带U型切槽素混凝土梁断裂特性

为了研究U型切槽的深度、切槽根半径以及骨料最大粒径对混凝土材料断裂特性的影响，本文制作了66根跨中带U型切槽的试验梁，包括了4种切槽深度、4种切槽根半径、3种粗骨料最大粒径变化的22组试件。试验采用三点弯曲方式对试验梁进行加载，利用数字图像相关方法获取切槽口张开位移，基于临界距离理论和能量密度准则对试件梁的广义断裂韧度进行分析。研究结果表明：在控制变量的原则下，试件的破坏荷载随着U型切槽深度和根半径的增加而减小，在最大粗骨料粒径为20 mm时最大；切槽口张开位移值与荷载值正相关，同一荷载下，切槽口张开位移值随着切槽深度、根半径以及骨料最大粒径增加而增大。将临界距离理论与能量密度准则得到的广义断裂韧度进行对比，说明临界距离理论可用于计算带U型切槽混凝土梁的断裂韧度及其对应的广义断裂韧度。

Study on fracture characteristics of concrete beams with U-notched

In order to study the influence of U-notched depth, root radius and maximum particle size on the fracture characteristics of concrete, 66 U-notched test beams were designed. They included 22 sets of specimens with four kinds of U-notched depths, four kinds of grooving root radii and three kinds of maximum aggregate. Three-point bending method was used to load the beam, and digital image correlation method was used to obtain the notch mouth opening displacement of the beams. Based on the theory of critical distance and strain energy density, this paper intends to analyze the generalized fracture toughness of the beam. The results show that the failure load of the specimen decreases, with the increase of the U-notched depth and root radius. When the maximum aggregate size is 20 mm, the failure load of the specimen reaches the maximum. The notch mouth opening displacement value is positively correlated with the load. And its value increases with the increase of groove depth, root radius and maximum aggregate size under the same load. The comparison between the theory of critical distance and strain energy density indicates that the theory of critical distance can accurately estimate the fracture toughness of the U-notched concrete beam and the corresponding generalized fracture toughness.