Evaluating out-of-plane stability for welded BRBs considering flexural restrainer and gusset rotations
Journal
Journal of Constructional Steel Research
Journal Volume
159
Pages
161-175
Date Issued
2019
Author(s)
Abstract
Buckling-restrained braces (BRB) have been widely used as cost-effective energy dissipators in seismic designs of steel buildings. However, several issues of out-of-plane (OOP) instability have been observed in previous research. The stability evaluation method commonly used in seismic design practice applies three limit states to check the stability of the steel casing, connections, and gussets separately. Nevertheless, they appear to be over-simplified, by adopting unreasonable end conditions and neglecting coupling effects among them. Therefore, this study adapts an advanced stability assessment procedure and proposes a new stability model that considers the flexural deformation of the restrainer, gusset rotations, and the aforementioned coupling effects. In addition, an evaluation method is developed for finite-element model analysis to compute the gussets' rotational stiffness and strength. To verify the effectiveness of the proposed model, four full-scale BRB specimens each 5.8 m long with a 988-kN nominal yielding strength, varying restrainer stiffness, gusset thickness, and with/without edge stiffeners or OOP end drift are tested. The proposed model satisfactorily predicts specimens' failure modes and buckling strengths with errors less than 6%. Test results show a 9% drop in buckling strength due to a 57-mm OOP end drift, highlighting the significant impact from the OOP end drift. The proposed model exhibits an improvement in the buckling strength of over 80% with a 24% enlargement in the restrainer diameter, indicating the critical effects of the restrainer's flexural stiffness. The research results can be adopted to improve the practice of BRB frame design.
Type
journal article