Study On The Fracture Performance Of The Three-point Bending Concrete Beam Reinforced With CFRP

Carbon fiber reinforced polymer (CFRP) has been widely used in rehabilitation and strengthening of concrete structures. The scholars in and out have conducted lots of theoretical and experimental studies on the carrying capacity and stiffness of CFRP reinforced concrete beams. Few research has been done on ductility and toughness of reinforced beams.With the development of structural analysis methods, the study on Mechanisms of fracture of concrete has also been widely taken seriously. Based on the former analytical theories, effective fracture toughness and K_R-curves of the reinforced beams are studied in this paper. The following work is carried on in this paper.Firstly, an analytical solution of concrete effective fracture toughness is been deducted. Based on fictitious crack model, this chapter proposes an analytical solution to calculate the effective fracture toughness of three-point bending beams. In the present study, the shape of softening curve in the fictitious crack is simplified to be bilinear. By using the proposed analytical solution, when the elastic modulus E_c and the flexural tensile strength f_r of thebeams are measured, the critical effective crack length a_c,the maximum applied load P_max and the effective fracture toughness K_IC^S can be predicted without any experiment.Then, based on the linear elastic fracture theory and the fictitious crack model, the crack extension fracture performances of standard three-point bending reinforced beams are analyzed experimentally and theoretically in this paper. The crack extension resistance curves (K_R-curves) of reinforced beams can be calculated from P - CMOD curves recorded in the experiment, and a comparison is made between the K_R-curves of the reinforced beams with different heights and different ratios of initial crack to beam height. The results indicate that, there still have the phenomena that the fracture process zone length would decease in the CPRP reinforced concrete beams; the effect of CFRP on crack extension resistance is the key factor in the crack extension resistance performance of CFRP-concrete composite structure; keep the size of the reinforced beams, change the ratio of initial crack to beam height or keep the ratio of initial crack to beam height, change the beams' size, would not influence the crack extension resistance performance.