A Study of Global Out-of-Plane Stability Model for BRBs Incorporating the Flexural Effects of Restrainers
| Autor: | Li-Wei Chen, 陳力維 |
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| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 106 Buckling-restrained braces (BRBs) have been widely used as cost-effective energy dissipaters for seismic steel buildings. However, several cases of out-of-plane (OOP) instability have been observed from past researches. In a prior research, a BRB specimen installed on first floor buckled with severe flexural deformation along the restrainer and plastic hinges forming at gussets during a full scale two-story RC frame test. Simplified procedures commonly applied could predict the high possibility of the buckling. These procedures are based on three independent stability assessments for the steel casing, the connection and the gusset respectively. Nevertheless, these three separate stability checks do not consider their coupling effects on the overall stability. Furthermore, the procedures appear to be over-simplified, using unreasonable assumptions on the end conditions. Takeuchi et al. proposed a set of advanced procedures to measure the global OOP stability. However, their buckling models cannot predict the aforementioned failure mode. This study adopts Takeuchi’s procedures and proposes a buckling model considering flexural restrainer and gusset rotations. In addition, evaluation methods are developed for FEM analysis in order to compute the gussets’ rotational stiffness and strength, as well as the additional moment demand at gussets caused by OOP end drift and initial imperfection along BRB restrainer. In order to verify the effectiveness of the proposed procedures, four full-scale BRB specimens each of 5.8m long with a 988-kN nominal yielding strength, varying restrainer stiffness, gusset thicknesses, with/without edge stiffeners or OOP drift demands were 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. Edge stiffeners detailed on the gussets’ long sides improved the buckling strength by 9%. The proposed model exhibits an improvement of over 80% in the buckling strength with a 24% enlargement in the restrainer diameter, indicating the critical effects of the restrainer’s flexural stiffness. The deformed shapes of specimens throughout the loading indicate that OOP drift tends to trigger more severe flexural deformation as axial loading increases, leading to a higher buckling potential. In addition, the initial imperfection along BRB restrainer was larger than expected due to improper supporting condition during mortar curing, shipping and handling. The research results can be adopted to improve the practice of BRB frame design. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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