Research on the bonding performance of TRC composite embedded CFRP bars and the flexural performance of reinforced beams

To improve the flexural performance of beams and compensate for the shortcomings of single reinforcement, this paper proposed a reinforcement method of TRC compound prestressed NSM-CFRP bars. The direct pull-out tests of 21 pull-out specimens and four point bending tests of six beams were carried out, and the effects of the CFRP bar diameter, slot size and bond length on the bonding performance of TRC compound embedded CFRP bars and the effects of the number of TRC layers and slot spacing on the flexural performance of the composite reinforced beams were investigated. The results show that the pull-out specimens have four damage modes: slip damage at the CFRP bar/structural adhesive interface, slip damage at the structural adhesive/concrete interface, splitting failure at the adhesive layer and concrete cracking failure around the slot, which are affected by the slot size, bar diameter and bond length. The average bonding stress and drawing load can be increased with increasing slot size. The drawing load increases with increase in the diameter and bonding length of the CFRP bars, but the average bonding stress decreases due to the uneven stress distribution. An appropriate increase in the number of TRC layers can increase the ultimate load and stiffness of the reinforced beam to a certain extent and reduce the maximum crack width, but too many layers of TRC reinforcement will be more likely to peel off and stop functioning, resulting in a reduction of the load carrying capacity. The slot spacing has no evident effect on the stiffness, bearing capacity and maximum crack width of the beam, but the narrow slot edge spacing will lead to the concrete tensile crack failure at the end of the beam, which is brittle, and can be avoided by reinforcing the ends, The bond-slip model for composite reinforced specimens was derived by fitting the bond-slip equation proposed by Cruz and Barro. Based on the maximum crack width calculation equation for reinforced concrete beams in the code, the maximum crack width calculation equation for composite reinforced beams under normal service limit load is proposed, and the differences between the theoretical and empirically obtained values are found to be small, indicating the good applicability of the calculation model.