考虑初始缺陷影响的混凝土梁动态弯拉破坏模式分析

DYNAMIC FLEXURAL-TENSILE FAILURE MODE ANALYSIS OF CONCRETE BEAM WITH INITIAL DEFECT

考虑到混凝土细观非均质性的影响,从细观角度出发,认为混凝土是由骨料、界面过渡区、砂浆基质及初始缺陷组成的四相复合材料,建立了混凝土简支梁的二维随机骨料模型。采用耦合材料应变率效应的塑性损伤本构模型来描述砂浆基质及界面的力学性能;假定骨料不产生损伤破坏,设定为弹性。对无缺陷、2%和5%孔隙率的混凝土梁进行弯拉破坏数值研究,探讨初始缺陷及加载速率对混凝土梁弯拉破坏模式、弯拉强度及宏观应力-应变关系的影响。数值结果表明:混凝土弯拉破坏模式及宏观力学性能具有明显的加载速率相关性;初始缺陷的存在对混凝土破坏模式及宏观力学性能具有很大的影响。

Considering the meso-cale heterogeneity, concrete was deemed as a four-phase composite composed of aggregate, mortar matrix, interface transitional zone(ITZ) and the initial defect in this paper. A two-dimensional random aggregate model of concrete beam was established. The plastic damaged model combined with the material strain-rate effect was employed to describe the mechanical properties of mortar matrix and the ITZ. It is also assumed that the aggregate was elastic, which would not be damaged. The numerical flexural-tensile study of the concrete beams consists of three different models, i.e. non-initial defects model, 2% porosity model, and 5% porosity model. The influences of initial defects and loading-rates on the flexural-tensile failure mode, flexural-tensile strength and macroscopic stress-strain relationship were discussed. The numerical results indicate that the flexural-tensile failure mode of concrete and the macro mechanical properties have obvious loading-rate dependency, while the existence of initial defect has great influence on concrete failure mode and macroscopic mechanical properties.