The nonlinear behavior of steel towers of cable-stayed bridges subjected to three-dimensional great earthquake ground motions is studied. Nonlinearities due to geometry changes and material sources of bridge tower elements are considered, and a tangent stiffness iterative procedure is used in the dynamic analysis to obtain the nonlinear seismic response. Numerical examples for three different tower shapes(A-type, H-type and gate-type models) are presented. The effects of various tower models and design parameters of the cable on the dynamic behavior of cable-stayed bridges are investigated. It is shown that the seismic performance of the steel towers with passive control devices is effective to reduce the reaction forces at the tower basements. The adoption of passive control systems can accomplish a significant reduction in seismic-induced forces, as compared to the case with no passive control device added.
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