Experimental characterization of nonlinear fluid viscous dampers according to the New European Standard

The paper illustrates the experimental results obtained in several tests performed on different types of Fluid Viscous Dampers (FVDs) differentiated for load capacities, strokes and shapes. The tests were carried out on one unit for each of the three kinds of FVDs used for the structural retrofit of the Engineering Faculty Edifice A of the University of L’Aquila, peculiarly damaged by the earthquake of April 6, 2009. The investigated FVDs are designed to behave in highly non-linear manner, i.e. with the constitutive law F=cv between the reacting force and the imposed velocity, with =0.15. Thus, the dampers provide high damping efficiency within a wide range of operative velocities. In the investigated case the required target constant c are equal to 100, 200 and 400 kN/((m/s)0.15) respectively, for the three types of devices, while the stroke are ± 60 mm, ± 90 mm and ± 130 mm. The use of dampers in a truss-type dissipative interconnection between the facade and the main structure and in the longitudinal coupling of adjacent substructures resulted in the need of devices of different pin-to-pin length, from about 1 m up to about 3.4 m. The longest damper for each type has been subjected to tests, for sake of safety. Both design and tests are according to the European Standard on Anti-seismic Devices EN 15129, that since August 1, 2011 substituted any existing National Standard on the same subject, requiring for CE Marking of anti-seismic devices. In particular, both type and factory production tests have been carried out, including pressure, low velocity, constitutive law, damping efficiency, seal wear and stroke verification tests. The experimental behavior demonstrated very stable cycling at any velocity, and a measured constitutive law fully within the tolerances required by the standard, e.g. ± 15 % in force.