Behavior of reinforced concrete columns with double spirals under axial and eccentric loads

To provide reliable lateral confinement in square reinforced concrete columns, a double spiral reinforcement was developed in this study. Sixteen column specimens were tested under axial and eccentric loads to investigate the structural behavior. The test parameters were the concrete strength, spacings of circular spirals, spacings of square spirals, and eccentricity. The failure modes and load-displacement relationships of the specimens were examined. The structural performances including the load-carrying capacity, stiffness, and ductility were analyzed. Results showed that the double spirals were fully developed and provided satisfactory confinement in square reinforced concrete columns under axial and low eccentric loads. The load-carry capacity, stiffness, and ductility of double spirals confined concrete columns were increased compared to those of conventional square reinforced concrete columns. A set of design formulas for the axial and eccentric load-carrying capacity of the double spirals confined concrete columns was proposed. The method can provide satisfactory predictions of the load-carrying capacity.