Experiments and modeling of structural behavior of different BFRP reinforcements in concrete compressive members

Previous investigations have primarily focused on the use of circular basalt fiber reinforced polymer (BFRP) bars in concrete compression members, neglecting the application of these lightweight composites in different structural sections. This study aims to address this research gap by examining the structural efficiency of square concrete compressive members reinforced with various BFRP sections. A total of eight samples were cast, including seven with BFRP angle sections, BFRP plate sections, BFRP tubes, and BFRP circular rebars, and one control sample with conventional steel rebars as the main reinforcement and stainless steel rebars as lateral reinforcement. All samples had a square cross-section of 200 mm width and 1200 mm height, except for the BFRP tube compressive member, which had a cross-section of 180 mm x 180 mm and the same height. The experimental results demonstrated that failure patterns were influenced by the reinforcement material, reinforcement section, and vertical spacing of stainless-steel stirrups. The sample with steel reinforcement exhibited the highest strength of 1451 kN. The ultimate strength reductions for samples with BFRP angle sections, BFRP plate sections, BFRP tubes, and BFRP circular rebars were 22%, 10.3%, 49.6%, and 10%, respectively. The study found that the vertical spacing of ties significantly impacted the load-deflection behavior. For angle section BFRP rebars, increasing the tie spacing from 50 to 100 mm resulted in a 9.50% increase in strength and a 22.20% increase in axial deflection. In contrast, for plate section BFRP rebars, increasing the tie spacing led to a 14.2% decrease in load and a 5.7% decrease in deflection. Members reinforced with BFRP circular rebars showed a 4% decrease in strength and a 13.4% increase in deflection. A finite element analysis (FEA) model was developed to evaluate the structural efficiency of members reinforced with BFRP sections and to conduct a parametric investigation. The concrete damaged plasticity (CDP) model was employed in the FEA to simulate concrete behavior. The proposed FEA model showed discrepancies of 7.2% for the ultimate load and 5.5% for the equivalent deflection and accurately captured crack patterns. Additionally, to compare with theoretical computations, predictions from three international codes were calculated to highlight differences between experimental measurements, FEA results, and theoretical predictions.