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In the semiconductor and liquid crystal display (LCD) industries, suspended ceilings are widely used in wafer and LCD panel fabrication plants (fabs). Despite several preventive measures having been taken, substantial financial losses have been incurred in past earthquakes, with one of the main causes attributed to damage or collapse of ceilings due to excessive ceiling sway during earthquakes. A practical approach of incorporating customised viscous dampers into suspended ceilings to mitigate their seismic response is described in this article. Unlike the convention in most fabs, where diagonal bracing rods are added between suspended ceilings and the structural floor slab to mitigate ceiling vibration, this new approach installs customised viscous dampers in between the ceiling and the column/wall. An analytical model to simulate the vibration of a suspended ceiling was developed. Shake table tests of the ceiling–structure model were then conducted to verify the effectiveness and feasibility of the proposed approach. The results indicated that, when equipped with viscous dampers, the displacement responses of a suspended ceiling can be significantly reduced. Incorporating the dampers into the ceiling with added bracing rods was found to give the best seismic performance. [ABSTRACT FROM AUTHOR]

The vibration responses of tall flexible tool (or equipment) platforms subjected to floor excitations at the platform base are considered more crucial than those of the short ones. This study examined the microvibration control performance of the proposed active piezoelectric mass damper (APMD) or driver for tall platforms subjected to internal automated guided vehicle- (AGV-) induced floor vibrations with larger intensity and broader bandwidth in liquid-crystal-display (LCD) fabrication factories (fabs). The APMD did not require auxiliary spring and damping elements to tune the natural frequency and reduce the stroke of the mass block as required by typical active tuned mass dampers (ATMDs). The motion equation of the proposed analytical model including a continuous three-span beam (or floor) system and an active-controlled tool platform under the action of the AGV moving forces was derived. The APMD, consisting of piezoelectric stacks and a mass block, was installed on the platform subjected to the base rotation excitation, which could be attributed to the uneven vertical floor vibrations induced by AGVs. Moreover, the direct output feedback control algorithm was adopted to determine the optimal feedback gain matrix for calculating the active control force. Time history analyses of the continuous beam-platform model under different AGV weights moving at the same speed were performed, and the corresponding velocity vibration spectra of the floor and platform were further obtained through one-third octave band spectrum analysis. Numerical simulation results revealed that the microvibrations of the platform without APMD generally exceed the VC-A level regardless of the AGV weight. Significant reductions of over 90% on the platform microvibrations could be achieved after the platform was implemented with the APMD, and vibrations met the desired vibration limit (VC-B). Moreover, the APMD exhibits comparable microvibration control performance to the ATMD and requires less mass of the mass block, stroke, and applied voltage under the same active control force. In real-life high-tech production fabs, AGV-induced platform microvibrations occur all the time; therefore, the proposed APMD with less power consumption could be an economical and feasible approach for persistent microvibration control of tall platforms in LCD fabs. [ABSTRACT FROM AUTHOR]