Impact of optimal longitudinal reinforcement on the curvature ductility capacity of reinforced concrete column sections

Abstract

The traditional practice of providing symmetric reinforcement in column cross-sections has been shown to be non-optimal for columns subjected to non-symmetric design loads. An approach for determining a continuum of acceptable combinations of reinforcement by means of a reinforcement sizing diagram (RSD) has been described recently. This approach allows the minimum (or optimal) reinforcement of a cross-section to be determined based on strength considerations. This paper compares the curvature ductility capacity of cross-sections designed with optimal reinforcement to that obtained for cross-sections having symmetric reinforcement, for discrete values of axial load between 0% and 65% of Agfck, where Ag is the gross section area and fck is the concrete compressive strength. Unconfined concrete and confined concrete behaviour are considered, with the latter based on the Mander model, for confinement satisfying the requirements of ACI-318-02 for high seismic zones. The use of non-symmetric longitudinal reinforcement is determined to cause small to moderate changes in the computed curvature ductility capacities relative to the values computed for conventionally reinforced columns.