Effect of Reinforcement Parameters on Interface Shear Performance of Thin-Walled NC Structures Strengthened with UHPC

Thin-walled structures are widely used in long-span bridges such as truss composite arch bridges due to their excellent mechanical properties and cost-effectiveness. However, long-term service can lead to defects including interface delamination and concrete carbonation. This study aims to clarify the regulatory mechanism of bonded rebar diameter on the static direct shear performance at the interface of existing normal concrete (NC) thin-walled structures strengthened with ultra-high performance concrete (UHPC). Using mechanical cutting combined with high-pressure water jetting as the interface treatment method, three sets of shear specimens with rebar diameters of 6 mm, 8 mm, and 12 mm were designed. Through static shear tests and nonlinear finite element analysis, the influence of rebar diameter on the shear performance at the interface was systematically examined. Research findings indicated that as the diameter of embedded rebars increases, the primary failure mode at the interface transitions from interface bond failure to NC matrix failure. Furthermore, as the diameter increased from 6 mm to 12 mm, the ultimate shear strength rose from 5.75 MPa to 9.19 MPa, representing a 59.8% increase. The residual strength increased from 1.5 MPa to 3.45 MPa, representing a significant 130% improvement. The failure slip distance increased from 0.35 mm to 0.44 mm, indicating enhanced ductility. Additionally, the established finite element model can accurately predict the mechanical behavior at the interface under different planting rebar diameters, with an error margin of less than 10% compared to experimental results. The research findings provided a theoretical basis for the design of planting rebar parameters in UHPC-strengthened thin-walled concrete structures.