Experimental Investigation of FRP-Reinforced Concrete Columns Under Concentric and Eccentric Loading

Abstract

The problem of corrosion of steel in reinforced concrete (RC) structures has urged the need for alternative reinforcement materials. One possible alternative is fiber-reinforced polymer (FRP) bars, which are non-corrosive, non-magnetic, and have higher tensile strengths and higher strength-to-weight ratios than steel bars. Nevertheless, owing to the low compressive strength of FRP bars, the currently available FRP RC design codes, such as ACI440.1R-15 and CSA S806-12, neglect the contribution of FRP bars to the columns’ ultimate capacities. In this study, the behavior of concrete columns reinforced with a relatively new type of FRP bars, basalt fiber-reinforced polymer (BFRP) bars, as well as glass fiber-reinforced polymer (GFRP) bars, is investigated. The study starts with a critical literature review on FRP-reinforced concrete columns, followed by analysis of experimental tests conducted on a total of 22 reinforced concrete square columns. The overall response of FRP RC columns is investigated considering several key parameters such as longitudinal reinforcement type (steel, GFRP and BFRP), BFRP longitudinal reinforcement ratio, transverse reinforcement type (steel and BFRP ties), BFRP transverse reinforcement spacing, and loading eccentricity (concentric and eccentric). The results showed that FRP RC columns demonstrated overall compression behavior similar to steel RC columns. Even though FRP RC columns had lower ultimate capacities than steel RC columns, the difference in the ultimate capacities decreased as load eccentricity increased. Moreover, FRP RC columns showed higher ductility than steel RC columns, at all load eccentricities. However, the contribution of FRP bars to the ultimate capacities of the columns was around 11% as compared to 31% for steel bars. Despite this, neglecting the strength contributions of FRP bars, as recommended by current FRP RC design codes, results in conservative predictions of the columns’ ultimate capacities. BFRP ties are found to be efficient in confining the concrete core and in increasing the columns’ deformation capacities. Reducing BFRP ties spacing would have more pronounced effect on confinement efficiency and ductility than on strength capacity of FRP RC columns.