of sensors, actuators and algorithms of robot behavior; • to solve problems in various fields, such as production automation, logistics, construction, etc.; • practices your skills in a safe and controlled environment. Among the benefits of using robotic simulators are next: • availability for a large number of students, as simulators are much cheaper than real jobs; • safety, as the virtual environment eliminates the risks associated with working with real robots; • flexibility that allows students to work at their own pace, explore different scenarios and experiment with different parameters; • interactivity with a realistic 3D-environment and visualization. This work presents an overview and analysis of software that allows modeling robot control systems and simulating their operation for various algorithms. A review and analysis of the proposed software tools for simulating robotic systems, which are used to teach bachelor's and master's degree students in the specialties of "Computer Science", "Information Systems", "Industrial Mechanical Engineering" and "Applied Mechanics" and have proven their effectiveness and effectiveness in distance learning at the Kyiv National University of Construction and Architecture.

The purpose of the proposed article is the analysis of the principles of the formation of the workload on the executive bodies of construction machines and technological equipment, which is due to the need for their improvement in order to improve the energy and technological indicators of technological processes.The methodology is based on search, research and creative approaches. The methods of development analysis, patent search, synthesis of technical solutions, simulation modelling was used. Scientific novelty. The study of various approaches to ensuring the implementation of the working movements of executive bodies of construction machines and mechanized technological equipment, the analysis of technical solutions allowed to substantiate the directions of development of drives of construction machines to ensure the necessary laws of movement of executive elements. The authors proposed constructive solutions for synthetic drives of construction machines and equipment, proposed energy-saving approaches aimed at reducing energy consumption. Research results. The article deals with important issues of analyzing the formation of loads on executive bodies of construction machines and equipment. Synthesized constructive solutions obtained in the course of patent research, analysis of modern technical solutions, rational technical design and expert evaluation are presented. A technical solution is proposed to ensure the implementation of adaptive feed in a hydraulic power drive, which can be used in the modernization of existing drives of construction machines and moving parts of mechanized technological equipment.

The purpose of the proposed article is the development and construction of a mechanized mobile platform for serving people, which is caused by the need to increase the safety of the operation of such technical means, in particular, in the case of the need for mass customer service. The methodology is based on search, research and creative approaches. The methods of development analysis, patent search, synthesis of technical solutions, simulation modelling was used. Scientific novelty. The study of the features of various approaches to the creation of effective mechanized moving platforms, the analysis of solutions and the dynamics of patenting made it possible to substantiate the directions of development of technical solutions and the prospects of developments. The authors proposed constructive solutions for mobile platforms, developed approaches to the technical implementation of increasing the safety of their operation, proposed energy-saving approaches aimed at reducing the energy consumption of mechanized means, which is especially relevant in the mass implementation of platforms for serving people. Research results. The article solves important safety issues of human service, in particular in the entertainment industry through the development of structural parts, drives and rules for the operation of mechanized moving platforms. Synthesized constructive solutions obtained in the course of patent research, analysis of modern technical solutions, rational technical design, and expert evaluation are presented. It was determined that the safety of the operation of mechanized moving platforms, which are intended for the transport of people in the field of tourism, depends on effective approaches to the design and components of the technical system in the form of a moving platform, its structural components, elements of its mechanism and the drive system as a whole, which with the optimization of technical indicators the stability of the overall system, the smoothness of movement and braking of the platform, the optimization of the materiality of the structure in total allow to have a qualitative effect on improving the safety of human operation.

The production of concrete mixes, along with their use in the production of building materials and structures, is one of the key processes in the construction industry during the construction, restoration and repair of buildings and structures. Because of this, the need to create modern concrete mixing plants that will meet the requirements of minimum energy consumption and maximum productivity of concrete mixture production is an urgent task. Not only the main operations, which include the dosing of the components of the mixture and their mixing, but also the maintenance operations, namely operations that ensure the timely movement of the components of the concrete mixture from warehouses to the main technological equipment, affect the set rhythm of the concrete mixture production. Conveyors of various types and designs are used to move bulk materials, such as crushed stone and sand. For the rational selection of such equipment in accordance with the characteristics of the cargo to be transported, knowledge of the types of conveyors, their structures and parameters, understanding of operation issues and methods of parameter calculation are required. In addition, it is worth paying attention to the following parameters: maximum cargo transportation productivity, low energy consumption per unit of moved products, low metal content of the structure. The work reviewed the most common designs of conveyors used to move bulk materials in concrete mixing plants, analyzed the disadvantages and advantages of conveyors, as well as technical parameters. As a result, the predominant directions for the use of belt and plate conveyors at construction enterprises were determined. The advantages of belt conveyors, which contribute to their widespread distribution, are high productivity, simplicity of design, reliability, quiet operation, low specific power consumption. When choosing a conveyor, it is recommended to choose the equipment with the highest productivity and the lowest power of the drive motors, however, the performance should be clearly related to other technological equipment.

Reach stackers are efficient and maneuverable machinery for an overload of overall containers in cargo terminals and ports today. Such machinery design determines the practical interest of the engineering industry specialists. However, the lack of information in open sources about structural or kinematic diagrams of equipment control mechanisms and recommendations for their calculation does not allow an effective approach to the creation and update of reach stackers. We developed the design procedure of the reach stacker control system, which considers the kinematic and geometric parameters of the container spreader, as a result of the conducted research. It can be used in the design stages of mechanisms for spreader lateral displacement, extension of the spreader sections, spreader inclination in the vertical plane, container fixation by spreader, spreader rotation, lifting-lowering and telescoping of the boom, as well as during the real operation modes of reach stackers in cargo terminals and ports.

Loading and unloading works are an integral part of the construction process. Cranes of various types were mostly use to perform these works. To ensure trouble-free operation and increase the reliability of cranes, when calculating structures and components of their working equipment, it is important to take into account dynamic loads, which are several times higher than static loads. Elements of dynamic loads in the crane suspension are its elastic components (flexible traction bodies) - ropes. The process of lifting a load from a rigid base and picking it up is considered, which divided into three stages: the first is the selection of clearances and the tension of the ropes; the second is the pre-opening stage of lifting the load; the third is the post-detachment stage of lifting the load. For each stage, the initial conditions accepted, the differential equations of the movement of loads compiled, their solution given taking into account many factors, and expressions derived for determining the forces in the load suspension. At the first stage, the duration of the gap selection (tension of the ropes) is determined, at the second stage, the speed of separation of the load from the base is determined, at the third stage, the maximum force in the elastic element determined. The method of determining the forces in the suspension of the load, the duration of the selection of clearances (tension of the ropes), the speed of separation of the load from the base, and the maximum force in the elastic element presented in the work allows you to significantly simplify the solution of complex equations, to determine simple expressions and to determine them with sufficient accuracy for practical calculations values.

The main of the problems of the development of two-link manipulators with an angular coordinate system is the lack of effective and universal control systems capable of implementing energy-intensive modes of movement. This is due to the design features of the pointer system of such manipulators and the methods of their use. During the operation of the manipulator, significant dynamic loads occur in its drive system, which create oscillations of the mechanical system and reduce the accuracy of work. The control system must also effectively compensate for such dynamic variations. Dynamic equations of motion used to build manipulator control controllers, which allow taking into account various features of using manipulators. These mathematical models necessarily contain one of the characteristics in the form of the combined moment of inertia of the mechanical system, which is important in the calculation of differential equations and the determination of kinematic parameters of motion. In this article, the combined moments of inertia of the boom system of a two-link manipulator with an angular coordinate system are determined. A study was carry out and it shown that the nature of the change in the combined moments of inertia influenced by the modes of movement of the boom system links. The results of the study showed that the combined moment of inertia of the boom system of the manipulator is not a constant value, which does not change uniformly under special operating conditions of the machine. To determine the combined moments of inertia, the method of bringing the kinetic energy of the moving system to the drive mechanism was apply. This is relevant, because in the future it will be necessary to adjust the unevenness of the movement of the manipulator links by the drive itself. The study was conduct for a typical linear motion mode and a motion mode with a change in speed along a parabolic trajectory.

The purpose of the work is to study the influence of hafnium additives on the mechanical properties and thermal stability of particles at elevated temperature during heat treatment of aluminum alloys with a high magnesium content. Two modifications of 1570 alloy were chosen for the study: without hafnium content and with its addition of 0.5 % by weight. Both alloys were subjected to homogenizing annealing at a temperature of 440 °C with different exposure modes, which ranged from 2 to 100 h. Microhardness was studied for various heat treatment modes, and the fine microstructure was studied as well using transmission microscopy. As a result, it was possible to identify that during annealing at a short exposure time (2–8 h), the alloy with the hafnium addition has higher microhardness values exceeding those of 1570 alloy by an average of 20 HV units. This is associated with the fact that in 1570 alloy with hafnium additives, during heat treatment, the number of precipitated particles increases while their average size decreases compared to the base alloy. At the same time, in 1570 alloy without hafnium content, when annealed at a temperature of 440 °C, there is no increase in microhardness. This is caused by the fact that in 1570 alloy without hafnium content, when cooled after casting, discontinuous decomposition occurs, which resulted in the fact that most of the scandium precipitates from the supersaturated solid solution in the form of dispersoids. This phenomenon is not observed in the alloy with hafnium additives, which indicates its ability to stop discontinuous decomposition during cooling the ingot after casting.

Biocompatibility makes magnesium alloys attractive functional materials in terms of their use as biodegradable implants. However, the technologies for manufacturing semi-finished products carry a possible diversity of the local strain rate and temperature within a rather wide range, which affects the processed material structure and properties. The purpose of this study is to determine the range of temperatures and resistance to deformation, at which there is no negative effect on the main structural characteristics of the processed material, using the example of a medical purposes alloy of the Mg–Zn–Y alloying system. The authors carried out mechanical tests of a biodegradable Mg–1Zn–2.9Y magnesium alloy at various temperatures and strain rates. The influence of temperatures in the range of 20...400 °C on the structure and properties of the Mg–Zn–Y system alloy is disclosed. Starting from a temperature of 350 °C, the process of dynamic recrystallisation is accompanied both by the complete restoration (return) of the original microstructure and by coarsening of the grain size, which can adversely affect the material functional characteristics. The high thermal stability of the biodegradable Mg–1Zn–2.9Y magnesium alloy is revealed, which probably results from the presence of the LPSO phase in it. The study shows that the deformation process is accompanied by twinning. At a strain rate of 2∙10−2 s−1 over the entire temperature range, the grain size distribution slightly narrows and shifts towards smaller diameters. The application of the obtained results in technological processes for manufacturing medical semi-finished products will help to solve the issue of microstructure instability at the stage of transition from a semi-finished product to a finished product during subsequent thermomechanical treatments.

Unsatisfactory quality of the surface layer of additive products, in particular increased surface roughness, prevents the widespread use of electron beam powder bed fusion (EBPBF). Electrospark treatment (EST) is one of the methods for smoothing and hardening the surface layer. The work shows the possibility of modifying the surface of additive VT6 alloy samples by reactive EST with multicomponent electrodes. For this purpose, the authors used electrodes made of the Fe48Cr15Mo14Y2C15B6 bulk metallic glass forming alloy and the FeCoCrNi2 high-entropy alloy. Based on the results of scanning electron microscopy, it was identified that after EST, both modified layers have a thickness of about 16 μm. X-ray diffraction phase analysis showed that in the case of treatment with an amorphous electrode they contain carboborides of the Ti(B,C) type, and in the case of treatment with a high-entropy electrode – intermetallic of the Ti2(Fe,Ni) type. The modified layers have average hardness values of 19 and 10 GPa and elastic modulus of 234 and 157 GPa, respectively, which significantly exceeds the values of these parameters for the EBPBF-grown VT6 alloy. Electric discharge modification of the surface with multicomponent electrodes led to a decrease in roughness by 8...11 times due to the melting of the protrusions and filling of the dimples with the melt to a depth of more than 50 μm. A comparative analysis of the results of tribological tests showed a change in the wear mechanism as a result of EST of the additive VT6 alloy. Wear resistance increased by 4 and 3 orders of magnitude when using electrodes made of a bulk metallic glass and high-entropy alloy, respectively.

The paper presents the results of the study of the end milling temperature of low-alloy steel depending on the cutting modes and the type of crystalline structure. The experiment was carried out on a PROMA FHV-50PD universal milling machine. The blanks were processed using a 12-12D-30C-75L-4F HRC55 carbide milling cutter. No cooling was used during processing. The obtained data were statistically analyzed to identify the dependence of the end milling temperature of low-alloy steel on the processing modes and the steel crystalline structure. When creating a mathematical model of cutting temperature, the authors carried out a bootstrap analysis to identify the significance of the parameters of the processing modes. The mathematical model was chosen using the Akaike informative criterion. It was found that mathematical models of the temperature dependence on processing modes for both types of crystalline structure include the cutting depth in the second power. At the same time, for steel in an ultrafine-grained state, both the cutting depth and the feed are statistically significant. It was not possible to detect the influence of cutting speed on temperature in the studied range of processing modes. Thus, when milling this group of materials, the force component primarily determined by the cutting depth exerts the predominant influence on the temperature regime. The level of cutting temperature when processing steel in an ultrafine-grained state is generally higher than when processing steel in a coarse-grained state, which should be associated with the increased physical and mechanical properties of steel with an ultrafine-grained crystalline structure.

The scale of heterogeneity of the structures of steels and alloys can be rather large both within one sample and within a product. The procedure adopted in practice for determining the integral values of crack resistance characteristics cannot always reflect this circumstance. In this regard, it is necessary to develop methods for assessing the crack resistance of a medium with a heterogeneous structure. In this work, the authors determined the crack resistance of large forgings made of heat-hardenable 38KhN3MFA-Sh steel (0.38%C–Cr–3%Ni–Mo–V) based on the critical crack opening δс and the J-integral. The presence of critical stages in the development of a ductile crack during testing was assessed by acoustic emission measurements. In combination with the obtained methods of digital fractography of 3D images of fractures, this allowed relating the shape and position of the leading edge of each crack jump to the load-displacement diagram. Measuring the crack opening geometry during the test showed the possibility of determining directly the coefficient of crack face rotation when estimating δс. In general, this allowed constructing a map of the distribution of parameter δс values over the thickness of the sample and estimating the scale of the scatter in crack resistance within one sample – up to 30 %. Such a localization of measurements, primarily of the δc parameter, is comparable to the scale of heterogeneity in the morphology of various types of structures, which was assessed based on the measurement of digital images of the dendritic structure, the Bauman sulfur print, non-metallic inclusions on an unetched section, and ferrite-pearlite banding in the microstructure. This makes it possible to link local crack resistance values to various fracture mechanisms and their accompanying structural components.

A coating based on a single-phase medium-entropy CrFeNi alloy with a face centered cubic structure has good ductility, relatively high anti-corrosion properties, low cost, but insufficient strength for its widespread use. It is assumed that adding strengthening particles in the form of tungsten carbides and borides to the CrFeNi equiatomic coating will lead to an increase in its mechanical properties. This work studies the influence of tungsten carbide and boride additives on the structure and microhardness of a CrFeNi equiatomic coating. The coatings were formed by layer-by-layer short-pulse laser cladding with preplaced powder on a multifunctional laser installation equipped with a solid-state laser with a lamp pump based on an Nd:YAG crystal. The change in phase composition when adding strengthening particles was detected using X-ray diffraction analysis and transmission electron microscopy (TEM). Both methods confirmed the precipitation of Cr23C6 chromium carbide in the deposited coatings. TEM photographs indicate that the precipitated phase is distributed along the grain boundaries of the γ-solid solution. The study found that the addition of 6 wt. % WC and 3 wt. % WB increases the level of microhardness of the CrFeNi coating by 26 % (from 340±6 to 430±12 HV 0.025). This occurs due to the presence of Cr23C6, WC particles in the structure and possible microdistortions of the crystal lattice of the γ-phase as a result of doping with tungsten atoms released during the dissolution of tungsten borides and carbides in the process of high-temperature short-pulse laser heating.

Magnesium alloys are considered promising materials for the production of bioresorbable implants. Their main disadvantages are low strength and corrosion resistance in biological environment. In the work, the authors studied the effect of severe plastic deformation using the equal channel angular pressing (ECAP) method on the structure, mechanical properties, and corrosion resistance of the Mg–8.6Zn–1.2Zr magnesium alloy. It was identified that one ECAP cycle at 400 °C leads to a substantial hardening of the Mg–8.6Zn–1.2Zr alloy by ~10 %, up to 330 MPa. Structural studies showed that dynamic recrystallisation plays a significant role in the structure transformation. ECAP leads to the formation of a bimodal structure with large deformed grains with an average transverse size of 20±4 µm and recrystallised grains with an average transverse size of 6±2 µm. It was found that with a decrease in the strain temperature up to 250 °С, the process of deformation-induced decay of the supersaturated solid solution takes place. Electrical conductivity of a sample after ECAP at 400 °C amounted 29±2 % according to the International Annealed Copper Standard (IACS), while second ECAP cycles lead to an increase in the electrical conductivity up to 32±2 % IACS. Using the electrochemical corrosion method, the authors found that one ECAP cycle at 400 °C leads to a slight decrease in the corrosion resistance of the alloy under study compared to the initial state. The study showed that the corrosion current increases from 24 to 32 µA/cm2, while the subsequent ECAP cycle at 250 °С increases the corrosion current more than twice (up to 57 µA/cm2).

One of the most effective ways to increase the processing plasticity of advanced superalloys (heat-resistant nickel-based alloys) is the formation of an ultrafine-grained (UFG) microstructure in bulk semi-finished products. Such a microstructure is a necessary condition for the manifestation of the structural superplasticity effect in the technological processes of manufacturing products from such superalloys. One of the most promising methods for producing UFG microstructures is thermomechanical treatment (TMT) according to the multiple isothermal forging scheme. It has been shown that the EK79 superalloy after TMT, with a gradual decrease in the processing temperature from 0.88 to 0.62 Ts (where Ts is the strengthening phase dissolution temperature) leads to the transformation of the initial microduplex fine-grained microstructure into a mixed UFG microstructure. Such a mixed UFG microstructure consists of: 1) relatively coarse (inherited from the fine-grain microstructure) particles – γ'-phase with a size of 3.0±0.8 μm; 2) γ-grains, and incoherent γ'-phase particles with a size of 0.3–0.5 μm; 3) strengthening coherent intragranular γ'-phase particles with a size of 0.05–0.1 μm, released upon cooling from the TMT temperature to room temperature. During uniaxial compression tests, the EK79 superalloy with such microstructure, demonstrates low-temperature superplasticity in the temperature range of 800–1000 °C. It has been found that an increase in the deformation temperature up to 1000 °C, leads to the increase of γ-phase grains to micron size. The maintenance of superplastic properties in the presence of relatively coarse incoherent particles in the microstructure of the second phase (γ'-phase) is apparently related to the fact that the deformation is localised in the UFG component.

The experience of many-year research has shown that optimizing the steel chemical composition and microstructural characteristics, as well as reducing its contamination with non-metallic inclusions (NMI), it is possible to significantly increase the corrosion resistance of oilfield pipeline steels and increase the time of their trouble-free operation. The influence of complex NMIs on the steel corrosion resistance is determined by both the chemical composition of NMIs and their quantitative ratios. Therefore, obtaining metal products of the required quality is possible only when using the “control by structure” principle. In the work, based on the analysis of brightness fields of images (on a sample scale) in 256 shades of gray, the authors proposed digital, metrologically supported procedures for measuring the NMI heterogeneity of low-carbon oilfield steels: eliminating the heterogeneity of field illumination, justifying the criteria for binarization and noise filtering. For low-carbon steels of various types of melting, the authors identified the key role of dispersed non-metallic inclusions ranging in size from 5–10 μm2 to 2 nm2 in the formation of the corrosion resistance of steels. This may explain why, in some cases, there is no interrelation between the corrosion rate and the fracture resistance of steels, the formation of which is determined by larger particles. When representing the NMI as a set of random points on the plane, the distribution of distances between the nearest ones is estimated based on Voronoi polyhedra statistics. The study shows that an increase in the kurtosis coefficient of distributions of polyhedra areas is accompanied by an increase in the corrosion rate of the steels under study. This indicates the negative impact of heterogeneity in the arrangement of dispersed NMIs on the corrosion resistance of steels.

Dispersion-strengthened composite materials belong to the group of promising structural materials characterised by a diverse combination of properties. The paper considers examples of the creation and heat treatment of composite materials based on aluminium alloys strengthened by the titanium carbide dispersed phase characterised by high hardness, elastic modulus, and good melt wettability. At present, self-propagating high-temperature synthesis (SHS) is the most accessible, inexpensive and effective way to obtain them. The authors substantiate the expediency and show their successful experience of the formation in the composition of the AMg2 and AMg6 industrial alloys of a titanium carbide dispersed phase with a particle size of 130 nm in an amount of up to 10 wt. % using the SHS method, which makes it possible to increase the hardness of the alloys. Additional heating of the AMg2–10%TiC and AMg6–10%TiC samples after synthesis also contributes to the further increase in hardness. The complex of studies of physical, mechanical and operational characteristics presented in the paper was carried out to compare the properties of the work-hardened matrix alloys and the samples of composite materials before and after heating. The test results showed that heat treatment reduces the porosity of the composites and significantly increases their hardness and microhardness. A slight decrease in compressive strength at a significant increase in wear resistance is observed. It was found that composite materials are characterised by high corrosion resistance to carbon dioxide and hydrogen sulfide corrosion corresponding to the level of matrix alloys. The results obtained allow recommending the developed materials for the production of parts of the connecting rod and piston group, bearings and other wear-resistant parts of friction units.

The paper presents the results of experimental design of a cortex of the embedded stress sensor, which allows to determine stresses in the cross-section of large-scale laboratory monolithic structures made on the basis of mineral and polymer binders (concrete, gypsum, etc.). The objectives of the design were to develop a constructive solution of the stress sensor housing based on strain gauges, which has small dimensions, low manufacturing cost, as well as high resolution and stability of readings over the entire sensitivity area (stress up to 400 kgf/cm2).The stress sensor allows to determine the stress in laboratory structures with high accuracy, without significantly affecting the stress-strain state of the section at different stages of operation of the structural element.

There are a large number of works on a comprehensive assessment of the seismic resistance of buildings and structures. However, these studies, as a rule, do not take into account the random nature of the seismic impact, which is a pronounced non-stationary random process. An adequate assessment of the seismic resistance of buildings and structures is possible only on the basis of methods that allow taking into account the large variability of seismic impact parameters. The article presents a probabilistic method for calculating multi-storey reinforced concrete buildings designed in seismic regions, taking into account the interaction of a building with a non-linearly deformable foundation. The developed technique makes it possible to provide the required level of seismic resistance for the designed buildings based on the non-collapse criterion. As an ex-ample, the calculation of a multi-storey reinforced concrete building is considered. External seismic action is represented as a non-stationary random process. The external seismic action is considered as a non-stationary random process, which is obtained by multiplying the stationary random process by a deterministic envelope function. The parameters necessary for constructing the envelope and the stationary random process were obtained from the results of processing the available database of intense earthquakes. The stationary random process was generated by the shaping filter method. The impact parameters are based on the results of processing the available database of intense earthquakes. When modeling reinforced concrete structures, a concrete model is used with the function of damage accumulation under cyclic loads, as well as taking into ac-count the degradation of the strength and stiffness of the material during an intense earthquake. Accounting for the interaction of the building with the soil base is implemented using the SSI interface (Soil Structure Interaction). To prevent the influence of waves reflected from the boundaries of a limited ground massif, a PML layer (Perfectly Matched Layer) is used. The calculation was carried out using explicit methods for integrating the equations of motion on a computing cluster using parallel computing technology. The presented technique makes it possible to investigate the nature of the destruction of reinforced concrete structures during intense earthquakes and to identify zones with a deficiency in bearing capacity. The proposed probabilistic approach to modeling seismic impact as an implementation of a non-stationary random process with given parameters, together with taking into account the nonlinear deformation of the reinforced concrete structures of the building and foundation, allows you to control the level of reliability and design buildings with a given seismic resistance.

Existing composite floor design approaches require technical data on strength and ductility of shear connectors, which can be defined only by shear tests. The article discusses the failure modes of composite floor shear connection, made of powder-actuated shear connectors. The influence assessment of the main detailing parameters on the strength and deformability of shear connectors was executed. The database for analysis included the results of shear tests performed by both the authors and other researchers. According to the results of the study, the dependence of the strength and deformability of shear connectors on their height, orientation relative to the shear force vector, the strength of the concrete slab and the geometric parameters of the profiled flooring was estimated.

Reinforced concrete beams can experience local low concrete strength under certain conditions, for example, poor construction practices can cause problems such as concrete voids, surface cavities, block cracking, surface sinks and create areas of low concrete strength. This study presents the response of flexural hinge-supported reinforced concrete beams with different local areas of low concrete strength along the span. Modified models are adopted to describe the concrete properties and an ideal elastic-plastic model is adopted for the steel properties. The beam was divided into three main parts: one sensitive to bending moment, the second sensitive to shear, and the third sensitive to bond. The variables included two types of concrete strength and one reinforcement diameter. The results show that the most critical region with low concrete strength along the span of the beam is the confluence zone near the supports, which is reflected in the ductility of the load-deflection curves. A new generalized empirical model is developed to predict the effect of bearing capacity reduction from local low-strength concrete.

The main indicators of durability, which characterize the time of operation of the structure before the onset of an emergency condition, are the total service life and the remaining service life, the determination of which allows a more reasonable approach to the issue of planning current or major repairs in the building. The most common engineering techniques that allow predicting the remaining service life for reinforced concrete structures are considered: according to standard terms and analogous objects, according to external signs, based on changes in reserve coefficients and strength criteria. Their modifications are given for a number of techniques. Based on the results of the analysis of the methods, their main advantages and disadvantages were established. As a proposal to improve the existing approaches, a methodology is proposed in which the interval between visual examinations is taken for the remaining period of operation.

In the modern construction complex of the city of Moscow for the protection of buildings and structures from man-made vibration arising from the movement of trains of rail transportation (subway trains, railroad lines and trams). To protect buildings and structures from anthropogenic vibration arising from the movement of rail transport trains (subway trains, railroad lines and streetcars), Moscow uses layered rubber-metal vibration isolators [1]. Most often, to determine their static and dynamic characteristics, the finite element method (FEM) is used, which makes it possible to determine all components of the stress-strain state and frequencies of free oscillations in the loaded state practically for any structural forms of isolators. However, for the most popular software packages that implement FEM, the problem of optimizing the structural shape of the vibration isolator still requires significant time expenditures for multiple changes of the finite element mesh, repeated setting of boundary conditions and implementation of a series of calculations. Only some of the software packages implementing the FEM solve optimization problems of the shape of the product being calculated, most often it is related to foreign software products with universal functionality. Variation-difference method (VDM) is the closest to the finite element method (FEM) in terms of its computational capabilities. It is possible to create program modules that repeatedly and automatically solve three-dimensional problems of elasticity theory taking into account the changed geometry of the vibration isolator: the dimensions of the product, the location of perforations within the rubber layers, as well as the thickness of the rubber layer and other parameters important for obtaining an effective technical solution for vibration isolation of buildings. Further, the article describes the method of implementation of the variational-difference method (VDM) as applied to the solution of the problem of determining the components of the stress-strain state inside a three-dimensional layered vibration isolator with perforations of different sizes having different locations relative to the contour of the vibration isolator, i.e., the solution of the problem of optimizing the three-dimensional shape of the vibration isolator is given.

The stress-strain state of precast monolithic reinforced concrete shells from enlarged elements taking into account the installation conditions. The results of experimental-theoretical studies of precast monolithic reinforced concrete shells of complex geometry assembled from enlarged elements are given. The studies were carried out on full-scale composite shells 48x48 m and diameter 96m, its enlarged elements 3x18m and 3x24m as well as on the shell model on a scale of 1:10 and 1: 4. The stress-strain state of shells of a similar type was studied with different mounting and splitting designs. Recommendations are given on rational methods for the construction of shells from enlarged elements for public buildings.

The paper discusses the main aspects of implementing BIM technologies in the management of multi-apartment buildings. It highlights the features of implementing the system, including the stages of creating a digital model of the building, requirements for personnel, and specific skills. The advantages and opportunities that arise in the management process of multi-apartment buildings with information modeling technologies are noted. Specifically, it simplifies processes such as document storage and transmission, organization of building operations, current repairs of buildings and structures, and more. The prospects for the implementation of information technologies in the housing and utilities sector in the Russian Federation are already outlined: by 2023, developers are required to use these technologies when planning and constructing multi-apartment buildings. The government is implementing a series of systemic initiatives and measures aimed at the digitalization of multi-apartment building management, supporting the development of the sector towards a service model, and ensuring comfortable living conditions for citizens. To support these initiatives, it is necessary to unify requirements for services, standards for data collection, transmission, processing, and access, and to clarify the rules of interaction among participants, taking into account the active implementation of digital technologies in practice. The primary principle of digitalization should be economic feasibility. The implementation of digital technologies should provide real value for developers, management organizations, owners of residential and non-residential premises, and authorities. To achieve digitalization results, it is necessary to create conditions that stimulate the efficiency of interaction between subjects involved in the digitalization of multi-apartment building management. In particular, it is required to establish requirements for the implementation of information technologies at the legislative level.

The study investigates a thermosetting polymer filled with montmorillonite. Montmorillonite is a naturally occurring layered mineral with particle sizes ranging from 8 to 12 µm. The thermosetting polymer was DER-330 epoxy resin and FCH-S hardener. Rheological and physical-mechanical studies of the properties of epoxy resin modified with montmorillonite were carried out. Viscosity versus shear rate is shown for uncured pure epoxy resin and resin modified with montmorillonite particles at room temperature. At low shear rates, a significant effect of montmorillonite on the properties of the composite is observed. The low shear rate further allowed epoxy molecules to leak between the layers of montmorillonite platelets, causing swelling and increasing the distance between them. As the shear rate increased from 8 to 20 s-1, the percolation time of montmorillonite decreased, which affected the decrease in viscosity. When the shear rate increases above 20 s-1, no significant changes in viscosity occur; for both samples a monotonic line is observed on the graph. The addition of montmorillonite to epoxy resin changes the chemical composition of the composite, which leads to changes in rheological and physical-mechanical properties. The addition of montmorillonite retards gelation, which can affect processability, cure time, and final properties of the composite. Morphological studies were carried out to determine the degree of dispersion of montmorillonite particles in the polymer composite using a transmission electron microscope. The uneven distribution of montmorillonite particles predominated in all samples. Apparently this is due to the curing conditions of the polymer composite and insufficient dispersion time. Physical and mechanical studies were carried out on samples made of a composite with montmorillonite in comparison with samples from pure epoxy resin. The flexural strength of samples made from the resulting composite is comparable to the strength of samples made from pure epoxy resin. In turn, the viscosity increased by 170%.

Рассмотрены нормы по расчету сжатых сталежелезобетонных стоек, а также экспериментально-теоретические исследования других авторов. Выполнено экспериментальное исследование работы сжатых стоек с малым эксцентриситетом на диапазоне гибкостей от 6 до 20. Выполнено численное моделирование различных вариантов конструкций: с бетонами от В30 (С25/30) до В100 (С90/105), с сердечником в виде двутавра, с сердечником в виде квадрата. Полученные данные экспериментов и расчетов сопоставлены с теоретическими кривыми коэффициента продольного изгиба. Установлено, что кривые коэффициента в СП 266.1325800 и Eurocode 4 имеют не корректную форму и не отражают действительной работы сталежелезобетонных сжатых элементов. Использование кривой СП 266.1325800, основанной на кривой для железобетонных конструкций, а также кривых Eurocode 4, которые приняты как для стальных сечений (по Eurocode 3) – не дает нормального запаса конструкций и не обеспечивает надежность. Оба норматива игнорируют различный характер работы бетонов обычной и высокой прочности. В результате исследований установлено, что класс прочности бетона на сжатие влияет на устойчивость стержней с гибкостью от 6 до 10, при этом влияния формы поперечного сечения сердечника (вида жесткого армирования) практически нет. Для гибкостей от 10 до 20 может быть принята единая для всех бетонов кривая коэффициента. Разработаны кривые коэффициента для расчета сжатых элементов при малых эксцентриситетах и кратковременном действии нагрузок; предложена формула расчета несущей способности сжатых стоек.

In the realm of geotechnical engineering, deep excavation projects face intricate challenges, especially concerning the stability of barrette walls, which are highly susceptible to deformation and stress at their joints. This study focuses on evaluating the deformation and force behavior of barrette wall joints at the position of greatest deformation. The Finite Element Method (FEM) is utilized to simulate the behavior of these structures under various load conditions. The Analysis of Variance (ANOVA) method is employed to statistically analyze the FEM data, assessing the impact of different factors on deformation and force distributions within the barrette wall joints. The specific objective of this study is to determine the statistical significance of the observed deformations and understand the influence of construction stages on joint integrity. This methodological synergy enhances the predictability of engineering assessments and ensures that design and construction decisions are grounded in solid empirical evidence. The study's findings emphasize the importance of precise monitoring and advanced predictive techniques to mitigate potential risks associated with deep excavations, particularly at critical joint locations. The results indicate that the deformation patterns are primarily influenced by the geometrical setup of the walls and the mechanical properties of the soils. The greatest deformations were typically observed where the wall joints experienced the highest bending moments and shear forces, conditions exacerbated by unfavorable soil mechanics and hydrostatic pressures. The clear and consistent increase in total displacement highlights the progressive destabilization of the wall as the excavation depth increases. By integrating ANOVA with FEM, this study contributes to enhancing safety and efficiency in deep excavation projects by ensuring that decisions are grounded in empirical evidence.

Modular blocks are widely used in industrial and civil engineering both as stand-alone structures and combined into block-modular buildings. Modular block consists of the load bearing frame, wall fencing, roof and floor decking. The modular block, with wall fencing made of corrugated sheet continuously welded to the beams, is a spatial system, with beams and corrugated webs working together. The steel modular block for the gas pumping unit on a gas turbine power plant is considered in the paper. Assessment of the corrugated web thickness effect on the load bearing capacity of the block is performed. Numerical investigation of stress-strain state of the blocks with different thickness of corrugated web is carried out by the finite element method. The values of the ultimate destructive load on the blocks with different thickness of the corrugated web are determined. The values of the allowable load on the block and the criteria for its limitation have been established depending on the stress-strain state of the block and the causes of destruction. For comparison, a calculation was made of a block with walls made of sandwich panels that are not included in the work of the frame. It is determined that ultimate load on the block with corrugated webs is 1,5-6 times greater than on the block with wall sandwich panels.

At a single action on a concrete and reinforced concrete structure short-term dynamic load, the value of which may exceed the value of the static load-bearing capacity of the structure, it was observed that failure will occur not immediately, but after a certain time (delayed failure time td). If the dynamic load action is stopped before the moment td, the structure will not collapse. Therefore, the accurate determination of the delayed failure time of concrete is an important and relevant problem. To solve this problem, the paper presents a visco-elastic-plastic model to describe the stress-strain state of concrete under dynamic loading. This model consists of 2 elements: a nonlinear spring A and a piston B connected in parallel. Element A describes the nonlinear elastic-plastic properties of concrete, and element B takes into account the high-strain-rate effect of concrete. Under the action of sudden dynamic loads with an intensity greater than the static bearing capacity of the concrete, piston B helps to inhibit the development of deformations initiated in element A. Based on the proposed model, the delayed failure time is defined by the time interval required for the deformation of concrete to reach its ultimate value. The main factors affecting the deformation and failure of concrete such as concrete compressive strength, overload level, and viscosity are also investigated. Specifically, as follows: The higher the static compressive strength of concrete, the lower the delayed failure time. When a dynamic force of greater intensity is applied compared to the bearing capacity of the concrete, the faster the specimen will destroy. In addition, the viscosity coefficient significantly reduces the strain rate of concrete and the corresponding delayed failure time increases as the viscosity increases.

Solution of the problem of two-dimensional theory of elasticity with the use of discrete-continual finite el-ement method in the presence of crack is under consideration in the distinctive paper. The original operational continual and discrete-continual formulations of the problem are given, an example of analysis are presented.

The article presents a probabilistic approach to the design of flexural elements made of cross-laminated timber (CLT) as one of the promising materials for sustainable construction. The variability of the elasticity modulus and the ultimate strength of the timber layers effects on the structural safety. Such uncertainty can be modeled by using probabilistic and statistical methods. Information is presented on tests of a three-layer CLT panel during bending, and statistical parameters are given for wooden control samples of the CLT panel layers. The implementation of the presented approach makes it possible to obtain an estimate of the reliability index or the failure probability for the CLT structural element according to the criterion of normal cross-sections strength. With a given target level of reliability or risk value, the reliability level of the design solution of a cross-laminated structure can be quantified.

In this paper, the problem of numerical modeling of the dynamic behavior of bending beams made of the materials with a developed internal structure is considered. The simulation is performed taking into account the non-local elastic properties of the material in time. According to the principals of nonlocal mechanics, it is assumed that elastic forces in a structure depend on the entire history of its deformation, and not only on the instantaneous deformed state. The proposed dynamic deformation model is proposed as an alternative to detailed three-dimensional models. The nonlocal dynamic deformation model is integrated into the algorithm of the FEA method to make it applicable to solving applied engineering problems. The numerical implementation of the model is performed in Python. A technique for selecting the scale parameter of a non-local model based on experimental data using the least squares method and the dichotomy method has also been developed and implemented. To identify the possibility of extrapolation of the scale parameter values determined according to the developed methodology, a series of numerical experiments were conducted, on the basis of which scale parameters for beams of different lengths were obtained and the stability of the nonlocal model was evaluated.