Axial compression testing of concrete prisms confined by FRP spike anchors and estimation of failure modes

Abstract

Reinforced concrete (RC) walls can exhibit poor drift capacity and premature concrete crushing if the compression region lacks sufficient confinement. Although fiber-reinforced polymer (FRP) jacketing has been used for confinement, wrapping FRP around the edges becomes challenging when adjacent components obstruct the process. To overcome this issue, a novel solution using FRP spike anchors is proposed in this study. These anchors provide confinement without requiring access to the wall edges, and they are installed by drilling holes through the structures, effectively addressing the obstructions. The study investigates the axially compressive behavior of concrete under this confinement approach. Axial compression tests were conducted on 18 concrete prisms confined with FRP spike anchors in addition to five unconfined concrete prisms. Their height by width by length dimensions were all 360 mm × 150 mm × 150 mm or 360 mm × 150 mm × 200 mm. The variables included anchor spacing and cross-sectional aspect ratio, namely length-to-width ratio. Test results indicate that the strain at peak and the failure strain of the confined concrete was respectively up to 1.85 and 5.28 times the ones of unconfined concrete when anchor spacing was 90 mm. An analytical method was developed to estimate the failure modes of the confined concrete prisms.