Behavior of large diameter carbon fiber anchors

Abstract

The use of fiber anchors is becoming more commonplace as part of an FRP retrofit of concrete or masonry structures. Such anchors are typically small diameter (sometimes referred to as spike anchors) and are mainly used to delay, or possibly prevent, debonding of externally-bonded FRP laminates. However, capacity prediction models developed for small diameter fiber anchors may not be extended to large carbon fiber (CF) anchors, herein defined as an anchor with a diameter greater than 19 mm. In this study, commercially available 19, 25, and 32 mm diameter CF anchors were tested. First, the behavior of straight CF anchors embedded in concrete under direct tensile loading was examined to obtain the benchmark rupture capacity of the anchors. Embedment depths varied between 10 and 13 times the anchor hole diameter. Then, the behavior of fanned CF anchors under direct tensile load was investigated, considering fan angles of 37 degrees and 57 degrees. Finally, the effect of column bending on the behavior of CF anchors was studied by installing anchors on previously tested large-scale reinforced concrete column-footing subassemblies. It was found that the anchor diameter, anchor fan angle, anchor hole diameter, and embedment depth of the anchor dowel impact the behavior of large diameter CF anchors. Further, confinement of the anchor fan in column applications with hoop direction carbon fiber laminates was found to have a substantial impact on the failure mode of large diameter CF anchors. It was found that for 25 mm diameter CF anchors with a well confined anchor fan, approximately 50% of the straight anchor rupture capacity is possible with a 559 mm long anchor fan with fan angle of 37 degrees and an embedment depth of the anchor dowel 10 times the anchor hole diameter.