Loading protocols for qualification testing of BRBs considering global performance requirements

The paper presents a research on testing protocols for seismic performance assessment and qualification of buckling-restrained braces (BRBs). The purpose of the study was to propose new loading protocols that consider the most demanding performance requirements available worldwide. In this study, the loading protocols for qualification testing of BRBs prescribed in the codes of four countries/regions, United States, Europe, China, and Japan, plus a non-official Canadian loading protocol, were consulted. The review focused on the background and characteristics, such as the maximum deformation amplitude, deformation range, and number of cycles, of each loading sequence. Then, a database composed of 35 BRB specimens, selected from 16 past experimental studies, was compiled to perform a series of simulations of quasi-static cyclic tests of BRBs under the five different loading histories. The OpenSees platform was used to carry out the modeling, calibration, and analyses. The demands imposed to BRBs were evaluated in terms of cumulative inelastic deformation and cumulative dissipated energy. In addition, the cumulative distribution of the hysteretic energy was defined as a parameter for the assessment of the amplitude-growth rule of the loading protocols. Based on the code review and analyses results, a series of criteria were established and two new loading protocols, GLP-1 and GLP-2, were proposed. Results demonstrated that both proposed loading histories impose superior cumulative inelastic demands and showed a good agreement with the reference cumulative distribution of the hysteretic energy. Thus, they are recommended as loading protocols for BRB qualification testing with global applicability.