Limit states of impact-buffered viscous dampers: A new model and the implications for the seismic fragility of bridges subjected to near-fault pulse-like ground motions

Impact-buffered viscous dampers (IBVDs) have been proposed as an effective solution for vibration control and impact mitigation in bridge engineering. However, the behavior of IBVDs under extreme seismic events remains inadequately understood, particularly regarding their limit states and the subsequent effects on bridge resilience. This study addresses this gap by proposing a new mechanical model that incorporates the limit states of IBVDs. Moreover, the effect of IBVD failure on the seismic fragility of a continuous rigid-frame bridge subjected to near-fault pulse-like ground motions is evaluated. The results of numerical and experimental investigations show that the proposed model effectively captures the mechanical behavior of IBVDs under limit states. Seismic fragility analyses indicate that IBVDs significantly reduce seismic demands and fragility, particularly at low and moderate intensities. However, as seismic intensity increases, the IDA and fragility curves for bridges with IBVDs gradually transition from those of damped to undamped bridges, highlighting the limitations of IBVDs' ultimate capacity. Additionally, when the pulse period of near-fault pulse-like ground motion is close to the structural fundamental period, resonance effects may cause IBVD failure before the seismic intensity reaches the design level.