Abstract. The increase of high-rise construction volume or «High-Rise Construction» requires the use of high-strength concrete and that leads to the reduction in section size of structures and to the decrease in material consumption. First of all, it refers to the compressed elements for which, when the transverse dimensions are reduced, their flexibility and deformation increase but the load bearing capacity decreases. Growth in construction also leads to the increase of repair and restoration works or to the strengthening of structures. The most effective method of their strengthening in buildings of «High-Rise Construction» is the use of composite materials which reduces the weight of reinforcement elements and labour costs on execution of works. In this article the results of experimental research on strength and deformation of short compressed reinforced concrete structures, reinforced with external carbon fiber reinforcement, are presented. Their flexibility is λh=10, and the crosssection dimensions ratio b/h is 2, that is 1,5 times more, than recommended by standards in Russia. The following research was being done for three kinds of strained and deformed conditions with different variants of composite reinforcement. The results of the experiment proved the real efficiency of composite reinforcement of the compressed elements with sides ratio equal to 2, increasing the bearing capacity of pillars till 1,5 times. These results can be used for designing the buildings of different number of storeys.
The test results on deformation and rigidity of short compressed reinforced concrete pillars with various types of external transverse and longitudinal composite reinforcement are given. The samples from heavy concrete with design strength class B30-35 were tested, having the same cross-section 250x125 (h) mm and length 1200mm with flexibility λh = 10. The pillars were reinforced with 4Ø12A500 in the longitudinal direction and with tied clamps Ø6B500, installed with the step of 180 mm - in the transverse direction. The purpose of the experiment was to determine the effect of the rigidity of reinforced elements on the deformability of short experimental samples. It was necessary to determine how the eccentricity of the load application influences on the variation in the rigidity of the reinforced elements. The purpose was also to obtain data on the deformability of pillars loaded with small eccentricities, i.e. when e0 = 0.16h. It was found that the most effective type for short pillars reinforcement is a three-layer holder, which has maximum rigidity and minimal deformability. However, its efficiency gradually decreases when the eccentricity of the load application increases.
Introduction. The paper presents experimental data on the change in the values of relative deformations of composite materials of external reinforcement, measured during testing of reinforced concrete pillars. In experimental studies, transverse and longitudinal composite reinforcement was studied, consisting of carbon fabric and carbon laminates (carbon rods). The experimental values of relative strains in composite reinforcement materials make it possible to determine the zones of the most and least stressed sections of composite materials. The purpose of this study is to determine the zones of the most and least loaded areas of composite reinforcement of eccentrically compressed reinforced concrete pillars. This is necessary to create new schemes for the most efficient amplification options. To achieve this goal, the following tasks were completed: five reinforced concrete pillars were manufactured and tested; during the test, strain gauges were glued, which made it possible to determine changes in the relative deformations of composite materials at all levels of loading; all data of relative deformations of composite materials were processed, analyzed and presented in the form of graphs.Materials and methods. In the process of testing reinforced concrete flexible struts, data were obtained on the change in relative deformations in composite materials. The measurements were made by strain gauges with a base of 2 cm glued along the fibers of the composite reinforcement. The zones for measuring relative deformations were chosen according to the nature of the work of the composite material. In total, the work considered the results of testing five reinforced concrete racks, in which carbon fiber fabrics were located in the transverse direction, and carbon rods and lamellas were located in the longitudinal direction.Results. As a result of the study, data on changes in the relative deformations of composite materials were obtained, while the sensors located on the transverse clamps work approximately the same with a relative deformation not exceeding 1.8×10-3. Such deformations are significantly lower than the limiting ones, which is evidence of the incompatibility of the existing structure and the reinforcement material at the limiting stages of loading. With a large gap between the composite clamps, the reinforcement elements practically do not work and the limiting deformations do not exceed 0.6×10-3.Discussion and Conclusions. As a result of processing the change in relative strains characterizing the stress level of composite materials, conclusions were drawn that allow us to state that in the compressed zone the maximum strain does not reach the limit values for composite materials, therefore, the number of transverse reinforcement layers can be reduced. For composite materials located in the longitudinal direction, premature destruction of composite lamellas was established, which made it possible to conclude that there was no joint work of reinforcement materials and concrete of the structure at ultimate breaking loads.
Introduction. For many years strengthening of the compressed reinforced concrete structures was fulfilled by methods based on using reinforced concrete cages and outer metal frames. These are rather time-consuming and expensive processes. The implementation of composite materials in the construction industry made it possible to quicken and simplify the works on strengthening, however with regard to compressed elements it turned to be very resourcedemanding to increase the bearing capacity of rectangular or square section structures. This is primarily due to the limitation in compression strain of the longitudinally located carbon fiber materials and a large decreasing coefficient for transverse composite strengthening. However, the development of new methods of strengthening, including the one considered in this work, will increase the efficiency of composite materials located in the transverse direction by 5–10 times, depending on different variable factors. This article aims to develop and justify a new method of strengthening the reinforced concrete columns by using mixed concrete-composite reinforcement.Materials and methods. This research relies on the results of theoretical calculations. The standard variant of strengthening a compressed reinforced concrete element has been considered and calculated as well as composite materials volume has been specified. Based on the standard calculation results the proposals, which take into account the effect of a new strengthening method, have been made in this article, the detailed methodology of calculation thereof has also been presented. The results of theoretical strength calculations along with comparison of the required volume of reinforcement materials are the key issues in the analysis and drawing conclusions.Results. The research has resulted in development, calculation and justification of the new method of strengthening, which allows reducing the volume of composite materials required for strengthening the compressed reinforced concrete columns.Discussion and conclusion. Three variants of calculating the strengthening of a reinforced concrete column with composite materials have been presented and reviewed in this work. One of which is a standard one, the other two are proposed by the authors. The developed method of strengthening implies rounding of concrete followed by jacketing with composite materials. These roundings can be considered in calculation or can be referred to as structural elements. In any case, the strengthening effect received from the proposed method becomes 5.3 and 10.5 times higher. Besides, further research ideas for continuing the development and study of the method of strengthening the centrally compressed reinforced concrete columns with composite materials are given in conclusion.
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