| Reinforced concrete (RC) is not suitable for use in harsh environment and large-span structures because of its poor durability and heavy weight, while Carbon Fiber Reinforced Polymer (CFRP) is considered as an ideal alternative to steel tendons due to its excellent performance, such as high strength, light weight, resistance to corrosion and fatigue and low electrical conductivity. In addition, Reinforced Cementitious Composite (FRCC) is also a new building material with a promising application in the field of civil engineering due to high strength, toughness and durability. Therefore, CFRP Tendons Reinforced FRCC structures will be lighter than RC, and it has better durability and fatigue behavior. This paper will carry out materials experimental study on CFRP tendons and FRCC firstly, then investigate fatigue behaviors of CFRP tendons reinforced FRCC flexural components, the details of this study are described as following:(1) The material properties of FRCC are studied, including axial tensile strength, axial compressive strength, compressive elastic modulus, tensile elastic modulus, ultimate tensile strain and ultimate compressive strain, and also providing the axial tensile stress-strain curves and axial compressive stress-strain curves. The results show that the mechanical performance of FRCC are significantly better than RC. According to the bridging stress of steel fibers, the elastic portion of axial compressive stress-strain curve for FRCC is 70%～80% of its upward stage, while the elastic portion of RC is only 40%～50% of its upward stage.(2) The material properties of CFRP tendons and CFRP stirrups are studied, and proposed a novel method for testing CFRP stirrups. The results show that the corners of CFRP stirrups are remains the weak parts, the tensile strength of CFRP stirrups will be increased by enhancing the corners. CFRP tendons have relatively high compressive strength and ultimate compressive strain. Compressive strength of CFRP tendons is up to 683MPa, which is 38.4% of its tensile strength, ultimate compressive strain exceeds 5000με. Compressive elastic modulus of CFRP tendons is about 80% of its tensile elastic modulus.(3) Five CFRP tendons reinforced FRCC flexural specimens are tested under static and fatigue loadings. Each specimen has identical cross-section and reinforcement. The influences of the cyclic stress level (the maximum cyclic stress to ultimate tensile stress) are investigated on specimens under repeated tension-compression. The differences between specimens under repeated tension-compression (stress ratio R=-1) and repeated tension-tension (stress ratio R=0.1) are also discussed. The results show that the failure mode of all specimens (specimens under repeated tension-compression and under repeated tension-tension) is the fatigue rupture of CFRP tendons. With the increase of the number of cycles, the cumulative residual strain of FRCC, the maximum compressive strain of FRCC, CFRP tendons’strain, deflection, as well as the maximum crack width show a significant three-stage appearance (a two-stage appearance could be partially observed from the result). Overall, the first stage takes 15 percents of the fatigue life and the end of the second stage exceeds 80 percents of the fatigue life. The fatigue life of specimens under repeated tension-compression is susceptible to fatigue loading levels, when fatigue loading level decreases 0.05, the fatigue life will be increase by 1.61 times. The fatigue life of specimen under repeated tension-tension is 2.11 times as that of specimen under repeated tension-compression at the same fatigue loading level.(4) The concept of 3D-CLD model is put forward, which can reflect the effect of upper limit fatigue stress, mean cyclic stress and average stress amplitude of cyclic stress on fatigue life of material. It reveals that the traditional 2D-CLD model is actually the projection of 3D-CLD model on the σa-o-σm plane. At the same time, CFRP tendons’damage is defined according to residual stiffness, and the fatigue damage model for CFRP tendons is proposed based on the T-C test data. In addition, according to continuum damage mechanics theory, the expression of FRCC’s fatigue damage is deduced based on cumulative residual strain. Then the fatigue damage model of FRCC is set up by damage mechanics, and finally the model parameters are provided based on the test data.(5) A nonlinear analysis method for the whole process of fatigue damage is presented, which can simultaneously consider the CFRP tendons and FRCC coupling and variable amplitude repeated stress. The non-linear analysis of entire fatigue process of CFRP tendons reinforced FRCC flexural components is carried out by programming procedure. The procedure can simulate CFRP tendons’ strain, FRCC’s strain, deflection and depth of compressive zone during the whole fatigue life. The simulation results show that the procedure can be used to predict the whole fatigue life of CFRP tendons reinforced FRCC flexural components under T-C and T-T, and predict results are close to test data.(6) The cumulative fatigue damage theory based on residual life is selected to calculate the amount of cumulative damage of CFRP tendons and FRCC. A procedure is developed to analyze the failure mode and fatigue life of CFRP tendons reinforced FRCC flexural components. In addition, fatigue stiffness is defined as the flexural rigidity. The fatigue damage model of CFRP tendons reinforced FRCC flexural components is deduced based on flexural rigidity. A procedure is developed to predict the fatigue life of CFRP tendons reinforced FRCC flexural components. The results shows that two methods can predict the fatigue life of CFRP tendons reinforced FRCC flexural components well. At the same time, an integral CFRP tendons reinforced FRCC noise barrier is proposed, the cumulative fatigue damage theory based on residual life is selected to predict the fatigue life of the novel noise barrier, the result show that it can fulfill the design requirements of 350km/h high speed railway in our country. |
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