Seismic Performance Analysis Of Precast Segmental Concrete-filled Steel Tube Self-centering Piers

Based on the experimental tests,the seismic performance and self-centering capacity of the precast segmental concrete-filled Steel Tube（CFST）self-centering piers were further studied by combining the theoretical analysis and numerical simulation.The main research outreaches and conclusions are as follows:（1）Based on the deformation characteristics and behavior of the precast segmental CFST self-centering piers,and considering the strain permeation effect caused by uncoordinated deformation of energy dissipation bars and concrete at the bottom,using“graphical multiplication”method and“modified equivalent cantilever beam”theory,the constitutive relation model（skeleton and hysteresis analysis model）,including the initial elastic stiffness,yield stiffness,yield force,and energy dissipation coefficients,for precast segmental CFST self-centering piers is proposed and verified using the pseudo-static test.The results show that the model has good agreement with the tests in terms of bearing capacity,stiffness and energy consumption.（2）Based on Open Sees platform,the fiber-section column element model for the precast segmental solid-sectional CFST self-centering bridge piers is established.The reliability of the model was verified by comparing with the existing test results.The number of built-in energy dissipation bars,initial tensioning force level of the posttensioning tendons,layout angle of external energy dissipation bars and other key design parameters are gived based on the finite element analysis of the hysteretic（internal energy dissipation）and restoring force performance（external energy dissipation）,and the ability to center is evaluated.The results show that,for no more then 1%residual displacement drift ratio limitation in the Japanese code for seismic design,the lateral strength contribution ratio of the energy dissipation bars,λ_ED,should not exceed 34.9%.To reduce the loss of prestress in the tendons,it is suggested that the initial tensioning force of the posttensioning tendons should not exceed 60%.For the external dissipation steel bar has a angle of 53.63^o,the maximum energy dissipation could be achieved.The definiation of self-centering ratio in the narrow sense is more widely acceptable during the evaluation,so it is more reasonable.（3）Based on the analysis result of precast segmental solid-section CFST self-centering bridge piers,taken into account the equivalent axial compressive strength bearing capacity,a design method for hollow section CFST self-centering bridge pier is proposed and verified with the fiber section model by introducing the energy dissipation and recovery coefficients.The seismic performance of solid section and hollow section CFST self-resetting bridge piers are compared and analyzed.The optimized ratio of the energy dissipation bars and the posttensioning tendons is given out.For the design method based on the energy dissipation and recovery coefficient,the separation of the two functional requirements of energy dissipation and self-centering is more convenient.Compared with solid secion CFST self-recentering piers,the ultimate bearing capacity of hollow section CFST self-recentering piers is increased by about 35.73%.When the ratio of the energy dissipation bars and the posttensioning tendons is 2:1,there is an ideal flag hysteresis relastionship for the piers.