Drift capacity of high-strength concrete columns with mixed-grade longitudinal reinforcements

A unique reinforced concrete column design method which aims to improve the ductile behavior of reinforced concrete columns by utilizing various steel grades for longitudinal reinforcements is evaluated in this article. Six large-scale reinforced concrete columns were tested, with the columns subjected to axial load and cyclic forces under reversed bending. The parameters varied in the test program including the axial loading level and the ratio and strength of longitudinal steel reinforcement. It was found from the test results that utilizing longitudinal high-strength steel reinforcement by the ratio of 30%, 50%, and 100% of the total longitudinal reinforcement in a column section will increase the lateral loading drift capacity by 18%, 26%, and 55% on average, respectively. Parametric studies via nonlinear finite-element approach were performed to study the influence of various design parameters on the ultimate drift capacity of reinforced concrete columns. The correlation between the ultimate drift capacity and the confinement level, the axial loading level, and the ratio and grade of longitudinal high-strength reinforcing bars was investigated. Design charts for various ultimate drift levels in terms of other design parameters were developed.