Bond strength and load-carrying capacity of GFRP rebars embedded in concrete: An experimental and analytical study

The increasing adoption of glass fiber-reinforced polymer (GFRP) rebars in concrete structures necessitates a thorough understanding of their bond behavior. This research presents an experimental and analytical study focused on the bond behavior and load capacity of GFRP bars embedded in concrete. The experiments investigate the bond behavior of GFRP bars with small diameters of 8 mm, 10 mm, and 12 mm in straight and end-headed configurations. Straight bars exhibited excellent bond performance and load capacity, developing most bond stress at an embedment length of 15 times the bar diameter (15d_b), resulting in the GFRP bars' rupture failure. Conversely, the end-headed bars (i.e., large heads with a length of 100 mm and small heads with a length of 50 mm) for GFRP diameters of 8 mm and 10 mm demonstrated limited efficacy. This finding suggests that end heads may not be a viable option for enhancing the load capacity in small-diameter GFRP bars. Based on the experimental results, a novel equation was proposed to predict average bond stress. In the second phase, the coefficients of the proposed equation were calibrated using data from 275 specimens (80 % of the dataset) extracted from previous studies. This equation incorporated bar diameter, embedment length, and concrete compressive strength while distinguishing between small- and large-diameter GFRP bars. Finally, it was validated against well-established models from different codes and research studies using 69 random specimens (20 % of the dataset) to demonstrate the satisfactory performance of the proposed equation. The proposed equation demonstrated superior predictive capability for load capacity, particularly for small-diameter GFRP bars, achieving the best performance with integral absolute error (IAE) and mean absolute error (MAE) values of 16.9 % and 18.4 %, respectively, compared to other models.