Tied Concrete Columns under Axial Load and Flexure

Fifteen 12‐in. (305 mm) square and 9‐ft (2.74 m) long reinforced concrete columns were tested under flexure to large inelastic deformations while simultaneously subjected to constant axial load. The main purpose of this research was to investigate the behavior of column sections confined by rectilinear ties. Major variables considered in this program included: (1) Distribution of longitudinal and lateral steel, including unsupported longitudinal bars and supplementary cross‐ties with 90° hooks; (2) level of axial load (0.46fc′Ag to 0.78fc′Ag); (3) amount of lateral steel (0.8% to 1.6% of core volume), and (4) spacing of ties (2‐1/8 in. to 6‐13/16 in. 54–173 mm). Test results indicate that a larger number of laterally supported longitudinal bars results in better performance of columns. Unsupported longitudinal bars and cross‐ties with 90° hooks confine concrete effectively only at small deformations and result in rapid deterioration of column behavior at a later stage, particularly under high axial load levels. The amount of lateral steel and the level of axial load have significant effects on the column behavior.