Loading protocols for seismic performance evaluation of buckling-restrained braces in RC frames

The selection of a proper loading protocol for seismic performance evaluation of structural dampers poses quite a challenge at the very first step of quasi-static cyclic tests. Existing loading protocols for buckling-restrained braces (BRBs) are mainly developed on the basis of the seismic responses of BRB-steel frame systems. However, the behavior of a BRB in reinforced concrete frames (RCFs) differs markedly from that in the steel frames. In this study, a set of loading protocols were constructed to provide a reference for seismic performance assessment of BRBs in RCFs. The methodology for the development of loading protocols was illustrated and a series of BRB-RCFs varying in building heights and story shear resisted by BRBs were designed. An extensive analytical investigation of seismic responses of BRBs under far-field, near-fault, and long-duration earthquakes was systematically evaluated and quantified. Based on the rainflow counting method, the control parameters in terms of numbers of cycles, amplitudes, and residual core strains were determined to construct loading sequences. The effectiveness of the proposed loading protocols was discussed and verified through comparisons with existing loading sequences and time-history analysis results of a validated BRB-RCF model. It is indicated that the proposed loading protocols can conservatively reflect the actual seismic damage demands with a reasonable agreement. • The seismic responses of BRBs under different types of earthquakes are systematically evaluated. • A damage index concept is employed to determine critical BRBs. • A set of new loading protocols for BRBs are recommended.