Advances in FPR anchoring systems for externally bonded carbon fibre reinforcements

The use of fibre-reinforce polymers (FRPs) to strengthen and repair existing reinforced concrete structures has notably increased in recent years thanks to the great advantages of these materials. One of the limitation of this technology though is its premature delamination from the substrate. Different existing codes for designing FRP reinforcements have considered this limitation and usually express it in terms of either the maximum deformation or maximum adhesion strength, which depends on different parameters including the substrate strength, the reinforcement width and thickness, and the fibre type. Several anchorage techniques have been developed to prevent or delay debonding failure, among which anchors made from fibre ropes or rolled sheets (known as FRP or spike anchors) have demonstrated to considerably enhance the joint strength ([1], [2]). To date, different existing guidelines for FRP reinforcements point to the improvement that can be achieved with such anchoring systems; however, their use in rehabilitation projects is still subject to tests that demonstrate their proper functioning as there is a lack of knowledge regarding the parameters involved in their behaviour. In order to characterise the anchor behaviour numerous experimental studies that include pull-out tests on isolates connectors ([3], [4]) shear tests on isolated anchors [5], and chiefly, shear tests on anchored joints ([5], [6], [7], [8], [9], [10], [11]) have been carried out. Most experimental studies to date have been conducted with hand-made anchors from rolled fibre sheets. With respect to manufacturing and installation, it is possible to distinguish between wet installed and pre-cured anchors. The main difference between these systems is the moment at which the portion of sheet that is going to be embedded is impregnated with respect to the moment of anchor insertion. Precured anchors have been used by authors such as Ozdemir [3], and Eshwar [4], while Orton [14], Niemitz [15], McGuirk and Breña [16] used fresh installation technique. The results of the tests realized on isolated connectors allowed the identification of the most critical parameters that affect the strength of the anchors themselves which include the embedded length, angle dowel and bending radius. As shear tests represent the maximum stresses for the adherent mechanism of the FRP-support interface, their results allow the study of the support-laminate interaction. The conclusions drawn by the authors mentioned defined that the geometry of the perforation as well as that of the anchor itself are decisive in the anchored joint behaviour. Regarding the embedded region of the anchor, the main variables are the anchor diameter, the embedded depth, drilling diameter and dowel angle. Parameters related with the anchor-to-reinforcement connection like the fan angle, the 107 bonded length and the anchor position with respect to the loaded end have also been proved to influence the behaviour of the anchored joint. This document collects recent advances in FRP anchoring systems. It also presents the configuration of an optimized connector manufactured from carbon fibre ropes based on the results of a previous investigation that serves as the basis for the experimental campaign that the authors are currently carrying out.