标准钢筋混凝土三点弯曲梁双K断裂特性试验研究

为研究缝高比对钢筋混凝土起裂韧度、失稳韧度等断裂参数的影响，以及钢筋在混凝土裂缝扩张过程中对裂缝的限制作用，设计制作了4组初始缝高比分别为0.2、0.3、0.4、0.5的标准钢筋混凝土三点弯曲梁，对其进行了断裂性能试验研究。根据试验现象分析了裂缝扩展过程，在此基础上建立了断裂韧度计算模型，给出了考虑钢筋限裂作用后的有效裂缝长度计算式。研究结果表明：在引入适应于钢筋混凝土的断裂韧度后，其裂缝扩展过程也可以用双K断裂准则来描述；当试件的初始缝高比大于或等于0.4时，钢筋混凝土三点弯曲梁的起裂断裂韧度和失稳断裂韧度与初始缝高比无关；声发射参量可以准确地确定试件的起裂荷载值，而且与传统的应变片法相比，声发射信号能更好地反映试件内部真实的起裂状态。

Experimental study on double-K fracture characteristics of standard reinforced concrete three-point beam

To study the influence of the crack-depth ratio on reinforced concrete fracture parameters such as the initiation fracture toughness, the unstable fracture toughness and the effect of the reinforcing bar on crack propagation in concrete, four groups three-point bending specimens with initial crack-depth ratios of 0.2, 0.3, 0.4 and 0.5 were designed and constructed. The fracture behavior of the beams was studied in details. A model for calculating fracture toughness of reinforced concrete was developed by analyzing crack propagation process of the three-point bending beams. Formula for calculating effective crack length of reinforced concrete was given. The research results show that crack propagation process of reinforced concrete can be described by double-K criterion after introducing fracture toughness, which is suitable for reinforced concrete. The values of initiation fracture toughness and unstable fracture toughness of reinforced concrete are independent of crack-depth ratio when crack-depth ratio is equal to or greater than 0.4. Acoustic emission parameters can accurately ascertain the crack initiation load of specimens. Compared with traditional stain gauge method, acoustic emission signal can better reflect the true state of fracture-initiation in the specimens.