Ricerc@Sapienza

The steady-state dynamic response of a structure isolated by a nonlinear wire rope spring operating in the direction of gravity is experimentally studied. The isolated structure consists of two cantilever beams with a lumped mass at the tip. The force-displacement cycles provided by the isolator show a hysteretic behavior due to inter-wire friction and geometric nonlinearities. The restoring force is nonsymmetric exhibiting softening under compression and hardening under tension. The device rheological response is identified using experimental data and a suitable mechanical model. The frequency response curves (FRCs) for increasing levels of the vertical base excitation are obtained for the standalone device, the isolated and non-isolated structure. The expected softening trend of the isolation system and the increase of the displacement amplitude at low frequencies are ascertained both theoretically and experimentally. The comparison between the FRCs of the isolated and the non-isolated structure shows a severe reduction of the transmissibility coefficient in a broad frequency range. This work represents a first step towards the full modeling, validation of the reduced order model of the hysteretic isolator, and the isolated structure towards a full optimization of the device isolation performance.