1. College of Civil Engineering, Hunan University, Changsha 410082, China;
2. Key Laboratory for Wind and Bridge Engineering of Hunan Province, Hunan University, Changsha 410082, China
Abstract:In order to study the impacts imposed by the random variable correlations on the time-dependent seismic fragility of bridges, an alternative bridge time-dependent seismic fragility analysis approach based on the Nataf transformation and uniform design (UD) was proposed. A multi-span continuous highway bridge was taken as case-study, and the nonlinear finite element of the bridge was built by using OpenSees program. Based on the deterioration of the diameter and sectional area of the longitudinal reinforcement due to the effect of chlorine ion induced corrosion (CIIC), the sectional nonlinear analysis and a one-record nonlinear time-history analysis were conducted to study the impacts of CIIC on the seismic capacity and seismic demand of bridge structure. Then, by taking the damage of bridge columns, lead rubber bearing (LRB), plate type elastomeric bearing (PETB) and abutments into account, the time-dependent seismic fragility curves of the case-study bridge were established. Finally, the impacts on the seismic capacity, seismic demand of bridge components and bridge time-dependent seismic fragility curves imposed by the variable correlations were qualitatively analyzed. It is concluded that: 1) the CIIC may reduce the ultimate flexural capacity of piers, whereas that may slightly increase the ultimate curvature and the ductility capacity of columns; 2) the corrosion of longitudinal steels duo to CIIC may reduce the bending demand of the bottom section of bridge piers, while that may increase the displacement and curvature ductility demand of piers to a certain degree, and the failure probability of bridge under different damage states increase constantly result from the degradation of the mechanic property of longitudinal reinforcement; 3) the proposed approach can effectively account for the correlations of structural random variables, and after considering the effects of such variable correlations, the ultimate flexural capacity of piers increase, whereas the seismic demand of pier top displacement, the yield bending moment, curvature ductility of pier bottom section and the failure probability of bridge at different points in time during the whole life-cycle design reference period of bridge structure have a certain reduction; 4) and neglecting the impacts imposed by variable correlations may overestimate bridge time-dependent seismic fragility.
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