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.

本研究以薄钢板剪力墙为基础，国内学者提出了一种由四角屈曲约束支撑（buckling-restrained braces）与中央剪切钢板组成的抗侧力结构体系。该体系可将结构的非弹性变形集中于中央耗能构件区域，便于灾后更换，降低震后修复成本。然而，在水平荷载作用下，该体系中的剪切钢板会产生显著的面外位移，阻碍其充分且稳定地耗散地震能量。为解决该问题，研究人员对前述屈曲约束支撑进行了改进，提出了一种外包式双钢管屈曲约束支撑。借助有限元分析软件，对7组该支撑设计方案的模型开展了单向与循环荷载模拟试验。本研究对比了内管长度、外套筒长度、外套筒与内钢管刚度比等不同参数对数值模拟结果的影响。研究结果表明，在受拉荷载作用下，外包式双钢管屈曲约束支撑的外套筒与内钢管协同受力；而在受压荷载作用下，外套筒与内钢管发生分离，仅内管提供受压刚度。因此，该支撑的受拉刚度与受拉承载力大于其受压刚度与受压承载力，且这一差异随外套筒与内钢管的刚度比升高而愈发显著。此外，该新型支撑展现出良好的延性与耗能能力。该外包式双钢管屈曲约束支撑可应用于类似交叉支撑的一系列复合结构体系中，通过利用自身受拉与受压刚度各异的特性，依托结构平面侧向位移充分发挥体系稳定耗散地震能量的能力。