Seismic evaluation of reinforced concrete bridges using capacity-based inelastic displacement spectra

A simplified seismic evaluation method using capacity-based inelastic displacement spectra is proposed for reinforced concrete (RC) bridges. The proposed method can not only estimate the maximum displacements of bridges, but can also discriminate the damage indices between the bridge columns, where the Park and Ang's damage index (DI) is considered a promising performance indicator due to its good relationship with the strength capacity state and actual visual damage condition of the bridge column regardless of the imposed loading history. To realize the accuracy and reliability of the proposed method, a hypothetical case study bridge was constructed and analyzed using various structural analysis programs and seismic evaluation methods. It was found that the proposed method can receive satisfactory estimates of the maximum displacement and DI for both far-field and near-fault ground motions when compared to the nonlinear time history analysis results of the bridge. In contrast, the AASHTO's and Caltrans' methods cannot reflect the response amplification effects caused by the frequency-content characteristics of near-fault ground motions and would therefore significantly underestimate the inelastic responses of bridges. When applying the proposed method to bridges having unequal-height columns and subjected to longitudinal seismic actions, it was found that for the short column of the bridge, the AASHTO's regularity criteria (maximum bent/pier stiffness ratio of 4 for the three-span case study bridge) would lead to a DI of approximately 3.5 times that of the tall column, resulting in significant damage localization and, hence, decreasing the overall lateral deformation capacity of the bridge.