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Effect of Damping Mechanisms on the Response of Seismically Isolated Structures.
Makris, N.; Chang, S. P.
National Science Foundation, Arlington, VA.; California State Dept. of Transportation, Sacramento. Div. of Structures., November 1998, 78 p.
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In this report the efficiency of various dissipative mechanisms to protect structures from pulse-type and near-source ground motions is examined. It is first shown that under such motions the concept of equivalent linear damping has limited meaning since the transient response of a structure is more sensitive to the nature of the dissipation mechanism, rather than to the amount of energy dissipated per cycle. Subsequently, physically realizable cycloidal pulses are introduced, and their resemblance to recorded near-source ground motions is illustrated. The study uncovers the coherent component of some hear-source acceleration records, and the shaking potential of these records is examined. It is found that the response of structures with relatively low isolation periods is substantially affected by the high frequency fluctuations that override the long duration pulse. Therefore, the concept of seismic isolation is beneficial even for motions that contain a long duration pulse which generates most of the unusually large displacements and velocities of near-source events.
; Damping; Vibration isolators; Earthquake engineering; Vibration damping; Displacement; Mathematical models