INFLUENCE OF CONCRETE TENSILE DUCTILITY ON COMPRESSIVE STRENGTH OF CONFINED COLUMNS

A theory founded on a suitable failure criterion for concrete and on a constitutive law in uniaxial tension derived from the failure criterion is developed for axially loaded confined concrete columns. The influence of the tension-softening behavior of the external concrete shell on the compressive strength of columns is considered, and curves are derived describing the failure axial stress as a function of the tensile strain in the cover. A critical value of the transverse reinforcement percentage is found, for which axial stress and load always increase in the total range of tensile strain. Simple expressions for axial stress and strain and for the corresponding compressive strengths are provided for three particular failure limit states. The experimental comparisons show that for static or quasi-static and for dynamic loading, failure occurs when the tensile peak or ultimate strain values are reached in the cover, while yielding of confining steel is even reached but only in the case of low transverse reinforcement percentages.