Seismic Risk Analysis Of Near-Fault RC Bridge Structure: Method And Application

In recent years,many earthquakes were found to contain the near-fault effect seismic record,bringing all kinds of engineering structures,including bridges,intense damage,causing wide attention in engineering seismic field.Due to the effects of the high energy pulse,it has been proven that bridges in near-fault zones face the higher seismic risk.In this paper,seismic risk analysis method of near-fault bridge structure is introduced and applied to research the effects of pulse on the seismic risk of near-fault RC bridge structure.The main results and conclusions are as follows:（1）Considering the uncertainties of the bridge structure and ground motion,adopting the appropriate damage index,choosing the spectral acceleration at the first period of the structure as the ground motion intensity measure,probabilistic seismic demand model of the bridge structure are established.Then the seismic fragility curves of bridge structure are obtained.The results show that the curves of bridge components and system under near-fault pulse-like ground motions are very close to those under near-fault non-pulse-like ground motions.（2）The transcendental probabilities of various damage levels of bridge structure under near-fault pulse-like and non-pulse-like ground motions for the given magnitude,the fault distance and field condition,were calculated based on the fragility analysis and the modified ground motion prediction equations（GMPEs）.The results show that the transcendental probabilities of various damage levels of bridge components and the bridge system under near-fault pulse-like ground motion are significantly greater than those under the near-fault non-pulse-like ground motion.And the expand coefficients of damage probability（the ratio of damage probability under pulse-like and non-pulse-like ground motion）decrease with the increasing of moment magnitude,increase with the increasing of fault distance and V_s30 （the time-averaged shear-wave velocity from the surface to 30 m）.（3）Taking a single site near the strike-slip faults as an example,considering the pulse effect,the seismic hazard analysis is done to calculate the acceleration response spectrum and the seismic hazard curves.The result shows that the seismic hazard significantly improved due to the pulse effect.（4）Seismic risk analysis of the bridge was done based on the seismic hazard analysis and the seismic fragility analysis,obtaining the risk probabilities of bridge components and the system exceeding different damage level for considering the pulse effect or not.The results show that when considering the pulse effect,the risk probabilities of bridge components and the system are significantly greater than those not considering the pulse effect.