Vol 18, No 4 (2022)

Energy saving, operational reliability of buildings and structures for various purposes is determined by the durability of building materials and products used in their construction. To date, frame building composites have been developed on the basis of polystructural theory. The frame technology for the manufacture of building products consists in the preliminary manufacture of frames from coarse-pored mixtures, followed by filling voids in the hardened frame with a matrix-plasticized binder, fine-dispersed or fine-grained composition, while the frames and matrix can be formed on various binders. This technology makes it possible to obtain building materials and products with a combination of the most diverse and even incompatible binders with a predetermined set of properties, i.e. opens the way to directional materials science. The paper presents the results of theoretical research and calculation of the technological physical and mechanical properties of frame composite building materials. The regularities of the structure formation of frame composites at the level of the formation of frames and matrices, as well as when they are combined, are revealed. It is established that the process of impregnating the frame with a matrix obeys the laws of motion of freely dispersed or connected dispersed systems. Formulas for calculating structural stresses in hardening frame composites are derived. Analytical dependences for calculating the thermal conductivity coefficient of products are obtained from phenomenological positions. Expressions for the calculation of the modulus of elasticity are obtained for models of ordered aggregates and the kinetics of the processes of destruction of frame composites under their loading is shown. Theoretical dependences for calculating the diffusion coefficient in frame composites on the main structure-forming factors are established.

The results of data analysis from complex field studies of vertical deformations of the rock base near-contact layer and full settling Boguchanskaya HPP concrete dam sections in order to determine the state of contact of the foot of the concrete dam with the rock base are presented. The purpose of the study is to control the state of the contact of the concrete dam foot with the foundation based on the analysis of a set of field studies of the vertical deformations of the near-contact zone of the foundation of the concrete dam sections and the total draft of the sections of the concrete dam to justify the stability of the concrete dam sections. In order to control the vertical deformations of the near-contact zone of the rock foundation, string control and measuring equipment (displacement sensors PLPS-10) was installed. The total draft of the concrete dam sections is measured by means of ceiling marks installed in the grout gallery. Analysis of the field data on total drafts of concrete dam sections and vertical deformations of the near-contact section of the rock foundation showed that the contact joint between the foot of the concrete dam sections and the foundation is in vertical compression. The results of the analysis of the available data of complex studies of vertical deformations of the near-contact layer of the rock foundation and the total draft of the concrete dam sections made it possible to substantiate the stability of the concrete dam sections.

The paper provides the conclusions of a comparative analysis of various approaches, design models, methods for analysis of a loaded structural system and the results of such analysis for a sudden failure of a structural member. It shows that the analysis methods recommended by Russian and foreign standards are based on the same methodology. And the recommended options for choosing secondary design schemes in static, quasi-static and dynamic formulations have different complexity, however, give results which are close enough and acceptable for practical purposes. Some differences in the results are associated with different approaches to consider the reaction redistribution time for the removed structural member, i.e., in essence, with the mode of failure of this member. The issue of criteria for a special limiting state is also discussed. The authors present the expediency of including an additional criterion in regulatory documents that considers the second-order effects on the buckling of the structural elements under accidental impacts and, accordingly, provisions for protecting structural systems against the exhaustion of the bearing capacity due to the loss of stability. As such criterion, the achievement of the limiting equilibrium point on the diagram “axial force vs. transverse deflection” can be adopted.

The aim of the research - to investigate the behavior of thin-walled beam I-section loaded with bending and torsion using theoretical, numerical, and experimental approaches. In this paper, the main criteria for consideration of the different methods of analysis is the geometric characteristic of the section. The results obtained by the finite element method, the numerical method, as well as experimental data are compared. The analysis by finite element method by considering an additional degree of freedom at a node to include the restrained torsion and the dimension of the stiffness matrix is thus 14×14. The results of the calculation according to this theory are compared with the numerical solution obtained using finite element software, and with the results of the experiment. The I-beam section subject to bending with torsion is considered. The deformations, strain, and stress distributions of open thin-walled structures subjected to bending and torsion are presented using experimental methods. The comparative results for the angle of twisting, deformations, and normal stresses in the frame element subjected to combined loading are displayed graphically. To evaluate the results, a theoretical, numerical, and experimental investigation of I-beam behavior under bending and restrained torsion was carried out. As a result of the comparison, it was revealed that the results obtained according to the refined theory proposed by the authors have good convergence with experimental data and are also quite close to the values obtained using commercial software.

Works on the study of the stress-strain state of the shell of an equal slope with an ellipse at the base have not been widely performed. The present paper is a part of a series of articles on the analysis of the geometry and stress state of torses of an equal slope with a directrix ellipse by various methods under different loads and support conditions. The derivation of the differential equations of equilibrium of the momentless theory of shells for determining internal forces in the torse with a directrix ellipse under the action of internal pressure is presented. The analytical results are compared with results obtained by the finite element method (FEM) and the variational difference method (VDM). The advantages and disadvantages of three calculation methods are determined, and it is established that VDM results are more accurate compared to FEM, but FEM-based software is a more powerful tool to perform the structural analysis.

An opportunity of conversion of algebraic surfaces with a main frame from three superellipses of general type into ruled surfaces of several views is shown. It is necessary to take one, two, or all of three superellipses in the form of a rhombus, i.e. it is necessary to assume exponents in explicit algebraic equations of suitable superellipses equal to one. It was illustrated that having taken one and the same main frame from three plane curves lying in the main coordinate planes, one can construct three algebraic surfaces of different orders. So, it is possible to introduce into practice great number of ruled surfaces with the preliminary given main frame from three superellipses. Some of them must be in the form of straight lines. As a result, fifteen shapes, i.e. five threes of ruled algebraic surfaces with a main frame from three superellipses were obtained with the help of three explicit equations or with the help of three systems of parametric equations. These surfaces contain a polyhedron on given rhombus plane, some types of cylindroids and conoids, and ruled surfaces not described in scientific literature before. All surfaces were visualized for concrete examples. Earlier, Professor A.V. Korotich introduced into practice a new group of surfaces which he called “Ruled quasipolyhedrons from conoids.” Some of the ruled algebraic surfaces presented in this paper can be put in this group of ruled quasipolyhedrons.