Mitigation of Concrete Cover Separation in Concrete Beams Strengthened with Fiber-reinforced Polymer Composites

Abstract

Strengthening of reinforced concrete (RC) beams using fiber reinforced polymers (FRP) is an effective method that is gaining more acceptance worldwide. However, failure of the strengthened beams at the plate-end region by concrete cover separation (CCS) compromises the effectiveness of such a strengthening system. Among available anchorage systems to remedy such problem, the use of FRP U-wraps at the end region of the externally bonded FRP has the potential to prevent CCS failure. Most studies in the literature suffer from poor design of test specimens and the use of random amounts of FRP anchorage. This resulted in nonconclusive findings and contradicting results on the real effectiveness of FRP U-wraps as an anchorage to prevent plate-end debonding failure. That in turn has been reflected in the lack of reliable design methods for the design of FRP U-wrap anchorage. In this paper, the effect of FRP U-wraps on the mitigation of CCS failure in FRP-strengthened RC beams was experimentally examined and quantified. The study included full-scale RC beams strengthened in flexure using carbon FRP (CFRP) sheets and anchored at the plate-end region using vertical CFRP U-wraps. The test variable was the amount of CFRP U-wrap that is required to achieve complete mitigation of CCS. The test results indicated the effectiveness of FRP U-wraps on mitigating CCS failure once the required area of CFRP U-wrap was placed. Relevant design models were presented and assessed against the experimental results of the current study. The comparisons indicated inaccurate predictions for the area of FRP U-wrap that is required to prevent CCS. This sheds the light on the need for developing a more reliable and accurate method for the design of an end anchorage to prevent CCS failure.