Flexural Strengthening of Reinforced Concrete Beams with FRP Bars Using Near Surface Mounted Technique and Different Anchoring Systems

Reinforced concrete (RC) beams may require flexural strengthening due to the corrosion of reinforcing bars or changes in the design load. The near surface mounted (NSM) and externally bonded (EB) techniques, using fibre-reinforced polymer (FRP) composites, are used for strengthening deficient RC beams. However, RC beams strengthened with both above techniques are susceptible to the debonding failure of the FRP composites. This study proposes innovative anchoring systems for the RC beams strengthened with NSM technique to prevent the premature failure of the NSM-FRP bars, utilising the full strength of the FRP bars and improving the ductility of the RC beams. The anchoring systems include the L-shaped GFRP bar anchor (L-anchor), U-shaped CFRP strips (U-strips) with double plate anchor (DP-anchor), U-shaped CFRP sheet (U-sheet) with GFRP compression anchor, GFRP channels, and GFRP channel strips. This study investigates experimentally and theoretically the efficiency of using anchoring systems for the RC beams strengthened either at the bottom or the sides using the NSM-FRP bars. The main experimental program was conducted to investigate the behaviour of large-scale RC beams strengthened with NSM-FRP technique incorporating different external anchoring systems under four-point bending loads. A total of 15 large-scale RC beams of 200 mm width, 300 mm height and a length of 2400 mm were cast and tested. The RC beams were divided into six groups. The first group included one unstrengthened reference RC beam. The second group included three RC beams strengthened with NSM-GFRP bars with L-anchor at each end. Two RC beams were strengthened with either one or two GFRP bars at the bottom of the beam, and one RC beam was strengthened with one NSM-GFRP bar on each side of the RC beam. The third group included three RC beams strengthened similar to the RC beams of the second group and anchored with U-strips and DP-anchor. The fourth group included three RC beams strengthened similar to the RC beams of the second group and anchored with U-sheet and the GFRP compression anchor. The fifth group included two RC beams strengthened at the sides with one NSM-GFRP bar with L-anchors and externally anchored with either GFRP channels or GFRP channel strips. The sixth group included three RC beams strengthened similar to the RC beams of the second group but using NSM basalt FRP (NSM-BFRP) bars with L-anchors.