Strong-axis instability of sandwiched buckling restrained braces in a two-story steel X-BRBF: Seismic tests and finite element analyses
Journal
Thin-Walled Structures
Journal Volume
157
Date Issued
2020
Author(s)
Abstract
This work presents tests and finite element analyses of a two-story, buckling-restrained braced frame (BRBF) with BRBs arranged in an X configuration along the building height, called an X-BRBF. The BRB in this work is composed of a core plate sandwiched by a pair of restraining members, called a sandwiched buckling restrained brace (SBRB). The weak axis of the SBRB core is transverse to the dual-gusset-plate connection and the in-plane movement of the frame to eliminate its weak-axis buckling. The objectives of two phase tests were to evaluate: (1) the seismic performance of SBRBs with a small width-to-thickness ratio of the core plate (=3), (2) the effects of free-edge stiffeners on the gusset and SBRB stability, and (3) the SBRB stability associated with beam buckling. All gusset connections had free-edge stiffeners in Phase 1 test, and free-edge stiffeners were removed from half of gusset connections in Phase 2 test. The X-BRBF in Phase 1 test exhibited good performance up to a second-floor drift of 1.6%, but in Phase 2 test the second-floor SBRB, caused by the lateral-torsional buckling (LTB) of the beam, experienced asymmetric buckling about the strong axis of the core at 1.6% second-floor drift. The other SBRB with no beam LTB showed one-side buckling about the strong axis at 2% drift (near an inter-story drift of 2.5%). However, the strength degradation of the specimen was not observed during the strong-axis instability of SBRBs, indicating acceptable orientation for excluding the weak-axis buckling of SBRBs. The strong-axis instability of SBRBs in Phase 2 test could be evaluated by using the stability concept with measured out-of-plane deformation of gusset plates. A nonlinear finite element analysis was conducted on the specimen for further investigation of SBRB instability.
SDGs
Type
journal article