Concept, Tests, and Optimum Design of Novel Negative Stiffness Friction Dampers for Seismic Protection of Long‐Span Bridges

ABSTRACT Viscous dampers (VDs) are widely used to mitigate the excessive responses of long‐span bridges. However, VDs face some intricate challenges in engineering practices, including high damping coefficient requirement, potential base shear amplification and tremendous damping force under high velocity. To address these issues, this study develops a compact, adjustable, and passive negative stiffness friction damper (NSFD), specifically designed for the structural characteristics and vibration features of long‐span bridges, and systematically investigates its control performance on their seismic responses. The concept and working mechanism of the NSFD are first introduced, and its mechanical model is developed. Experimental tests were then conducted on prototype devices, confirming the accuracy of the theoretical mechanical model. Subsequently, a simplified analytical model of a long‐span bridge with the NSFD is established, and an optimum design method is proposed for NSFD. Finally, a finite element (FE) model of a long‐span bridge with NSFD is developed, and the control performance of NSFD is systematically evaluated under natural seismic records. The results demonstrate that the NSFD exhibits pronounced negative stiffness and frictional energy dissipation effects, with its mechanical characteristics easily adjusted through the design parameters of the cam blocks and disc‐spring assemblies; the developed nonlinear model accurately reproduces the mechanical behavior of the NSFD. Moreover, the NSFD could significantly reduce the longitudinal displacement and acceleration of the main girder, while its impact on tower base shear and bending moment remains negligible. Furthermore, the NSFD achieves control performance comparable to that of VDs with high damping levels, offering a promising passive solution for enhancing the seismic resilience of long‐span bridges.