Study of integral and differential strength and deformation characteristics of centrifuged and vibrating centrifuged concrete on activated Portland cement

In this work, the study of integral and differential strength and deformation characteristics of centrifuged and vibrating centrifuged concrete on activated Portland cement was carried out. Mechanical activation of cement was carried out using a specialized grinding unit. Manufacturing of centrifuged and vibrating centrifuged samples was carried out on an experimental laboratory centrifuge. All samples were made of concrete of the same composition. The optimum values of technological parameters of centrifugation and vibrating centrifugation are given. The scheme of obtaining small-size specimens from a common annular section to determine the strength and strain characteristics was developed. According to the results of the study it was found that the improvement of integral and differential strength and strain characteristics when using activated Portland cement is observed for both centrifuged and vibrating centrifuged specimens. However, the samples made by vibrating centrifugation technology have better strength and strain characteristics than the samples made by centrifugation. According to the results of the study, it was found that the activation of Portland cement at its rational values is the best way to enhance variatropy.

CALCULATION OF CENTRALLY COMPRESSED CONCRETE FILLED STEEL TUBULAR COLUMNS OF ANNULAR SECTION TAKING INTO ACCOUNT PHYSICAL NONLINEARITY

In the article, the resolving equations are obtained for the calculation taking into account the physical nonlinearity and creep of centrally compressed concrete filled steel tubular columns of annular cross-section. The examples of the calculation of the bearing capacity with a short-term load are given. The solution was carried out numerically in the Matlab environment using the finite difference method. The deformation theory of plasticity by G.A. Geniev was used.

Investigation of differential strength and deformation characteristics of centrifuged and vibrocentrifuged concretes on activated Portland cement

In this work, a study of the strength and deformation characteristics of the variatropic layers of centrifuged and vibrocentrifuged concretes on activated Portland cement was carried out. Mechanical activation of cement was carried out using a specialized grinding unit - a planetary ball mill "Aktivator-4M". The optimal mode of grinding Portland cement is proposed. For the manufacture of centrifuged and vibrocentrifuged samples, an experimental laboratory centrifuge TsSRL-1 with a DC electric motor with thyristor power supplies was used, and the form vibrations were carried out due to additional dowels (protrusions) put on the shafts. All samples were made from concrete of the same composition. In total, four basic samples of annular cross-section were manufactured and tested with the following dimensions: outer diameter D = 450 mm; inner hole diameter d = 150 mm; total height H = 1200 mm. The optimal values ​​of technological parameters of centrifugation and vibrocentrifugation are given. A scheme is proposed for obtaining small-sized samples to determine the strength and deformative characteristics of various layers of a sample by cutting them out of a common annular section. According to the results of the study, it was found that the activation of Portland cement at its rational values ​​is the optimal way to enhance variatropia.

Investigation of the integral strength and deformation characteristics of centrifuged and vibrocentrifuged concretes on activated Portland cement

In this work, a study of the integral strength and deformation characteristics of centrifuged and vibrocentrifuged concretes on activated Portland cement is carried out. Mechanical activation of cement was carried out using a specialized grinding unit. The manufacture of centrifuged and vibrocentrifuged samples was carried out on an experimental laboratory centrifuge. All samples were made from concrete of the same composition. In total, four basic samples of annular cross-section were manufactured and tested with the following dimensions: outer diameter D = 450 mm; inner hole diameter d = 150 mm; total height H = 1200 mm. The optimal values ​​of technological parameters of centrifugation and vibrocentrifugation are given. A scheme has been developed for obtaining small-sized samples from a common annular section to determine the strength and deformation characteristics. According to the results of the study, it was found that an improvement in the values ​​of integral strength and deformation characteristics when using activated Portland cement is observed in both centrifuged and vibrocentrifuged samples. It was found that samples made by vibrocentrifugation technology have the best strength and deformation characteristics than samples made by centrifugation. The conclusion is made about the technology of vibrocentrifugation as the most preferable for the manufacture of reinforced concrete products of annular section.

Dynamics of high-rise structures taking into account the viscoelastic properties of the material

The article deals with forced vibrations of a high-rise axisymmetric structure, represented as a viscoelastic beam of an annular section with a variable slope of the generatrices and variable thickness. The research was conducted to analyze the behavior of a high-rise structure for various kinematic effects. The task is to determine the displacements of the points of a high-rise structure at different time points under different kinematic effects. The methods were developed and a computer program was built; forced vibrations of high-rise axisymmetric structures under various kinematic actions, considering viscoelastic properties of the material, were investigated in linear, nonlinear, and viscoelastic formulations. The study of the dynamic behavior of a high-rise structure, taking into account the nonlinear and dissipative properties (different in nature) of the material, shows that the combined consideration of all these properties brings the resulting pattern closer to the one observed in reality. That is, the amplitude of the structure’s oscillations does not grow infinitely, but gradually decreases over time, and the maximum possible consideration of nonlinear and dissipative properties leads to the fastest damping of oscillations.

Modeling the reinforced concrete shell with a protective structure

The results of the mathematical modeling and experimental studies for the stress-strain state of the annular section of the reinforced concrete shell with the protective structure are presented. Computer simulation has been formulated as a stationary temperature problem. The distribution of deformations and stresses is shown using the equations of the elastic theory. A comparison of theoretical dependences on the results of experimental studies of physical models is given. Conclusions are drawn about the possibility of using them in the calculations of reinforced concrete protective structures.

FORMALIZATION OF THE CONCEPT OF A SLIT CAPILLARY TAKING INTO ACCOUNT THE CONTACT ANGLE OF WETTING

Расчеты процессов распределения и переноса жидкости в пористых средах осуществляют, принимая во внимание ее капиллярные свойства в поровом пространстве. С учетом выведенной нами ранее расчетной формулы для предельного размера капилляра с круглым поперечным сечением, краевого угла смачивания и параметра удельного поверхностного натяжения получена расчетная формула предельного размера для капилляров с щелевым и кольцевым сечением. Установлено, что полученные расчетные формулы предельных размеров для трубчатых капилляров щелевого плоского и кольцевого сечения с учетом краевого угла смачивания идентичны. Отличие формул для капилляров с щелевым и кольцевым сечением от формулы для капилляра круглого поперечного сечения определено только функцией, зависящей от краевого угла смачивания. Значения предельных размеров капилляров с щелевым сечением на 10–17,5% меньше, чем капилляра с круглым сечением. Поверхность отклика позволила оценить влияние удельного поверхностного натяжения и функции краевого угла смачивания на изменение величины предельного размера капилляров. Результаты исследований могут быть использованы для повышения эффективности расчетов тепломассообмена в пористых средах в пищевых производствах и других аналогичных задач. The calculations of the processes of saturation and transfer of fluid in porous media are based on taking into account of its capillary properties in the pore space. Given our previously derived formulas for the maximum amount of capillary with a circular transverse section, wetting angle and parameter specific surface tension obtained calculation formula size limit for capillaries with a slit and annular transverse section. It is established that the obtained calculation formulas of the limit sizes for tubular capillaries of slotted flat and annular section with the account of the wetting edge angle are identical. The difference between the formulas for capillaries with slotted and annular section and the formula for a capillary with a circular transverse section is determined only by a function that depends on the wetting edge angle. The values of the limit sizes of capillaries with a slotted transverse section are 10–17,5% less than those of a capillary with a circular transverse section. The response surface allowed us to evaluate the effect of specific surface tension and the function of the wetting edge angle on the change in the capillary size limit. The research results can be used to improve the efficiency of calculations of heat and mass transfer in porous media in food production and other similar tasks.