Design method for columns in reinforced-concrete frames with buckling-restrained braces

An improved design procedure for reinforced-concrete (RC) columns in conjunction with buckling-restrained braces (BRBs) in RC-BRBF was developed in this paper for solving the variable axial loading problem induced by BRBs. The proposed method provides a limit value of axial compression ratio for RC columns based on the equivalent axial compression ratio in order to ensure the ultimate lateral displacement capacity of the primary, the secondary, the third and the fourth level of RC columns could reach 2.7%, 2.4% and 2.1%, and provides a recommended ductility factor for RC columns based on the structural ductility capacity in order to achieve satisfactory ductility performance. It is shown that the limit value of axial compression ratio depends on the ultimate drift capacity as expressed by the equivalent axial compression ratio, and the ratio of the characteristic axial forces of the columns under the equivalent gravity and seismic actions, respectively. The improved method could effectively account for the influence of additional variable axial loads on the RC columns connecting to BRB, and ensure that RC columns could reach the limitation of ultimate lateral displacement capacity. The analysis results also reveal that the system economy could be enhanced though optimizing the section dimensions of RC column by the proposed method, and the RC-BRBFs meet 'three seismic fortification levels'. Besides, the limitation of axial compression ratio factor is rational. © 2020, Editorial Office of Journal of Building Structures. All right reserved.