Passive and hybrid control systems for seismic protection of a benchmark cable-stayed bridge

In this paper, the effectiveness of passive dampers and a hybrid control system consisting of passive viscous dampers installed in parallel with semi-active dampers is investigated. Recently, the authors proposed an analytical model for long-period pulses in near-field ground motions. The effectiveness of passive dampers is investigated using the analytical pulses model and 44 recorded near-field ground motions. Numerical results show that the pulse model successfully captured the behavior of the bridge subject to near-field ground motions with pulse periods in the vicinity or larger than the fundamental period of the bridge. For this condition, passive dampers are quite effective. However, their effectiveness degrades significantly when the period of pulses is significantly smaller than the fundamental period of the bridge. A nonlinear semi-active controller based on optimal polynomial control theory has been developed for the proposed hybrid control system. In the proposed hybrid control systems, passive dampers continuously reduce the vibration of the bridge. Semi-active dampers are triggered only when the required control force to meet vibration control objectives exceeds the capacity of passive dampers installed in the bridge. Hence, the proposed hybrid control system not only reduces response quantities, but also protects passive dampers by reducing force demand on passive dampers during very strong earthquakes. The performance of the proposed hybrid control system has been investigated using 3 prescribed and 50 other ground motions. Numerical simulation results show that the proposed hybrid control system is quite effective in reducing peak response quantities of the bridge subject to impulsive type near-field ground motions. Simulation results also show that semi-active dampers are triggered only a few times during near-field ground motions. For far-field or long-period ground motions, e.g. Mexico earthquakes, only passive dampers are adequate to meet control objectives. Hence, notable advantages of the proposed hybrid control systems are the reduced use of external energy, lesser heating of the control devices and protection of passive system hardware during strong earthquakes. Copyright (c) 2005 John Wiley & Sons, Ltd.