Том 21, № 1 (2025)
- Жылы: 2025
- Мақалалар: 7
- URL: https://journals.rcsi.science/1815-5235/issue/view/22013
- DOI: https://doi.org/10.22363/1815-5235-2025-21-1
Бүкіл шығарылым
Analysis and design of building structures
Influence of Joint Type on Member Forces in Metal Ribbed-Ring Dome Frame Taking into Account Different Number of Supporting Columns
Аннотация
The influence of the type of joint on the internal forces in the elements of the metal frame of a ribbed-ring dome, and specifically considering different number of supporting columns, was studied. In this respect, cyclic symmetry of the columns along the entire contour of the dome is preserved. All elements of the dome frame and the columns are made of steel pipes. The objects of the study were dome frames, which differed from each other, both in different nodal connections and in different numbers of supporting columns. The domes have the same geometric structure and dimensions, the same cross-sections of the same type of frame elements and carry the same loads. The study was performed by analyzing computer models of the frames. Models with different joints were obtained by gradually converting the originally assigned hinges into rigid connections, and variation in the number of columns was implemented by regularly removing them from the original computer model. In the calculation process, internal forces N and M in the frame elements of all models were determined, which were compared with each other. Comparative diagrams of internal forces N and M in the frame elements of the original and all transformed models are obtained. The behavior of the elements of ribbed-ring domes with different nodal connections for frames with different numbers of columns is evaluated. According to the results of the study, significant changes in bending moments M in the lower ring and axial forces N in the columns were noted. Moreover, the nature of these changes depends on the type of nodal connection.



Analytical and numerical methods of analysis of structures
Experimental Study of High-Temperature Exposure Effect on Reinforcement-Concrete Bond in Corrosion-Damaged Reinforced Concrete
Аннотация
The object of this study is the bond between reinforcement and concrete after exposure to high temperatures and corrosion, which is critical for assessing the durability of reinforced concrete structures. The analysis of scientific sources revealed that at temperatures above 300°C, the bond deteriorates due to thermal expansion of the reinforcement, degradation of the cement matrix, and crack formation. Simultaneously, corrosion reduces adhesion and weakens mechanical interlocking, accelerating concrete deterioration. However, the combined effect of these factors remains insufficiently studied, and the existing bond models do not fully account for their simultaneous impact. In this experiment, concrete specimens with A500C reinforcement were subjected to electrochemical corrosion and heated to 400°C. Pull-out tests revealed a significant reduction in bond strength, attributed to the destruction of the adhesive layer and changes in the interaction mechanism: in unheated specimens, the bond was ensured by plastic deformations of concrete, whereas in heated specimens, it was maintained by friction against corrosion products. Comparison with previous studies on the influence of temperature, reinforcement types, and heating rates confirmed the consistency of the results and clarified the role of pre-existing corrosion. The obtained experimental data not only validates the existing studies, but also extends them by incorporating the effect of pre-corrosion, which was previously considered in a limited scope. The findings can be used to predict the consequences of thermal exposure, assess the residual strength of structures, and develop restoration methods.



Fracture of Wedge-Shaped Body Under Compression
Аннотация
The aim is to study the fracture process of a wedge-shaped body during compression. A large number of researchers have turned to the classical solution of the elasticity theory problem of the loaded wedge-shaped body, but the problem of a supported wedge of a finite shape still has no analytical solution. The authors conducted a study of the failure mechanism of such bodies by both computational and experimental methods. To carry out the numerical analysis, the implementation of the progressive limit state method at critical levels of strain energy in the form of the force method was used, in combination with the method of approximation of continuum by an equivalent truss. The equivalent truss model of the wedge used here clearly demonstrates the process of removing structural members due to them reaching limit states. The technique of progressive limit states, based on the consecutive identification of “weak links” in the structure, in which the limit state occurs first, made it possible to construct fracture models of the considered body. The results of the performed analysis are presented in the form of fracture models of wedge-shaped bodies. The failure mechanism of wedge-shaped bodies was also investigated by experimental methods. Wedge-shaped gypsum specimens were compressed at the tip of the wedge and brought to fracture. The differences between the obtained fracture patterns and the classical results known from the theory of elasticity obtained for infinite wedge-shaped bodies are shown. A comparison of experimental and numerical results is performed, and a conclusion is made about the real fracture patterns of wedge-shaped bodies with a supported part.



Thin Elastic Shells Theory
Determination of Optimal Cylindrical Shells in the Form of Second-Order Surfaces
Аннотация
Thin shells with cylindrical and conical middle surfaces are most popular. Many shell-type structures have been built in the form of rotational and translational surfaces, for which there are several dozen optimality criteria. Hyperbolic, parabolic, elliptic, and circular cylindrical roofs with rectangular base are considered, for which, as evidenced by thorough literature review, there is no comparative analysis of strength, stability, and dynamics. Nevertheless, architects are already trying to expand the classification range of ruled middle surfaces of zero Gaussian curvature with a rectangular base by including torse surfaces. Five thin cylindrical shells outlined by second-order algebraic surfaces with different generating plane curves are studied. The stress-strain state of hyperbolic, parabolic, elliptic and circular cylindrical roofs with rectangular base subjected to static load of self-weight type is investigated. The roofs have the same dimensions of the base, the same height, thickness and structural material, that is, a comparative calculation is performed. It is established that the smallest (maximum) membrane stresses occur in the ellipsoidal shell with an incomplete half-ellipse, and the smallest (maximum) bending and equivalent stresses occur in the parabolic cylindrical shell, which is confirmed by the results of previously performed calculations using the analytical momentless theory. Therefore, it is recommended to use ellipsoidal cylindrical shells with an incomplete half-ellipse in cross-section for building structures. Currently, almost all problems of structural mechanics of shells are solved by numerical methods, therefore, the displacement-based finite element method was chosen to solve this problem.



Seismic resistence
Estimation of the Influence of Surface Soil Layers on the Parameters of Maximum Reaction Spectra
Аннотация
Surface layers are usually composed of relatively loose soils that differ significantly in seismic characteristics from deeper layers. This makes it difficult to apply general initial seismic information that does not take into account local geotechnical conditions. In general, seismic effects are given in the form of maximum response spectra for rocky or rigid soils. To take into account local geological conditions, soil correction factors are used, which do not always correctly describe the amplification of vibrations. For obtaining analytical relationships, the problem-solving technique of the theory of elasticity based on the properties of the Fourier image of finite functions was used. Using the reciprocity theorem, the displacements of the free surface from the load at the interface, which is given by the incident wave, have been determined. The methods of setting initial seismic effects in modern norms documents of different countries are described. A methodology is developed that allows to take into account the influence of soft soil layers on the parameters of the maximum response spectra. The expression for the amplification coefficients of the maximum response spectra in the surface layers of soils is obtained, which allows to estimate the local geotechnical conditions more accurately, taking into account the resonance effects of surface vibrations. An example of determining the amplification coefficients of ground vibrations for the ground conditions of the Syrian Arab Republic is given.



Construction materials and products
Effect of Ultrafine Additives on Mechanical Properties of Concrete
Аннотация
The study is aimed at assessing the mechanical properties of concrete modified with ultrafine powders produced from construction waste by fine grinding. To achieve this goal, concrete samples with different contents of ultrafine powders in the cement matrix were prepared and tested. The mechanical properties of the samples were assessed in terms of compressive strength and modulus of elasticity. The tests were carried out on concrete samples aged for 7, 14, 21 and 28 days, followed by an analysis of the average values of the three measurements for each time point. The results of the study showed that concrete mixtures containing ultrafine powders have improved mechanical properties compared to control samples. The optimal content of ultrafine powders is 20% of the cement weight. The compressive strength of such concrete samples exceeds the reference values by 46% after 28 days of hardening. This indicates the possibility of using ultrafine powders to improve the performance of concrete structures. Experimental studies have shown that the size, concentration, and chemical composition of ultrafine particles significantly affect the mechanical properties of concrete mixtures modified with ultrafine powders of construction waste



Experimental researches
Applicability of Strain Gauge Methods for Experimental Determination of Operating Stress of Construction, Road and Agricultural Machines Attached to Tractors
Аннотация
The operating stress of construction, road and agricultural machines is determined during experimental and factory tests using force sensors. The aim of the research is to improve the methods of experimental determination of horizontal forces transferred by mobile implements using strain gauges combined with the elements of fastening of technological machines. The stress-strain state and deformations of measuring strain gauges at their different arrangements on strain gauge pins of circular cross-section are considered. When determining the horizontal load on the vehicle with the use of pre-calibrated strain gauge pins, it was experimentally established that the mentioned strain gauges can additionally react to the vertical load, which leads to the emergence of systematic errors in estimating the horizontal load. To eliminate this, it is proposed that before the main calibration of the horizontal force sensors, it is necessary to pre-determine the position at which the calibrated strain gauge will not respond to the vertical force, by rotating it relative to the longitudinal axis and then ensuring fixation in this position. The influence of axial forces on strain gauge pins, picked up by the strain gauges, can also lead to distortion of the stress field in the body of the strain gauge. Taking into account this influence on the strain gauge pins requires additional experimental studies.


