全级配混凝土梁动强度提高机理研究

Dynamic strength enhancement mechanism of a fully-graded concrete beam

基于细观力学方法对全级配混凝土梁的动强度提高机理进行研究.假定混凝土由骨料、砂浆和界面三相材料组成,按全级配混凝土实际配比生成随机混凝土骨料模型.采用塑性损伤模型并考虑材料的应变软化,利用全级配混凝土梁的静弯拉(破坏)试验标定骨料、砂浆和界面的参数.在此基础上对冲击荷载下全级配混凝土梁的动弯拉破坏过程进行数值模拟,重点讨论惯性效应和应变率效应对混凝土材料强度增强因子的影响.研究结果表明:(a)当应变率小于8s-1时,材料惯性对梁的极限荷载影响可以忽略不计;当应变率大于8s-1时,材料惯性对全级配混凝土强度的动力增强因子(SDIF)影响增大.(b)当应变率小于20s-1时,率效应对SDIF影响较大,在高应变率区SDIF主要受材料惯性的影响.此外,探讨了初始缺陷(损伤)对全级配混凝土梁破坏荷载的影响.

The dynamic strength enhancement mechanism of a fully-graded concrete beam was studied based on mesomechanics. Assuming that the concrete composites are composed of aggregate particles, cement matrix, and an interface transitional zone （ITZ）, the numerical aggregate models were generated randomly based on the actual aggregate grade of fully-graded concrete. A plastic-damage consideration, was adopted. The material parameters model for concrete, in which strain softening was taken into of the aggregate particles, cement matrix, and ITZ were identified through a static flexural-tension experiment. Based on the identified parmneters, the dynamic fiexural-tension failure process of the fully-graded concrete beam was numerically simulated under an impact load. The effects of inertia and strain rate on the dynamic increase factor （SDIF） were analyzed. The results show the following： （a） The inertial effect on the limited load could be neglected when the strain rate was lower than 8s^-1 ; when the strain rate was greater than 8s^-1, the inertial effect on SDIF of the fully-graded concrete beam increased. （b） When the strain rate was lower than 20sl, the strain rate had a significant effect on SDIV, whereas the SDiV was mainly controlled by the inertia effect. In addition, the effect of initial damage on the failure load of the fully-graded concrete beam was studied.