This paper proposes an alternative time-dependent seismic fragility assessment framework considering the variable correlation of structural random parameters for aging highway bridges subject to non-uniform chloride-induced corrosion attacks. The proposed systematic framework is implemented to perform a probabilistic time-dependent seismic fragility assessment for a typical multi-span reinforced concrete continuous girder (MSRCCG) bridge. Effects of non-uniform chloride-induced deterioration on the time-evolving seismic capacity, seismic demand of reinforced concrete (RC) columns, and the time-dependent seismic fragility of the case-study bridge are investigated using nonlinear sectional moment-curvature and nonlinear time history analysis. Furthermore, this paper performs comparative studies to investigate the influence of variable correlation of structural random parameters on the time-variant seismic capacity, seismic demand of RC columns, and time-dependent seismic fragility of the case-study bridge. The results indicate the following conclusions: (1) Non-uniform chloride-induced corrosion may change the vulnerable position and the damage mechanisms of RC columns; (2) Due to non-uniform chloride-induced deterioration, the flexural capacity and curvature ductility of RC columns may exhibit a nonlinear reduction, while there is a nonlinear accelerated growth of time-dependent seismic fragility for aging highway bridges along their service lives; (3) The time-variant seismic capacity (i.e., the flexural capacity and curvature ductility) and seismic demand of RC columns tends to have a certain reduction and increase by ignoring the variable correlation of structural random parameters, respectively; and (4) The time-dependent seismic vulnerabilities of aging highway bridges may be overestimated by ignoring the variable correlation of structural random parameters.

RC bridge substructures exposed to chloride environments inevitably suffer from corrosion of reinforcement embodied in concrete. This deterioration issue leads to the loss of reinforcement areas and a reduction in seismic capacity of reinforced concrete (RC) bridge substructures. To quantify the effect of steel corrosion on seismic fragility estimates, this paper proposes an improved time-dependent seismic fragility framework by taking into account the increase in the corrosion rate after concrete cracking and the reduction in seismic capacity of RC bridge substructures during the service life. Additionally, an analytical method based on a back propagation artificial neural network (BP-ANN) is proposed to provide probabilistic capacity estimates of deteriorating RC substructures. A three-span T-shaped girder bridge is selected as a case study bridge to provide improved time-dependent seismic fragility estimates that consider uncertainties in the material properties, geometric parameters, deterioration process and ground motions. The obtained fragility curves show that there is a nonlinear increase in the exceedance probability of deteriorating RC bridge substructures for different damage states during the service life. In addition, time-dependent seismic fragility analysis shows that the cases of considering only the effect of an increase in seismic demand or the reduction in seismic capacity as well as neither of them may lead to a significant underestimation of the seismic vulnerability of deteriorating RC bridge substructures.