FRP-to-concrete joint assemblages anchored with multiple FRP anchors

Mechanical anchorage can enhance the strain capacity of externally bonded fibre-reinforced polymer (FRP) composite plates which are used for the strengthening of concrete members. Anchors made from FRP, which are known as FRP anchors or spike anchors, are an effective anchorage because they can be applied to a wide variety of FRP-strengthened structural elements such as beams and slabs. Limited research and understanding of FRP anchors in isolation or in groups is, however, hindering their rational design. As a result of such a knowledge gap, a series of tests is reported in this paper on forty-one FRP-to-concrete joints anchored with single as well as multiple FRP anchors in addition to two unanchored control joints. Apart from the number of anchors, the location of the anchors is investigated in addition to the method of anchor installation. The displacement controlled nature of the tests has enabled the complete load-slip responses of the joints to be captured, as well as FRP plate strains, and such results facilitate valuable insights to be gained in behaviour and understanding. The optimal arrangement of anchors tripled the strength of anchored joints relative to the unanchored control joint average. In addition, the slip capacity was generally increased at least five fold. Finally, a simple analytical model is also presented which is shown to compare reasonably well with the test results.