Although some studies have been conducted to simulate the dynamic response of bridge piers under barge impact, several essential modeling issues (e.g., reasonably exerting permanent loads and simplifying FE models) are not well examined. Hence, high-resolution FE models are meticulously developed in this paper to simulate barge collisions with a typical four-span continuous girder bridge. Numerical results highlight the importance of the gravity load for barge impact-induced responses. A simplified bridge model is proposed to improve computational efficiency. The proposed simplified method is found to be more accurate than that of the one-pier two-span (OPTS) model. Also, it is observed that although the peak impact force increases with impact energy, the impact-induced displacement does not always increase. It is attributed to the fact that the spectral characteristics of the impact force-time history have a significant influence on the impact-induced responses. To improve the impact resistance, three strengthening methods based on ultra-high-performance fiber-reinforced concrete (UHPFRC) are investigated and compared. It is found that strengthening columns with two-end UHPFRC jackets is superior to other strengthening methods when considering cost-benefit ratio. Finally, a multi-objective optimization design procedure is presented for the UHPFRC-strengthened columns. •Reasonably including the influence of permanent loads is crucial to numerically evaluate barge-impact resistance of bridge piers.•The proposed simplified model retaining the whole girder exhibits better accuracy than the OPTS model.•The responses of bridge piers do not always increase with the impact energy due to the characteristics of barge impact loads.•The strengthened column with two-end UHPFRC jackets is more promising than the other strengthening schemes.•A multi-objective optimization design method is developed for UHPFRC-strengthened columns.