Axial Behavior of Concrete Prisms Confined by FRP Laminate and Spike Anchors

Reinforced concrete (RC) buildings constructed before introducing ductile design requirements may exhibit undesirable seismic behavior. One such vulnerability is the lack of confinement to end regions that may lead to nonductile compression failures for RC walls. To overcome this vulnerability, strengthening nonductile RC walls is often required. The addition of confinement to end region concrete can be implemented using carbon fiber-reinforced polymer (FRP) laminate and spike anchors. The main issue encountered when applying this strengthening method is the lack of existing design guidance on this confinement method, due to a lack of experimental data to validate the approach. The objective of this study was to provide the necessary experimental data to quantify the behavior of concrete confined with FRP laminate and spike anchors. Static monotonic axial compression tests were conducted on 46 concrete prisms confined with FRP laminate and spike anchors and the other six unconfined concrete prisms. These prisms represented the end regions of RC walls. The variables investigated for the confined test prisms included anchor spacing, anchor cross-sectional area, and cross-sectional aspect ratio. It shows that peak strength increased significantly with the decrease of anchor spacing and the increase of anchor cross-sectional area. An increase in anchor cross-sectional area had a more considerable influence on the failure strain than a decrease in anchor spacing. The cross-sectional aspect ratio of the prisms had an insignificant impact on failure strain. When gross anchor cross-sectional area was constant in the confinement arrangement, larger peak strength, strain at peak, and failure strain were generally observed in prisms confined with smaller and more closely spaced anchors. Design recommendations were given on the test variables based on test results.