Experimental And Numeical Study On Seismic Performance Of New Hybrid Reinforced Concrete-Filled Fiber Reinforced Polymer Tubes Bridge Piers

Bridge piers are the main resistant lateral members in the bridge seismic systems. The failure of piers or the damage of upper structures can destroy bridges during an earthquake. Not only the severely damaged bridge piers need to be reconstructed, but also the minor injured piers with serious residual displacement need to be rebuilt because the upper structures can’t be pushed back their original positions. Consequently the bridge piers require not only having high strength and good ductility, but also having excellent applicability and recoverability after the earthquake. For the seismic design of a pier, actually, it is better that the residual displacement cannot be occurred or controlled in an allowable range. Thus the residual displacement is an important index of post-earthquake recoverability of bridge piers.In order to improve the post-earthquake recoverability of bridge piers, this thesis proposes a new type of hybrid reinforced concrete-filled fiber reinforced polymer tubes bridge pier. Their main features concerned include:(a) high tensile strength FRP rods can continue to increase the bearing capacity of piers even after yielding of the steel reinforcements, thus the bridge piers have the stable post-yield stiffness, i.e., the secondary stiffness; (b) the bridge piers are surrounded by FRP tubes along the entire piers directions, so the ultimate bearing capacity of piers can be effectively increased; furthermore, the bridge piers have significant advantages of high corrosion and harsh environments owing to the high durability of FRP.In the light of the real bridge piers, four reinforced bridge piers are manufactured in the thesis:common reinforced concrete columns (RC columns), hybrid reinforced concrete columns (HRC column), concrete filled FRP tubes column (CFFT column), and new hybrid reinforced concrete-filled fiber reinforced polymer tubes column (HCFFT column). The four specimens are tested under constant axial forces and low-cyclic reversed loads. On the basis of experimental results, a numerical simulation model is developed and parametric analysis is conducted. Hysteretic model is investigated eventually. The focus on the seismic performances of all specimens is failure mode, the stiffness, the bearing capacity, the ductility, the hysteretic behavior, the energy dissipation capacity. Finally, a numerical model was developed by the software of OpenSees and experimental results are validated the applicability and efficiency of the model. After the validation is testified, the numerical model is used to analyze the effect of various parameters on the seismic performances.Some concluding remarks are drawn as follows:(1) The experiments show that the new type of composite columns, especially HCFFT column, has stable bearing capacity and good ductility. Compared with the RC column, the HCFFT increases 84 percent in the ductility coefficient and it decreases over 10% in the residual deformation. This indicates that the new type of composite columns shows more stable and excellent recoverability.(2) The analytical values derived from the finite element numerical model agree well with the experimental results, and the numerical model is used for the parametric analysis and elastic-plastic time-series analysis. The simulation shows that the HCFFT is remarkably less that the RC column in the residual displacement.(3) Hysteretic models are presented for four types of composite elements, which provide solid foundation for the design theory of the new type of composite piles.