Time-variant Seismic Fragility Of Precast Segmental Bridge Column

In order to study the seismic performance of precast segmental bridge column(PSBC)under cyclic loading and dynamic response under ground motion excitation,this paper takes an engineering example bridge pier as a case study,considers the time-variant steel corrosion in offshore environment,and uses OpenSees finite element software to establish the calculation models of PSBC and monolithic reference column(MRC)respectively,to study the influence of different design parameters on their seismic performance and seismic response,and to explore the influence of steel corrosion on the seismic performance of 2 forms of bridge piers during the bridge service life.The main research contents and conclusions of this paper are as follows.(1)An offshore bearing bridge pier was studied to predict the degradation of material properties during the bridge service life,considering the effect of chloride ion erosion.The results show that: taking the bridge service for 100 years as an example,the yield strength of the energy dissipation reinforcements of the PSBC are approximately 26% lower than that of the completed bridge;the yield strength of the longitudinal reinforcements of the MRC are approximately 11% lower than that of the completed bridge.OpenSees finite element software was used to establish the PSBC calculation model,and the existing test results were used to verify the correctness of the proposed model and the reasonableness of the parameter selection.(2)According to different design parameters,11 finite element models of PSBC are established to study the influence of their seismic performance under horizontal cyclic loading.The results show that: increasing the compressive strength of concrete and increasing the tension stress of prestressing tendons will improve the horizontal bearing capacity,ductility,energy dissipation capacity and self-resetting ability of the specimens;in addition,increasing the steel ratio of energy dissipation reinforcement will also improve the horizontal bearing capacity,ductility,post-yield stiffness coefficient and energy dissipation capacity of the specimens,and increasing the shear-span ratio will also improve the post-yield stiffness coefficient and self-resetting ability of the specimens.(3)Establish finite element models of PSBC and MRC based on engineering example bridge pier,and conduct incremental dynamic analysis to study the difference of seismic performance of PSBC and MRC under ground vibration excitation;establish11 finite element models of PSBC according to different design parameters to study the influence of their dynamic response under ground motion excitation.The results show that: under ground motion excitation,the maximum drift of PSBC is greater than MRC,and the residual drift of PSBC is less than MRC;decentralized configuration of prestressing tendon positions can effectively reduce the maximum drift and residual drift of PSBC;increasing the steel ratio of energy dissipation reinforcement can effectively reduce the joint-opening peak value of PSBC;increasing the compressive strength of concrete can effectively reduce the loss of prestress before and after the earthquake action..(4)Based on the theoretical fragility method,the time-variant damage indexes of PSBC and MRC were given for the whole life cycle,and the time-variant fragility analysis is carried out by considering the influence of steel corrosion.The results show that: the equivalent bending moment and ultimate bending moment of PSBC and MRC both decrease with the extension of bridge service time;the exceeding probability of the 2 forms of bridge piers in the whole life cycle is positively related to the peak ground acceleration(PGA)and the service time of the bridge;in the whole life cycle,the exceeding probability of PSBC in the 4 damage states is greater than that of MRC,the median PGA of PSBC in the 4 damage states is smaller than that of MRC,and the median PGA of PSBC decreases more than that of MRC as the extension of bridge service time;taking the moderate damage state as an example,the median PGA of PSBC and MRC decreases about 20% and 12%,respectively,at 100 years of service compared with that of the completed bridge.