Corrosion in concrete structures: A case study of existing I-girder Bridge

The aging infrastructure of bridges in Karachi, Pakistan, has become a pressing concern due to the combined effects of harsh environmental conditions, and increased traffic loads. This study focuses on assessing the performance of existing bridges, with a specific emphasis on bridge bents suffering from atmospheric corrosion in reinforcement. Through numerical analyses, fragility functions, and incremental dynamic analysis (IDA) curves, the research demonstrates that as material degradation from corrosion increases, the base shear capacity, energy dissipation, and ductility of the structures significantly decrease. Corroded bents exhibit reduced seismic capacity, with a marked increase in the likelihood of collapse under inelastic deformations. Therefore, five damage states, ranging from minor to critical, were identified, and it was observed that corroded materials have a higher probability of reaching severe damage states at lower displacement levels. Results show that a significant loss in bridge capacity or backward shift in fragility functions for increasing grade of corrosion. In the transverse direction, the backward shift in fragility curves observed from 10-30% whereas, in longitudinal direction it is around 25-30% from slight to collapse limit states. These findings highlight the urgent need for corrosion mitigation strategies to maintain the structural integrity of corroded bridge infrastructure.