Finite Element Analysis of Casing-Encased Double-Steel-Tube Buckling-Restrained Braces

Based on thin steel plate shear walls， domestic scholars have proposed a lateral force-resisting structural system composed of buckling-restrained braces at the four corners and a central shear steel plate. This system can concentrate the structure’s inelastic deformation within the central energy-dissipating element area， facilitating replacement and reducing post-earthquake repair costs. However， under horizontal loads， the shear steel plates in this system experience significant out-of-plane displacement， which hinders their capacity to fully and stably dissipate seismic energy. To address this issue， improvements have been made to the aforementioned buckling-restrained braces， proposing a casing-encased double-steel-tube buckling-restrained brace. Using the finite element analysis software， seven models of this brace design were subjected to unidirectional and cyclic loading simulations. This study compared the effects of varying parameters， such as inner tube length， outer sleeve length， and the stiffness ratio between the outer sleeve and the inner steel tube， on the numerical simulation results. The results showed that under tensile loading， the outer sleeve and the inner steel tube of the casing-encased double-steel-tube buckling-restrained brace cooperated in bearing the load， while under compressive loading， the outer sleeve separated from the inner steel tube， with only the inner tube providing compressive stiffness. Consequently， the brace’s tensile stiffness and tensile bearing capacity were greater than its compressive stiffness and compressive bearing capacity. This difference became more pronounced with a higher stiffness ratio between the outer sleeve and the inner steel tube. Furthermore， the proposed brace exhibited good ductility and energy dissipation capacity. This casing-encased double-steel-tube buckling-restrained brace can be arranged in a series of composite structural systems similar to cross bracing， which can fully utilize the capacity of the structural system to stably dissipate seismic energy through the lateral displacement of the plane of the self-restrained structure with different tensile and compressive stiffnesses.