Seismic performance of structural systems equipped with buckling-restrained braces

Buckling-restrained braces (BRBs) are often employed for the seismic retrofit of existing systems and the design of new systems given their significant contribution in terms of stiffness and added damping. However, since BRBs are characterized by a low lateral post-elastic stiffness, their use may lead to excessive residual deformations that may jeopardize the reparability of the building. Moreover, accumulation of plastic deformations in the BRBs may endanger the capability of withstanding multiple earthquakes and aftershocks. The objective of this paper is to provide insight into the performance and residual capacity of dual systems made of BRB frames coupled with moment-resisting frames. This study considers a simplified single degree of freedom model which permits to investigate a wide range of configurations. A non-dimensional formulation of the equation of motion is introduced, the statistic of the normalized peak and residual displacements and cumulative ductility of the system is evaluated under a set of ground motion records. Different values of the BRB target maximum ductility and different coupled frame properties are considered. The results of this study provide useful information for the preliminary design of dual systems made of BRB frames coupled with moment-resisting frames