High-strength concrete columns confined by low-volumetric-ratio lateral ties

Presently, test results and stress–strain models for poorly confined high-strength concrete (HSC) columns are in short supply. This is particularly so for columns with a tie volumetric ratio smaller than 2.0%. This paper presents concentric loading test results for square reinforced concrete columns confined by low-volumetric-ratio lateral ties. The test variables included measurements of concrete compressive strength; measurements of tie yield strength; and the tie volumetric ratio. The results showed that high-strength columns under axial compression exhibit less lateral expansion than normal-strength columns do. Further testing confirmed that a bowing of lateral ties in high-strength concrete specimens cannot be observed. Lateral ties of columns consisting of high-strength concrete and higher-grade lateral ties did not yield; additionally, increasing the tie yield strength did not significantly improve the confinement effect. A final finding was that, in columns having nearly the same ρs⋅fsy value, specimens with higher volumetric ratios of a lower-grade tie yield strength performed better than those with lower volumetric ratios of a higher-grade yield strength.