Seismic Performance of Steel Dual Systems with BRBs and Moment-Resisting Frames

Buckling-restrained braces (BRBs) are energy dissipation devices which have proven to be very effective in improving the performance of existing and new building frames. However, their post-elastic stiffness may lead to excessive residual deformations in the systems to be protected, and this may cause irreparable damage and jeopardize the capability of withstanding multiple shocks. Previous studies demonstrated that buckling-restrained braced frames (BRBFs) can be used in conjunction with special moment-resisting frames to form a dual system, able to minimize the residual drifts and optimize the performances of the BRBFs. The objective of this present paper is to provide recommendations regarding the proportioning in terms of forces, stiffness and ductility of the two systems. For this purpose, an extensive parametric analysis under the single degree of freedom approximation for the dual system is carried out to shed light on the parameters that control the seismic performance and residual capacity of frames equipped with BRBs. A non-dimensional formulation of the problem allows investigating wide ranges of configurations, including the case of BRBFs and the case of BRBFs forming a dual system with moment-resisting frames. The results of this study provide useful information for the preliminary sizing and the optimal choice of the design parameters of structural systems equipped with BRBs.