Optimal specifications of inertial mass damper used for building connection system

A vibration control system using building connection is one of the most popular methods in passive structural control of building structures. Most of the previous researches on this subject deal with buildings connected by steel dampers or oil dampers. There is a limited number of papers which deal with buildings connected by inertial mass dampers (IMD). It is well known that IMD has some advantageous properties, i.e. an input reduction effect, a lengthening effect of natural period and a tuning damping effect. While IMD between two buildings does not have the input reduction property, the response of a building with longer natural period can be reduced more effectively than the building connecting by steel dampers or oil dampers due to the lengthening property of natural period and the tuning damping effect. However, many previous researches are based on the frequency-domain formulation using a two-mass connection model and the effects of higher modes and connection height are not always taken into consideration. In addition, there is no research focusing on the energy characteristics of buildings connected by IMD. We propose a substructure tuned-mass-damper (TMD) connection damping system in this paper. In this system, the substructure vibration is synchronized with the main structure by connecting with IMD. It may be difficult to reduce the response transfer function from the height of the so-called fixed point by connecting with oil dampers. On the contrary, it may be possible to reduce the height of the fixed point by connecting with IMD. The purpose of this paper is to clarify the damping effect and the optimal properties of IMD between two buildings. The optimal quantity of IMD is obtained by using the fixed-point theory and the energy analysis for a two-mass connection model and an MDOF connection model. Its validity is verified by time history analysis. IMD between two buildings does not absorb energy, but it transfers energy from the building with longer natural period to the building with shorter natural period. It is shown that too much quantity of IMD makes two buildings getting rigid and an effect of oil dampers parallel to IMD is getting worse. We dealt with multiple analysis models with different connection heights. The numerical analysis showed that the optimal quantity of IMD in the buildings connected at higher levels is larger than that in the buildings connected at lower levels. The optimal quantity of IMD that minimizes the input energy into the main structure is made clear by using the energy-based method for a double impulse (a representative of a pulse-like earthquake ground motion) and a multi-impulse (a representative of long-duration and long-period earthquake ground motion). The maximum response under pulse-like motions cannot be reduced by connecting with IMD. However, the effect of reducing the vibration amplitude after the maximum response is remarkable. In addition, the reduction rate of the maximum response to long-duration and long-period ground motions is large. The energy analysis method can consider the effects of higher modes and the vibration after the maximum response. The optimal quantity of IMD derived by using the energy analysis is shown to be the most effective for the reduction of response especially when connecting at lower levels. It is concluded finally that the method using the energy transfer function is effective for the buildings connected by IMD