受压UHPC圆形墩柱抗冲击试验及简化分析方法

为了研究受压UHPC墩柱的抗冲击性能，开展UHPC墩柱和普通钢筋混凝土墩柱的落锤冲击试验，试验变量为轴力。试验中测量冲击力和墩柱位移，并采用高速摄像机记录冲击过程中墩柱裂缝发生、发展直至破坏的全过程。在此基础上，建立基于纤维非线性有限元和两自由度质量-弹簧-阻尼系统的简化分析方法，用于分析受压墩柱的冲击响应。通过与试验结果对比，验证简化分析方法的有效性。基于简化分析方法进行了墩柱抗冲击极限承载能力分析和参数影响分析。研究结果表明：受压UHPC墩柱的抗冲击能力显著优于普通混凝土墩柱，多次冲击作用下总耗能远高于普通混凝土墩柱；UHPC具有良好的抗压性能和耐撞性，促使了"压力拱效应"的出现，能够显著提高受压墩柱的抗冲击性能；无轴压UHPC墩柱在冲击作用下呈现出典型的少筋破坏，当UHPC用于受弯构件或低轴力情况时，相比普通钢筋混凝土构件需提高最小配筋率要求；受压UHPC墩柱耗能能力约为普通混凝土墩柱的2.27倍；当冲击能量一定时，提高受压UHPC墩柱的配筋率和配箍率，能有效地减小墩柱跨中峰值位移和残余位移，但峰值力变化较小；相同配筋率时，提高冲击能量，跨中位移、残余位移、冲击力峰值也相应增大。

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.