Dynamic Fracture Mechanics Study on the Shear Failure Mechanism of Reinforced Concreate Members subjected to Inpact Forces

1.基于化学反应动力学中的速率过程理论，将固体断裂的随机过程理论应用于钢筋混凝土构件的剪切断裂问题.从理论上得到了弯曲剪切断裂和粘结剪切劈裂两种不同断裂模式下剪切断裂概率的分布函数，包括剪切力的速度效应和破坏区的尺寸效应。结果表明，破坏概率越大，对应的剪切破坏模式越明显，这取决于剪切力速度的大小.对不同剪跨比的钢筋混凝土悬臂梁在自由端冲击荷载作用下的剪切破坏机理进行了试验研究。试验中采用了详细而精密的垂直和纵向CMOD、斜向剪切裂缝发展速率、钢筋和混凝土的应变分布以及某些点的加速度测量仪器。研究结果对高速荷载作用下梁的力学发展规律有重要的认识.基于LSDYNA程序的数值分析，模拟了撞击后梁的波传播行为。从能量的角度研究了不同冲击增量对主剪切裂纹扩展的影响。

1. Based on the theory of rate processes in the kinetics of chemical reaction, a stochastic process theory for the fracture of solid bodies is applied for the shear fracture problems of reinforced concrete members.2. The distribution functions of the shear fracture probabilities are theoretically obtained, including both the velosity effects of applied shear force and failure zone sizes, for the two different modes of the flexural shear fracture and the bond-shear splitting one. It is shown that the larger amount of failure probability leads to the corresponding mode of shear fracture, depending on the magnitudes of shear force velosity.3. A series of experimental studies on the shear failure mechanism of the reinforced concrete cantilever beams with some different shear-span ratios and crack-like notches were carried out under impact loading applied at the free end. Detailed and elaborate measuring instruments for CMOD in both vertical and longitudinal directions, diagonal shear crack development rate, strain distribution of steel and concrete and acceleration at some points were employed in the tests. As the results, some important findings on the mechanism development of the beams under high speed loadings were obtained.4. From numerical analysis based on the LSDYNA program, wave propagation behaviour of the beams after the impacts were simulated. Effect to the successive development of main shear crack due to every applied impact increment, in energy bases, were investigated.