Nonlinear Response of RC Columns Subjected to Equal Energy-Double Impact Loads

Defining the damage and deflection from impact by using only the impact energy could be misleading due to the effect of impact momentum. In addition, reinforced concrete columns might be subjected to repeated impact loading. Hence, this study presents the numerical simulation of 16 RC columns with identical sizing and reinforcement details, subjected to equal energy-double impact loadings using a free-falling mass at midspan. The impact energy was kept constant for both impacts. For each analysis, the impact momentum was varied by varying the velocity and mass of the impactor. The axial load ratios of the columns are between 0.0 to 0.3 of the compressive strength of the concrete cross-section. The results clearly addressed the momentum effect on the impact responses. The momentum level affected the specimens' damage behavior under the same input impact energy. A high momentum impact yielded more global flexural damage with large deflection, and a low momentum impact produced more local damage with a slight deflection. The axial load helps maintain the impact resistance capacity. However, the failure determined by the flexural damage pattern under the first impact was changed when subjected to the second impact to the shear mode with the presence of axial load. Further, the colliding index considering the momentum was used in the deflection prediction equation. The proposed equation improved the deflection calculation accuracy of reinforced concrete beams under equal energy but different momentum impact.