Vol 16, No 2 (2020)

Relevance. By its nature, seismic action is represented by the accelerogram a pronounced multidimensional random process, generally containing six components. The calculation in the deterministic formulation does not always allow to adequately assess the reaction of the system. While the calculation in the probabilistic formulation more adequately reflects the work of the system and makes it possible to evaluate its seismic resistance with a given security. The aim of the work is to assess the actual load-carrying capacity safety margin and the taken when designing coefficient K1, taking into account the permissible damage to buildings and structures for the steel spatial frame when calculating on the seismic action. Methods. In the article, the steel spatial frame was calculated for two sets of accelerograms, with dominant frequencies close to the main frequencies of the frame's natural vibrations. Each set was synthesized as a family of unsteady random seismic impact implementations. The calculation was carried out on two-component seismic action in nonlinear dynamic formulation in the software complex LS-DYNA. Previously, the frame was designed in accordance with national standard SP 14.13330.2014 “Construction in seismic areas on the seismic action” of the design earthquake level in the software complex PC LIRA 10.8. According to the developed probabilistic method for each set the actual load-carrying capacity safety margins were obtained and the coefficients K1 were estimated. Results . An analysis of the results shows that the steel frame under consideration has a sufficiently large margin of load-carrying capacity, and the coefficient K1 is taken in norms excessively conservatively. The developed technique allows to correct the value of the accepted coefficient K1 for buildings and structures of certain structural schemes. That in its turn will increase the economic efficiency of construction in seismic areas and ensure the reliability of the designed buildings and structures.

Research aim. The aim of the present research was an analysis of a metal ribbed ring-shaped dome metallic ribs stress state at different stages of a skeleton overhang erection process. The considered dome is hemispherical and is assembled bottom-up of individual elements. Due to a varying slope of meridional ribs elements at different relative elevations their stress state changes during mounting. The effect of the overhang erection process onto the stress state of the metal dome meridional ribs has been investigated. The relationship between the stress state of a meridional rib and mounting of each next dome skeleton tier has been established. Methods. A mathematical model of the metal ribbed ring-shaped dome assembled of steel H-shaped elements with rigid connections has been developed. Several extra models corresponding to different skeleton erection stages have been also generated to determine stresses in the meridional ribs at these stages. Response of each dome mathematical model under dead-weight load has been simulated. The obtained values of stresses in the meridional ribs within different models have been compared with corresponding design stresses values. Results. The dependence of the metal dome meridional rib stress state onto the stages of overhang erection process has been plotted. A degree of utilization of ribs steel strength at different erection stages has been represented by diagrams. An estimation of the dome skeleton stress state during overhang erection has been given. Imminence of assembly stresses during overhang erection and their influence onto dome structural reliability has been pointed out.

Relevance. Different models of contact between bodies are used in determining the stressed and deformed state in the strip lying on the base. It is necessary to evaluate the qualitative and quantitative nature of the change in stress in the strip depending on the coupling of the strip and base. The aim of the work - to analyze the effect of the coefficient of friction on the value of stresses in an anisotropic band when interacting with a rigid base. Methods. The solution is based on the equations of the plane problem of the theory of elasticity of an anisotropic body under the conditions that the band is closely adjacent to the base and the tangent force on the contact plane is proportional to the normal pressure. Displacements and stresses at any point of the strip are written in the form of the method of initial functions through the functions of displacements and forces on the lower plane, which depend on the nature of the load applied on the upper plane and the conditions of contact between the strip and the base. After the transformations, the calculation formulas for displacements and stresses are expressed using the Fourier integral transform through the normal surface load in the form of improper integrals. Results. Formulas for determining displacements and stresses are obtained for the variant of loading a strip with a concentrated force. These formulas are used to construct influence functions for the problem of equilibrium of an anisotropic strip lying on a rigid base, taking into account friction. Graphs of the effect of the coefficient of friction and the direction of the anisotropy axes of the material on the stress state of the strip are presented. The results of stress calculation are compared using anisotropic and isotropic models.

The aim of the work - to give the possibility to expand mind of designers and architects projecting structures in the form of traditional and non-canonical ruled surfaces. These surfaces have several unquestionable advantages with a point of view of their forming, designing, and making of factory-made goods and erections in the form of ruled surfaces and analysis methods. Methods. Choosing ruled surfaces for classification, one can use methods of their determination by vector, parametrical, implicit, and in explicit equations. Only analytical ruled surfaces are considered which were examined and presented in scientific-and-technical literature. Results. All known at present time ruled surfaces are given in a graphic form. The determinations of some little known ruled surfaces are presented in a paper. The original sources, where these surfaces are examined or their application in real structures and erections are considered, or methods of determination of stress-strain state in thin-walled shells with ruled middle surfaces are presented, are given in references.

The aim of the work - comparison of the results of determining the parameters of the stress-strain state of plane-loaded elastic bodies based on the finite element method in the formulation of the displacement method and in the mixed formulation. Methods. Algorithms of the finite element method in various formulations have been developed and applied. Results. In the Cartesian coordinate system, to determine the stress-strain state of an elastic body under plane loading, a finite element of a quadrangular shape is used in two formulations: in the formulation of the method of displacements with nodal unknowns in the form of displacements and their derivatives, and in a mixed formulation with nodal unknowns in the form of displacements and stresses. The approximation of displacements through the nodal unknowns when obtaining the stiffness matrix of the finite element was carried out using the form function, whose elements were adopted Hermite polynomials of the third degree. Upon receipt of the deformation matrix, the displacements and stresses of the internal points of the finite element were approximated through nodal unknowns using bilinear functions. The stiffness matrix of the quadrangular finite element in the formulation of the displacement method is obtained on the basis of a functional based on the difference between the actual workings of external and internal forces under loading of a solid. The matrix of deformation of the finite element was formed on the basis of a mixed functional obtained from the proposed functional by repla-cing the actual work of internal forces with the difference between the total and additional work of internal forces when loading the body. The calculation example shows a significant advantage of using a finite element in a mixed formulation.

Relevance. The paper considers shot blasting, which is a widely used method for improving the surface properties of parts (such as fatigue strength, hardness, and elongation) due to cold plastic deformation, which results in nanostructuring of the surface of the processed material, accompanied by a reduction in the grain size of its crystal structure. The conditions for the formation of a nanostructured surface layer when processing parts with a shot stream are studied. The aim of the work is to determine the conditions of nanostructuring during shot blasting due to plastic deformation, determined by the impact of the shot, which collides with the treated surface at high speed. Methods. To solve the stated problems, we used the solution of the contact problem of the theory of elasticity on the action of a concentrated force on the elastic half-space, the role of which is played by the workpiece. The conditions of the onset of plastic deformation in the surface layers of the workpiece are determined. Cold plastic deformation provides nanostructuring of the surface layer of the workpiece, increasing strength, fatigue life, atomic diffusion and improving tribotechnical characteristics. Results. Based on the contact problem of the theory of elasticity, the problem of the formation of a nanostructured layer on the surface of the workpiece during shot blasting has been solved. An analytical dependence has been obtained, which allows predicting the transition of the material to a plastic state and nanostructuring the surface of the workpiece during shot blasting.

Relevance. Hydroelectric facilities include reinforced concrete retaining walls. They are intended to protect the main structures from the collapse and sliding of soil massifs. Retaining walls are characterized by significant size, relatively low content of reinforcement, the presence of horizontal interblock seams, which considerably affects the features of the work and the state of retaining walls. The normative documents that were in force during the design and construction of most retaining walls (the second half of the last century) did not fully take into account the features of the retaining walls, as a result of which long-term operation revealed deviations from the design premises, including excessive displacement of the top of the walls, the disclosure of horizontal interblock joints, which exceeded the design values. In a number of cases, reinforced concrete structures of retaining walls were reinforced in areas of interblock joints. The aim of the work is to conduct experimental studies of reinforced concrete retaining walls, including taking into account their reinforcement by inclined reinforcing bars. Methods. The technique of experimental studies of hydraulic engineering reinforced concrete structures was applied in accordance with regulatory documents and the developed program of experimental studies of reinforced concrete retaining walls. The results obtained showed the opening of horizontal interblock joints, the formation of inclined cracks emerging from the joints. An increase in the strength of reinforced concrete structures of retaining walls and a decrease in their deformability due to reinforcement by inclined rods in the area of the interblock weld were recorded.

Structures are designed using current seismic design codes which are mostly based on Force-Based Design approach. The aim of the work is to implement the Performance-Based Seismic Design (PBSD) approach in concrete buildings. PBSD, which is a new concept in seismic design of structures, is a reliable approach capable of providing more detailed information on the performance levels of both structural and non-structural elements. Methods. In this study Performance-Based Seismic Design has been utilized on reinforced concrete irregular frame. In order to do this pushover analysis was done. Story drift ratios were chosen as deformation limits to define the performance levels for specific earthquake hazard levels. The results of this study show that Performance-Based Seismic Design gives a structure with better seismic load carrying capacity, thereby achieving the objective of performance as well as economy. It is also possible to conclude that PBSD obtained by above procedure satisfies the acceptance criteria for immediate occupancy and life safety limit states for various intensities of earthquakes.