This study investigates the probabilistic seismic damage characteristics of a five-span RC simply supported girder bridge with double-column piers designed for a high-speed railway (HSR). The objective is to assess the bridge’s fragility by developing a refined nonlinear numerical model using the OpenSEES (Version 3.3.0) platform. Incremental dynamic analysis (IDA) was conducted with peak ground accelerations (PGA) ranging from 0.05 g to 0.5 g, and fragility curves for pier columns, tie beams, and bearings were developed. Additionally, a series–parallel relationship and a hierarchically iterated pair copula model were established to evaluate system fragility. The results indicate that as PGA increases, the damage probability of all bridge components rises, with bearings being the most vulnerable, followed by pier columns, and tie beams exhibiting the least damage. The models accurately simulate the correlations between members and system fragility, offering valuable insights into the bridge’s performance under seismic conditions.

High-strength steel wires in bridge stay cables are susceptible to chloride attack and wet–dry cycling during long term service. Furthermore, the resulting spatially non-uniform evolution of corrosion morphology can lead to the degradation of their static mechanical properties. In this study, high-strength steel wires with a nominal diameter of 7 mm were subjected to copper-accelerated acetic acid salt spray (CASS) exposure for 0–80 d, followed by 3D laser scanning and uniaxial tensile testing. Corrosion depth, surface roughness, and cross-sectional area loss were first quantified. Based on these morphological indicators, a 3D cellular automaton (CA) model incorporating an axially stationary correlated random field was developed. The maximum cross-sectional area loss ratio was subsequently adopted as the characteristic damage parameter for evaluating mechanical degradation, and a quantitative relationship between the CA simulation results and the degradation of static mechanical properties was established. The results show that, with increasing corrosion duration, the corroded regions on the wire surface progressively expanded, coalesced, and deepened, producing a spatially non-uniform morphology characterized by alternating zones of severe and mild corrosion along the axial direction. From 20 to 80 d, the maximum cross-sectional area loss ratio increased from 13.307% to 31.175%. Subsequently, the developed CA model successfully reproduced the evolution trends of the corrosion morphology indicators, with relative errors of less than 19% compared with the 3D scanning measurements. By incorporating the maximum cross-sectional area loss ratio obtained from the CA simulations into the mechanical degradation relationships, the mean prediction errors for Young’s modulus, yield strength, and ultimate tensile strength were 2.788%, 2.581%, and 3.198%, respectively, relative to the experimental results. These results demonstrate that coupling the CA model outputs with the mechanical degradation relationships provides an effective approach for predicting the residual mechanical properties of high-strength steel wires subjected to different corrosion durations.