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为研究三点弯曲混凝土梁挠度δ与裂缝口张开位移CMOD的关系,对五组尺寸相同、强度不同的预制切口梁进行三点弯曲试验,获得加载全过程的P-δ曲线和P-CMOD曲线。由于试验中的P-δ曲线和P-CMOD曲线同步测得,取相同P值下对应的δ值与CMOD值,即可得到一一对应的δ值与CMOD关系。分析表明:δ-CMOD关系可分为非线性和线性两部分,采用数值分析确定两部分的拟合参数;针对混凝土强度的影响,提出各参数关于强度的经验公式。最后,通过对不同批次、相同成分的混凝土断裂能对比分析,证实了本文拟合关系的可靠性。采用本文公式由CMOD计算的断裂能G_F~(P-δ(CMOD))的标准偏差为5.93N/m,远小于由挠度实测值计算的断裂能G_F~(P-δ)的标准偏差21.05N/m,且G_F~(P-δ(CMOD))的平均值更接近已知的混凝土的断裂能。
In order to study the relationship between deflection δ and cracked open displacement CMOD of three-point curved concrete beams, three-point bending tests were conducted on five pre-cut beams with the same size and different strengths to obtain the P-δ curve curve. Since the P-δ curve and the P-CMOD curve in the experiment are measured synchronously, the corresponding δ value and CMOD value under the same P value can be obtained. The results show that the δ-CMOD relationship can be divided into two parts, nonlinear and linear, and the fitting parameters of two parts are determined by numerical analysis. Based on the influence of concrete strength, the empirical formula of each parameter about strength is proposed. Finally, by comparing the fracture energy of concrete with the same composition in different batches, the reliability of the fitting relationship in this paper is verified. The standard deviation of fracture energy G_F ~ (P-δ (CMOD)) calculated by CMOD is 5.93 N / m, which is much smaller than the standard deviation of fracture energy G_F ~ (P-δ) calculated by the deflection measurement of 21.05 N / m, and the average value of G_F ~ (P-δ (CMOD)) is closer to the fracture energy of the known concrete.