Unified Strength Model for FRP Anchors under Pullout and Concrete-Related Failure Modes

Externally bonded fiber-reinforced polymer (FRP) systems effectively strengthen RC structures but are often limited by interfacial debonding. Fiber-reinforced polymer (FRP) anchors have emerged as a practical solution to bypass this limitation, improving load transfer and overall structural efficiency. Despite the growing acceptance of FRP anchors, the understanding of pullout failure modes remains incomplete, particularly in situations where deep embedment is impractical, such as thin concrete toppings. Differences in manufacturing methods, such as bundled FRP anchors and precured dowel anchors, lead to varying capacity contributions, further complicating their design and application. This study conducted 24 single-lap shear tests on precured shallow-embedded FRP anchors, considering parameters such as concrete compressive strength, insertion angle, embedment depth, and dowel diameter. A unified strength model was developed to predict capacity under mixed concrete pryout and pullout failure modes. Capturing key geometric and material parameters, the model applies to both straight and bent anchors, as well as bundled fiber and precured dowel anchors. Validation against 147 published tests and 139 International Code Council Evaluation Service (ICC-ES)-certified results showed strong agreement (R2 up to 0.94), confirming its reliability across a broad range of configurations and enhancing its suitability for shallow embedment applications. Notably, precured anchors exhibited more consistent performance and higher predictability than bundled anchors, attributed to their uniform manufacturing quality and reduced variability during installation. The results also highlight the significant impact of anchor diameter, embedment length, and insertion angle on pullout capacity, advancing the application of FRP anchors in structural retrofitting, particularly in shallow embedment scenarios.