Feasibility of active control of cable-stayed bridges: An insight into Ting Kau bridge

This paper presents a feasibility study of active seismic response control of cable-stayed bridges with reference to the Ting Kau Bridge (TKB). The TKB is a selected as a representative modern cable-stayed bridge for this vibration control study due to its unique features. Two issues explored pertaining to the development of an active structural control system for the TKB: (i) control-oriented modeling of cable-stayed bridges, and (ii) control strategy development. A three-level modeling strategy is proposed for control design and synthesis. The Level I model is a three-dimensional finite element model that accurately depicts the spatial configuration and dynamic properties of the bridge. The Level II model, which is reduced from the Level I model and contains only the so-called important modes, is a modal model used for response prediction, state estimation and control efficacy evaluation. The Level III model that only contains a few dominant modes is used to determine the control law. The scale of the Level II and III models and the selection of important and dominant modes are dependent on the specific bridge and determined through deterministic and random seismic response analysis of the bridge. With regard to control strategy development, the random nature of earthquake excitation is recognized, and a stochastic optimal control scheme, in conjunction with optimal state estimation, is adapted for the active/semi-active control of cable-stayed bridges. The effect of earthquake excitation features (e.g. dominant frequency, damping) can be accounted for in the proposed control strategy. The feasibility of this control strategy for active seismic response mitigation of the TKB is identified.