Abstract: In this paper, a new damage index is proposed for RC bridge piers using the concept of earthquake input energy distribution in a structural system. The damage index was defined as the ratio of the hysteretic energy to the earthquake input energy to take into account the cumulative effects of stiffness degradation, inelastic deformation, and material nonlinearities throughout the loading history. A damageassessment method was also developed in accordance with material strain. For this purpose, a set of circular RC bridge piers tested under cyclic/seismic loadings was simulated to calibrate the reliability of the proposed damage index and strain-based damage limit states. The results confirmed the ability of the damage index to predict the damage levels of piers under cyclic and seismic loading. The damage index was also compared to some existing damage indices. The comparison showed that the proposed damage index is a relatively simple and practical approach that can provide a reasonably gradual progression of damage throughout the loading history more convincingly than other damage models.