Effect of Artificial Saw-Cut Notch Depth on the Bond–Slip Behavior and Modeling of CFRP-to-Concrete Interfaces

Carbon fiber-reinforced polymer (CFRP) composites are widely used for strengthening concrete structures, but the bond behavior of CFRP–concrete interfaces in cracked concrete remains insufficiently understood. This study investigates the effect of saw-cut notch depth on the interfacial bond behavior between CFRP sheets and concrete through double-shear tests. Twelve specimens were prepared with saw-cut notch depths of 0, 10, 20, and 30 mm, where the crack width of the cracked specimens was fixed at 1 mm. The ultimate bearing capacity, CFRP strain transfer behavior, load-relative displacement response, interfacial bond shear stress distribution, and local bond–slip relationship were systematically analyzed. The results show that increasing saw-cut notch depth weakens both the bearing capacity and deformation capacity of the CFRP–concrete interface. Compared with the uncracked specimens, the average ultimate load decreased by approximately 5.0%, 9.2%, and 14.7% for crack depths of 10 mm, 20 mm and 30 mm. Deeper cracks promoted earlier expansion of the CFRP strain transfer region toward the free end and accelerated the development of interfacial relative displacement. The shear stress distribution further indicated that the saw-cut notch altered the interfacial stress transfer path and promoted earlier redistribution of bond shear stress along the bonded length. Based on the experimental results, an empirical normalized curve-shape function was developed to describe the effects of saw-cut notch depth and distance from the notch on the normalized local bond–slip response. Within the present dataset, the calculated curves showed general consistency with the experimental normalized curve trends, particularly in the post-peak descending branch.