Міцність залізобетонних колон при силових і високотемпературних впливах

Abstract

UA: Наведено результати досліджень напружено-деформованого стану залізобетонних колон будинків при сумісній дії силових навантажень і високої температури. Для розробки розрахункових методик прийнято передумови та допущення, які враховують поведінку конструкцій при навантаженні і дії високої температури. Розроблено методику і отримано залежності зміни характеристик міцності арматури різних класів при високотемпературних впливах. Розроблено методику і проведено дослідження вогнестійкості колон, що дозволило отримати характеристики матеріалів після високотемпературних впливів для подальшого визначення залишкової несучої здатності. Розроблено методику розрахунку вогнестійкості та міцності залізобетонних колон МСЕ, яка дозволяє отримати розподіл температури по перерізу і врахувати зміну характеристик міцності та деформативності бетону й арматури при нагріванні. Результати роботи впроваджено при визначенні межі вогнестійкості колон проектованих будинків. EN: The content of the thesis. In the introduction it substantiates the relevance of the topic, formulates the purpose and tasks of the research, scientific novelty and practical value of the work, and also the general characteristic is presented. Chapter 1 is given over to analyzing modern methods for calculation and design of load-bearing reinforce-concrete members of buildings and structures working in compression under various influences. The existing proposals for taking into account the nonlinear properties of reinforced concrete are analyzed. It is noted that a feature of the calculation methods proposed by various authors is the use of various assumptions on concrete strength. Various material behaviour models are considered. The application of various models requires using the corresponding stress-strain diagrams for concrete under various influences. The influence of the reinforced concrete inelastic properties on the behaviour of axial elements can be taken into account by reducing the stiffness characteristics of the cross sections. Since reinforce-concrete columns are as a rule under-reinforced, taking into account inelastic properties even to a first approximation will allow us to perform the limit state design of the first group and the second group with sufficient accuracy for practical purposes. The analysis of existing methods has allowed us to determine that the methods for calculating the stress-strain state and the bearing strength of reinforce-concrete columns under various influences have not been brought to practical use. Determination and assessment of the technical state and justification of possible further reliable operation of reinforce-concrete column structures after force and high-temperature influences are a complex task, the solution of which is absent nowadays. The research objectives are formulated based on the analysis of the current state of the issue. In chapter 2 the methodological approach of the estimation of the technical state of constructions of frameless buildings with reinforce-concrete framework.The primary

purpose of realization of the works of the building construction technical state estimation is the receipt of the controlled (qualificatory) parameters of the technical state. The estimation of the technical state of building constructions is conducted by comparison of the controlled parameters with corresponding project parameters, and also on results of checking calculations. The controlled parameters are determined during realization of visual and instrumental inspections. In the chapter the features of determination of the technical state of constructions after fire effect are also brought. Bearing strength, bending and crack resistance of constructions after fire effect determined during the process of development of rehabilitation project of separate constructions and full buildings. The worked suggestions are used for determination of the technical state and development of project of strengthening of ceiling flags after a fire. Chapter 3 presents the results of experimental studies concerning changes in the strength characteristics of reinforcement under high-temperature influences and fire resistance of columns. To obtain experimental evidence indicating the nature of deformation and failure of steel reinforcement when exposed to high temperatures, a study of samples made of reinforcing steel of various classes was carried out in accordance with the requirements of current regulatory documents. To test the columns for fire resistance, two identical samples with a cross section of 600x600 mm and a height of 2000 mm were made. Samples were produced in metal formwork at the Brovary plant for reinforce-concrete products. After preliminary tests (to determine the material characteristics), the columns were tested for fire resistance. These tests were performed using the appropriate equipment of TEST LLC testing centre. A special test furnace and appropriate measuring equipment were used for the tests. After testing the columns for fire resistance, cutting was performed to further determine the strength of concrete and reinforcement. Chapter 4 contains proposals for determining the fire resistance of reinforced concrete columns and other structures in compression. The procedure has been developed for calculating the fire resistance of reinforced concrete columns using a thermo-technical calculation, which allows for the accepted assumptions to determine the temperature distribution in the cross section of the column when heated. The calculation is performed using modern software systems that are based on the finite element method. The temperature distribution in the column cross section allows taking into account the change in the characteristics of strength and deformability of concrete and reinforcement for further calculations of the bearing strength and fire resistance of reinforce-concrete columns. The evidence of the obtained results implementation in the practice of inspection and design of structures after various influences is given. General Conclusions set out the main results obtained in the course of the research. The urgency of the problem concerning calculation of load-bearing reinforce- concrete structures in compression, taking into account the strength properties of reinforced concrete under various influences, is noted for Ukraine.