Study on Impact Tensile Strength of Concrete and Impact Falure of Reinforced Concrete Members

(1)提出了一种新的混凝土冲击抗拉强度测试方法。这种测量方法是基于冲击杆件和试件杆件自由端反射的拉应力波的叠加和集中。采用气枪布置和应力杆技术进行冲击拉伸实验。该装置由气枪射出的撞击杆和输入杆组成，输入杆的一端与撞击杆发生共线碰撞。输入杆的另一端与试件杆的一端紧密接触。(2)从应力波在杆中传播的简单理论出发，讨论了混凝土试件的测试原理和冲击破坏行为。利用有限元软件MARC进行了轴对称二维分析的数值模拟，与实验测量结果吻合较好。(3)进行了几种混凝土试件的冲击拉伸试验，并进行了直拉、劈拉、弯曲、压缩等静强度试验。混凝土试件中的断裂位置几乎与拉应力集中的预测位置相对应。通过对试验数据的统计分析，发现混凝土的冲击抗拉强度受加载速率的影响很大，且是静力值的两倍以上。

(1) A newly developed measuring method for impact tensile strength of concrete has been proposed. The measurement method is based on the superposition and concentration of tensile stress waves reflected both from the free ends of a striking bar and a specimen bar. The impact tensile experiment is conducted by means of an air gun arrangement and a stress-bar technique. The setup consists of a striking bar shot out from an air gun and an input bar colliding collinearly with the striking bar on its one end. Another end of the input bar is in tight contact with one end of a specimen bar.(2) The measuring theory and the impact breaking behavior of concrete specimens were discussed on the base of the simple theory of stress waves propagated in a bar. They were verified by not only the experimental measurement but also the numerical simulation in axsymmertrical two demensional analysis using FEM code MARC.Reasonable agreements between the experimental measurement and calculated results were obtained.(3) The impact tensile experiment of some kinds of concrete specimens was performed, together with static strength tests such as direct tension, splitting tension, bending, and compression tests. The breaking position in a concrete specimen bar almost corresponded to the predicted position at which tensile stress concentration was initiated. It was found from the statistical analyses of the experimental data that the impact tensile strength of concretes was significantly influenced by loading-rates, and was found to be more than twice the static value.