Behavior of Normal- and High-Strength Confined Concrete

The objective of this study was to evaluate and model the behavior of concrete under triaxial compression using various loading paths and to better understand the mechanism of confinement. A total of 110 cylindrical specimens 54 mm (2.1 in.) in diameter and 110 mm (4.3 in.) long were tested in which variables included unconfined concrete strength, lateral confining pressure, level of damage caused by axial preload, and active or simulated passive confinement. The confined strengths of up to 107, 177, and 314 MPa (15, 26.7, and 45.5 ksi) were observed, respectively, for concretes with unconfined strengths of 36, 84, and 120 MPa (5.2, 12.1, and 17.4 ksi). The results suggest that concrete subjected to axial preloads of up to 80% of unconfined strength can be retrofitted without losing any significant benefits of confinement. Analytical models, essential to model the confinement mechanism, are proposed for dilation behavior of confined normal-strength concretes (NSCs) and high-strength concretes (HSCs) under triaxial compression.