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该文使用数字图像相关方法实时观测三点弯试验中切口混凝土梁全场变形,分析混凝土梁断裂破坏过程中水平位移和应变的变化规律,基于切口处水平位移和应变变化规律确定起裂荷载,并研究冻融循环次数和纤维掺量对混凝土起裂韧度、失稳韧度、临界开口位移的影响,结果表明:对于C30混凝土而言,起裂韧度和失稳韧度随冻融次数的增加而减小,降幅约为0.6 MPa·m~(1/2)~0.80 MPa·m~(1/2),两种韧度随玄武岩纤维掺量增加有小幅增加,最大增幅分别约为0.1 MPa·m~(1/2)和0.2 MPa·m~(1/2),说明玄武岩纤维能提高C30混凝土的抗冻性,但提高程度是一定的,玄武岩纤维不能完全抑制冻融对混凝土的损伤;纤维掺量对失稳韧度的提高幅度要比起裂韧度大;起裂韧度增益比和失稳韧度增益比都随纤维掺量增加先增大后减小,两种韧度增益比均在纤维掺量为2.0 kg/m~3时最大,因此,在混凝土强度等级为C30时,2.0 kg/m~3可作为最佳纤维掺量;临界开口位移随冻融次数增加而增大,随纤维掺量变化效果不明显,与纤维增强作用相比冻融损伤是影响断裂过程变形性能的主要因素;最后在试验结果的基础上,建立了起裂韧度和失稳韧度随纤维掺量和冻融次数的拟合模型。
In this paper, the digital image correlation method is used to observe the deformation of cut-to-length concrete beams in three-point bending test in real time. The horizontal displacement and strain variation during the failure of the concrete beams are analyzed. Based on the horizontal displacement and strain changes, The effects of the number of freeze-thaw cycles and the fiber content on the fracture initiation toughness, the fracture toughness and the critical displacement of the concrete were studied. The results show that the fracture toughness and the instability toughness of the C30 concrete vary with the number of freeze-thaw cycles The decrease is about 0.6 MPa · m ~ (1/2) ~ 0.80 MPa · m ~ (1/2). The two tenacities increase slightly with the increase of basalt fiber content, and the maximum increases are about 0.1 MPa · m ~ (1/2) and 0.2 MPa · m ~ (1/2) respectively. It indicates that basalt fiber can improve the frost resistance of C30 concrete, but the degree of improvement is certain. Basalt fiber can not completely inhibit the freeze- ; The fiber content increased the instability toughness more than the fracture toughness; the toughness gain ratio and instability toughness gain ratio increased first and then decreased with the increase of fiber content, while two kinds The toughness gain ratio is the largest when the fiber content is 2.0 kg / m ~ 3. Therefore, when the concrete strength When the grade is C30, 2.0 kg / m ~ 3 can be used as the optimal fiber content; the critical opening displacement increases with the increase of the number of freeze-thaw cycles, but the effect of fiber dosage is not obvious. Compared with the fiber reinforcement, The main factors influencing the deformation performance of the fracture process are discussed. Finally, based on the experimental results, a fitting model of fracture toughness and instability toughness with the fiber content and the number of freeze-thaw cycles is established.