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.
The article discusses the possible design solutions to improve the seismic resistance of stone buildings. In particular - the device of anti-seismic belts at the floor level, the device of dowels and nodes for connecting the floor slabs with the walls and among themselves, the reinforcement of the walls with steel clips, as well as the installation of transverse frames, if the maximum distances between the transverse walls’ axes are not observed.
The article presents data on the bearing capacity of columns with various combinations of prestressed and conventional reinforcement. The areas of the most effective use of such structures with different eccentricities and flexibilities are shown. The ecology of reinforcement steel is an important task that the designers of reinforced concrete structures face. The creation of effective constructive solutions, that allow to combine high technical characteristics with economic use of reinforcement steel, has become urgent and is necessary for today's development of the construction industry.
In the works [1,2,3,4,5] it was shown that the solution of these problems was possible by creating conditions for the full employment of building materials properties - reinforcement and concrete.
The working reinforcement is characterized by its application in the conventional and prestretched forms. At the same time, the works done in the recent years show that reinforcement, subjected to precompression, can be used in the compressed zone [6,7,8].
It is most effective in rigid reinforced concrete columns. Thus, precompression of all longitudinal reinforcement or its part allows to increase the strength of non-flexible columns with not high relative eccentricities of the external longitudinal force. At the same time, in order to obtain the greatest effect caused by the precompression of the reinforcement, certain conditions must be observed.
The article deals with the main advantages of reinforced concrete columns with recessed fittings. The method of testing the prototype columns is described. In addition, the influence of various factors on the fracture pattern and bearing capacity of such columns is explained. The standard reinforced concrete columns are given below and the optimal parameters for saving reinforcing steel are observed [1-7].
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