Spike anchors are one of the most promising techniques to prevent or delay debonding in FRP reinforcement sheets. There are several parameters affecting the anchors' capacity, such as the embedment length and dowel angle. Regardless of the anchors' capacity, their contribution to the overall strength of the anchored joint is affected by a larger number of variables, including the bonded length behind the anchors, the number and arrangement of the anchors, and the contact surface between the anchor fan and the FRP sheet. This paper presents experimental results of 10 tests conducted on concrete beams. In the tests, anchored joints reached peak loads up to 155% of those of unanchored, bonded joints. The main finding of the research is that the bond length in front of and behind the anchors affects both the peak load and the overall behaviour, with unbonded anchored joints exhibiting a poor behaviour and premature slippage of the anchor, without achieving its failure due to fibre rupture.
Keywords: FRP-to-concrete bond; anchorage system; bond length; spike anchors.