The Brittle Failure of Fluid Viscous Dampers and the Related Consequences on the Reliability of a Medium-Rise Steel Building

Damper failures are generally brittle mechanisms, which can compromise the capacity of the structure to withstand the seismic action, leading to a lack of robustness of the overall system. The brittle failure is due to the attainment of the maximum force capacity, because of end-stroke impacts, which causes an arising of the forces, or to an excessive velocity of the piston (over-velocity). Moreover, anti-seismic devices need to be designed with proper safety margins against their failure in order to reach a target safety level. Seismic standards generally prescribe safety factors (reliability factors), that in the case of Fluid Viscous Dampers (FVDs) are applied to stroke and velocity, with values that are not homogenous among seismic codes. The effect of damper failure and different reliability factors on both the fragility and the seismic risk of the structural system is investigated by performing multiple-stripe analysis and monitoring different global and local demand parameters of a medium-rise steel moment-resisting frame building, widely studied in literature, thanks to an advanced model implemented in OpenSees, which considers the brittle mechanism. Moreover, the problem of damper failure is also analysed in terms of fragility functions, providing information about the dependency of the probability of failure with the seismic intensity.