| As the substructure of a bridge system, reinforced concrete pier plays a role in supporting the deck and transferring the load. Based on current ductile design philosophy, seismic energy is dissipated through plastic deformation within the pier in an earthquake. As a result, large residual deformation exists which affects the serviceability and brings repair difficulties. In this paper a self-centering (SC) concrete pier with external energy dissipaters is proposed which could minimize residual drift, and damage is concerntrated on replaceable energy dissipaters; corrosion-resistant material is applied to improve structure durability in chloride environments. Regarding this novel structure, the configuration of SC pier is presented and the mechanical behaviors of the structure are investigated through theoretical, experimental, numerical and fragility study. The main work of this paper is summarized as follows:(1) Fist, the rational configuration of the SC pier is investigated. Reinforced concrete piers and foundations are shop fabricated separately before they are field assembled using unbonded posttensioned (UBPT) tendons. Brackets are set on the pier for fixing the energy dissipating bars, which could be installed and replaced conveniently. As the overturning moment exceeds the imminent gap opening moment, gap opening occurs at the pier-foundation interface, the pier rocks as a rigid body and dissipats energy through external energy dissipating(ED) bars. After earthquake, the gap closes due to the PT forces. The bottom segment of the pier is encased in a jacket to prevent concrete crushing. Jacket, PT tendons and ED bars are made of glass fiber reinforced polymer (GFRP), basalt fiber reinforced polymer (BFRP) and aluminum alloy respectively, so as to obtain enhanced durability.(2) The mechanical behaviors of the SC pier is analyzed theoretically. A complicated model and simplified model was established respectively, based on which the lateal force vs. displacement relationship is deduced, including computational formulas of the deformation, displacement, lateral stiffness and equivalent viscous damping ratio of the structure. Formulas of the energy dissipation ratio and equivalent viscous damping are also provided. Good agreement is observed between analytical and experimental results. The proposed theoretical models can thus be used in the design of SC piers.(3) Fifteen cyclic load tests are conducted to study the seismic performance of the pier. The influence of PT force, aluminum bars configuration, PT tendon material, GFRP jacket on lateral stiffness, energy dissipation capacity and damage pattern is investigated. Desirable self-centering capacity and low level of damage of the pier is observed from the tests.(4) Based on theoretical and experimental study, the numerical simulation of the SC pier is carried out using the Open System for Earthquake Engineering Simulation (OpenSees). Gap opening and closing, self- centering capacity provided by PT tendons, energy dissipation by aluminum bars are taken into account. Good agreement is observed between numerical and test results, which shows the effectiveness of the proposed model.(5) To this end, fragility analyses are carried out on one RC pier and one SC pier based on the preceding finite element model. Fragility curves obtained from incremental dynamic analysis and regression analysis show that SC pier has a slightly higher exceeding probability when maximum drift is taken as the seismic performance index, but has a much lower exceeding probability when residual drift is taken as seismic performance index. |
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