Performance of reinforced concrete columns confined with spiral reinforcement

The study proposes a practical strengthening method for improving the seismic behavior of reinforced concrete square columns using spiral as lateral reinforcement in moderate seismic zone regions. Two specimens one without ductile detailing and the other with ductile detailing designed as per Indian standard specifications and six specimens with spiral ties (in one direction and cross directions) at 25 degrees, 35 degrees, and 45 degrees of inclination were tested under constant axial load and cyclic lateral loads to study the feasibility of the provision of spiral ties as a seismic-strengthening method. The important variable used was the angle of inclination of the spiral bars. Test results revealed that the column specimen strengthened with cross spirals at 25 degrees had almost similar performance and ductility behavior when compared with the control specimen with ductile detailing and specimen strengthened with cross spirals at 35 degrees had better performance and ductility behavior when compared with the control specimen without ductile detailing and can be adopted in moderate seismic regions. Considering the enhanced behavior, such as the strength, stiffness, and ductility, along with the construction easiness, for better performance of columns in moderate seismic zones, angle of inclination of 35 degrees is sufficient.