Dynamic impact performance of axially and eccentrically loaded reinforced concrete columns

The impact resistance of reinforced concrete (RC) columns is strongly affected by axial loading conditions, yet the combined influence of axial-load eccentricity and lateral impact remains insufficiently understood. This study numerically investigates the dynamic response and failure mechanisms of axially and eccentrically loaded RC columns under lateral impact, with particular emphasis on the role of axial boundary conditions. A high-fidelity finite element (FE) model was first developed and validated against quasi-static eccentric loading tests and lateral impact experiments. A supplementary comparison with available eccentric-impact test data was also conducted to further assess the model applicability to columns subjected to combined eccentric axial loading and impact. To reproduce the axial-load variation and inertial interaction between an isolated column and the surrounding structure, different axial boundary conditions were compared with a representative five-story RC frame model. The results show that the gravity mass (GM) boundary provides the best overall agreement with the benchmark, with peak and residual displacement errors of 3.52% and 1.60%, respectively, together with an axial-force NRMSE of 0.118 and a correlation coefficient of 0.872. Based on the validated modelling framework, parametric analyses were performed to examine the effects of impact velocity and eccentricity ratio. The results indicate that impact velocity primarily governs the input kinetic energy and overall deformation demand, whereas axial-load eccentricity increases residual deformation and promotes a more asymmetric and localized plastic-damage distribution near the column base and impact region. Within the investigated parameter range, higher eccentricity results in larger peak and residual lateral displacements and more concentrated damage near the column base. The findings highlight the importance of considering realistic axial boundary conditions and eccentric axial loading in component-level impact assessment of RC columns.