Behavior and Predictive Model of Large-Scale Externally Bonded FRP Strips Anchored to Reinforced Concrete Structures

Fiber-reinforced polymer (FRP) anchors are known to enhance load transfer and prevent premature debonding in externally bonded fiber-reinforced polymer (EB-FRP) systems, yet experimental data and design guidelines for single- and multianchored EB-FRP systems under realistic field conditions remain limited. This study investigates the structural performance of anchored EB-FRP joints through a three-round experimental program consisting of 48 large-scale single-lap shear tests on reinforced concrete blocks (up to 1,520 × 450 × 150 mm). The program systematically varied anchor configurations, dowel diameters (7–25 mm), anchor spacing (305–1,215 mm), FRP strip thickness (0.5–6 mm), and concrete compressive strength (19.5–36.1 MPa). A 3D digital image correlation system was used to capture full-field strain and slip profiles, anchor engagement, and interfacial debonding. Anchoring substantially improved both load capacity and slip/deformation response. Sequential engagement was observed in multianchor configurations, and failure modes were governed by the capacity ratio between anchor rupture and strip fracture. An empirical simplified multilinear load–slip model was developed to describe debonding, anchor activation, and subsequent tension-cable action, in which the debonded FRP strips behave like a cable transferring load through the anchors. Model predictions showed strong agreement with test data (R2 = 0.86 for peak load and R2 = 0.81 for ultimate slip). Predictive expressions for anchor capacity and debonding strain were also validated. The results provide a validated framework for the performance-based design of anchored EB-FRP joints and offer guidance on anchorage detailing for structural strengthening applications.