Loss-based seismic retrofitting design for existing RC structures considering actual damage states

In recent years, seismic retrofitting design for existing structures has attracted extensive attention from researchers. However, conventional retrofitting approaches are generally based on the assumption of an undamaged original structure and neglect the consideration of economic losses. To address this limitation, a loss-based seismic retrofitting design method for reinforced concrete (RC) structures considering actual damage states is proposed in this study. The proposed framework consists of three parts: (1) conversion from loss demand to displacement demand, (2) conversion from displacement demand to force demand, and (3) customized design of the retrofitted structure. Furthermore, a numerical simulation method for existing RC structures considering their actual damage states is introduced. To facilitate practical engineering applications, an existing RC frame structure is used as an example, in which section enlargement and buckling-restrained brace (BRB) strengthening techniques are adopted for retrofitting. The results indicate that the expected annual losses (EALs) of the retrofitted structures designed using the proposed method are below the target limits across all limit states, demonstrating a significant improvement in seismic performance and fulfillment of the initial design requirements. These findings verify the effectiveness of the proposed loss-based seismic design method for retrofitting existing structures.