Control of torsionally asymmetric structures
The effects of near-field earthquakes with large velocity pulses has motivated passive damping requirements for the protection of seismically isolated structures. Structures in which the first mode damping exceeds twenty or thirty percent typically do not exhibit classical modes and simulation via the superposition of uncoupled second order equations is not possible. When the damping effects are created by non-linear mechanisms such as yielding or friction, the behavior of the structure is amplitude dependent and an analysis is commonly carried out in the time domain. In this paper, earthquake time history analyses are applied to study the influence of isolation damping on higher-mode effects and inter-story drift ratios. Because higher mode effects, lateral-torsional coupling, and bi-directional ground motions are all important attributes of the dynamic behavior of these structural systems, a simple comparison of isolation damping mechanisms can not be carried out via simple single or two degree of freedom realizations. So, in order to incorporate realistic details in the study of the dynamic behavior of these structures, and also to provide general conclusions, a set of L-shape planned, 8-story building models with different isolation periods, isolation damping characteristics, and levels of isolation stiffnesses are studied.
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