Fatigue performance of reinforced concrete beams strengthened with CFRP sheets

The paper presents the results of an experimental and analytical study involving the static and accelerated fatigue testing performance of nine reinforced concrete beams externally strengthened with different number and configuration of CFRP sheets. The beams were tested for the stress ranges of 0.25fy–0.35fy, 0.45fy–0.65fy, 0.65fy–0.90fy, and 0.45fy–0.90fy. After validating a nonlinear finite element analysis (NLFEA) with experimental test results, NLFEA was extended to provide a better understanding of the effect of fatigue stress range, number of CFRP layers, and the CFRP contact area with concrete on the performance of the reinforced concrete (RC) beams. The stress ranges have a significant effect on the permanent deflection at mid-span especially for the stress range of 0.45fy–0.90fy. Cyclic fatigue loading produced a time-dependent redistribution of the stresses that lead to a sudden drop in concrete stresses and a mild increase in steel and CFRP sheet stresses as fatigue life was exhausted. In addition, the authors recommend fatigue design considerations for calculating the reduction in the stiffness and ultimate load capacity due to fatigue loading.

► The stress ranges show an effect on the ultimate strength, stiffness, and permanent deflection.
► The wet-dry cycles in 15% by weight salt-water for 2.5 years has no effect on the fatigue performance.
► There was no sign of debonding or CFRP rupture during the fatigue loading.
► Fatigue loading leads to sudden drop in concrete stress and a mild increase in steel and CFRP sheet.
► The increase in CFRP/Concrete contact area have a considerable decrease on permanent deflection.