Experimental control of the mechanical properties of pressurized fluid viscous dampers over twenty years after their production.

The stability over time of the mechanical properties of seismic dampers is a fundamental re-quirement to guarantee the maintenance of their protective action on the buildings and in-frastructures where they are installed. This requirement can only be checked experimentally, by repeating at a considerable interval of time the qualification tests carried out on the de-vices immediately after their production. This topic is addressed in the paper, focusing on Pressurized Fluid Viscous (PFV) dampers, which have been the subject of over than twenty-five years of research activities by the first two authors. During the first season of these ac-tivities, several testing campaigns have been developed on various types of PFV devices, which allowed identifying their mechanical characteristics. Some of the experimental inves-tigations carried out in the early 2000s are currently being repeated on the same devices tested at that time. A synthesis of the new laboratory campaign completed on a first pair of PFV spring-damper is presented herein, comparing the results with those of the original qualification tests. The identification process developed on both data sets allows to assess a complete stability of the mechanical properties and response capacities of the examined de-vices over this significantly long-time span.