基于细观模型的含腹筋混凝土梁受剪承载力尺寸效应

考虑混凝土细观非均质性及钢筋与混凝土之间相互作用，建立了钢筋混凝土梁破坏行为模拟的三维细观数值分析模型。以悬臂梁为例，在数值模拟结果与已有试验结果吻合良好的基础上，扩展模拟了腹筋率、剪跨比及加载方式对大尺寸钢筋混凝土梁（最大梁深为2 000 mm）剪切破坏尺寸效应的影响规律。模拟结果表明：无腹筋梁抗剪名义强度尺寸效应显著，中国《混凝土结构设计》规范提出的截面高度影响系数难以全面的反映梁剪切破坏的尺寸效应现象；腹筋会抑制梁抗剪强度的尺寸效应，随着腹筋率的增加，梁的抗剪强度尺寸效应逐渐减弱；随着剪跨比的增加，梁的抗剪承载力有所减弱，同时，尺寸效应现象也略有减弱；相比于单调加载，循环加载下梁将产生低周疲劳脆性破坏，使得梁抗剪强度尺寸效应更加明显。

Meso-scle simulation of size effect in shear capacity of reinforced concrete beams with web reinforcement

A 3D meso-scale simulation model was developed to study the failure behavior of reinforced concrete (RC) beams, in which the concrete heterogeneities and the nonlinear concrete-steel interaction were taken into account. The developed meso-scale simulation method was then validated by comparing the simulation results with the available tests for RC cantilever beams. In addition, the effects of stirrups ratio, shear-span ratio and loading mode on the size effect in shear strength of RC beams with a maximum depth of 2 000 mm were explored. The simulation results indicate that:1) The shear strength of beams without web reinforcement presents obvious size effect, and the influence coefficient of section height proposed by Chinese Code for design of concrete structures cannot fully reflect the size effect of RC beams; 2) The web reinforcements can inhibit size effect on the shear strength of RC beams, and the size effect on shear strength of beams gradually weakens with the increase of stirrups ratio; 3) As the shear-span ratio increases, the shear capacity of the beam decreases, and the size effect becomes to be weakened; 4) Compared with monotonic loading, cyclic loading leads to the low-cyclic fatigue failure of RC beams, and thus it makes the size effect in shear strength more prominent.