Failure of a bridge member drastically changes the equilibrium state of the bridge. The release of the internal force of the failure member produces dynamic effects such as impact or vibration and the dynamic effect may cause the collapse of the entire bridge at worst. However, the nonlinear dynamic analysis which can evaluate the redundancy including the dynamic effect requires a large computational cost. To overcome this problem, a few methods to evaluate the redundancy including the dynamic effect by nonlinear static analysis have been proposed. The basic idea of these methods to take the dynamic effect into account is to employ inertia force constructed along with the natural vibration modes of the bridge. Although the natural vibration modes include important information of the vibration of the bridge, they have low relevance to the forced vibration excited by unbalanced force due to the member failure. Therefore, in this thesis, we propose a method to determine the inertia force by a relative displacement between two states obtained through the nonlinear static analysis. The validity of this method is confirmed by comparing the redundancy evaluated by the present method with that by the nonlinear dynamic analysis. From the comparison, we find that the accuracy of the proposed method is 2% for a truss bridge and 6% for a langer bridge.

Key Words : steel bridge, redundancy analysis, static nonlinear analysis, dynamic effect

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