带裂缝服役混凝土结构力学性能的多尺度模拟方法

为了研究既有裂缝及其扩展对服役混凝土结构力学性能的影响，建立了以随机骨料和黏结单元为基础的细观结构黏聚区模型，并进一步建立了带裂缝混凝土梁的一致多尺度等效模型。在开裂区域引入符合牵引分离准则的黏结单元来考虑裂缝的随机扩展，通过随机骨料投放来模拟骨料、砂浆等混凝土的细观结构组成。采用已有试验结果对细观结构黏聚区模型进行了验证，该方法能够模拟混凝土裂缝的随机扩展及其应力-应变全过程曲线。然后，对不同裂缝深度的混凝土试件进行单轴拉伸试验的数值模拟，采用一致多尺度模型对不同裂缝深度的混凝土梁进行模拟，并对其计算效率和精度进行了比较。结果表明：对于初设裂缝深度小于0.3h(h为混凝土试件高度)，试件尺寸对混凝土抗拉强度的影响很小，而当初设裂缝深度大于0.3h时，试件尺寸对混凝土抗拉强度的影响明显；随着初设裂缝深度的增加，混凝土的抗拉强度和弹性模量以及混凝土梁的抗弯刚度、受弯承载力逐渐减小；在不同区域采用不同控制尺度建立的一致多尺度细观结构等效模型能够模拟混凝土梁的裂缝及其随机扩展，并且能在不显著影响其计算效率的情况下保证其计算精度。

Multi scale simulation method of mechanical behaviors of existing concrete structure with crack

A cohesive zone model considering mesoscale structure of concrete was established to investigate influences of existing crack and its propagation on the mechanical behaviour of existing concrete structures. Based on this model, a concurrent multiscale equivalent model for a concrete beam with cracks was developed. The cohesive zone model was used to simulate the random propagation of cracks by inserting cohesive elements following a traction-separation criterion into a random aggregate model, in which mesoscale constitutes, such as aggregates and mortar, were included. This model was validated with experiment results, which was able to simulate the random propagation of cracks and the complete stress-strain curve of concrete. For different crack depths, uniaxial tensile test of specimens and three-point loading tests of concrete beams were separately simulated with the cohesive zone model and the concurrent multiscale equivalent model. Simultaneously, the computational efficiency and accuracy were also analyzed. The results indicate that there is an obvious size effect when the crack depth is larger than 0.3h (h is the height of concrete specimen), while the size effect is very small when the crack depth is less than 0.3h. As the crack depth increases, the tensile strength and elastic modulus of concrete specimens, as well as the flexural stiffness and bearing capacity of concrete beams gradually decrease. The concurrent multiscale equivalent model, in which different regions are controlled by different scales, can accurately simulate the crack and its random propagation in concrete beams without the computational efficiency being significantly affected.