vibration mitigation of rail noise barriers by hysteretic absorbers

A strategy is proposed to mitigate the noise barrier vibrations due to the train passage in high speed lines employing a hysteretic vibration absorber. the barrier is modelled as a generalized single degree of freedom system; the absorber consists of a light mass attached to the main structure by a hysteretic element whose restoring force is described by the bouc-wen model. the resulting two degrees of freedom system is studied, and it is shown that, for control purposes, beneficial conditions are obtained when the two oscillators are close to the resonance conditions (1:1). a procedure for a preliminary design of the absorber is highlighted; a parametric analysis varying the absorber characteristics is carried out and the optimal values are obtained by maximizing the barrier response performance. the absorber is then realized exploiting high damping rubber elements whose constitutive parameters have been identified through experimental tests. the effectiveness of the realized absorber is assessed by performing dynamic analysis of the two degrees of freedom system under the train excitation at a reference speed and comparing its performances with those of the designed one, observing a similar reduction of the barrier response. finally, a sensitivity analysis of the performances varying the train speed shows that, even if the stiffness and damping of the absorber are amplitude dependent, its efficiency is confirmed in the speed range of high speed trains.