Seismic Vibration Control of Nonlinear Structures Using the Liquid Column Damper

A design methodology for a variation of the conventional liquid column damper (LCD) (by attaching a spring connection to the LCD) as a seismic vibration control device for structures with nonlinear behavior has been proposed in this paper. The proposed method with the nonconventional damper has the advantage of being applicable to nonlinear structures having high initial stiffness (short natural period) in the linear range below yield with subsequent period lengthening in the postyield phase, where the conventional LCD would be ineffective. The reason for the lack of effectiveness is not only due to the damper parameters designed for the linear structure becoming inapplicable when the structures move to the inelastic regime but also because of the restriction imposed by the high natural period of the conventional damper on its applicability to comparatively stiff structures (for tuning). The methodology in this paper, thereby incorporating the use of a modified model of the LCD system, namely a spring-connected one, removes the requirement on the natural period of the liquid in the LCD and further, the design is based on the parameters of an equivalent linear system for the nonlinear structure. The latter has been represented by a single-degree-of-freedom system with bilinear hysteresis. A procedure for obtaining the equivalent linear system for the nonlinear structure by adopting a temporally averaged linearization technique has been outlined. A few different response parameters known to have damaging effects on structures, such as number/extent of nonlinear excursions of yield level, permanent set, decay of vibration (duration of response), in addition to the reduction in peak response has been the focus of this paper. The efficacy of the proposed method has been examined through simulation studies using recorded accelerograms.