Title:
Experimental Study on the Effect of Concrete Cover Confinement on GFRP Bars Under Axial Compressive Loading

Authors:
Phattaraphong Ponsorn, Thailand

Abstract:

Glass fiber reinforced polymer (GFRP) bars are increasingly used as reinforcement in concrete structures due to their corrosion resistance; however, limited experimental data exist on how concrete cover confinement influences the compressive behavior of GFRP bars, particularly when compared with conventional steel bars. This study experimentally investigates the effect of concrete cover confinement on the axial compressive capacity of GFRP bars. A total of 54 short column specimens were tested under axial compressive loading, including unconfined GFRP bars, unconfined steel bars, pure concrete specimens, and concrete‑confined GFRP and steel bars. Three bar diameters, 10, 12, and 16 mm, were considered, with varying concrete cover diameters to evaluate the influence of the concrete cover area‑to‑bar area ratio. The test results indicate that concrete confinement significantly enhances the axial compressive capacity of GFRP bars, with the combined strength increasing as the concrete cover thickness increases. For all bar diameters, the ultimate load capacity of concrete‑confined GFRP bars have a trend to exceed the simple summation of the capacities of the individual bar and pure concrete, demonstrating an effective confinement. Comparisons with steel bar specimens reveal that the confinement effect for GFRP bars is generally comparable, although slightly lower in the first and third sets of specimens. Overall, the experiment finds that concrete cover provides some beneficial confinement for GFRP bars under compression, and the effectiveness of this confinement is primarily governed by the ratio of concrete cover area to bar area. The results contribute to the compressive behavior of GFRP‑reinforced concrete and provide useful experimental data for future analytical and design approaches.

DOI: http://dx.doi.org/10.51505/ijaemr.2026.11235