Fatigue shear performance of RC beams strengthened with SRG and SRP jacketing

Fatigue shear failure of reinforced-concrete (RC) beams is a critical concern for ageing infrastructure, yet experimental evidence on the fatigue effectiveness of U-shaped steel-reinforced grout (SRG) jacketing remains limited. This study experimentally evaluates U-shaped SRG jacketing in RC beams and benchmarks it against steel-reinforced polymer (SRP) jacketing to clarify the role of matrix type under fatigue loading. Eight beams with identical geometry were tested under asymmetric three-point fatigue loading at 4 Hz with a load range of 30–70% of the static peak shear strength. The main variables were the shear span-to-depth ratio ( a / d = 2.0 and 3.5) and textile density (1.57 and 3.14 cords/cm). For a/d = 2.0, the control beam failed at 75 cycles; low-density SRG and SRP increased fatigue life to 227 and 2165 cycles, whereas the high-density SRG specimen failed prematurely at 29 cycles due to limited grout penetration and early loss of composite action. For a/d = 3.5, fatigue life increased markedly, with the control reaching 12,525 cycles, low-density SRG and SRP reaching 21,935 and 60,895 cycles, while the high-density SRG specimen again failed early at 25 cycles, indicating that dense SRG configurations are vulnerable to premature debonding and incomplete composite action in cement-based systems under fatigue loading. Deflection, stiffness degradation, jacket strain and per-cycle energy dissipation exhibited a staged evolution with cycling. Overall, SRG can enhance shear fatigue resistance when adequate impregnation and interfacial engagement are achieved, while SRP provides a more stable response for dense textiles by maintaining composite action under cyclic loading. • Quantified shear fatigue response of RC beams with SRG and SRP jackets. • Stiffness loss and per-cycle energy dissipation were quantified for eight beams. • Most SRG/SRP jackets extended fatigue life; dense SRG limited penetration and life.