Challenges in shear strengthening using FRP strips

The effective use of Fiber Reinforced Polymer (FRP) strips for shear strengthening remains a challenge for many applications. This assessment is based on the review of more than 500 beam shear tests in which externally bonded FRP strips were used for strengthening. These tests include a series of 31 new experiments by the authors on large reinforced concrete tee-beams and on prestressed concrete bulb-tee bridge girders. This new experimental research examined the influence of steel transverse reinforcement, pre-cracking, anchorage, FRP rigidity, size, and other factors on the effective strain in the FRP reinforcement to consider in calculating the contribution of this reinforcement. This paper provides a critical review of all acquired test data and then makes a comparative evaluation of 21 relationships that were developed by researchers and/or are used in codes-of-practice to account for the shear strength provided by FRP reinforcement. The result of this examination revealed the strong dependency of FRP effectiveness on beam test details, the difficulty in providing shear strengthening for prestressed bridge beams, and the wide variation in shear strength that is predicted by relationships that have been proposed for this purpose.