Design considerations based on size effects of anchored carbon fiber reinforced polymer (CFRP) systems

Due to their high strength, limited architectural impact, and speed of installation, externally applied carbon fiber reinforced polymer (CFRP) materials are gaining use in infrastructure rehabilitation. To be effective, CFRP materials must be adequately anchored to develop their full capacity. Many anchorage materials and systems have been proposed for CFRP strips and laminates. CFRP spike anchors can develop the full tensile strength of CFRP strips and offer several advantages over other anchorage methods. Namely, they are easy to install, flexible, which allows them to overcome geometric complications, and resilient to environmental and corrosive factors. However, only a limited number of studies have been conducted on CFRP strips anchored using CFRP anchors. These studies identified clear size effects that influence the strength of CFRP anchors and strips. However, past research was conducted on relatively small anchor and strip systems that are on the low end of practical sizes for infrastructure retrofit and repair applications. The objectives of this study were to investigate size effects in anchored CFRP systems and provide design guidelines for CFRP anchors. Twelve tests were conducted on concrete beams reinforced in flexure with anchored CFRP strips up to 10-in. wide. The primary parameters investigated were: width of CFRP strip, number of layers of fabric in CFRP strips, number of anchors per strip width, ratio of anchor to strip cross-sections, anchor fan overlap length, and chamfer radius of the anchor hole. The full distribution of strains at the surface of the anchored CFRP strips was monitored using an optical measurement system. These measurements helped evaluate the effectiveness of various anchor details in distributing strains across strips. The experimental program confirmed the size effects uncovered in previous studies. CFRP anchors were able to fracture CFRP strips at stresses above the expected and design stresses provided by the manufacturer. However, the larger the CFRP strip area developed per anchor, the lower the stress at fracture of that strip. In addition, the anchor-hole chamfer radius was found to influence both anchor strength and the strain distribution in CFRP strips. Guidelines for designing and detailing CFRP anchors are given based on experimental results.