Drift capacity of concrete columns reinforced with high-strength steel

The use of high-strength steel bars (having a yield stress of 80 ksi or more) as reinforcement for concrete columns has the potential to reduce steel congestion and lower costs related to transportation and installation of the bars. However, limits on the yield stress of reinforcement have been in place in the United States since 1963. The limits were instated primarily based onthe results of tests of beams and concentrically loaded columns. In this study, high-strength steel is reconsidered for use as reinforcement in concrete columns to resist lateral loads. The focus is on columns designed to resist loads induced by earthquakes.;Eleven column specimens were tested under lateral displacement reversals. Columns reinforced longitudinally with high-strength steel had limiting drift ratios between 4 and 8%. The drift ratios reached by these columns were comparable to drift ratios reached by columns reinforced with steel bars having a nominal yield stress of 60 ksi.;The energy dissipated by columns reinforced with high-strength steel was less than the energy dissipated by columns reinforced with Grade-60 steel. Numerical analyses of models of hypothetical multi-story moment-frame buildings indicate that buildings with columns reinforced with high-strength steel are not likely to experience consistently larger drifts than similar buildings with columns reinforced with Grade-60 steel.;The evidence presented suggests that high-strength steel bars are a viable option for longitudinal reinforcement in columns of multi-story moment-frame buildings designed to resist earthquake motions.