Seismic Fragility Study On The Continuous Beam Bridge Over High-speed Railway Based On IDA Method

Performance based seismic design(PBSD)of structures has gained growing social attention over the last few years.Of critical importance in the PBSD framework,seismic fragility analysis is valuable in multiple applications,such as seismic design and seismic performance evaluation of structures.Presently in China,applications of fragility analysis chiefly lie in building engineering and highway bridges,while there is a dearth of research into high-speed railway bridges.A typical continuous beam bridge over high-speed railway in China is taken as the research object to carry out the following studies:(1)With the help of a great multitude of domestic and foreign references,basic methods of seismic vulnerability analysis are elaborated,various means of developing fragility curves are briefly introduced,and steps to conduct vulnerability analysis of bridge structures are summarized.(2)Detailed summaries and comparisons are made regarding two sorts of common ballastless track structures in domestic high-speed railway,and the structural characteristics of double-block ballastless track are emphatically introduced afterwards.(3)Two finite element models are established on the basis of a(48+80+48)m continuous girder bridge over domestic high-speed railway,one of which is called integrated model for it considers the restraint effect of double-block ballastless track system on the bridge structure,and the other of which is called traditional model for it fails to take the restraint effect into account.In the meantime,the parameter values and modeling methods of double-block track system are presented.(4)Several ground-motion time histories(GMTHs)are selected from PEER ground motion database in accordance with a few factors,including soil conditions and structural natural vibration characteristic.Sectional performance of the pier is evaluated through moment-curvature analysis.Data from the literature,coupled with sectional analysis,are used to define the limit states(LSs)for the pier and displacement ductility ratio is employed as the damage index of the pier.Fragility curves of the both models are developed through incremental dynamic analysis(IDA)and a comparative analysis is therefore made.The restraint effect of track system on the seismic vulnerability of the bridge is subsequently studied.(5)In light of the current engineering practice that the low-reinforced concrete gravity pier with a reinforcement ratio of less than 0.5% is extensively used in China's high-speed railways,limit states of the pier with a low reinforcement ratio are re-defined.Seismic fragility of the pier with reinforcement ratio from 0.1% to 0.5% and influence law of the reinforcement ratio of pier in the integrated model to its seismic vulnerability are thus studied.(6)Based on the traditional reliability theory and calculation formulas of system failure probability,overall seismic fragility analysis of the pier system is performed to evaluate its seismic performance.