Title: Stress-Strain Relationship of Confined and Unconfined Concrete

Author(s): M. M. Attard and S. Setunge

Publication: Materials Journal

Volume: 93

Issue: 5

Appears on pages(s): 432-442

Keywords: columns (supports); confined concrete; high-strength con-cretes; stress-strain relationships; structural design; triaxial stresses:

DOI: 10.14359/9847

Date: 9/1/1996

Abstract:
Experimentally determined full stress-strain curves from standard triaxial tests are presented. Confining pressures of between I to 20 MPa (14.5 to 29OO psi) were applied. Five mixes were studied using three types of aggre-gates, two of the mixes without silica fume and three with silica fume. The uniaxial compressive strengths varied between 60 to 130 MPa (8700 to 18,855 psi). An analytical model for the full stress-strain relationship for confined and uniaxially loaded concrete is empirically developed and is shown to be applicable to a broad range of concrete strengths between 20 and 130 MPa (2900 to I8,855 psi). The main parameters required to establish the full stress-strain relationship are peak stress, elastic modulus, strain at peak stress, stress and strain at the injection point of the descending curve, and, for confined concrete, the stress and strain at one further point on the descending curve. Empirical expressions for these parameters are developed that are functions of uniaxial compressive strength and level of confinement. Data on the form of the descending curve from the triaxial results is used to extrapolate the descending curve for the uniaxial case. It is argued that the uniaxial descending curve obtained in this manner is a better representation of the softening behavior under uniaxial conditions than that obtained from standard cylinder tests.