Abstract: Anti-impact design is a very important aspect to ensure the safety of reinforced concrete (RC) bridges against extreme loads, such as explosions from terrorists attacks and accidental collisions of rockfalls and vehicles. The impact behavior of the pier columns, which is the most important vertical components in the bridge structures, have attracted much attention in recent years, and experimental studies on the impact behavior of scaled pier columns have been conducted by many researchers. It has been acknowledged that the size effect has a significant influence on the dynamic response of structural elements. Therefore, in this study, the performance of the prototype reinforced concrete pier columns under lateral impact loads was investigated. Using a numerical simulation technique, three-dimensional finite element models of a prototype pier column under impact loading were established and validated through comparisons with impact tests in the literature. A new damage assessment method based on the sectional damage factor was presented to determine the damage level of reinforced concrete pier columns. The effects of impact parameters such as impact mass, impact velocity, and impact stiffness on the failure mode and damage mechanism of reinforced concrete pier columns were also identified in detail. The simulation results show that the energy dissipation of reinforced concrete pier columns under impact loading can be divided into local energy dissipation in the contact area and overall energy dissipation in the whole component. When the initial kinetic energy of the impact body remains constant, different combinations of the impact mass and velocity can lead to a significant discrepancy in the damage mechanism of reinforced concrete pier columns. The proposed damage assessment method based on sectional damage factors can be utilized to accurately describe the failure state of the reinforced concrete pier columns. In addition, the contribution of the axial load to the impact capacity of reinforced concrete pier columns is limited, and the columns are more likely to suffer shear failure with the increasing axial force. The impact stiffness has a significant effect on the impact force and the dynamic response of reinforced concrete pier columns.