Experimental study on the coordinated behavior of the Combined Viscous-Steel Damping System (CVSDS) for multi-level seismic mitigation

Passive energy dissipation devices, such as the viscous fluid damper (VFD) and the steel yielding damper (SYD), are widely adopted to alleviate structural seismic responses. The Combined Viscous-Steel Damping System (CVSDS) is proposed as a hybrid passive damping device for multi-level seismic mitigation. As two components in the CVSDS, VFD, and SYD are adopted to resist frequent and rare earthquakes, respectively. This study aims to investigate and compare the seismic behavior of CVSDS, VFD, and SYD by shake table tests. Seismic excitations with different intensities are applied to a single-degree-of-freedom system. The comparison of displacement and hysteresis behavior is analyzed by time history analysis and Dynamic Time Warping (DTW) method in the time domain. The time-frequency characteristics are explored by the Wavelet Transform (WT) in the frequency domain. The results indicate that the locking function of the CVSDS remains inactive during low-intensity earthquakes, but is triggered during high-intensity ones. Locking depends on the preset locking force and external loads. Both the analyses in the time domain and frequency domain demonstrate that prior to locking, CVSDS and standalone VFD display similar characteristics, but locked CVSDS resembles standalone SYD. CVSDS allows for VFD with smaller tonnage and stronger vibration control capacity. Increased vibration frequency will be observed in the locked CVSDS during strong earthquakes due to the supplementary stiffness of the SYD.