| Carbon Fiber Reinforced Polymer (CFRP) tendon and Fiber Reinforced Cement Composite (FRCC) are the two new kinds of high strength building materials.The CFRP tendon has many excellent properties such as low weight and high strength, fatigue-resistant and corrosion-free, which is likely to be the material of external prestressing tendons replacing the steel strand. It has become one of the research hotspots. However,the brittle failure performance about the CFRP tendon and concrete contribute to the poor ductility of the structure with the CFRP reinforcement.But the material FRCC mixed with steel fiber can overcome the weakNess easily as a result of its high strength and larger ultimate compression strain. Meanwhile its higher tensile property plays an important role in improving the structure’s crack resistance. In order to get the steel reinforcement free from the corrosion and realize the structure durability, the external-prestressed FRCC structure with CFRP tendons has important engineering value, which make it possible for promoting the development of the long-span structure.The main materials consist of the domestic light round CFRP tendons with different diameters and the Fiber Reinforced Cement Composite.The test were carried out on the topic flexural behavior of fiber reinforced cement composite beams prestressed with CFRP tendons in this paper, including the material property and the performance of the beam members. At the same time, the experimental study on the flexural behavior of the simply supported beam prestressed with CFRP tendon were also conducted, the main content of this study are as follows:(1) Static load anchoring performance test research about the diameter of the 8 millimeters and 11 millimeters CFRP tendons is carried out via the wedge anchorage of carbon fiber reinforced polymer prestressed reinforcement independent developed by our group, which mainly include the ultimate tensile strength, the elasticity modulus and the elongation to gain the stress-strain curve. The test shows that the wedge anchorage of carbon fiber reinforced polymer prestressed reinforcement in this experiment can basically meet the need of succeeding in reaching the limit state of the CFRP tendon without slipping, which indicates the wedge anchorage has the practical value in engineering to some degree.(2) The material properties of FRCC are studied by carrying out the prism block and eight characters model test, including the influence of main parameters, such as tensile strength, compressive strength, modulus of elasticity, ultimate tensile strain and compressive strain, providing the stress—strain curve. Meanwhile the corresponding constitutive equations are established based on the test results.(3) One normal concrete beams prestressed with CFRP tendons and 5 FRCC beams prestressed with CFRP tendons are investigated. The main considered parameters are the concrete strength the diameter of the CFRP and the prestressing force. The detailed studies and corresponding analysis on the flexural behaviors, strain distribution, stress increment in prestressing tendons, failure modes as well as the crack pattern are conducted based on the test results and the experimenting phenomenon. In addition, the corresponding experimental results were compared in relation to the different parameters and the reasons of the differences between the results are discussed.It turns out that the FRCC beams have higher ultimate bearing capacity than the common reinforced concrete beam and the FRCC beams prestressed with CFRP tendons have better ductility and deformation capacity. Besides, the distribution and the development paths of cracks show that the crack patterns of the FRCC beams present small and dense feature, which is mainly related to the material properties of FRCC. The steel fiber in the FRCC can restrain the spread of the crack and provide the bridging traction when cracking, leading to the plastic performance of the material to develop more fully and the crack distribution more uniform.(4) The theoretical research on the beams prestressed with external CFRP tendons are made based on the experimental study. Firstly the existing methods of the stress increment of external pre-stressing tendons are introduced to reveal the force mechanism, including the bond reduction coefficient、the theory based on the plastic hinges、comprehensive reinforcement percentage and so on. Then the relationship between the length of the plastic hinge and the height of co increment of external pre-stressing tendons are calculated by the method based on the deflection, which arrive at an agreement with the test data. mpression area is derived according to the Pannel model and the results about the stress.(5) The cracking moment is calculated according to the research results on the plastic coefficient of cross-section and the results are compared. It shows that the plastic coefficient of cross-section can better conform to the experiment when it is set as 1.65. Meanwhile the stiffness analysis in the serviceability states is performed by taking account of the effect of the tensile zone and the maximum crack width is firstly calculated via two approaches based on the length of the plastic hinge and on account of the reduction of the area of externally prestressed tendons.Then the influence coefficient of the tension zone from the steel fiber and peak compression strain are introduced by considering the beneficial impact from the steel fiber in the material FRCC to come up with the correct calculation formulation for calculating maximum crack width of the FRCC beams prestressed with external CFRP tendons. Finally compare the theoretical value with the test results and they agree well.(6) The FRCC beam prestressed with external CFRP tendons take an advantage over the external prestressed concrete beams on the good capability of the limit deformation. As a result of CFRP tendon is a kind of linear material without the yield point. The traditional idea about discussing the ductility is not entirely suitable when analyzing the ratio of the limit displacement and the the yield displacement. Therefore the ductility index is redefined to reflect its essence attribute by adopting the idea of energy proposed by Naaman and Jeong that mainly reveal the relation among the elastic energy,the plastic energy and the total energy. Finally the unloading stiffness curve is determined by the weighted thought and compare the ductility index of the theoretical value based on the energy concept with the test results to determine the ductility level of the FRCC beam prestressed with external CFRP tendons.(7) The finite element model via the software OpenSees for the test members are built to verify the rationality of the model by comparing the theoretical value with the test value. Then the different parameters about mechanical index having an influence on the mechanical property are analyzed to observe its development trend, mainly referring to the ultimate bearing capacity, deflection, the stress increment of external pre-stressing tendons and so on.As a general view from the test results and analysis value, it turns out that the FRCC beam prestressed with external CFRP tendons have higher ultimate bearing capacity, excellent crack distribution pattern and better ductility level than the common reinforced concrete beam on the condition that they keep the same reinforcement ratio and prestress degree. The better ductility level make it possible to develop the long span and lofty structure,the excellent crack distribution pattern in the normal service stages also is benefical to control the durability and long-term performance. |
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