The importance of bridges in urban and intercity transportation systems is well recognized. However, the geometric irregularity of bridges can significantly exacerbate their performance during earthquakes. This issue has led to the development of new and complementary regulations in recent years. Environmental constraints, such as the topography of the construction site, are crucial factors contributing to these irregularities, resulting in complex dynamic behaviors. Notable instances of bridge irregularity include unequal stiffness of adjacent and non-adjacent columns, unequal span lengths, and the presence of curves in the plan. One of the most significant factor contributing to these irregularities is the unequal height of columns, which makes shorter columns more prone to damage due to their higher stiffness. Furthermore, the concentration and penetration of chloride ions into the concrete environment, known as chloride-induced corrosion, is a common environmental factor that deteriorates the properties of column materials. This phenomenon can increase the vulnerability of reinforced concrete bridges during earthquake exitation.
In this study, seven RC bridge configurations were evaluated. These configurations include one regular configuration, three configurations with varying column heights, and three configurations with varying span lengths. All bridges have prestressed concrete box decks and four spans and were designed using the CSi Bridge software. After verifying the design accuracy in both OpenSees and CSiBridge, ensuring correct distribution of mass and stiffness as well as static force distribution, the nonlinear behavior of the columns was validated through cyclic analysis, and the analysis parameters were calibrated using experimental sample results. According to AASHTO recommendations for elastic deck behavior, elastic beam-column elements were used to model the deck. The nonlinear behavior of the columns was modeled using fiber formulations and force beamColumn elements. Unlike complex formulations, force beamColumn elements model the actual structural behavior and provide more accurate results. For the initial validations, the bridge columns were modeled using elastic beam-column elements. To model the effects of column behavior degradation, fatigue materials in the OpenSees software were used, which simulate the fatigue of longitudinal reinforcements. Additionally, during the bridge modeling process, necessary values and parameters were calibrated to best account for the effects of longitudinal reinforcement fatigue. Subsequently, nonlinear time-history analysis considering various percentages of reinforcement corrosion was performed in OpenSees software. Rayleigh damping was used in all analyses with a value of 5%. The assumed corrosion percentages were 0, 10, 20, 30, 40, and 50 percent, and the abutments were modeled using zero-length nonlinear springs. In relation to modeling chloride corrosion effects, degradation of mechanical properties of the concrete cover, degradation of mechanical properties of the concrete core, degradation of bond strength between steel and concrete, degradation of mechanical properties of longitudinal and transverse reinforcements, longitudinal reinforcement slip, and longitudinal reinforcement fatigue were all modeled. Finally, the results of the time-history analysis were extracted in the form of maximum column drifts and the maximum drift observed in each model under 11 applied records. The vertical earthquake component was neglected in this study, and all records were applied in the longitudinal and transverse directions. The results indicate that increasing the corrosion percentage leads to an increase in column drift in both longitudinal and transverse directions. Additionally, in all irregular bridges, the sensitivity of drifts to corrosion percentage increased, and the drifts increased at a faster rate. In irregular bridges with unequal span lengths, as corrosion exceeds 30 percent, the rate of increase in transverse drift in all these bridges increased, with the increase rate being up to 6 times higher.