THE BRITTLE FAILURE OF FLUID VISCOUS DAMPERS AND ITS CONSEQUENCES ON THE SAFETY AND RELIABILITY OF STRUCTURES

Fluid Viscous Dampers are efficient passive devices for the seismic protection of structures. Nevertheless, they could be characterized by a brittle failure related to the exceedance of their strength capacity that, once achieved, may strongly affect the behaviour of structures in which such devices are installed. The failure, indeed, can be due to both over-velocity (increase of the force due to an excessive velocity of the piston) and to forces arising after the end-stroke attainment (impact). The breakdown can arise at the design condition and beyond them, leading to a quick transition from a damped behaviour to an undamped one. Moreover, the behaviour of the structure with a reduced number of devices still active can be even worse than the behaviour of the bare frame (without any device). A model able to describe the brittle failure of the devices has been implemented within the OpenSees ambient to evaluate the consequences of the breakdown on the structures. In this paper the model is applied to a benchmark steel frame building whose performance is investigate in terms of global response and seismic risk. Moreover, aiming to reduce the uncertainties related to the design demand of the dissipative devices, different values of amplification factors relevant to both velocity and stroke are also investigated.