Introduction. Spun reinforced concrete columns are widely used in the present-day international construction practice. Known formulas, used to calculate temperatures of cross sections of reinforced concrete structures, needed to assess their fire resistance limit, are successfully applied to homogeneous structures that have solid sections. However, they are inapplicable to spun reinforced concrete columns due to their structural features. The purpose of this work is to develop a method for solving a thermal problem of spun reinforced concrete columns and adapt existing calculation formulas.Materials and methods. This work addresses the heating of spun reinforced concrete structures in case of fire. Ansys Workbench was employed to perform the computer simulation needed to study the influence of the characteristics of spun reinforced concrete columns on their heating. Results and discussion. In the course of the theoretical studies, the effect, produced by column cavities, the heterogeneity of spun concrete and thin walls of these structures on the heating of their cross sections was assessed with regard for the results of full-scale fire tests of spun reinforced concrete columns. Correction coefficients were obtained in order to take account of these factors. A regression equation was derived as a result of the simulation performed in the context of a full-scale factorial experiment involving coefficient khol, which takes into account the rising temperature of hollow reinforced concrete structures in comparison with solid ones. Khet heating acceleration coefficient is applicable to spun reinforced concrete structures due to the heterogeneity of concrete in the cross section. This coefficient represents a function of the wall thickness. Coefficient kth, which allows for the heating acceleration in the course of crack opening in thin-walled structures, varies in the range of 1.00…1.40. The concrete cracking temperature is 550 °C.Conclusion. A new method allows to solve the thermal problem of fire resistance of spun reinforced concrete columns. The engineering formula used to calculate the temperature in a cross-section was adapted. The results of computer-aided simulation and calculation of temperature values, performed using the adapted formula, show acceptable convergence with the experimental data.
Цель. На основании экспериментальных и теоретических исследований изучить огнестойкость железобетонных колонн, изготовленных методом центрифугирования. Методы. Экспериментально-теоретические исследования физико-механических и теплофизических характеристик центрифугированного бетона в нормальных условиях и при высокотемпературном нагреве. Натурные испытания центрифугированных железобетонных колонн под совместной температурно-силовой нагрузкой. Аналитическое решение теплотехнической и статической задач огнестойкости центрифугированных железобетонных колонн. Компьютерное моделирование на базе платформ Ansys Workbench и ЛИРА-САПР. Результаты. Выявлено различие физико-механических характеристик центрифугированного бетона в поперечном сечении конструкций заданной толщины в нормальных условиях, а также различие в их относительном изменении при высокотемпературном нагреве. Установлены экспериментальные зависимости коэффициента условий работы центрифугированного бетона при пожаре. Экспериментальным путем установлена схема разрушения центрифугированных железобетонных колонн при пожаре, а также изучено их поведение при пожаре. Выявлена сниженная склонность центрифугированного бетона к хрупкому взрывообразному разрушению при пожаре по отношению к вибрированному бетону. Установлено влияние неоднородности центрифугированного бетона в поперечном сечении изделий, тонкостенности и воздушной полости изделий на их огнестойкость. Разработана методика расчета пределов огнестойкости центрифугированных железобетонных колонн. Разработан табличный метод оценки пределов огнестойкости серии центрифугированных железобетонных колонн. Область применения исследований. Результаты исследования могут быть использованы при оценке пределов огнестойкости центрифугированных железобетонных колонн, а также при разработке изменений в технические нормативные правовые акты в области оценки огнестойкости железобетонных конструкций.
PURPOSE. One of the significant requirements for buildings and constructions is providing fire safety, which includes standardization of building structures fire resistance. The experience in applying thin-walled elements has shown high efficiency, technological and operational advantages. Bearing significant power loads, reinforced concrete columns often have low fire resistance (R30... R60), which poses certain risks in case of fire and limits their application in construction industry. To increase structures fire resistance, structural fire retardance is applied. The purpose of this work is to set the fire resistance limits of reinforced concrete columns protected by non-combustible Knauf Fireboard gypsum slabs of various thicknesses on a steel frame and obtain the generalized tabular data based on this research. METHODS. Model fire tests of spun reinforced concrete columns with structural fire retardance have been carried out, as well as simulation of heating a series of hollow and solid section reinforced concrete columns with structural fire retardance in ANSYS finite element analysis system. FINDINGS. Experimental data have been obtained on heating spun reinforced concrete columns of an annular section with an external diameter of 560 mm with a wall thickness of 55 mm and a protective concrete layer thickness of 20 mm for longitudinal reinforcement (12 mm diameter) protected by non-combustible Knauf Fireboard gypsum slabs with 12.5 mm, 20 mm and 40 mm thickness on a steel frame, and unprotected ones (without applying a power load). ANSYS finite element analysis system design models have been developed and the heating of a series of spun annular sections and vibration-compacted solid sections of reinforced concrete columns protected by structural fire retardance have been simulated. For these structures, fire resistance ratings have been calculated at a load-bearing capacity utilization factor of 0.7. Based on a certain array of values of fire resistance limits of reinforced concrete columns, tabular data have been obtained to assess the fire resistance of these structures with structural fire retardance. RESEARCH APPLICATION FIELD. The obtained results can be applied by design bureaus, state fire supervision authorities and state construction expertise in assessing fire resistance ratings of reinforced concrete spun columns of annular section and vibration-compacted solid section protected by structural fire retardance as well as in selecting parameters for these structures that provide specified fire resistance rating without carrying out a series of time-consuming calculations. CONCLUSIONS. Fire tests combined with simulation in ANSYS finite element analysis system make it possible to carry out a lot of calculations and obtain tabular data on assessing fire resistance of reinforced concrete columns with structural fire retardance which significantly reduces labor costs at designing building structures.
The paper presents a complex of laboratory and theoretical studies of physical and mechanical properties in centrifuged concrete while using samples of sectoral cross-section which are cut in layers from a finished product. A post made of concrete having B40 grade for compression strength and manufactured while using centrifugation with the help of РТЦ-5 machine. Assessment of heterogeneity across section thickness has been carried out by visual determination of composition changes in cross section, determination of strength, density of the obtained concrete samples, and water content over cross section of concrete mix. According to the results of a visual study on composition of a concrete structure it has been revealed that 1/8 part of the structure (from an inner surface) does not have a large aggregate. Later, as it moves to periphery, there is an increase in coarse aggregate and a decrease in size and number of cells between grains of gravel. An analysis of experimental data has shown that properties of the centrifuged concrete in samples being sawn in layers change significantly: density of concrete in samples of an inner layer is lower by 8 % than in samples of an outer layer, and compressive strength of concrete – by 34 %, water content of concrete mixture of samples of the inner layer has turned out to be by 43 % higher than in samples of the outer layer. Approximating curves showing regularities of changes in density, concrete strength, water content of concrete mixture over thickness have been constructed in the paper. Linear and exponential equations have been obtained that describe changes in physical and mechanical properties of centrifuged concrete over section depending on structure properties as a whole, which, taking into account the obtained correction factors k1 and k2, can be used with an acceptable level of confidence in practical calculations of centrifuged concrete structures. Relationship between strength of centrifuged concrete varying over cross section and action of a centrifugal force of inertia has been revealed in the paper. An equation has been obtained that relates the strength of centrifuged concrete to its density. Analysis of the research results makes it possible to assert that the main source of loading perception in centrifuged concrete structures is outer layers.
Цель. Разработать экспериментальный макет тренажера для подготовки спасателей-пожарных, включающий программное обеспечение и элементы имитации эффектов физических воздействий на обучающегося в условиях виртуальной реальности, а также исследовать влияние эффектов обратной тактильной связи на обучающихся. Методы. Общая методология работы предусматривала использование теоретических методов исследования (анализ, синтез, сравнение). Влияние эффектов обратной тактильной связи на обучающихся определено методом измерения частоты их сердечных сокращений в ходе рандомизированного исследования с двумя параллельными группами. Результаты. На основе анализа опыта применения технологий виртуальной и дополненной реальности в образовательной деятельности сформулированы назначение, состав, структура и функции экспериментального макета тренажера с имитацией эффектов физических воздействий в условиях виртуальной реальности для подготовки спасателей-пожарных (ЭМТ). Разработанный ЭМТ, включающий VR-гарнитуру (для управления симуляцией и передачи визуальных и звуковых эффектов), VR-костюм (для обеспечения обратной тактильной связи за счет электростимуляции нервно-мышечных структур) и оригинальное программное обеспечение, позволяет погружать обучающихся в виртуальную среду, имитирующую условия чрезвычайной ситуации (пожар в квартире жилого дома) и воздействие на них опасных факторов пожара. С использованием ЭМТ исследовано влияние эффектов обратной тактильной связи на обучающихся. Показано, что применение ЭМТ позволяет снизить количество ошибок, совершаемых обучающимися при ликвидации пожара в квартире жилого дома в виртуальной симуляции, от 2,5 до 4,0 раз по сравнению с использованием технологий виртуальной реальности без применения эффектов обратной тактильной связи. Область применения исследований. Результаты работы могут быть применены для создания тренажера с имитацией эффектов физических воздействий в условиях виртуальной реальности с целью его использования в образовательном процессе для подготовки спасателей-пожарных.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.