Bending Capacity And Cracking Behavior Of Fiber Reinforced Self-Consolidating Concrete Beams Containing Conventional Reinforcement

The main bearing elements of tunnels are tunnel segments, thus the cracking resistance, the security and durability of tunnel segments are highly desired. However, the large size of traditional RC segment usually leads to local cracking and breakage during the transportation and installation process, causing steel rebar corrosion. Fiber reinforced self-consolidating concrete (FRSCC) combines the high workability, high durability of self-consolidating concrete (SCC) and high cracking resistance, high toughness of fiber reinforced concrete (FRC). The application of FRSCC in the shield tunnel segment can solve the security and durability problems caused by segment damage or cracking. Meanwhile, the steel fiber can also partly replace the longitudinal rebar, thus optimizing the arrangement of reinforcing bars. This work is supported by the National Natural Science Foundation of China (No.51078058). To promote the application of FRSCC in the shield tunnel segment and other structures, the following researches are carried out in this paper:workability, mechanical properties of FRSCC, bond behavior between deformed bars (steel rebar and GFRP rebar) and FRSCC, flexural behavior of FRSCC simply supported beams and symmetric inclination beams. Meanwhile, prediction models for the ultimate bearing capacity at ULS, midspan deflection and maximum crack width at SLS of FRSCC RC beams are proposed in this paper. The detailed contents and conclusions of this thesis are as follows:(1) According to the widely used test methods for workability of SCC, the flowability, passing ability and segregation resistance of FRSCC was evaluated. Meanwhile, the compressive strength, splitting tensile strength and flexural toughness of hardened FRSCC were also investigated. Therefore, the mix proportion of FRSCC, which can meet the requirement of workability and strength was obtained.(2) The bond behavior between deformed bars (steel rebar and GFRP rebar) and FRSCC was investigated by centered pull-out test. Meanwhile, according to german guideline (DBV), the energy absorption capacity and equivalent bond strength were employed. The results showed that the addition of steel fiber improved the bond strength and bond toughness between deformed bars and concrete matrix significantly. The hybrid use of steel fiber and macro PP fiber further enhanced the bond behavior, which shows obviously positive hybrid effect.(3) Experimental research of 12 simply supported FRSCC beams under four point bending test was performed. The influences of reinforcement ratio, fiber type and fiber content on failure mode, cracking pattern, load-deflection curves, load-reinforcement strain curves and strain distribution across the section were analyzed. The results indicate that the fibers can significantly improve the failure mode, enhance the flexural bearing capacity and reduce the crack width and crack spacing. However, the effect of fibers decreased with the increasing of reinforcement ratio.22 kg/m3 steel rebar can be replaced by 50 kg/m3 steel fiber when the reinforcement ratio is 0.44%, while the addition of 50 kg/m3 steel fiber can’t be equivalent to 15.6 kg/m3 rebar when the reinforcement ratio is 0.96%.(4) Based on the layered cross section analysis method, a prediction model for flexural bearing capacity was developed by considering the stress transfer mechanism and distribution of fibers at cracked section. The proposed model was compared with four other model in different standards by test results from chapter 4 and steel rebar reinforced FRC beams in literatures. Comparisons between the predicted and experimental results showed that the proposed model could estimate flexural strength accurately and be used for flexural analysis.(5) Based on the balance of area moment, considering the fiber contribution at cracked section, a method for calculating the maximum midspan deflection at serviceability limit states (SLS) of steel rebar reinforced FRC beams was predicted, and the results agreed well with the test data. In addition, based on bond-slip theory, considering the fiber contribution at cracked section and stress transfer mechanism, a method for calculating the maximum crack with at SLS of steel rebar reinforced FRC beams was proposed. The proposed model was compared with other three models from different codes by test results from chapter 4 and steel rebar reinforced FRC beams from literatures, and the results showed that the proposed model could estimate crack width accurately and could be used for crack analysis.(6) Experimental research of 8 FRSCC inclination beams under four point bending test was performed. The influence of reinforcement ratio, fiber type and fiber content on the crack pattern, crack propagation, load-midspan deflection curves, load-reinforcement strain curves and strain distribution at cross section of symmetric inclination beam were investigated. All the symmetric inclination beams failed in flexural modes. The results showed that fibers could improve the failure mode of inclination beams. With the addition of fibers, the crack numbers increased, the crack width and crack spacing decreased significantly. Due to the presence of the axial force, the crack force, yield force, ultimate force of inclination beam were enhanced significantly compared with the corresponding simply supported beams, but reduced deformation corresponding to ultimate force was also observed. The addition of fibers could enhance the deflection corresponding to the ultimate load and improve the ductility of the inclination beam significantly.