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Because of many advantages over other control systems, semi-active control devices have received considerable attention for applications to civil infrastructures. A variety of different semi-active control devices have been studied for applications to buildings and bridges subject to strong winds and earthquakes. Recently, a new semi-active control device, referred to as the resetable semi-active stiffness damper (RSASD), has been proposed and studied at the University of California, Irvine (UCI). It has been demonstrated by simulation results that such a RSASD is quite effective in protecting civil engineering structures against earthquakes, including detrimental near-field earthquakes. In this paper, full-scale hardware for RSASD is designed and manufactured using pressurized gas. Experimental tests on full-scale RSASDs have been conducted to verify the hysteretic behaviours (energy dissipation characteristics) and the relation between the damper stiffness and the gas pressure. The correlation between the experimental results of the hysteresis loops of RASADs and that of the theoretical ones has been assessed qualitatively. Experimental results further show the linear relation between the gas pressure and the stiffness of the RSASD as theoretically predicted. Finally, shake table tests have also been conducted using an almost full-scale 3-storey steel frame model equipped with full-scale RSASDs at the National Center for Research on Earthquake Engineering (NCREE), Taipei, Taiwan, and the results are presented. Experimental results demonstrate the performance of RSASDs in reducing the responses of the large-scale building model subject to several near-field earthquakes.

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This research aims to investigate the dynamic characteristic of rocking bridge columns subjected to quick release loads. Precast columns anchored by unbonded steel bars at the centre of each column can rock on the foundation surface without inducing any residual deformation after earthquakes. The restoring force of columns relies on gravity load from the superstructure and tensile strength in anchor bars. Radiation damping is evaluated through each impact of column rocking. To validate the theoretical damping proposed by previous researchers, four columns were constructed. Research parameters included steel or plastic materials used as rocking interfaces, area of anchor bars, aspect ratio and size effect of columns. Test results revealed that stocky columns slid apparently in the first impact then rocked, but taller columns rocked with minor slips in the entire motion. And freestanding columns slid significantly in the first impact that led to a higher damping. Radiation damping due to impact in the entire motion for all tests was within 5%.