PROPOSITION OF SEMI-ACTIVE CONTROLLED TUNED MASS DAMPER ADAPTABLE TO A STRUCTURE'S PERIOD FLUCTUATION

Recently, there have been increasing applications of tuned mass dampers (TMD) to existing high-rise buildings for seismic upgrading against large earthquakes. These devices have the advantages of requiring few construction points, and their influence on users and damage to a building's appearance are minimized. However, most have been applied to steel structures, because RC and SRC structures have the characteristics that cracks are generated under large earthquake loads, which extends their natural periods. Once the natural period is extended, it does not return to its original period, so a TMD with tuning deviation cannot achieve the required damping performance. To use TMDs for structures with period fluctuation, the following two methods have been mainly studied. The first is to install multiple TMDs. This method has the advantage that we can design them as a passive system. However, since all weights are not synchronized to the natural period of the main structure, the damping efficiency is lower than that of a perfectly tuned single TMD. The second method is to configure the TMD with a variable spring and a variable damper, and adapting them to a fluctuating vibration period. In this case, all weight is synchronized to the fluctuating natural period, and the damping efficiency is better than that of multiple TMDs. However, for high-rise buildings, the required weight becomes several thousand tons, and it is too difficult to realize a mechanism that can support the weight stably and change stiffness arbitrarily. This paper proposes a semi-actively controlled TMD that is adaptable to the period fluctuation of the target structure. This TMD consists of two linear springs in series and a semi-active variable damper, and the resonance frequency of the system can be controlled by changing the damping coefficient of the variable damper. After describing the principle of the tuning mechanism using a complex stiffness model, a simple method for determining the system parameters is proposed. The control performance of the proposed TMD is compared with those of conventional systems including multiple TMDs by employing random vibration theory, and its feasibility and potential capability is confirmed. Additionally, to comprehend an acceptable control time lag for transient vibration, a number of time domain analyses for white-noise disturbances are conducted, and the results are summarized statistically.