Delayed-Action Mechanism of Buckling-Restrained Brace Using Gusset Plates with Multiple Slot Holes

Previous research has indicated that buckling-restrained braces (BRBs) increase the lateral story stiffness, resulting in a shortening of the natural period, which leads to an increase in the seismic input into the buildings, especially in high-rise buildings. Additionally, research has also revealed that the long-period seismic motions with a long duration possibly induce a difficulty to ensure the toughness of the BRB members, owing to the large cumulative strains caused by the repeated axial forces. To overcome these issues, this paper proposed a displacement-restraint buckling-restrained brace (DR-BRB) in which no axial force appears initially, and the axial force occurs with a delay under the designated vibration amplitude. Therefore, the natural period can maintain the same level as the moment frame. This study performed five cyclic loading tests to reveal the delayed-action mechanism of BRBs, using gusset plates with multiple slot holes. The test results confirmed that the designated starting point of the brace action is accurate, and the hysteretic behavior of the brace is good. Furthermore, the design equations of the joints were formulated and verified through the test results. Finally, the joint behavior and validity of the proposed design equations were verified by finite element analyses for the single bolt model and the overall joint model.

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