Experiments and a Simplified Analytical Method of an Axially Loaded Circular UHPC Column Under Impact Loading

To study the performance of an axially loaded ultra-high performance concrete (UHPC) column under an impact load, drop-hammer impact tests on UHPC and conventional reinforced concrete (RC) columns were conducted in this study. The test variable was the axial force. Impact forces and column displacements were measured in the experiments, and the entire process (e. g., crack occurrence, development, and failure) was recorded by a high-speed camera. A simplified analytical method based on fiber-based nonlinear finite elements and two-degree-of-freedom mass-spring-damping systems was proposed to evaluate the impact response of a column. The developed simplified analytical method was validated by comparing the numerical results with the experimental displacements and impact forces. Ultimate load-carrying-capacity and parametric analyses were conducted for UHPC and RC columns under impact loading. The results demonstrate that the impact resistance of the axially loaded UHPC column is greatly superior to that of the conventional RC column. The total energy consumption under repeated impacts is much higher than that of the conventional RC column. The UHPC exhibits good compressive performance and crashworthiness, which promotes the appearance of the "arch effect" and can significantly improve the impact resistance of the axially loaded UHPC column. The UHPC column without axial force exhibits the typical failure of a lightly reinforced beam. When UHPC is used for bending or for members with low axial forces, the minimum reinforcement ratio must be increased as compared with conventional RC members. The load-carrying capacity of the axially loaded UHPC column is approximately 2.27 times that of the conventional RC column. When the impact energy is constant, increasing the longitudinal and stirrup reinforcement ratios of the UHPC column can effectively reduce the peak displacement and residual deflection, but the peak force changes less. Under the same conditions, when the impact energy is increased, the mid-span displacement, residual displacement, and peak impact force are also increased accordingly. © 2019, Editorial Department of China Journal of Highway and Transport. All right reserved.