Advances in Science and Technology Vol. 156

Abstract: The research work is devoted to the study of the stress-strain state of a structure comprising a cylinder with a sphere using numerical approaches and Green’s functions. The results obtained include the analysis of stress distribution, study of deformations and determination of stress concentration zones. Safety factors are assessed and the influence of boundary conditions on the behaviour of the structure is revealed. The application of numerical methods allowed for a detailed study of the interaction of the sphere, providing an opportunity to analyse the exact properties and assess the influence of various factors in complex structures. It should be noted that the results obtained, which were evaluated taking into account all factors, affect the real system and can be predicted with a deviation error of 1%.

Abstract: In this paper, the boundary element method (BEM) is investigated and computer simulations are conducted to study the patterns of structure formation of non-isometric elements. The modeling of this study covered various aspects, including shape, radius, angle from the stable radius, porosity, average coordination number, simulation time, component falling force, and electrostatic constant. The simulation results provided important information about the properties and interaction of non-isometric components under different conditions. It was found that the obtained parameters can be effectively predicted for further research. It should also be noted that important processes, such as deformation and material behavior, colloidal aspects, dynamic modeling of the movement of components with complex shapes, and features of nanotechnology, were observed in parallel with computer simulation.

Abstract: In this scientific work, mathematical modeling of tetrahedron elements in the finite element method is presented, which includes the determination of geometric shape, shape functions, and material properties. Unknown fields such as displacement vectors, strain, and stress tensors are considered. The methodology of applying the principle of virtual work and equilibrium equations is described, allowing the derivation of a system of differential equations to describe the behavior of the tetrahedral element. Integration over the volume and consideration of boundary conditions help reduce the equations to a system of linear algebraic equations for numerical solution using the finite element method. It was found that modeling tetrahedral elements with a specific given radius (for example, R=0.3 mm) involves stages such as geometry determination, element generation, shape function formation, stiffness matrix computation, and solving a system of linear equations. The radius R of tetrahedral elements is taken into account at all stages, ensuring accuracy and reliability in tetrahedra modeling. The research also focuses on the fact that the occurrence of minor errors in iterative processes may result from several factors, including iteration step, the number of iterations, stopping criteria, linear or nonlinear material behavior, solution method selection, the presence of geometric inhomogeneities, and element size.

Abstract: The paper analyzes the forms of impact of non-design loads from shock air waves on building structures. The problem of forecasting the dynamics of the explosive load on a building structure (for example, the covering of a buried structure) is solved by the simultaneous solution of the equation of the spatial distribution of excess pressure in the front of a shock air wave and the dependence of the time of its action on the speed of its front. Since the speed of the shock air wave is constantly changing, the equation of the time of the wave action has a differential form, and its solution is established on the assumption that the simultaneous action of the wave on the surface of the building structure occurs on an area that is limited by the width of the shock wave front. On the basis of this, a grapho-analytic technique for determining the spatio-temporal dependence of the change in excess pressure in the plane of the building structure at the time of impact of the shock wave was developed. This dependence is established in the form of a table or graph, which is a loading curve.

Abstract: The paper presents the results of experimental studies and computer modeling of reinforced concrete and fiber-reinforced concrete cross-beam systems. The authors have made a special stand, the design of which allows for experimental studies of the load-bearing capacity, deformability and crack resistance of cross-beam systems under concentrated and distributed static loads. Samples of reinforced concrete and steel fiber concrete were tested, which are systems consisting of four mutually perpendicular beams of rectangular cross-section. The samples are reinforced in the lower zone with longitudinal reinforcement of class A400C with a diameter of 8 mm. Steel fiber concrete samples have additional dispersed reinforcement with steel fiber with curved ends in an amount of 1% by volume of concrete. A methodology for finite element modeling and calculation of cross-beam systems in ANSYS 17.1 has been developed, and the results obtained experimentally and based on computer modeling have been compared. Tests have shown that dispersed reinforcement leads to an increase in the load-bearing capacity of the system by 1.23 times. In finite element analysis, this increase was 1.18 times. The load-bearing capacity of the reinforced concrete cross-beam system obtained by the finite element method is 13% less than in the experiment, and that of the fiber-reinforced concrete system is 15% less. The number of cracks in a fiber-reinforced concrete system increases significantly (2 times), but the length of the cracks decreases by 2.1 times, and the width of their opening is significantly reduced - from 3 mm to 0,5 mm.

Abstract: The results of determining the bearing capacity, deformability and crack resistance of full-size airfield slabs made of reinforced concrete and fiber-reinforced concrete are presented on the basis of experimental studies conducted in laboratory conditions. The slabs were manufactured by Velikodolinsky Reinforced Concrete Plant LLC by order of the Odessa State Academy of Construction and Architecture. The authors have developed a stand for testing slabs using a cantilever loading scheme in accordance with the regulatory documents in force in Ukraine. Two slabs were studied: a serial reinforced concrete airfield slab and the same slab, but with additional steel fiber reinforcement in the amount of 1% of the volume of the concrete mixture. It has been shown that the load-bearing capacity of airfield slabs with additional reinforcement with steel fiber increases significantly; at the same time, deflections are reduced and crack resistance increases. The bearing capacity of airfield slabs with additional dispersed reinforcement increased by 29%. The maximum deflection decreased by 12.7%. The nature of crack formation changed qualitatively: the process began at a higher load, and the final crack opening width decreased significantly. These results indicate the high efficiency of additional reinforcement of airfield slabs with steel fiber.

Abstract: The article is devoted to the issues of modeling and analysis of the protective structures’ designs under the influence of explosive loads. An analysis of shock waves is carried out, the nature of their propagation and impact on buildings, as well as methods for their modeling in the LIRA-SAPR software. Some proposals for preventing the collapse failure of the structure due to the impact of missile fragments are given. The article discusses different types of point explosions - air and ground. The diagram of the formation of waves during an air explosion and a characteristic wave pattern during a ground explosion is given. The propagation of waves during a ground explosion is analyzed. A mathematical model for determining shock wave parameters is given. An example of the calculation of the protective structure constructions against a blast wave in PC LIRA-SAPR (LIRA-FEM) under the action of a surface blast effect is provided. The results of the non-linear calculation of the roof slab for resistance to collapse failure in the case of an emergency explosive impact on an area up to 80 m² are presented.

Abstract: Calculation formulas are given in the analytical form, which allow to study the bending of beams on a non-homogeneous solid Winkler elastic foundation. An example demonstrates the practical application of the developed method. The case is considered when the bed coefficient changes according to a parabolic law, and the variable distributed load acting on the beam is given by a linear law. The results of the calculation by the author's method are presented in numerical and graphical formats. For comparison, the calculation results obtained by the finite element method are also provided.

Abstract: The paper presents the results of work on changing the mass of closed gears by the example of a single-stage cylindrical gearbox. Two variants of the solution for the problem are considered. In the first variant, it is proposed to reduce the thickness of the walls of unloaded areas to the constructive minimum. The other solution involves the replacement of the unloaded areas of the gearbox housing with non-metallic inserts. To produce the inserts, ZELLAMID plastic is recommended. Both variants are based on the method of topological optimization of housing parts. The Fusion 360 software product (Shape Optimization option) is applied as a tool. A 3D model of the gearbox housing was developed from which unloaded areas were removed followed by topological optimization of the housing carried out, which made it possible to reduce the mass significantly.