Inelastic Second-Order Analysis for Slender GFRP-Reinforced Concrete Columns: Experimental Investigations and Theoretical Study

Designing reinforced concrete (RC) columns reinforced entirely with fiber-reinforced polymer (FRP) bars requires an explicit definition of the slenderness upper and lower limits for use in code provisions. To date, limited research has focused on experimentally assessing the behavior of slender FRP-reinforced concrete (FRP-RC) columns. Therefore, North American codes and guidelines lack design provisions. This study was conducted to enrich the research database with a total of 20 full-scale columns reinforced with steel or glass FRP (GFRP) bars. The columns were 305 mm in diameter and had slenderness ratios of 14, 19, 23, 26, and 33 were tested under concentric and eccentric loading. The steel-reinforced columns were tested to serve as a benchmark for their GFRP-reinforced concrete (GFRP-RC) counterparts. The interrelated effects between the slenderness ratio and the load eccentricity level were investigated with four different eccentricity-to-diameter ratios of 0%, 16%, 33%, and 66%. Test results proved the efficiency of GFRP bars as internal reinforcement for slender RC columns. The research program was then extended, developing a second-order model for slender FRP-RC columns. A good correlation was observed between the experimental results and the model developed analytically. In addition, based on the stability analysis, it was found that the available design equation for stability failure of steel-reinforced concrete (steel-RC) columns was appropriate and could also be applied to GFRP-RC. Finally, the experimental results and the analytical model indicated that a maximum slenderness limit of 18 was appropriate for short GFRP-RC columns bent in a single curve.