Abstract
The objective of this paper is to disclose a limitaion of response spectrum method for maximum earthquake response of connected vibration control structures. In general, higher mode with very large damping factor such as over 40% can be ignored in response spectrum method for maximum earthquake response. However, natural mode with over 100% damping factor (i.e., overdamped mode) of connected vibration control structures sometimes plays a significant role in maximum earthquake response. Simple index of predominance factor of overdamped mode in maximum earthquake response is proposed and a contour map of the index is shown in mass ratio - stiffness ratio plane. The reason why over damped mode of connected vibration control structures sometimes plays a significant role in maximum earthquake response is illustrated with complex natural modes.
