Enhancing seismic performance of brace frame using self-centering friction damper with variable slip stiffness

A novel self-centering friction damper with variable slip stiffness (VSFD) is proposed to achieve ideal selfcentering capability and limit the responses of the brace frame structure under the extremely rarely occurring earthquake (EROE), and its critical difference from the self-centering friction damper with constant slip stiffness (CSFD) is the hardening post-yielding stiffness. Through mechanical analysis, the VSFD exhibits ideal flag-shaped hysteretic behavior with the desired self-centering and energy dissipation capacity. The experimental study confirms that the hysteretic behavior of the VSFD is affected by friction coefficient, slope angle and transverse compressive force. The combination of disc spring stacks with various stiffness can provide variable compressive stiffness for the VSFD. The ratio of the residual sliding load to the initial sliding load increases with precompressive force, and so does the self-centering capacity. The hardening post-yielding stiffness ratio is proportional to the ratio of strong to weak stacks of the disc springs. The displacement corresponding to the hardening point decreases as the preloading weak stacks' deformation capacity decreases. The VSFD can dissipate energy even if the deformation is small, and the damping ratio drops with increasing deformation, precompressive force and compressive stiffness. The updated displacement-based design procedure is proposed and the comparative dynamic time history analysis is conducted for the brace frames with different kinds of braces. The results show that the seismic responses of brace frames with the CSFDs and VSFDs are comparable under the rarely occurring earthquake (ROE), which meet the performance objectives, while the latter has smaller displacement response and larger floor acceleration than the former owing to its hardening post-yielding stiffness. Due to the considerable residual deformation under the ROE and EROE, the response of brace frame with the conventional friction dampers (CFDs) differs dramatically.