Response time of MR dampers for seismic semiactive control: experimental measures and possible prediction

A wide experimental activity on two prototype magnetorheological (MR) semiactive (SA) dampers manufactured in Germany was conducted during an Italian research project, and it was partially devoted to investigate their promptness in the response. The experimental campaign has been performed on two properly designed setup configurations, by considering two different behaviours for the tested MR devices: a 'passive' behaviour (i.e., by keeping constant the feeding current during the entire test), or a 'semi-active' one, by driving them through an energy-based control algorithm. The experimental analysis of the devices’ response time is presented in detail: it is shown how the control delays are strongly dependent on the effectiveness of the electric part of the control hardware, generally being less than 10 ms if special care is paid in designing the whole control chain. On the base of the experimental results, simple relationships are proposed to be assumed for the prediction of the amount of delay to be expected when a given change of current is going to be commanded, as well as the probability distributions of such delays calculated by fitting statistical available data. These distributions can be helpful for taking into account, in a refined model of a semiactively controlled structure, the probability of occurrence of expected delays and/or to calibrate the compensation techniques included in some SA control algorithms, aiming at reducing the harmful effects these unavoidable delays may cause on the control effectiveness in terms of structural response reduction.