Shaking table tests of prestressed damping-isolation units using a spring and rubbers

To improve the seismic performance of suspended ceiling structures, various vibration-damping devices have been developed. However, the devices made of metals have a limit in that they cause large deformation and seriously damages the exterior of the suspended ceiling structure from the wall. As a results, their strengthening effect of the suspended ceiling structure was minimal. Thus, this study employed a spring and vibration-proof rubber effectively controlled vibrations without increasing horizontal seismic loads on the ceiling to enhance the seismic resistance of suspended ceiling structures. The objective of the study is to examine the dynamic properties of a seismic damping-isolation unit (SDI) with various details developed. The developed SDI was composed of a spring, embossed rubbers, and prestressed bolts, which were the main factors enhancing the damping effect. The shaking table tests were performed on eight SDI specimens produced with the number of layers of embossed rubber (ns), presence or absence of a spring, prestressed force magnitude introduced in bolts (fps), and mass weight (Wm) as the main parameters. To identify the enhancement effect of the SDI, the dynamic properties of the control specimen with a conventional hanger bolt were compared to those of the SDI specimens. The SDI specimens were effective in reducing the maximum acceleration (Ac max), acceleration amplification factor (ap), relative displacement (oR), and increasing the damping ratio (f) when compared to the control specimen. The Ac max, ap and fR of the SDI specimens with two rubbers, spring, and fps of 0.1fby, where fby is the yielding strength of the screw bolt were 57.8%, 58.0%, and 61.9% lower than those of the conventional hanger bolt specimens, respectively, resulting in the highest f(=0.127). In addition, the 𝛼𝑝 of the SDI specimens was 50.8% lower than those specified in ASCE 7 and FEMA 356. Consequently, to accurately estimate the 𝛼𝑝 of the SDI specimens, a simple model was proposed based on the functions of fps stiffness constant of the spring (K), Wm, and ns.