Influence of CFRP Spike Anchors on the Performance of Flexural CFRP Sheets Externally Bonded to Concrete

Abstract

Fiber-reinforced polymer (FRP) composites are widely used in the strengthening and retrofitting of reinforced concrete (RC) members to enhance their flexural and shear capacities. Strengthening with FRP systems has been proven effective due to their superior properties such as high strength-to-weight ratio and corrosion resistance. However, the debonding of FRP laminates from the concrete substrate is a major concern as it results in a brittle member failure. Anchorage systems could delay early debonding of the FRP laminates and improve the FRP-to-concrete bond. Carbon FRP (CFRP) spike anchors are commonly used as anchorage systems due to their compatibility with CFRP laminates and versatility to suit a varied range of applications. However, research to study the effects of different anchor parameters on strength enhancement has been limited. Hence, this study investigated the effect of CFRP anchor diameter, embedment depth, and dowel angle on the capacity of concrete beams strengthened with externally bonded CFRP laminates. All beams were tested using the four-point bending flexural test. Test results of anchored strengthened beams showed an increase in load-carrying capacity and CFRP strain utilization of up to 50% and 84%, respectively, when compared to the unanchored strengthened beams. In addition, larger embedment depth and insertion angle showed a significant effect on the capacity of the specimens. Finally, anchoring CFRP laminates with different anchor parameters delayed debonding failure with different anchor failure modes. Increasing the anchor diameter up to 12 mm prevented anchor rupture. Furthermore, increasing the embedment depth increased the beam capacity but resulted in anchor rupture. Anchoring CFRP laminates at large angles shifted the anchor rupture failure to partial anchor pullout. This study demonstrates that CFRP spike anchors, when properly designed and installed, can delay the brittle debonding failure mode, thus enhancing the load-carrying capacity of strengthened members.