Seismic behavior of structures equipped with variable friction dissipative (VFD) systems

Usually, to mitigate the stresses in framed structures, different strategies are used. Among them, base isolation, viscous/friction/metallic yielding dampers and tuned mass dumpers have been widely investigated. Fluid Viscous Dampers (FVD) probably result the most diffused for the simplicity in the applications. However, these type of dampers request limited interstorey drifts to avoid dangerous effects. Further, they have an elevate cost. On the contrary, friction dampers are not so expensive but request high interstorey drifts to give a significant contribute in the dissipation of energy during an earthquake. In this paper an approach for the energy dissipation by friction, modified with respect to the usual one, is proposed. The device is a braking system borrowed from the mechanical engineering able to modulate its capability of dissipation, named Variable Friction Damper (VFD). Differently from the Constant Friction Damper, the VFD device investigated in this study provides a specific additional (variable) damping force with the increasing of the displacement. The feasibility of this braking system, the amount of energy that can be dissipated and the overall performances of structures equipped with this type of system are discussed in detail. Finally, dynamic performances of structures equipped with FVD are compared with those obtained by using VFD, highlighting the efficiency of the proposed device.