CONTROL METHOD BASED ON ENERGY ABSORPTION RATE OF SEMI-ACTIVE CONTROLLED TUNED MASS DAMPER ADAPTABLE TO A STRUCTURE’S PERIOD FLUCTUATION

Abstract

In recent years, there have been an increasing number of cases where a tuned mass damper (TMD) has been adopted as a countermeasure against long-period ground motions for steel frame high-rise buildings. They are also used to improve habitability under small and medium earthquakes and strong winds, and their effectiveness has been reported based on observation records. To apply this kind of TMD to reinforced concrete (RC) buildings, it is necessary to consider period fluctuation, because the natural period of a RC structure becomes longer due to cracks generated under a large earthquake, and tuning deviation becomes a serious problem. In order to avoid deterioration of seismic control performance, the authors propose a new configuration of a semi-active tuned mass damper, as shown in Fig. 1. This system is suitable for a semi-active TMD with a large weight since its resonance period can be controlled only by switching the damping coefficient of the variable dampers. In the previous study, we described its principle and design method, and confirmed its response control performance. In this paper we focus on the control method for semi-active TMDs.

Two types of the control methods for the semi-active TMD have been described in previous studies. The first is to tune the TMD to the dominant frequency of the excitation. Nagarajaiah et al. proposed a control method that uses the short time Fourier transform to observe the dominant frequency, and adjust the resonant frequency of the TMD in real time. It is well known that tuning the TMD’s resonant frequency to the excitation frequency is effective when the excitation is a stationary sine wave. However, this control method does not work well under unsteady and wide frequency seismic motions. The second is to tune the TMD to the natural period of the main system estimated by system identification. Hori et al. proposed a control method that identifies the natural period of the building by a least squares method with a forgetting factor using an ARX model. However, in order to obtain appropriate results by system identification, trial and error process is necessary to set appropriate parameters. Therefore, in automatic control, it is impossible to immediately perform appropriate processing of observation records, and it is difficult to apply system identification to seismic control devices that require stability and redundancy.

This paper proposes a new control method that focuses on the absorbed energy by the TMD, and it solves the above mentioned problems. In this method, we set some virtual TMDs that correspond to the control mode of the variable TMD, and select the mode with maximum energy absorption rate. This control method is physically clear, and easy to apply since it needs only one observation point to operate. In this paper, we first present the analytical models and input waves and outline the control methods in previous studies, and discuss their performance. Next, we describe the concept and algorism of the proposed control method. Its principle is explained using time domain analysis, and it is confirmed that the proposed control method is stable against various situations. Finally, the seismic response analyses of simulated RC building model are operated. We confirm the superior response control performance of the Proposed TMD and the proposed control method by comparing it with those of conventional passive TMDs.