Flexible Frames as Self-Centering Mechanism for Buildings Having Buckling-Restrained Braces

Buckling-restrained braces have been found to be an efficient way to provide seismic-resistance to buildings. In spite of the many structural advantages they offer, several studies have found a lack of ability of buckling-restrained braces to promote a self-centering behavior. Under this circumstance, it has been suggested that the use of this type of braces should be complemented with robust moment-resisting frames with the purpose of reducing residual (permanent) drifts at the end of the main-shock excitation, and thus, the vulnerability of braced frames to aftershocks. Unlike previous studies, the results presented in this paper demonstrate that design strategies can be developed to achieve adequate self-centering behavior of buildings whose structural system is composed of flexible moment-resisting frames and buckling-restrained braces. Particularly, it is concluded that if the flexible frames provide at least one-sixth of the lateral stiffness of the dual structural system while remaining practically undamaged (operational) after the ground motion, the system will exhibit adequate self-centering behavior in spite of the fact that the bracing system may develop significant plastic behavior.