Title: Flexural Strength and Ductility of Circular Hollow Reinforced Concrete Columns without Confinement on Inside Face

Author(s): F. A. Zahn, R. Park, and M. J. N. Priestley

Publication: Structural Journal

Volume: 87

Issue: 2

Appears on pages(s): 156-166

Keywords: axial loads; bending; columns (supports); ductility; flexural strength; moment-curvature relationship; reinforced concrete; reinforcing steels; spiral reinforcement; tests.

DOI: 10.14359/9295

Date: 3/1/1990

Abstract:
The flexural strength and ductility of circular hollow reinforced concrete columns with one layer of longitudinal and spiral reinforcement placed near the outside face of the section is investigated. Such hollow sections are not confined through the wall thickness. The results of analytical moment-curvature analyses are compared with experimental results obtained from six columns tested subjected to axial compression and cyclically varying lateral load. The experimental results confirmed the analytical prediction that for such columns the available flexural ductility is controlled by the position of the neutral axis at the flexural strength with respect to the unconfined inside face of the section. Columns with low axial load, moderate longitudinal steel percentage, and a reasonably thick wall were found to perform in a ductile manner at the flexural strength, similar to solid columns. However, columns with high axial load, high longitudinal steel percentage, and a thin wall were found to behave in a brittle manner at the flexural strength, since the neutral axis is forced to occur away from the inside face of the tube towards the section centroid and, as a result, crushing of concrete occurs near the unconfined inside face of the section. Design recommendations and example design charts for curvature ductility are presented.