INFLUENCE OF THE CORE-RESTRAINER CLEARANCE ON THE MECHANICAL PERFORMANCE OF SANDWICH BUCKLING-RESTRAINED BRACES

The out-of-plate clearance between the core member and the restrainer is an important parameter for evaluating the hysteretic performance of a buckling-restrained brace (BRB) and may make a significant impact on its low-cycle fatigue capacity via the friction value of the core member under compression. A theoretical derivation and finite element analysis are conducted on BRBs with various clearances, in which the distribution of the friction and axial strain along the core member is obtained. The results reveal that the contact force between the core member and the restrainer under compression increases with the clearance, leading to increased friction on the contact area of the core member and a nonuniform strain distribution along the core member. Moreover, an experimental study of 8 "sandwich" BRB specimens with different clearances was conducted. The test results indicate that the compression-strength adjustment factor of the BRBs increases with the clearance; moreover, the maximum cycle number under large axial strain is significantly decreased, indicating a lower energy dissipation capacity. Additionally, a higher stiffness demand of the restrainer is needed for an excessively large clearance, which leads to a poor cost performance. In conclusion, a threshold value for the core-restrainer clearance should be proposed, and a determination method is suggested via a formula derivation at the end of this paper. Copyright (C) 2020 by The Hong Kong Institute of Steel Construction. All rights reserved.