EXPERIMENTAL STUDY ON MECHANICAL BEHAVIOR OF HIGH STRENGTH CONCRETE CONFINED BY HIGH-STRENGTH STIRRUPS UNDER CONCENTRIC LOADING

On the basis of concentric loading tests of 31 HSC columns confined by high-strength stirrups, this paper evaluated the influences of tie yield strength, tie spacing, and tie configuration. The results show that high strength concrete confined by high-strength stirrups exhibits better strength and ductility, and using high-strength stirrups is an effective measure to prevent the stress-strain curve from descending sharply; confined concrete with close spacing, high-strength and complex tie configuration exhibits higher carrying capacity and improved ductility; additionally, with the same value of ρ_v · f_yv, specimens with higher volumetric ratios of ordinary tie yield strength have better performance than those with lower volumetric ratios of high-grade tie yield strength; transverse reinforcement with high strength does not yield at peak strength, thus the high strength can be used as a safety margin to ensure good ductility of confined concrete prior to the ultimate failure. Based on the test data worldwide, the formulas to determine the peak strength and ultimate strain of high-strength concrete confined by high-strength stirrups are proposed.