Use of High-Strength Bars for the Seismic Performance of High-Strength Concrete Columns

To accommodate the ever increasing height of high-rise buildings and required large column-spacing, and assure a high structural performance to supporting elements, use of high-strength materials is sought as a solution. Accordingly, an experimental investigation of the effectiveness of very-high-strength steel bars in improving the performance of ultra-high-strength concrete columns is described. The concrete of 171 MPa strength contained steel fibers. Two grades of high-strength steel bars were used for longitudinal bars in columns. While the SD685-grade is already used in practice, the SD980-grade is still under development. The 1/4 scaled columns were subjected to high levels of compression and tension, and to cyclic lateral loads with an anti-symmetric double curvature bending. The tested columns proved to be ductile and showed good performances. The maximum recorded lateral strength values were at least 30% and 10% greater than those obtained by using ACI and AIJ equations, respectively. The advantage of using steel fibers was apparent by the limited and narrow cracks even at large lateral drifts. It is also suspected to have an impact on preventing buckling of the longitudinal reinforcement. The SD980-grade bars were found very effective in terms of tension axial strength, delay of crack evolution and shear strength degradation, and to be slightly less effective than the SD685 grade bars in terms of shear strength and energy dissipation.