Experimental and FE studies on the bonding performance of basalt FRP bonded to notched concrete beams and improving with anchorage

Fiber Reinforced Polymer (FRP) composites have been widely used for the repair and strengthening of the reinforced concrete (RC) structures. One of the main problems encountered in these methods is premature debonding failure of externally bonded FRP strip before reaching the strength capacity. In this study, experimental and finite element (FE) studies have been performed to investigate and improve the bonding performance of FRP strips externally bonded to the notched concrete beam surface. Parameters investigated through the experimental studies are (a) bond length, (c) concrete surface quality, (c) BFRP fan anchor, (d) BFRP U wrap anchor, and (e) a new steel anchor type; and that of numerical studies are (a) bond length, (b) concrete surface quality, and (c) a new steel anchor type. Specimens were tested by four-point flexural test under monotonic loading. The change of crack load, ultimate load, deflections, and failure modes were investigated by the results of the experiment and FE analysis. Then, Parametric studies were performed to determine an effective bond length, an efficient thickness of BFRP strips and an effective steel anchor location. According to the findings from the experimental and FE model study, the debonding failure of the non-anchored specimens is caused by the separation of a few millimeter-thick concrete layers from the concrete surface to which the FRP strips are adhered. The results of the experimental study showed that joining the ends of the BFRP strips with steel anchors increased the load-bearing capacity by 24–26% compared to UW and Fan anchors and by 29–43% compared to non-anchored samples; the developed FE model also confirmed these results. In order to effectively utilize the strength capacity of the BFRP strip, anchoring the end of the strip and evenly distributing the load on the BFRP strip proved to be more effective than solely extending the adhesive length