Time-delay effects on the sensitivity and robustness of semi-active TLCD control under far and near field earthquakes

Semi-active structural control systems have attracted increasing attention due to their superior vibration mitigation capability compared with passive systems. However, their effectiveness may deteriorate in the presence of time delays that inevitably occur in real-time applications, particularly depending on earthquake characteristics. This study presents an experimental and numerical investigation of the performance and robustness of a semi-active piston tuned liquid column damper (SP-TLCD) system under near-field and far-field earthquake excitations using several semi-active control strategies. Shaking-table experiments were conducted on a single-degree-of-freedom (SDOF) structure under uncontrolled, passive, and semi-active configurations, while numerical models of the SDOF system and a four-story linear multi-degree-of-freedom (MDOF) structure were employed to systematically investigate time-delay effects. Vibration mitigation performance was evaluated using peak and root mean square (RMS) displacement-based indices. The results indicate that semi-active control strategies generally provide higher RMS vibration reduction than passive control; however, their effectiveness is strongly influenced by the selected control strategy, time delay, and earthquake characteristics. The findings highlight that the performance of semi-active TLCD systems should be evaluated not only under ideal conditions but also in terms of robustness against time-delay and seismic uncertainties. To facilitate such assessment, a simplified index-based framework is proposed that integrates delay sensitivity, record-to-record variability, and adverse-effect risk into a unified robustness evaluation metric.