Shear strength of reinforced concrete columns with five-spiral reinforcement

Five-spiral transverse reinforcement for square reinforced concrete columns has been proven to possess a confinement capability superior to that of conventional rectilinear tie reinforcement. The objective of this research is to investigate the shear capacity of five-spiral reinforcement. Large-scale shear-critical five-spiral columns and comparable conventional tied columns were tested using double-curvature lateral cyclic loading. Test results showed that with the same amount and similar yield strengths of shear reinforcement and concrete compressive strengths, the column with five-spiral reinforcement exhibited a slightly lower shear strength than the counterpart tied column. All the five-spiral columns showed a lower speed of strength degradation after the peak load than counterpart tied columns. Failure of the five-spiral column under a high axial load was caused by fracture of the spirals. In contrast, failure of the rectilinear tie reinforcement was caused by premature failure of the hook anchorage. A modified Discrete Computational Shear Strength (DCSS) model was developed in this research for calculating the shear strength of five-spiral reinforcement. Comparison with the test results showed that the modified DCSS model provides conservative estimation of shear strength contributed by five-spiral reinforcement. Moreover, the DCSS model provides a degree of conservatism similar to the code equation for tie reinforcement.