Buckling-Restrained Braces for Seismic Retrofitting of RC Structures: State-of-the-Art and Critical Review

Many existing reinforced concrete (RC) buildings were constructed before modern seismic design codes were introduced, making them vulnerable to damage during strong earthquakes. Buckling-restrained braces (BRBs) have become an effective retrofitting option because they can dissipate seismic energy through stable yielding under both tension and compression. This paper reviews recent developments in BRB technology, with a focus on mechanical behavior, experimental performance, numerical modeling, and their use in the seismic retrofitting of existing RC structures. The review discusses different BRB systems, including conventional mortar-filled BRBs, all-steel assembled braces, self-centering systems, multi-stage energy dissipation devices, and externally attached precast sub-structures. It also examines important factors that affect cyclic performance, such as core yielding length, friction between the steel core and casing, strain hardening, and low-cycle fatigue. Previous experimental studies have shown that BRBs can improve the lateral strength, stiffness, and energy dissipation capacity of RC frames while reducing deformation demands on vulnerable structural members. However, conventional BRBs may still experience significant residual drifts after strong earthquakes, which has led researchers to develop hybrid and self-centering systems. This review also discusses numerical modeling methods, performance-based design approaches, seismic fragility assessment, and practical difficulties related to BRB installation in existing buildings. Although considerable progress has been made, several challenges remain, including gusset plate instability, connection behavior, fatigue under repeated seismic loading, and force transfer between external retrofitting systems and existing RC frames. Further research is needed to improve large-scale experimental validation, numerical modeling accuracy, and the long-term performance of sustainable and replaceable BRB systems. Overall, this paper summarizes the advantages and limitations of current BRB technologies and identifies areas for future research to improve the seismic safety and resilience of existing RC structures.

Keywords: Buckling-restrained braces (BRBs); Seismic retrofitting; Reinforced concrete structures; Energy dissipation; Hysteretic behavior; Self-centering systems; Seismic resilience.