Vol 18, No 3 (2022)

Experimental determination of the parameters of the force resistance of reinforced concrete structures aimed at protecting them from emergency beyond design impacts is an important direction in improving the safety of buildings and structures. In this connection, the purpose of the study was an experimental assessment of the deformation parameters in the complexly stressed elements of reinforced concrete frames under special impact in the form of a sudden column removal. Experimental studies were carried out for two frames, one of which was tested when removing the middle column, the second - when removing the extreme. Experimental two-span structures of reinforced concrete frames are designed with three floors in height, reinforcement was made with spatial reinforcing cages that provide resistance to torsion with bending. The results of experimental and theoretical studies of reinforced concrete frame structures under special influences and an assessment of displacements, cracking and destruction of the considered complex-stressed structural elements under such influences are presented. It is established that the type of stress state, the formation and width of crack opening significantly affect the dissipative properties of the structural system.

Concrete is widely used as a building material throughout the world. However, its use in building structures is limited due to its low tensile strength. This problem can be partially solved using steel bars reinforcement, as well as using dispersed reinforcement with various types of fibers. The authors propose the simultaneous traditional reinforcement of a concrete structure with steel bars with additional dispersed reinforcement with natural coconut fibers, relatively cheap and widely available in many countries in Africa, Asia and Latin America. The purpose of this study is to analyze the effectiveness of the proposed solution by comparing the required amount of steel reinforcement (by weight) for a beam made of traditional concrete and a similar beam with additional dispersed reinforcement with coconut fibers. Deflections and cracking in beams were investigated. The analysis was carried out using Autodesk Robot Structural Analysis Professional 2022 software. The results showed that a beam additionally reinforced with coconut fiber requires 11% less steel reinforcement (by weight) compared to a similar beam made of traditional reinforced concrete. In addition, the coconut fiber reinforced beam experienced 6% less deflection and significantly less stress cracking compared to a simple concrete beam. These results proved that the approach proposed in the work noticeably improves the performance of reinforced concrete in the structure, and also makes it possible to obtain significant savings in reinforcing steel.

The usage of traditional approximating functions directly to the desired displacement vector of the internal point of a finite element to determine it through nodal unknowns in the form of displacement vectors and their derivatives is described. To analyze the stress state of a geometrically non-linearly deformable shell of rotation at the loading step, the developed algorithm for forming the stiffness matrix of a hexagonal finite element with nodal values in the form of displacement increments and their derivatives was used. To obtain the desired approximating expressions, the traditional interpolation theory is used, which, when calculated in a curved coordinate system, is applied to the displacement vector of the internal point of a finite element for its approximation of class C(1) through nodal displacement vectors and their derivatives. For the coordinate transformation, expressions of the bases of nodal points are obtained in terms of the basis vectors of the inner point of the finite element. After the coordinate transformations, approximating expressions of class C(1) are found for the components of the displacement vector of the internal point of the finite element, leading in a curved coordinate system to implicitly account for the displacement of the finite element as a rigid whole. Using calculation examples, the results of the developed method of approximation of the required values of the FEM with significant displacements of the structure as an absolute solid are obtained.

It was ascertained that investigations on classification of architectural styles for shells and shell structures are absent. Only one published paper is available where architectural styles with indication of dates of appearance of the styles and dates of attenuation of their application are presented and the names of their founders are given. Now, the interest for the design, analysis, and building of thin-walled shells and shell structures is rising. There are no countries without erected shell structures. Hence, it is necessary to make more exact the classification of these erections and the distribution of them into groups. An aim of this work is collection of information about all known architectural styles as applied to shells and shell structures, and grouping of them due to characteristic traits and indications. All architectural styles were divided into five groups, i.e. avant-gardism, art deco style, modernism, ecotech style, and the newest styles. A special scheme, where distribution of architectural styles on these groups is applied to the examined structures, is given. Mutual influence of styles was revealed and presence of architectural directions and style flows in several styles was shown. The conclusions presented in this paper can demand the future accurate definitions and developments because specialists do not have common views to the list of architectural styles and to their classifications.

The movements of a reinforced net are considered. Mesh systems are used in various areas of modern technology, aviation, fishing, and construction. In recent years, much attention has been drawn to the complete equations that describe the motion of a deformable thread. In accordance with the studied task, the reinforcement of the net is carried out by adding terms in the equations of motion. In the planar case, the static behavior of the structure is investigated, and equations of motion are derived that allow the study of motion. The problem of wave propagation in deformable filament systems, taking into account a significant deviation of the filament shape from the original rectilinear one, is mathematically very difficult, since the equations of motion are a system of nonlinear differential equations in partial derivatives. To solve the problem, the method of characteristics is used. As well the method of characteristics solves the problem of the propagation of unloading waves (in the case of a load, shock waves arise). Depending on the velocity distribution at the boundary, the distribution of the strain constant on the characteristics is determined. The results are constructed by numerical integration of the integrals of the characteristics found by the method. The solution using the characteristic equations shows the occurrence of traveling waves.