Reconsidering the use of high-strength reinforcement in concrete columns

Current US building codes impose restrictions on the yield stress of steel bars used as longitudinal reinforcement in concrete columns. This paper revisits the origins of these restrictions and investigates the feasibility of using yield stress in excess of 80 ksi (550 MPa) to reduce the amounts of reinforcement required in structures to resist seismic loads. Analytical data from hypothetical cross sections and experimental data from tests are used to demonstrate that for columns with axial loads below the balanced point, the reduction in longitudinal reinforcement is not associated with reductions in strength and limiting curvature. The analytical and experimental results indicate that the reinforcement in a column can be decreased in direct proportion to an increase in yield stress.The evidence presented supports the hypothesis that for columns with low axial load, the use of high-strength bars can lead to reductions in congestion without critical consequences in performance.

► Building codes limit the yield stress of reinforcing bars in concrete columns.
► The use of high-strength bars to reduce longitudinal reinforcement was investigated.
► Focused on columns resisting cyclic lateral loads and low axial loads (<0.3fc′Ag).
► Reduced ratios of high-strength bars provided adequate strength and curvature.