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control strategy. Model reduction is necessary to achieve a reduced-order model suitable for control
design purpose. Based on both modal analysis and observability/controllability evaluation, a controloriented,
reduced-order model for the 1KB has been formulated (Ni et al 200Ib). The proposed
modeling strategy consists of three level models. The Level I model is the three-dimensional finite
element model that aims to depict 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 mode-space model used for response prediction, state estimation and control efficacy
evaluation. The Level III model containing only limited dominant modes is used for control synthesis
and analysis. The scale of the Level II and III models and the selection of important and dominant
modes are dependent on specific bridge under consideration.
Numerical verification of effectiveness of the proposed control method for seismic mitigation of the
TKB has been conducted under different AMD configurations and various earthquake excitations. In
this study, the Level III model consisting of 22 dominant modes is used for control design, while the
Level //model consisting of 47 important modes is used for response prediction and control
evaluation. The earthquake excitations are considered to apply to the TKB in the longitudinal, lateral
TABLE 1
RMS DISPLACEMENT RESPONSES AND REDUCTION OF TKB USING AMDS
Uncontrolled
Controlled
Reduction
(%)
Uncontrolled
Controlled
Reduction
(%)
Ting Kau
tower top
&(m)
0.1018
0.0614
39.73