Extending the Fatigue Life of Reinforced Concrete T-Beams Strengthened in Shear with Externally Bonded FRP: Upgrading versus Repairing

Abstract

Rehabilitation and upgrading of existing civil infrastructures have become a major concern that definitely requires attention. The use of externally bonded carbon-fiber-reinforced polymer (EB-CFRP) to strengthen deficient RC beams has gained in popularity and has become a viable and cost-effective method. Fatigue behavior of RC beams strengthened with fiber-reinforced polymer (FRP) is a complex issue due to the contribution of many variables such as the load range, the applied frequency, and the number of cycles. Very few studies have been conducted in shear under cyclic loading. This study has examined the fatigue performance of RC beams strengthened in shear using EB-CFRP sheets. The investigation involved nine laboratory tests performed on full-size 4,520-mm-long T-beams. The specimens were subjected to fatigue loading up to 6 million load cycles at a rate of 3 Hz. Two retrofit (loading) options (upgrading and repairing) and three different transverse-steel reinforcement ratios (Series S0, S1, and S3 specimens) were considered. Test results were compared with the upper fatigue limits specified by codes and standards. The specimens that did not fail in fatigue were then subjected to static loading up to failure to evaluate their residual capacity. The test results confirmed the feasibility of using the EB-CFRP sheets to extend the fatigue service life of RC T-beams for both loading options. They also revealed that the presence of transverse steel enhanced the fatigue performance of strengthened RC beams. Finally, it was found that the gain contributed by EB-FRP sheets to shear resistance decreased with the addition of internal steel stirrups, confirming the existence of an interaction between transverse-steel reinforcement and EB-FRP.