考虑抗拉强度及峰值后软化曲线非均质性的混凝土梁三点弯破坏过程数值模拟

NUMERICAL SIMULATION OF FAILURE PROCESS OF THREE-POINT BENDING CONCRETE BEAM CONSIDERING HETEROGENEITY OF TENSILE STRENGTH AND POST-PEAK SOFTENING CURVE

采用FLAC模拟了混凝土梁三点弯曲条件下的破坏过程,其中考虑了抗拉强度及峰值后软化曲线非均质性,得到了梁的载荷-CMOD曲线、梁跨中横截面上的水平方向应力及塑性拉伸应变的分布规律、应变软化区域及真实裂纹长度的变化规律、拉伸破坏单元及真实裂纹的发展规律。结果显示载荷-CMOD曲线的数值结果与C40混凝土的实验结果基本吻合。考虑抗拉强度及峰值后软化曲线的非均质性之后,真实裂纹多点启动。一些真实裂纹出现之后,发生聚合,同时,新的真实裂纹启动。在峰值后,随着CMOD的增加,应变软化区域长度的增加速度变缓。当真实裂纹出现之后,应变软化区域的长度基本保持不变。随着CMOD的增加,首先,梁绕跨中横截面没有转动;之后,梁绕跨中横截面的转角基本保持不变;随后,梁绕跨中横截面的转角变得越来越大。拉应变局部化区的厚度大致等于3个―4个单元的长度。

Considering the heterogeneity of the tensile strength and post-peak softening curve, failure processes of two three-point bending concrete beams are numerically modeled using FLAC. The load-CMOD curve, the distributions of the horizontal stress and plastic tensile strain in the middle span of the beam, the length of the strain localization zone and real crack, and the distributions of failed elements in tension and real crack are presented. Quantitatively, the numerical load-CMOD curves are consistent with the experimental results of C40 concrete. After the heterogeneity of the tensile strength and post-peak softening curve are considered, real cracks are initiated at several spots. Then real cracks initiated coalesce and simultaneously new real cracks are initiated. After the peak load, the increasing tendency of the length of the strain-softening region becomes slower at higher CMODs. After real cracks are initiated, the length of the strain-softening region approximately remains constant. As CMOD increases, initially, the beam does not rotate around the cross section in the middle span and then the rotational angle approximately remains constant that is followed by the rotational angle becoming larger and larger. The thickness of the tensile strain localization region is about 3 to 4 times of the element size.