Reinforced concrete bridges are essential components of urban and intercity transportation networks, and their seismic performance becomes more critical when geometric irregularities are present. In practice, site constraints, topography, and construction limitations often lead to bridge configurations with unequal column heights or unequal span lengths. Such irregularities may alter the distribution of stiffness and seismic demand, resulting in higher displacement concentration and increased vulnerability during earthquakes. In addition, chloride-induced corrosion is one of the most common deterioration mechanisms in reinforced concrete bridges, reducing the mechanical properties of reinforcing steel and concrete and potentially amplifying seismic damage over the service life of the structure.
This study evaluates the seismic performance of straight reinforced concrete bridges considering the combined effects of geometric irregularity and chloride-induced corrosion. One regular and six irregular four-span reinforced concrete bridge configurations with three-cell box-girder decks were designed using CSi Bridge according to seismic design requirements. The irregular configurations included bridges with unequal column heights and bridges with unequal span lengths. The numerical models were subsequently developed in OpenSees using fiber-based force-based beam-column elements. The linear behavior of the models was verified by comparing modal properties and gravity reactions obtained from CSi Bridge and OpenSees. Moreover, the nonlinear behavior of the bridge columns was validated using experimental cyclic test results from the PEER database. Chloride-induced corrosion was incorporated by considering deterioration of cover concrete, confined core concrete, longitudinal and transverse reinforcement properties, and low-cycle fatigue degradation of longitudinal bars. Corrosion levels ranging from 0% to 50% were examined. Nonlinear response history analyses were then conducted using 11 far-field ground motion records.
The results indicate that increasing corrosion consistently increases column drift demands in both longitudinal and transverse directions. For bridges with unequal column heights, the transverse drift was more sensitive to corrosion than the longitudinal drift, mainly due to the single-column bent configuration. The most critical case among these bridges occurred when the shortest column was located at the middle bent. For example, 20% corrosion increased the transverse drift of this configuration by approximately 22%, while the corresponding increase in the longitudinal direction was about 9.5%. The results also show that, under 30% corrosion, the increase in transverse drift was approximately 18% for the regular bridge and about 25% for an irregular bridge, confirming the greater vulnerability of irregular configurations to corrosion-induced degradation. For bridges with unequal span lengths, the drift response increased markedly after the corrosion level exceeded 30%. In these cases, the rate of increase in transverse drift after 30% corrosion reached up to six times the rate observed before this corrosion level. The most critical response among the span-irregular bridges was observed in the configuration with adjacent unequal spans and an asymmetric deck layout. Overall, the findings demonstrate that chloride-induced corrosion can significantly intensify the adverse seismic effects of bridge irregularity, particularly in configurations with stiffness imbalance, asymmetric span arrangement, and critical short-column behavior.