Düzce Üniversitesi Bilim ve Teknoloji Dergisi (Jul 2021)
The Effects of Steel Core Imperfection, Gap Size and Friction Coefficient on the Behavior of All-Steel Buckling Restrained Braces
Abstract
Buckling restrained braces (BRBs) which are generally composed of a steel core and a encasing(buckling restrainers) are utilized to resist lateral forces in high seismic regions since BRBs exhibit high energy dissipation capacity, ductility and stiffness. The steel core carries both compressive and tensile forces. During the compression, the core starts buckling and the encasing tries to prevent this buckling. However, due to the unbonding layer/gap between the encasing and steel core, the steel core eventually buckles and contacts with the encasing. Buckling phenomenon is also associated with the initial imperfection and gap size. In this study, the effects of the initial imperfectionof steel core, gap size (1-5 mm)and friction coefficient (0.01-0.5)between the encasing and steel core on the behavior of BRBs are investigated. Pursuant to this goal, numerical analyses using a finite element tool ABAQUS were conducted. A total of 19 numerical models were developed and monotonically loaded. Initial imperfection was implemented to the models using buckling mode shapes.The results revealed that increasing gap size leads to a reduction in load-carrying capacity. It is recommended to keep gap sizes between 1 and 2 mm. On the other hand, initial imperfection does not significantly affect load-carrying capacity and global behavior. However, it was also observed that the fluctuations in load increase as the amplitude of the mode shape and gap size increase. Moreover, the friction coefficient should be kept between 0.01 and 0.05; otherwise, undesired behaviors can be observed.
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