Seismic Vulnerability Analysis Of Reinforced Concrete Bridges Subjected To Near-fault Ground Motion

In recent years, near-fault ground motion is one of the hot issues in earthquakeengineering research. Due to the effects of its high energy pulse, it has been proventhat bridges in near-fault zones face the higher seismic risk than that of far-field.Seismic vulnerability analysis is an effective seismic risk assessment method, whichquantifies the seismic performance of a structure in a sense of probability anddescribes the correlation between ground motion intensity levels and structuraldamages from a macroscopic view. In this paper, studies are performed to research thedifferent effects of damage levels of reinforced concrete bridges subjected to far-fieldground motion and near-fault ground motion from the angle of seismic vulnerabilityanalysis. The main results and conclusions are as follows:(1) Based on the former method of developing seismic fragility curves by scalarIM, a method for the seismic vulnerability analysis of bridge structure based onvector-valued IM is presented in this paper. In this method, seismic fragility functionsof different bridge components are firstly established. Then, by considering thecorrelation of different bridge components, the seismic fragility function of bridgesystem is established.(2) The nonlinear behavior of reinforced concrete bridge piers subjected toearthquakes is simulated using beam with hinges element which is based on Manderconcrete model and Chang-Mander isotropic hardening nonlinear steel model,pile-soil-bridge structure interaction is considered by Penzien model and Mackie-Stojadinovic spring model is used to simulate abutment. Then, according to theresearch results about damage states and damage indexes, damage indexes of differentbridge components in different damage states are defined.(3) Considering the uncertainties of the bridge itself, three-dimensional nonlinearanalysis models of bridge structure are built. Then, earthquake records (far-field andnear-fault) satisfied the site condition II in Chinese bridge seismic code are chosenfrom PEER strong motion database and the nonlinear dynamic time history analysesare conducted. By comparing the effectiveness of commonly used intensity measuresin the assessment of seismic response of bridge structure, the two parameters ofvector-valued IM are chosen. (4) Seismic vulnerability analyses of the reinforced concrete bridge subjected tofar-field ground motion and near-fault ground motion are performed. The studiesindicate that vector-valued IM can result in a significant reduction in the dispersion inthe vulnerability analysis of the bridge and seismic fragility surfaces developed byvector-valued IM allow the uncertainties related to the effects of the second intensitymeasure to be considered within risk assessment. A bridge system is more vulnerableto earthquake damage than any other components and the system level failure eventsmust be taken into account when performing the seismic vulnerability analysis forbridge structure. Near-fault ground motion makes the bridge more vulnerable toearthquake damage, studying the seismic performance of bridge structure from theangle of seismic vulnerability analysis can reflect the seismic response law of bridgestructure subjected to near-fault ground motion from a sense of probability and it hasan important significance to study seismic problems of bridges in near-fault zones.