Reliability of a r.c. frame equipped with linear and nonlinear fluid viscous dampers.

Retrofit interventions with Fluid Viscous Dampers (FVDs) are efficient to reduce the vulnerability of existing buildings. In particular, external dissipative system based on FVDs are very promising since they present some feasibility advantages with respect to more classic solutions involving devices installed within the existing frames. The response at the design and serviceability conditions of this kind of systems have been widely studied, both in the case of linear and nonlinear devices. The effect of the seismic uncertainty as well as that related to the dampers properties has been also addressed. Conversely, to date, there is a lack of knowledge about the capacity of FVDs and on the safety factors to be assumed to guarantee proper reliability levels. In this paper, as preliminary study aimed to fill the aforesaid gap, a two-story moment resisting frame structure retrofitted with FVDs is considered as case study, and incremental dynamic analyses (IDA) are performed in order to assess the system response under multiple intensity levels. The retrofit intervention consists of external pinned towers equipped by FVDs activated by the rocking motion at the base of the towers. The efficiency of system is investigated, by also modeling the devices’ failure due to the attainment of the end-stroke. The results from IDA show that both the achievement of force or stroke capacities produce the system failure, so their values should be carefully balanced in order to avoid a premature collapse. Further investigations are necessary to assess adequate values for capacity factors to be used in design for device strength and stroke.