Evaluation on the effect of anchor embedment depth on the flexural capacity of concrete prisms

Abstract

Using fiber-reinforced polymer (FRP) composites to strengthen and retrofit existing reinforced concrete (RC) structures has gained wide acceptance owing to the superior properties of FRPs such as high strength-to-weight ratios and corrosion resistance. Externally bonded FRP (EB-FRP) laminates can be applied to enhance the flexural and shear capacities of RC beams and improve the ductility of RC columns. However, the premature debonding of FRP laminates from the concrete substrate is a major concern and usually results in a brittle member failure. To tackle this issue, many studies proved that adequate anchorage systems could improve the FRP-to-concrete bond, and therefore results in delaying the FRP debonding and further developing the tensile strength of the FRP laminates. One of the most commonly used anchorage systems is FRP spike anchors. Compared to other anchorage systems (for e.g., metallic anchors), FRP anchors have high compatibility with the FRP laminates. In addition, FRP spike anchors are noncorrosive and have high tensile strengths. Although several studies addressed FRP spike anchors in flexural and shear strengthening of RC beams and slabs, the literature still lacks comprehensive information on the effect of all anchor parameters on the performance of the strengthening system. As a result, the aim of this study is to investigate the effect of anchor embedment depth on the behavior, strength, and effectiveness on the FRP spike anchorage system. Six concrete prisms were cast and strengthened with carbon FRP (CFRP) laminates and spike anchors then tested in flexure under four-point bending tests. Test results showed that installing anchored CFRP laminates increased the capacity of the plain concrete prism by 80-120%. Anchoring the laminates at different embedment depths of 50mm, 75mm, 100mm, and 125mm enhanced the capacity of the unanchored prisms by 11%, 13%, 15%, and 33% respectively. Thus, it was concluded that increasing the anchor embedment depths increased the ultimate load carrying capacity of the prisms.