Behavior of Short and Slender RC Columns with BFRP Bars under Axial and Flexural Loads: Experimental and Analytical Investigation

The recently published ACI 440.11-22 code permits the use of glass fiber-reinforced polymer (GFRP) bars as compression reinforcement in concrete columns subjected to combined axial and flexural loads. However, owing to a lack of experimental investigations, there are no current codes specifically for basalt fiber-reinforced polymer (BFRP) reinforced concrete structures. In this study, the behavior of short and slender concrete columns under axial and flexural loads was investigated. Twelve concrete columns were constructed and tested. Test variables were column slenderness ratio (short versus slender columns), eccentricity-to-depth ratio, and reinforcement type (BFRP versus steel). The test results showed the effectiveness of BFRP bars as internal reinforcement in short and slender concrete columns subjected to concentric and eccentric loadings. To generate axial load-moment interaction diagrams, the columns were tested under four different levels of load eccentricity-to-depth ratios of 0, 22.2%, 44.4%, and 66.7%. Regardless of the reinforcement type or slenderness ratio, columns tested under concentric or small eccentricity loadings exhibited a brittle compression-controlled material failure mode, while that tested under high eccentricity loads showed a tension-controlled failure mode. The developed second-order moment is higher in BFRP RC columns than in steel RC columns, this can be attributed to the lower modulus of elasticity of BFRP bars. Subsequently, the research program was expanded to develop an analytical model considering the second-order effects, and then the predicted axial load-moment interaction diagrams by the developed model were verified against experimental test results in the current study and available tested columns in the literature, the verification proved the accuracy of the new model. The findings of this study are an important step toward establishing code guidelines for employing BFRP bars and ties as internal reinforcement in concrete columns.