Fiber Reinforced Polymer (FRP) anchors are an effective method to increase the bond strength and/or ensure load path continuity between FRP materials and the concrete substrate when FRP materials are used as Externally Bonded Reinforcement (EBR) to strengthen and/or repair existing structures. While advances in developing a design methodology have been made on the fiber rupture and concrete cone failure modes for FRP anchors, the FRP-to-FRP bond behavior has received limited research attention. In an effort to develop design equations to calculate FRP-to-FRP bond capacity to be used by engineers, an extensive experimental program was undertaken to characterize the behavior of adhesively bonded FRP-to-FRP lap joints. Two force-based models to calculate the FRP-to-FRP bond capacity were proposed considering the influence of the critical bond length on lap joint behavior. A study to characterize the statistical properties of the experimental data was undertaken, and 95 and 99.87 percentile models were developed based on the statistical distribution of the experimental data set. Main conclusions inferred from the study and ideas for future work are also presented.

Introduction

Externally Bonded Fiber Reinforced Polymer (EBR-FRP) systems are widely used as a method for strengthening of existing structures. FRP materials feature a high strength to weight ratio, which is one of the main advantages of using FRP materials to improve the capacity of existing structures. FRP sheets, consisting of a varying number of fiber tows interweaved together, are one of the most commonly used products in EBR-FRP systems. The sheets are saturated with epoxy resins to form a composite matrix and then adhered to the external surface of the structure, but premature debonding of the FRP sheets from the concrete substrate is one of the main drawbacks of EBR-FRP systems [1]. Another common problem is the obstructions caused by structural or nonstructural elements that prevent the complete wrapping of the structure. Both of these problems limit the FRP design strain that the engineers can use when implementing EBR-FRP systems. The use of FRP anchors has been identified as one possible method to minimize premature FRP-to-concrete debonding [2,3], by transferring load from the FRP sheet directly into the RC structure. FRP anchors (as shown in Fig. 1 [4]) consist of a bundle of fibers splayed in a fan shape and bonded onto the FRP sheet at one end, with the bundle of fibers being embedded into the structure at the other end. FRP anchors typically feature a high concentration of stresses at the section where the fan transitions into the dowel, commonly known as the key portion of the anchor.