SEISMIC RESPONSE OF CABLE-STAYED BRIDGE STEEL TOWER PROVIDED WITH BRACING SYSTEM

Abstract eng:
Cable-Stayed bridges consist of many structural components, which contribute to the overall resistance ability of the system. These structural syntheses give a valuable environment for the nonlinear behavior due to material nonlinearities and geometrical nonlinearities of the relatively large deflection of the structure on the stresses and forces. To improve the bridge seismic performance and to control expected damage, the necessity has arisen to develop more efficient bridge structural systems that can lead to resist the seismic actions. The seismic response of steel structures can be improved by providing bracing elements which can resist the lateral forces affecting the structure. In this paper, the feasibility of providing bracing system as damping elements in cable-stayed bridge steel tower is studied. The steel tower of Tappu cable-stayed bridge located in Hokkaido, Japan is considered as model of study. The steel tower is taken out of the bridge and modeled as three-dimensional frame structure. The proposed braced model is to provide the tower by X-bracing elements connecting the upper part of the tower. The study based on comparison of the seismic response of the original un-braced tower and that of proposed braced tower. A nonlinear dynamic analysis program based on total Lagrangian formulation using linearized finite displacement theory and fiber model has been developed to be used in this study. The finite element procedure for the nonlinear time history analysis of the steel tower under seismic loadings is set up. Geometric and material nonlinearities are implemented and bending-axial force interaction is considered. The evaluation of the proposed bracing system response was based on displacements at tower top and vertical forces and moments at supports. The results of this study show that the seismic response of cable-stayed bridge steel tower can be improved by providing bracing elements which will enhance the seismic ductility of the tower. The proposed bracing system, in this study, can reduce the horizontal displacement of the bridge tower and moment at tower base. In addition, shearing and vertical forces at tower base have slight effect.

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