Effective Bond Length of FRP Sheet Bonded to Concrete

Abstract

Fiber-reinforced polymers (FRP) have shown outstanding performance in shear and flexural strengthening of concrete structures when anchored appropriately. However, premature de-bonding failure of the FRP sheet can limit its strength enhancement capacity. Numerous experimental and analytical studies have been carried out to evaluate the effective bond length, but huge discrepancies exist in the results due to a lack of a standard testing procedure and analysis method. Therefore, a specific empirical or analytical equation cannot be adopted to determine the effective bond length. This paper presents the findings from double shear tests conducted to evaluate the effective bond length using the strain distribution profiles. The variables studied were the length of bond, 75–150 mm, and type of FRPs, carbon FRP (CFRP) and glass FRP (GFRP). Test results showed that increasing the bond length beyond the effective length did not increase the failure load but increased deformations mainly due to elastic elongation of de-bonded FRP sheet. Effective bond lengths of approximately 70 and 100 mm were measured for GFRP and CFRP, respectively. Increased FRP stiffness appears to result in a greater effective bond length and higher average bond stress, however, bond slip remain unaffected. A comparative study of the effective bond length models available in different FRP standards was carried out using the current test data along with the database from past studies and a model was proposed to capture the effective bond length. Recommendations are made to modify the current effective bond length model in the CSA-S806-17 standard.