Research On Seismic Vulnerability Models Of Piers Under Near-fault Ground Motions

Near-fault ground motions have aroused many earthquake engineering scholars’ interest in recent years for their special characteristics which are different from conventional ground motions.The piers which serve as the main components of bridges usually suffer damage more seriously under the near-fault ground motions.Seismic vulnerability analysis is an important step in the procedure of seismic risk assessment which establishes the relationship between the intensity measure and damage states,and then the seismic performance of structure can be quantified in a sense of probability.The seismic vulnerability models of piers under near-fault ground motions are studied in this paper,the main research works are as follows:(1)The characteristics of near-fault ground motions were analyzed.Fault distance,magnitude and PGV/PGA were chosen as the distinguishing indexes and the selection criteria of ground motions were established by the value of indexes.Totally 30 near-fault and far-field earthquake records were selected basis on the criteria and then the ground motion records were calibrated,filtered and truncated in order to facilitate the analysis..Residual displacement of piers was found to be one of the significant seismic response parameters according to related researches in recent years.Finite element analytical models of piers were built by using OpenSees software.Concrete01 WithSITC material was selected as piers’ concrete constitutive model,and then the residual displacement could be captured more accurately.Seismic responses of piers were compared and analyzed under different types of ground motions.(2)According to the existing bridge design codes in China as well as survey results,the design parameters of pier samples with the corresponding values were determined.36 pier samples were designed by orthogonal design method.The displacement ductility coefficient and residual displacement drift ratio were elected as the damage indexes by the analysis of commonly damage indexes and the limit values of damage states were identified accordingly.The seismic responses of piers were obtained by the incremental dynamic analysis method.Three different methods were adopted,including the estimation method based on the multiple-stripe analysis idea,the frequency point regression methods from the Monte Carlo sampling or the probability density function integration,to build up the fragility curves which were based on different damage indexes.The differences of seismic fragility models of piers under the near-fault and far-field ground motions were further analyzed.The influence of various damage indexes on vulnerability models was discussed and the causes of deviation between different methods were preliminary explored.(3)Based on the receiver operating characteristic method,the widely used ground motion intensity measures were evaluated by comparing with the indexes of the area under the ROC curves,accuracy and fragility logarithm standard deviation.The effectiveness of double intensity measures was further studied.The seismic vulnerability surfaces of piers were established based on the double intensity measures.The differences of seismic fragility surfaces were compared and analyzed under near-fault and far-field ground motions.The differences between seismic fragility curves and the seismic vulnerability surfaces were further studied.The results showed that the damage states of piers could be more accurately evaluated by considering two ground motion intensity measures in the seismic vulnerability analysis.