Analytical Assessment of FRP Confined Circular Reinforced Concrete Sections under Concentric Axial Compression

Abstract

Purpose: This analytical study compares confinement equations for a 400 mm circular reinforced concrete section with eight D16 bars, assumed CFRP or GFRP wraps, and concrete strengths of 20, 25, and 30 MPa. Methods: Thirty input combinations represent 27 unique conditions. Lam–Teng results are compared with explicitly labeled ACI 440.2R-17 evaluations, including its minimum confinement-ratio criterion. Results: At 25 MPa, two to four CFRP layers increase predicted concrete strength by 45.6–91.3% and ideal section capacity by 36.3–72.6% in the adopted Lam–Teng implementation. The one-layer ratio is 0.069138, below its 0.07 strength-gain threshold; the retained flat-branch idealization gives no strength increase but a higher terminal axial strain. All six one-layer ACI cases are below the 0.08 ratio criterion and are excluded from strengthening-capacity conclusions. For ratio-qualified cases at 25 MPa, ACI strength values are 4.0–6.2% lower. With a peak concrete strain of 0.002, its terminal strain rises from 8.8‰ at two layers to 10.0‰ at three layers and remains capped at four layers. For the matched 25 MPa four-layer input systems, GFRP terminal strain is 13.33% higher than CFRP. Conclusion: This difference is conditional on the assumed material properties. Reproducible calculations and threshold sensitivity are supplied; the study does not establish experimental accuracy, cyclic seismic performance, or an economic optimum.