Estimation of Yield Curvature for Direct Displacement-based Seismic Design of RC Columns

Significant research efforts have been devoted in recent years to the development of displacement-based seismic design methodologies, recognizing the shortcomings of traditional, code-specified force-based design procedures. Recent advances in direct displacement-based seismic design of columns rely on the estimates of yield curvature for the determination of seismic design forces to satisfy the specified seismic performance levels. This paper presents simple expressions for estimating the effective yield curvature for normaland high-strength circular reinforced concrete (RC) columns based on moment-curvature analyses of a large number of column sections. Such expressions can be programmed into the spreadsheet format and can be used for the displacement-based design of RC columns. Influence of different parameters on the effective yield curvature has also been quantified. Effective yield curvature is presented in terms of the gross diameter of the section and the yield strain of the longitudinal reinforcement together with three modification factors that take into account the effects of the compressive strength of concrete, the axial load ratio and the quantity of longitudinal reinforcement.