Vol 16, No 3 (2020)

Relevance. When calculating building structures for dynamic effects, the method of expanding the desired solution in a series according to the forms of natural oscillation is traditionally used. Depending on the complexity of the tasks to be solved, it is required to take into account a different number of forms - from the first few forms to tens or hundreds of forms. The results obtained are all the more accurate the more forms the calculation takes into account. As a rule, the contribution to the required parameters of the stress-strain state of the structure of unaccounted for higher oscillation forms is not evaluated in any way, although in some cases this must be done. In addition, the important question arises of performing the calculation with a reduced number of considered forms so as to obtain a sufficiently accurate result. The aim of the work. This work is devoted to the method of static accounting of higher forms of oscillation in the problems of the dynamics of building structures. The basic principles of the method are described, its use on a spatial rod system loaded with several harmonic forces with different frequencies is considered. Methods. The method of static accounting of higher forms of oscillations studied in this work requires the solution of one dynamic problem with a small number of forms and an auxiliary static problem. An important circumstance of the approach is that the static problem must be solved in two ways: the exact one and the decomposition method according to its own forms of oscillation, after which the static correction to the dynamic solution is calculated. Results . The approach proposed in the article can significantly reduce the computational cost of dynamic calculation in comparison with the classical approach with comparable accuracy of the results. This may be of value in solving problems of complex dynamic effects and for structures with inhomogeneous rigidity.

The aim of the work - to analyze the theory, which is widely used in the calculations of various constructions and buildings, consisting of five theories that do not correspond to each other (or erroneous), which reject the fundamental properties of structural concrete and the principles of the Eurocode. Methods. According to the authors and their research this theory contains: a set of theories of various purposes rejecting each other, including erroneous, physically impossible jumps from one theory to another, jumps of various design schemes, unacceptable in the elastoplastic stage. In it: there are mathematical errors; the fundamental concepts of the classical and general theory of calculation are distorted; the principle of designing bearing capacity in ultimate conditions and the process of continuous loading of structures established by the Eurocode are rejected; the fundamental properties in Eurocode of structural concrete are replaced; it is stated that the theory is determined not by the properties of materials, but by the partialities of the developers; references are made to the abstract results of experiments. Results. We analyze the theory of calculating for mass application which accompanied by the necessary mathematical calculations and experimental estimates.

The aim of the work is to present the trend of the advancement of steel design code and practical approach of steel frame design from the current AISC-LFDR to the advanced analysis. As the trend of steel frame analysis method is from first-order elastic analysis to second-order inelastic analysis which is an advanced analysis. Methods. In this paper the comparison between the load - displacement curves of several structural analysis methods is presented. Case studies are considered to analyze by different methods and comparison of practical advanced analysis method with PROKON software. The case studies includes a two-story one bay steel frame and four bays of twelve-stories steel frame. The results of first-order elastic, elastic buckling, second-order and nonlinear analyses of an unbraced frame are compared and their difference is presents. The proposed software for advanced methods demonstrates the accuracy and the computational efficiency in predicting the nonlinear analysis response of steel frame structures.

The aim of the work - to research changes in the dynamic stiffness of pile foundations from the distance between the piles during vertical vibrations using experimental data from literature sources and solving wave models describing the vertical vibrations of a thin plate with round cuts. Methods. To verify the reliability of solutions of wave models describing changes in dynamic stiffness during vertical vibrations of pile foundations, it is used data obtained in experiments to determine the eigenfrequencies of 3×3 groups of friction piles with different distances between them. Also the data obtained from forced vertical oscillations of 2×2 groups of friction piles connected by pile-caps at different loads and distances between piles was used. In the processing of available amplitude-frequency curves for determining the dynamic stiffness the inverse problem is solved using the theory of nonlinear oscillations. The correspondence between the measured and predicted data is evaluated, when describing the behavior of the pile-ground system. Results. It is established that the relations that take into account the mutual influence of piles in the group, obtained in the framework of wave models solutions and used for calculating dynamic stiffness in vertical vibrations of pile foundations, allow us to obtain satisfactory results in accuracy. The deviation of the calculation results from the experimental data does not exceed 15%.

Relevance. Wood is one of the most widely used building materials throughout history, and because of its physical-mechanical properties it mainly has been used in flexed and compressed elements. Eucalyptus was introduced to Latin America in the mid-19th century and nowadays is one of the most used woods for construction in the Andean region of Ecuador. To designing slender structural elements under axial loading engineers usually use the Euler formula, but it is applicable only if the compression stress does not exceed the proportional limit. One way to determine if the compression stress will be below the proportional limit is by comparing of the slenderness of the element with the limiting flexibility of its material which allows knowing if the buckling will occur in the elastic zone where Euler formula applies. The aim of the work - determine the magnitude of the limiting flexibility of eucalyptus, since this wood has been the subject of some investigations, however, no information about the limiting flexibility magnitude for the calculation of axially compressed elements. Methods. The laboratory tests to determine the magnitudes of the modulus of elasticity, proportional limit, admissible compression stress and limiting flexibility was carried out. Results. This experimental investigation shows that the magnitude of the limiting flexibility or so-called critical slenderness ratio for eucalyptus globulus is 59.

At present, there is a renewed interest in the design and application of wall structures in architecture and construction. With the advent of modern computers, refined methods for calculating shells, new building materials, the development of differential geometry and the rapid growth of numerical methods of calculation, it became possible to create architectural masterpieces from shells of canonical and non-canonical forms, which can be the hallmark of a city or country. This emerging trend among young Russian and foreign specialists inspires optimism among scientists who are researching thin-walled shells. The article considers some results of the work of the Department of Civil Engineering of the Engineering Academy of the Peoples’ Friendship University of Russia on attracting students to architectural design and involving undergraduates in researches on architecture, the theory of thin-walled spatial structures and their application in construction and architecture. The publications of students in this field are presented.