Nonlinear Vibration Absorber with Pinched Hysteresis: Theory and Experiments

A nonlinear vibration absorber exploiting the pinched hysteresis of mixed wire ropes made of NiTiNOL and steel is proposed. The mixed wire ropes are assembled in a mechanical device which, by bending them, provides the restoring force to the oscillating mass. The assembly of mixed wire ropes, subject to cyclic end displacements, gives rise to a pinched force-displacement behavior due to the simultaneous occurrence of interwire friction and phase transformations. A modified Bouc-Wen model is adopted to represent the pinched hysteresis while the differential evolutionary (DE) algorithm is employed to identify the constitutive parameters that reproduce the experimental force-displacement cycles. The DE algorithm is also utilized to optimize the restoring force of the absorber toward mitigation of the dynamic response of the main structure to external disturbances of various magnitudes. The pinched hysteresis provides an equivalent damping ratio and resonance frequency, which tend to become almost constant in a given oscillation amplitude range, thus overcoming detrimental detuning problems typical of other nonlinear absorbers. The absorber performance is evaluated in the context of a multistory steel building model mounted on a shaking table. The comparison between controlled and uncontrolled responses shows a very good attenuation performance within the design frequency bandwidth.