Hysteretic Energy Dissipation And Seismic Resiliency Of Precast Piers With High-strength Bar

High-strength bars incorporated with precast piers instead of ordinary steel bars can reduce the reinforcement quantity,expedite the joint construction and improve its seismic performance,which is of great significance for promoting the development of precast pier assembling technology.A series of quasi-static loading and low-cycle fatigue tests have been carried out in this paper.The main research contents and results are listed as follows:(1)The seismic performance of precast piers with high-strength rebars is studied.Firstly,a set of quasi-static tests are carried out,which show that the seismic performance of precast pier can be significantly improved by replacing ordinary rebar with high-strength rebar according to the same area,such as increasing yield displacement,peak lateral force and ultimate displacement,and reducing residual displacement,stiffness degradation rate and seismic damage.Secondly,the lateral displacement mechanism of precast pier is analyzed and the pushover analytical formula is given.Finally,a modified fiber FE model is constructed to predict the monotonic pushover and hysteretic behaviors of precast piers accurately,which employs the constitutive law of unbonded ED bars near the joint interface.(2)The influence of high-strength rebar on seismic behavior of prestressed precast pier is explored.The experimental results show that high-strength rebar replacing ordinary rebar according to the same area can increase the peak strength,self-centering capacity and post-yield stiffness ratio of precast piers with unbonded prestressed tendons,which also enhance the pier damage and unloading stiffness degradation ratio.In terms of simulation analysis,the proposed fiber FE model considering the joint is in good agreement with the testing result.The analysis shows that higher axial load ratio in precast pier results in greater lateral strength and energy dissipation,but significantly decreasing the ductility and strength after peak strength.(3)Low cyclic loading tests for bridge piers with high-strength rebar are carried out in this paper,which consist of two groups: precast and cast-in-situ specimens.When the cyclic loading drift does not exceed the yield drift,the fatigue strength of the pier does not degrade significantly.After exceeding the yield drift,the larger the fatigue loading drift,the greater the damage at first loop,and the smaller the fatigue life.An exponential-type degradation model with the peak lateral force at the first loop as the coefficient and the cycle count as the base is proposed,and a fatigue damage model is established to evaluate the damage level of the bridge pier.A modified OpenSees FE model is constructed to simulate the low cycle fatigue test.(4)A seismic evaluation method is developed to evaluate the resilience of concrete piers.Four characterized resilience parameters are defined,and their desired expectations of seismic resilience are expounded according to their physical significance.On the basis of the fatigue test observation and evaluation,it can be testified that the resilience of the precast pier with high-strength rebar is better than the one with conventional rebar at large.(5)A multi-factor comprehensive assessment method is proposed to determine the precast pier connection in the design.Firstly,the definition,description and score of the main evaluation factors are given,and the quantitative method of comprehensive assessment is developed,which combines the weight coefficients of the specific application case.Afterwards,integrated with the practical precast piers of Weihai Xiqufu Bridge,this paper takes four typical connections as examples to illustrate the application methods and gives the design recommendation order.(6)The seismic design strategy and displacement-based seismic design method for precast pier are presented.Taking the precast pier of Weihai Xiqufu Bridge as an example,the seismic design method proposed is applied.