Stress–Strain Relationship of C-Shaped Steel Tube-Confined Concrete Under Axial Compression

Axial compression tests were conducted on four groups of C-shaped steel tube-confined concrete specimens. The results demonstrate that the C-shaped steel tube effectively confines the core concrete, significantly enhancing the peak compressive stress by 14.1% to 22.1% compared to unconfined concrete, resulting in a more gradual descending branch of the stress–strain curve, and effectively improving the ultimate deformation capacity of the concrete with peak strain increasing by a factor of 1.45 to 1.68. The influences of steel plate thickness and reinforcement on the compressive stress–strain curve of the confined concrete were systematically analyzed. Based on the analysis of the strain in the steel tube and the stress state of the confined concrete during testing, a method for calculating the effective confining stress on the core concrete is proposed. A uniaxial compressive stress–strain model for C-shaped steel tube-confined concrete is developed based on the Mander model. Comparisons show that the proposed model agrees well with the experimental stress–strain curves, with predicted peak stresses within 5% of experimental values and predicted peak strains within 7% deviation.