Analytical study on axial compression-Bending interaction behavior of fiber reinforced square concrete columns with GFRP rebars

Fiber-reinforced polymer (FRP) rebars have become an attractive alternative for replacing steel reinforcement due to their superior corrosion resistance. Columns reinforced with GFRP rebars can fail in a brittle manner than those reinforced with steel rebars. Adding discrete fibers in GFRP-reinforced concrete (RC) columns can improve its ductility by bridging the cracks formed in concrete. Both steel and synthetic discrete fibers can be combined to form hybrid fiber-reinforced concrete (HFRC) which synergizes the advantages of both fiber types. An analytical approach is presented here to estimate the axial compression (P) and bending moment (M) interaction behavior of FRC GFRP columns. Moment-curvature analysis using suitable constitutive relations for concrete and GFRP bars under compression and tension is adopted. Bending moment capacity at different axial compression loads is established. Later, P-M interaction curves for square RC columns with GFRP rebars and discrete fibers are obtained and validated with test results. After that, a parametric study is carried out to understand the effect of concrete strength, amount of reinforcement, and different fiber dosages for GFRP RC columns. Results show that adding fibers can improve the bending and compression capacities at all combinations of axial and bending loads. The axial compression and bending capacity of the steel RC and GFRP columns with equal reinforcement ratios showed that GFRP HFRC had higher capacity than steel RC column sections under combined axial and bending loads.