Fatigue assessment of non-metallic anchors for post-tensioning CFRP tendons

The utilization of carbon fibre reinforced polymer (CFRP) tendons in post-tensioning applications is hindered by the absence of a reliable anchorage system. The use of conventional anchors developed for steel tendons results in premature failure of the CFRP tendons. This is attributed to the low shear strength of the CFRP tendons being unable to resist the stress concentrations from the sharp corrugations of the conventional wedges as they bite into the CFRP tendon. Other metal anchors require special adaptations to work with FRP tendons, often involving soft metals or resins. Corrosion can be a problem, and the resins creep. Therefore, it was decided to develop a new anchor both metal- and resin-free. With CFRP tendons, the new anchor provides a corrosion-free post-tensioning system. The anchor holds the tendons through mechanical gripping. The anchor components are made of ultra high performance concrete (UHPC) with compressive strength in excess of 200 MPa and reinforced with chopped carbon fibres to provide excellent durability and fracture performance. CFRP sheets are used to provide the required confinement of the anchor barrel. The anchor size needs to be reduced for better use. The experimental assessment of the fatigue strength of the new system is described here. The provisions established by the Post-Tensioning Institute for adequate fatigue performance are used as the acceptance criteria.