Experimental Evaluation and Strain-Based Design of Inclined FRP Anchors for RC T-Beam Flexural Strengthening

The use of externally bonded fiber-reinforced polymer (FRP) composites to strengthen RC structures has gained wide adoption due to the favorable mechanical properties and corrosion resistance of FRP materials. A key limitation, however, is intermediate crack-induced (IC) debonding, which often causes premature failure before full FRP utilization. This study examines the role of inclined FRP spike anchors in mitigating IC debonding and improving the flexural performance of RC T-beams strengthened with carbon FRP sheets. Five full-scale T-beams were tested: one control, one strengthened without anchors, and three strengthened and anchored with 16-mm-diameter FRP dowels spaced at 300, 400, and 500 mm. Anchored beams demonstrated marked gains in strength and ductility compared with the unanchored specimen. The best response was achieved with 400 mm spacing, yielding a 28% increase in load capacity and a 113% improvement in midspan deflection. Anchors at 300 and 500 mm spacings provided load increases of 16% and 19%, with deflection gains of 38% and 93%, respectively. All anchored specimens failed by FRP rupture with anchor pullout, indicating that the 100 mm embedment depth may be insufficient. Performance was also influenced by anchor location, because premature pullout occurred when anchors were placed in high-stress regions. The findings confirm that inclined FRP spike anchors enhance strain utilization and delay debonding. Practical implications include guidance on anchor spacing and embedment, alongside a conservative strain-based design formulation for 90° bent anchors in shear spans.