Dynamic behaviors of reinforced NSC and UHPC columns protected by aluminum foam layer against low-velocity impact

Two strategies were proposed in this study to improve the safety of RC columns under low-velocity impact loading. One is setting up the protective closed-cell aluminum foam (CCAF) layer on the surfaces of RC columns for general structures, and the other one is utilizing the combination of the CCAF layer and UHPC for important structures. For verifying the effectiveness of these two strategies, both experimental and numerical investigations on the dynamic behaviors of reinforced normal strength concrete (R-NSC) and ultra-high-performance concrete (R-UHPC) columns protected by the CCAF layer against low-velocity impact were presented in this study. Two R-NSC columns and two R-UHPC columns were tested by the free-falling drop-weight system. The failure modes, failure process, time history of impact force and deflection were discussed in detail. Moreover, a 3D finite element model was developed to further investigate the impact dynamic behaviors of R-NSC columns and R-UHPC columns protected by the CCAF layer. The test results demonstrated that the CCAF layer can protect both R-NSC columns and R-UHPC columns effectively by reducing the impact force and absorbing a large amount of impact energy. Correspondingly, the safety of RC columns was also effectively improved since the impact force between the target and the impactor was reduced significantly by the adoption of the aluminum foam layer, and it verified strategy one. Furthermore, R-UHPC columns showed a better impact-resistant performance than R-NSC columns, especially, R-UHPC columns with the CCAF layer showed superior impactresistant performance, and it verified strategy two. The finite element model can predict the dynamic behaviors of aluminum foam protecting R-NSC and R-UHPC columns with reasonable accuracy. Eventually, the energy absorption of the specimens was investigated by the numerical model.