Assessment of the Flexural Bond Stresses of New Generation GFRP Bars

Presented By: Jesus Ortiz, University of Miami
As a result of the limited data available when the current ACI 440.11-22 development length equation was developed, certain parameters were disregarded. Additionally, the equation was based on bars that are no longer in use today, and significant advancements have been made in FRP material properties and production methods since its calibration. Conflicting research findings have led to differing perspectives on its reliability, with some suggesting it yields overly conservative results, while others argue it may overestimate bond strength. To address this concern, an experimental study was conducted to assess the bond stresses between GFRP bars and conventional concrete in under-reinforced concrete beams. The beams were reinforced using a single M16 (No.5) Glass/Vinyl-ester FRP sand-coated bar. Three different lap splice lengths (i.e., 40-, 60-, and 80-times bar diameter) were selected based on available literature. The results indicate that the bond is primarily governed by surface friction, with negligible impact from relative slippage. The lap-spliced specimens exhibited slippage failure but exceeded design moments based on ACI provisions, indicating efficient performance. Stiffness remained comparable to that of the un-spliced beam, suggesting intact bond capacity despite some slippage. Average bond stress calculations closely aligned with ACI maximum bond stress values. Overall, the study offers valuable insights into GFRP bar behavior and bond capacity.