| Along with the rapid social development and the advancement of science and technology, people are now paying more attention to the usage of spaces, therefore there are more and more high-rise buildings appearing in our daily lives. Forms of structure of these high rise and super-tall buildings are always shear walls or other structure forms relative to it, in addition, coupling beams, with is the first defensive line for Wall Structurces, its importance goes without saying. Recently, with the development of he theory about concrete, requirements for coupling beams designing are stepping into a higher level. It is required that, under violent earthquake, coupling beams should have a good ductility, so that it can coordinate the deformation between structure of coupled shear walls and fully absorb seismic energy. Its main form of damage is ductile fracture. However,coupling beams is very sensitive to shear, coupling beams with small span-to-depth ratio made by common concrete often create shear failure, makes it difficult to realize the design philosophy, with is called "strong column-weak beam ". Improvement of shear performance of coupling beam has been a research subject with great importance and many specialists and scholars have made numbers of researching works on it. Some outstanding achievements on this topic have been got, but they all have defects in themselves.When concrete is mixed with a specific volume of steel fibre, it will become steel fibre reinforcing concrete (SFRC). According to the fact that tensile strength of steel fibre is highly beyond that of concrete, when it randomly distributed into concrete, it will improve the performance of tensile, bending and shearing strength of concrete, enhancing concrete’s toughness and ductility. If we replace the common concrete in coupling beams with steel fibre reinforcing concrete, there is no doubt that both bearing capacity and energy dissipation capability of coupling beams will be enhanced. In this way, design philosophy of ductile fracture would be realized under violent earthquake.Based on the test code according to the strained condition of SFRC coupling beams, six kinds of SFRC beams with different compressive strengths are designed in this article, in order to be used in analysis on their main mechanical behaviors under low cyclic loading, main jobs to be finished:(1) On the basis of the real stress condition of coupling beams under earthquake effect, design experimental devices according to its mechanical behavior and design reasonable experiment plan based on test code.(2) Record the expand and distribution of cracks of six kinds of SFRC coupling beams with different compression strength under low cyclic loading in detail. Draw spine curve and load-displacement hysteresis curve based on experimental data. At the same time, to research deeply on their ductility, energy dissipation, stiffness and other performances. With strength of SFRC increasing, its ultimate bearing capacity increases to some extent, but its ductility and energy dissipation increase shows a peak shape, rather than linear progress with the increase of its strength, performance will achieve optimal situation when the compression strength rises to CF60, the peak value, performance will be weaken when the strength higher or lower than it.(3) through the analysis and comparison on experimental data, to arrive at the calculation formula of the ultimate bearing capacity for SFRC coupling steams with different compression under low cyclic loading effects. |
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