FRP U-Wrap Anchorage for Preventing Concrete Cover Separation: Experimental Study and Design Method

Abstract

Fiber-reinforced polymer (FRP) systems are commonly used in the flexural strengthening of reinforced concrete beams. However, concrete cover separation (CCS) is one of the main debonding failure modes that negatively impact the strengthening efficiency. This premature failure mode occurs at a lower fraction of tensile strain capacity of the longitudinal FRP reinforcement. Placing FRP U-wrap anchorage at the end regions of FRP longitudinal plates appears to be a promising technique that could mitigate or prevent CCS. This study characterized, experimentally, the effect of FRP U-wraps in enhancing the strengthening efficiency by mitigating CCS in FRP-strengthened RC beams. The study included full-scale RC beams strengthened in flexure using FRP sheets and anchored at their ends using FRP U-wraps. The beams were simply supported and tested under four-point bending. The test variables were the width and layout of the FRP U-wraps. The test results indicate the effectiveness of FRP U-wraps in preventing CCS once the required area of U-wrap is provided. The paper also presents a proposed design method for quantifying the minimum area of FRP U-wrap anchorage required to prevent CCS. The proposed design method was verified using the test results obtained from this study and also from a database of beams reported in the literature. Based on the findings of the study, recommendations are suggested for the design of a FRP U-wrap anchorage system that is capable of preventing CCS in FRP-strengthened RC beams.